Resistance Training Recommendations to Maximize Muscle Hypertrophy in an Athletic Population: Position Stand of the IUSCA - International Journal ...
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Schoenfeld, B. J., Fisher, J. P., Grgic, J., Haun, C,T., Helms, E T., Phillips, S, M., Steele, J.,
Vigotsky, A, D. (2021).Resistance Training Recommendations to Maximize Muscle Hypertrophy in
an Athletic Population: Position Stand for the IUSCA.
International Journal of Strength and Conditioning
https://doi.org/10.47206/ijsc.v1i1.81
Resistance Training
Recommendations
to Maximize Muscle
Hypertrophy in an Athletic
Population: Position Stand
of the IUSCA
Brad J. Schoenfeld1, James P. Fisher2, Jozo Grgic3, Cody T. Haun4, Eric R. Helms5, Stuart M. Phillips6,
James Steele2 & Andrew D. Vigotsky7
1
Department of Health Sciences, CUNY Lehman College, Bronx, NY, USA; 2School of Sport, Health, and Social
Sciences, Solent University, Southampton, UK; 3Institute for Health and Sport, Victoria University, Melbourne,
VIC 8001, Australia; 4Fitomics LLC, Birmingham, Alabama; 5Sports Performance Research Institute New Zealand
(SPRINZ), Faculty of Health and Environmental Science, Auckland University of Technology, Private Bag 92006,
Auckland 1142, New Zealand; 6Department of Kinesiology, McMaster University, Hamilton, Canada; 7Departments of
Biomedical Engineering and Statistics, Northwestern University, Evanston, IL, USA.
ABSTRACT Keywords: muscle growth; muscle size; strength
training; lean mass; sport.
Hypertrophy can be operationally defined as an in-
crease in the axial cross-sectional area of a muscle
fiber or whole muscle, and is due to increases in the INTRODUCTION
size of pre-existing muscle fibers. Hypertrophy is a
desired outcome in many sports. For some athletes, In adulthood, muscle hypertrophy is a process driv-
muscular bulk and, conceivably, the accompanying en mainly by loading during resistance training (RT),
increase in strength/power, are desirable attributes which is supported by dietary protein intake (1)
for optimal performance. Moreover, bodybuilders and sufficient dietary energy (2). Hypertrophy can
and other physique athletes are judged in part on be operationally defined as an increase in the ax-
their muscular size, with placings predicated on ial cross-sectional area of a muscle fiber or whole
the overall magnitude of lean mass. In some cases, muscle, and is due to increases in the size of pre-ex-
even relatively small improvements in hypertrophy isting muscle fibers and not to an increase in fiber
might be the difference between winning and los- number [hyperplasia – see (3) for a recent review].
ing in competition for these athletes. This position Several processes contribute to hypertrophy, includ-
stand of leading experts in the field synthesizes the ing shifts in muscle net protein balance favoring new
current body of research to provide guidelines for net protein accretion (4), and satellite cell content
maximizing skeletal muscle hypertrophy in an ath- and activation (5).
letic population. The recommendations represent a
consensus of a consortium of experts in the field, Hypertrophy is a desired outcome in many sports.
based on the best available current evidence. Spe- For some athletes, muscular bulk and, conceivably,
cific sections of the paper are devoted to elucidating the accompanying increase in strength/power, are
the constructs of hypertrophy, reconciliation of acute desirable attributes for optimal performance. More-
vs long-term evidence, and the relationship between over, bodybuilders and other physique athletes are
strength and hypertrophy to provide context to our judged in part on their muscular size, with placings
recommendations. predicated on the overall magnitude of lean mass.
Copyright: © 2021 by the authors. Licensee IUSCA, London, UK. This article is an
open access article distributed under the terms and conditions of the
Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).Resistance Training Recommendations to Maximize Muscle
International Journal of Strength and Conditioning. 2021 Hypertrophy in an Athletic Population: Position Stand of the IUSCA
In some cases, even relatively small improvements RT in humans. Readers interested in more nuanced
in hypertrophy might be the difference between win- physiological discussion of hypertrophy are en-
ning and losing in competition for these athletes. couraged to consult recent comprehensive reviews
of the scientific literature that provide an updated
This position stand of leading experts in the field model of the process of muscle hypertrophy in more
synthesizes the current body of research to provide detail (3,6,7).
guidelines for maximizing skeletal muscle hypertro-
phy in an athletic population. The recommendations To appreciate how skeletal muscle hypertrophies in
represent a consensus of a consortium of experts response to RT, a brief description of skeletal mus-
in the field, based on the best available current ev- cle structure and composition is warranted. Skele-
idence. Specific sections of the paper are devoted tal muscle is sheathed with connective tissue that
to elucidating the constructs of hypertrophy, rec- is primarily composed of collagen protein (8). Skel-
onciliation of acute vs long-term evidence, and the etal muscle is ~75% fluid, which is compartmental-
relationship between strength and hypertrophy to ized into intracellular (i.e., beneath the muscle fiber
provide context to our recommendations. membranes or sarcolemma) and extracellular (i.e.,
outside muscle fiber membranes) space. The intra-
cellular fluid has been referred to as the sarcoplasm
CONSTRUCTS OF HYPERTROPHY which can be thought of as an aqueous media that
suspends intracellular components (e.g., orga-
Tremendous progress in understanding the physio- nelles, myofibrils). The extracellular space primarily
logical process of muscle hypertrophy in response consists of fluid, connective tissue, and vasculature.
to RT has been made over the past century of scien- Connective tissue can occupy as much as ~20% of
tific research. Mechanical and potentially metabolic skeletal muscle tissue and separates muscle into
stress experienced by skeletal muscle cells during fascicular bundles of muscle fibers (8). Muscle cells
RT results in an eventual upregulation in muscle pro- (referred to as muscle fibers) are multinucleated and
tein synthesis (MPS), which ultimately leads to pro- consist primarily of myofibrils, a mitochondrial retic-
tein accretion and measurable changes in muscle ulum, and a specialized organelle called the sarco-
size that can be detected using a variety of meas- plasmic reticulum (7).
urement techniques from a macroscopic to micro-
scopic scale (6). Although skeletal muscle hyper- Myofibrils within a skeletal muscle fiber are the con-
trophy has been defined differently in the scientific tractile units that contain sarcomeres and produce
literature, at its core, the term denotes an increase force following neural recruitment, the mitochondrial
in muscle size or mass. For the purpose of this po- reticulum is involved in energy production, and the
sition stand, muscle hypertrophy refers to skeletal sarcoplasmic reticulum is the site of calcium stor-
muscle tissue growth (i.e., positive changes in the age and release to facilitate muscle contraction. Ev-
size of muscle), and this can be conceptualized as idence indicates these are the three major compo-
a process that occurs over time. Although the com- nents of muscle fibers (9). Estimates from research
position and structure of human skeletal muscle has suggest that a majority of the intracellular environ-
been well characterized, specific molecular chang- ment of a muscle fiber (~85%) is occupied by myofi-
es and structural adaptations to various types of RT brils (10-12). Beyond the myofibrils and reticulums,
are still being unraveled in humans. muscle fibers contain many other organelles (e.g.,
ribosomes), metabolic enzymes, and ions that oc-
RT can involve a plethora of training methods de- cupy less cellular space but support critical phys-
pending on the aim of the program, equipment used, iological functions. Additionally, muscle fibers con-
and individual constraints (among many other fac- tain stored substrates in the form of glycogen and
tors). Distinct forms of RT (e.g., bodyweight exercise triglycerides for energy. On average, glycogen con-
versus barbell loading) can affect the morphological stitutes ~2–3% and intramuscular triglycerides ~5%
and molecular adaptations in skeletal muscle, and of skeletal muscle (13,14).
this can ultimately affect the magnitude of muscle
hypertrophy. Later sections in this position stand will Evidence suggests that increases in muscle fiber
cover RT program variables for maximizing hyper- size (e.g., fiber cross-sectional area) in response to
trophy and their application to program design. This weeks-months of RT primarily occur as a result of
section provides a brief overview of the current state regular increases in myofibrillar MPS and myofibril
of the scientific evidence regarding the general na- accretion (3). Myofibrillar protein accretion is theo-
ture or mode of muscle hypertrophy in response to rized to be associated with an increase in myofibril
Copyright: © 2021 by the authors. Licensee IUSCA, London, UK. This article is an
open access article distributed under the terms and conditions of the 2
Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).Schoenfeld, B. J., Fisher, J. P., Grgic, J., Haun, C,T., Helms, E T.,
International Journal of Strength and Conditioning. 2021 Phillips, S, M., Steele, J., Vigotsky, A, D.
size (due to an increased number of sarcomeres in sponses at the desired time. This is an exciting area
series) or number (myofibril splitting or myofibrillo- of ongoing muscle physiology research and future
genesis, including adding sarcomeres in parallel) in studies can help to decipher the specific nature
individual muscle fibers (6). This has been referred of muscle growth in response to a variety of train-
to as “conventional hypertrophy” and several lines of ing methods. With this in mind, the scientific liter-
evidence provide support for this model in response ature clearly shows muscle hypertrophy occurs in
to chronic RT (3,7). Jorgensen et al. (3) presented a response to certain methods of RT across a wide
compelling “Myofibril Expansion Cycle” theory that range of individuals.
involves hypertrophy of individual myofibrils to a
critical size and then myofibrils splitting into “daugh-
ter” myofibrils. This can ultimately manifest as an in- RELATIONSHIP BETWEEN HYPERTROPHY AND
crease in the size of individual muscle fibers, and STRENGTH
eventually an increase in muscle size. In addition
to this evidence, a comparatively limited number of The inclusion of hypertrophy-oriented RT in sport
studies suggests “sarcoplasmic hypertrophy” may is often based on the premise that a larger muscle
also contribute to a small degree of the observed in- equates to a stronger muscle. This notion is pred-
creases in muscle size in response to various types icated on the basic mechanical tenet that forc-
of RT (7). Sarcoplasmic hypertrophy can be defined es in parallel are additive. Since the sarcomere is
as a disproportionate increase in the volume of sar- the fundamental force-generating unit of a muscle,
coplasm and its constituents relative to myofibril more sarcomeres in parallel should, and do, pro-
accretion. In other words, sarcoplasmic hypertro- duce more force (15,16). However, it has been ar-
phy may occur through an increase in cellular com- gued that this theory does not hold when applied to
ponents other than myofibrils (e.g., fluid, enzymes, RT-induced changes in muscle size and changes
organelles). At present, the evidence suggests that in strength. In 2016, Buckner et al. (17) noted that
sarcoplasmic hypertrophy may play a limited role in evidence for the presumptive strength-hypertrophy
the hypertrophic response to RT (myofibrillar pro- relationship was lacking, and the authors proceed-
tein accretion appears to account for the majority ed to argue that hypertrophy and strength gains are
of fiber growth) and this response may be transient independent phenomena (18,19). Their argument
to facilitate myofibril accretion. Some research sug- can be reduced to three points: First, hypertrophy
gests that the phenomenon may be more specific to is not necessary for strength gain—individuals can
higher volume, higher repetition RT (7), although the gain strength without gaining muscle; second, hy-
limited evidence precludes the ability to draw strong pertrophy is not sufficient for strength gain—indi-
conclusions on the topic. viduals can gain muscle without gaining strength;
finally, hypertrophy does not contribute to strength
Rather than viewing these phenomena in opposition gain—that is, hypertrophy is neither necessary nor
to one another, it seems prudent to consider a phys- sufficient for strength gain, nor does it contribute to it
iological rationale for how such adaptations may in any way. These arguments, particularly the latter,
support one another or occur to differing degrees have not gone uncontested—they catalyzed a se-
depending on the training stimulus. In a recent re- ries of new discussions, experiments, and analyses
view, Roberts et al. (7) presented a potential physi- (18,20-31).
ological rationale for how sarcoplasmic hypertrophy
may occur as a distinct adaptation in response to The contention by Loenneke et al. (18) that hypertro-
certain types of RT or in support of myofibrillar hy- phy is neither necessary nor sufficient for strength
pertrophy. For example, sarcoplasmic hypertrophy gain is generally agreed upon (e.g., (20,21)). How-
may occur earlier in the process of hypertrophy to ever, the argument that hypertrophy is not a contribu-
spatially and energetically prime the cell for myofi- tory cause remains hotly debated (18,20). The argu-
bril hypertrophy. However, a limited number of hu- ment for hypertrophy contributing to strength gain is
man studies exist that have investigated the specific primarily theoretical and secondarily associational.
nature of ultrastructural and compositional chang- In theory, adding sarcomeres in parallel via the ac-
es in response to different types of RT. Moreover, crual of myofibrillar proteins should result in greater
hypertrophic responses to a standardized training force output (20), but reality is less simple. First, the
program can vary widely between individuals. This multiscale and multi-compositional nature of muscle
precludes a strong position on specific program de- complicates matters (32,33). In addition to myofibril
sign variables that could emphasize sarcoplasmic protein changes, noncontractile proteins and factors
versus myofibrillar hypertrophy, or optimize the re- affecting both the physiology and intrinsic mechan-
Copyright: © 2021 by the authors. Licensee IUSCA, London, UK. This article is an
open access article distributed under the terms and conditions of the 3
Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).Resistance Training Recommendations to Maximize Muscle
International Journal of Strength and Conditioning. 2021 Hypertrophy in an Athletic Population: Position Stand of the IUSCA
ics of the muscle accompany myofibrillar hypertro- however. First, it has previously been stressed that
phy (18,19,34-36), meaning changes in strength may the within-subject strength-hypertrophy relationship
not scale linearly with changes in muscle size (32). is of greater interest than the between-subject rela-
Second, the theory is further complicated when con- tionship; if one wishes to model the between-subject
sidering the outcomes measured. On the strength relationship, they should adequately account for be-
side, coordination requirements of isometric and tween-subject heterogeneity. Ideally, such a study
multi-joint dynamic efforts differ appreciably. As a would use a within-subject model consistent with the
result, isometric and dynamic strength gains are of- proposed data-generating process (21), but Jessee
ten discrepant, with dynamic strength increases of- et al. (30) did not. Second, these models assume
ten vastly outpacing isometric strength increases in no residual confounding; however, typical training
trainees that “practice” the dynamic movement [see studies do not collect enough mechanistic data to
Fig 3 in (37) and “Training Studies” in (20)]. Thus, it obtain an unbiased estimate of the mediation ef-
has been argued that isometric strength outcomes fect, since physiological variables other than growth
should follow the theory more closely than dynam- are affected by exercise interventions (21). Finally,
ic strength outcomes (20,21). On the hypertrophy nearly all of the strength-hypertrophy studies to date
side, the measurement used to determine “muscle have been of relatively short duration and have col-
size” will affect the outcome since different meas- lected suboptimal measures of strength and hyper-
urements assess different constructs (6,15). As has trophy (20).
been argued previously, myofibril protein content
should be most closely associated with strength As experimentalists, Loenneke et al. (18,40) argue
outcomes (15,20), but typically, measurements are that the associational evidence is just that, correla-
grosser (21). Thus, although the theory of adding tions, and we need experimental evidence to estab-
sarcomeres in parallel is straightforward, several ex- lish that hypertrophy is a contributory cause. This is
perimental and measurement factors would tend to reasonable in theory but arguably problematic in re-
cloud any relationship should one exist. ality. Experiments can show causal evidence for the
effect of an independent variable on the dependent
The second argument for a relationship is associ- variable. However, it is inconceivable that hypertro-
ational. Both within and across individuals, mostly phy can be an independent variable—hypertrophy
weak, positive relationships are observed between is a dependent variable since the intervention is the
hypertrophy and strength gain (21,27), suggesting independent variable. Unless the experimenter can
at least some statistical dependence. Importantly, (randomly) assign hypertrophy independent of other
the changes in size and strength observed to calcu- adaptations, proper experimental evidence may be
late these correlations are relatively small, meaning futile.
measurement and biological variability may affect
or even dominate the variance-covariance struc- Despite proper experimental evidence being un-
ture (18,20). Despite measurement error tending to obtainable, clever experimental designs may ap-
attenuate effects unless there is structure (bias or proach the question from a more applied perspec-
covariance) in the error (20,21,38,39), Loenneke et tive. Buckner et al. (41) randomized participants’
al. (18) insist these relationships represent the cor- limbs to hypertrophy (8 week) + strength (4 week) or
relation between the noise and biological variability rest (8 week) + strength (4 week) to assess whether
of each measurement. Of course, these are still as- biceps brachii hypertrophy would augment subse-
sociations and not experimental evidence of a con- quent elbow flexion strength increases—the effects
tributory cause (18,40). were negligible. However, the growth observed was
also small and similar to biceps brachii thickness
To remedy the inferential shortcomings of corre- standard error of measurement [~1 mm, see (42)].
lations, Nuzzo et al. (29) suggested modeling the If the growth was hardly measurable, should it be
strength-hypertrophy relationship using hypertrophy enough to augment strength? More studies along
as a mediator to properly account for confounders these same lines may be fruitful, but with longer du-
and draw causal conclusions. In a between-subject rations and more, higher quality measures.
mediation analysis of a 6-week training study consist-
ing of 151 participants, Jessee et al. (30) did just that If the reader is interested in tight, controlled, exper-
and observed negligible indirect effect estimates— imental evidence regarding the strength-hypertro-
statistical evidence against hypertrophy being a me- phy relationship, then the conservative conclusion is
diator of strength gain. These modeling approaches that the jury is still out. Such an experiment may be
and their implementations are not without limitations, impossible, and the best evidence we have at pres-
Copyright: © 2021 by the authors. Licensee IUSCA, London, UK. This article is an
open access article distributed under the terms and conditions of the 4
Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).Schoenfeld, B. J., Fisher, J. P., Grgic, J., Haun, C,T., Helms, E T.,
International Journal of Strength and Conditioning. 2021 Phillips, S, M., Steele, J., Vigotsky, A, D.
ent is hindered by methodological shortcomings. In that RT results in sensitization of muscle to hyper-
the authors’ eyes, it strains credulity that force-pro- aminoacidemia, that only essential amino acids are
ducing elements can be added in parallel but do not required to support a full and robust MPS response,
have any additive effect; such a claim would imply that leucine is the key amino acid that triggers the
that the myofibrils’ specific strength decreases with rise in MPS and that adding carbohydrates (with the
training, but this is not observed in practice (43,44). resultant hyperinsulinemia) does not contribute to
Rather, it is our opinion that a combination of con- stimulating MPS when protein is sufficient. We also
founding factors (e.g., swelling, neural adaptations, have a good idea of the dose-response relationship
coordination, etc.), measurement nuances (e.g., between ingested protein dose and the stimulation
whole muscle vs. myofibril hypertrophy), and meth- of MPS after resistance exercise (65,66). If mixed
odological shortcomings (e.g., short durations) yield meal-induced rises in MPS are translatable from
much of the literature in this area to be relatively unin- isolated proteins, and we apply a margin of error in
formative for answering the ultimate question, “Does making this estimation, then it appears that per-meal
an increase in an individual’s muscle size contribute doses of protein that maximally stimulate MPS are
to an increase in that individual’s strength?” 0.35-0.5 g protein/kg bodyweight/meal (4). These
estimates are based on the ingestion of higher qual-
ity, mostly animal-derived proteins, that have been
RECONCILING ACUTE VS LONGITUDINAL DATA tested to date.
Several methods have been developed to study the A key question is whether short-term (hours) infu-
fundamental processes – MPS and muscle protein sion-determined measures of MPS, and when avail-
breakdown (MPB) – that contribute to protein accre- able MPB and net muscle protein balance, are rel-
tion within muscle (4). Of these two processes, the evant in the longer-term and ultimately aligned with
locus of control in young, healthy persons is MPS, phenotypic adaptation? Broadly, there are exam-
which fluctuates 3- to 5-fold more than MPB (45,46). ples of short-term protein turnover estimates align-
Not surprisingly, MPS is responsive to amino acid ing with longer-term training studies. For example,
and protein ingestion and loading, and there is a ingestion of bovine skimmed milk was shown to be
synergistic stimulation of MPS with the combination more anabolic than a protein-matched isoenergetic
of these two stimuli (4,45). Notably, it is only when soy drink (67), which aligned with outcomes from a
hyperaminoacidemia, due to protein or amino acid subsequent trial (68). Similarly, short-term respons-
ingestion/infusion, occurs that rates of MPS exceed es of MPS to lifting with lower and higher loads (55)
those of MPB and muscle protein net balance be- aligned with unilateral (69) and independent group
comes positive (46); however, this is a transient re- comparative outcomes (70); namely, that when low-
sponse (47,48). When hyperaminoacidemia occurs er loads were lifted to the point of failure, they are
in the post-RT period, then MPS is stimulated to an as effective at stimulating hypertrophy as heavier
even greater degree and for a longer duration (48), loads. Nonetheless, there are other scenarios where
and net protein balance becomes even more pos- acute responses have not aligned with longer-term
itive (49). The persistent and greater stimulation of outcomes. For instance, the acute (1-6h) post-ex-
MPS over MPB with regular RT results in small but ercise MPS response was not related to the extent
significant increases in muscle protein net balance of muscle hypertrophy (71); however, this may not
(50), which then eventually results in muscle hyper- be surprising given that the post-exercise MPS re-
trophy (51). sponse was only a fasted-state response (71) and,
as outlined above, it is in the fed-state when protein
Our understanding of the meal- and exercise-in- accretion occurs.
duced acute (hours) changes in MPS and MPB,
which admittedly are much more methodologically The use of ingested deuterated water to measure a
challenging to undertake, have been elucidated via ‘medium-term’ (days-to-weeks) MPS response (see
experiments utilizing the infusion/ingestion of stable (72) for review of the methodology) showed good
isotopes – for an extensive review see (52). Using alignment with longer-term hypertrophic respons-
the stable isotope infusion methodology has ex- es; however, the early (first week) MPS responses
panded our understanding of how resistance exer- were not correlated with hypertrophy, but respons-
cise (53,54), loads lifted during resistance exercise es at both the 3rd and 10th week of training were
(55), the role of protein quality (56,57), essential ami- (73). It was speculated that the lack of alignment of
no acids (58), leucine (59-61), and carbohydrates earlier MPS responses with hypertrophy was that
influence MPS (62-64). From this work, we know muscle damage was being repaired early in the RT
Copyright: © 2021 by the authors. Licensee IUSCA, London, UK. This article is an
open access article distributed under the terms and conditions of the 5
Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).Resistance Training Recommendations to Maximize Muscle
International Journal of Strength and Conditioning. 2021 Hypertrophy in an Athletic Population: Position Stand of the IUSCA
program, whereas it was a more ‘refined’ response MANIPULATION OF PROGRAM VARIABLES
at 3 and 10 weeks of training when MPS was con-
tributing to protein accretion (73). Similarly, when It is believed that the manipulation of RT variables
RT programs were tested head-to-head in the same plays an important role in optimizing muscular gains.
individual, integrated MPS responses were also re- The following section provides evidence-informed
lated to muscle cross-sectional area changes (74). guidelines based on our current understanding of
the topic.
Muscle hypertrophy is a complex process that in-
tegrates neural, muscular, and skeletal systems. Load
Hence, one would expect a polygenic regulation of
such a process. The fact that RT-induced muscle Overview
hypertrophy varies substantially between individu-
als highlights a strong intrinsic (i.e., resident within Loading refers to the magnitude of resistance em-
the muscle itself) component to hypertrophy (74,75). ployed during training. Loading can be expressed
Clearly, part of the innate responses to RT comes as a percentage of some measure of maximum
from changes in MPS; however, changes in riboso- strength (e.g., 1 repetition maximum [RM], or max-
mal content and satellite cell number and activation imum voluntary contraction [MVC]) or a specific
also contribute to hypertrophy (76). Thus, it is un- target repetition goal (e.g., 10RM). Researchers
surprising that changes in MPS, measured acutely have long proposed the presence of a “hypertro-
or in the medium-term, do not capture all aspects of phy zone,” whereby maximal increases in muscle
hypertrophy. Hypertrophy requires an orchestrated growth are achieved when training in a range of ~6
coordination between multiple bodily systems, and to 12RM (78,79). Evidence indicates competitive
optimal functioning of more than one system is re- bodybuilders most often employ this range in their
quired for an optimal response. However, the exist- quest to maximize muscle development (80). How-
ence of so-called responders and non-responders ever, emerging research challenges the concept of
to RT is a hallmark of just about every RT study that a specific hypertrophy loading zone.
recruits participants who are naïve to the stimulus
of loading their muscles (77). It is also becoming Evidence from the Literature
clearer that transcriptomic programs underpin the
capacity for hypertrophy (75). Common single-nu- Evidence from acute studies is conflicting about
cleotide polymorphisms (SNP) observed to be as- whether there is a hypertrophic superiority to a giv-
sociated with muscle mass were shown not to be en repetition range. Some studies indicate a greater
associated with RT-induced hypertrophy (77); none- MPS response with heavier versus lighter loading
theless, a previously unidentified SNP in the intron schemes (81,82), while others do not (55). Discrep-
variant of the GLI Family Zinc Finger 3 (GLI3) gene ancies in findings conceivably may be explained by
did demonstrate an association with increases in differing levels of effort between protocols. Specif-
muscle fiber cross-sectional area and satellite cell ically, studies reporting an anabolic advantage to
number with RT (77). heavier loads also matched the total work performed
between conditions so that the low-load training
In summary, acute research into intracellular signal- stopped well short of failure (81,82). In contrast,
ing and MPS provide important observations into the research in which there was a matched level of ef-
hypertrophic response to RT. Although we cannot fort found similar MPS responses (55). Although the
necessarily infer chronic hypertrophic adaptations totality of this research is somewhat limited in this
from acute responses, these studies can provide in- regard, findings suggest that MPS is relatively un-
sights into mechanisms by which adaptations might affected by the magnitude of load provided training
occur. Moreover, triangulation of acute evidence involves a high intensity of effort.
with longitudinal data can strengthen our confi-
dence in the support or refutation of a given theory Longitudinal research provides compelling evidence
about the applied aspects of hypertrophy training, that similar hypertrophy occurs across a broad
and thus will be taken into account when making our spectrum of loading ranges. A 2017 meta-analysis
recommendations. by Schoenfeld et al. (83) did not find a significant
difference in measures of hypertrophy between
studies comparing high- versus low-load training
programs (>60% 1RM andSchoenfeld, B. J., Fisher, J. P., Grgic, J., Haun, C,T., Helms, E T.,
International Journal of Strength and Conditioning. 2021 Phillips, S, M., Steele, J., Vigotsky, A, D.
tively). This meta-analysis only included studies in er load range training (90). These findings should
which the training sets were taken to muscle failure. be considered preliminary, however, and in need
The pooled effect size (ES) and the corresponding of further research to draw stronger inferences. The
95% confidence interval (CI) in this meta-analysis potential implications will be further discussed in the
were in the zones of trivial differences between the section on periodization.
loading schemes (ES: 0.03; 95% CI: −0.16, 0.22).
Sub-analysis showed the results held true irrespec- Some researchers have posited that there may be
tive of whether training was performed in upper vs. a fiber type-specific hypertrophic response to the
lower body exercises. In accord with these findings, magnitude of load, with high-loads targeting type II
a subsequent meta-analysis on the topic concluded fibers and low loads targeting type I fibers (91). In
that hypertrophy was load-independent when com- support of this theory, several studies have report-
paring the effects of low- (>15 RM), moderate- (9-15 ed that low-load blood flow restriction (BFR) training
RM), and high-load (≤8 RM) training protocols (84). induces preferential hypertrophy of type I fibers (92-
Some researchers have speculated that light-load 94). However, although low-load training is generally
training has an inherent hypertrophic advantage considered a milder form of BFR exercise (95), BFR
when performing the same number of sets, given may induce hypertrophy via different mechanisms
that the greater number of repetitions during light than traditional low-load RT. When comparing tra-
load training results in a higher volume load (sets × ditional low-load vs. high-load RT, current evidence
repetitions × load). However, when pooling the data is mixed on the topic; some studies report a fiber
from studies comparing different repetition ranges type-specific response between conditions (96-98)
but equating volume load via the performance of while others show no differences (69,70,99). Simi-
additional sets for the moderate-load condition, ev- lar to the acute MPS data, inconsistencies between
idence shows similar hypertrophy between moder- findings may be attributed to differences in the in-
ate- and low-load conditions (personal correspond- tensity of effort; studies reporting no between-group
ence). Further, the network meta-analysis of Lopez differences in fiber type adaptations involved train-
and colleagues (84) revealed negligible heteroge- ing to failure while the sets in studies that showed
neity, suggesting differences in outcomes may be preferential fiber type hypertrophy terminated sets
primarily due to sampling variances across studies. before failure.
Gaps in the Literature Finally, there appears to be a lower threshold for
loading, below which the stimulus for hypertrophy
The effects of hypertrophy across loading zones becomes less effective. A recent study indicated that
have primarily been studied in binary terms, com- 20% 1RM elicited suboptimal hypertrophic gains in
paring distinct loading zones (i.e., heavy- vs. mod- the quadriceps and biceps brachii compared with
erate- vs. light-load). While this provides important loads ≥40% 1RM when performing the leg press
insights from a proof-of-principle standpoint, it fails and arm curl, respectively (100). It should be noted
to account for the possibility that different combina- that there is substantial inter-individual variability in
tions of loading zones can be employed in program the number of repetitions achieved at a submaximal
design. Studies have reported that the magnitude RM that can be attributed to a combination of fac-
of load may promote divergent intracellular signal- tors including genetics, modality (free-weights vs.
ing responses, with selective activation of different machines), area of the body trained (e.g., upper vs.
kinase pathways observed between moderate- and lower), exercise type (single vs. multi-joint exercis-
low-load conditions (85,86), although evidence is es), and perhaps others (79), which should be con-
somewhat contradictory on the topic (87). Conceiv- sidered when interpreting the evidence.
ably, the amalgamation of such responses could
have a synergistic effect on anabolism. Indeed, Consensus Recommendations
some longitudinal evidence indicates that training
across a spectrum of repetition ranges, either on Athletes can achieve comparable muscle hypertro-
an intra-week or intra-session basis, may amplify phy across a wide spectrum of loading zones. There
muscular development compared to training in a may be a practical benefit to prioritizing the use of
moderate loading zone (88,89). Moreover, there is moderate loads in hypertrophy-oriented training,
a possible benefit of initiating a hypertrophy-orient- given that it is more time-efficient than lighter loads
ed training cycle with a short block of very heavy and less taxing on the joints and neuromuscular sys-
strength-oriented training to potentiate greater use tem than very heavy loads. Furthermore, it should
of heavier loads prior to a block of moderate to light- be considered that training with low-loads tends to
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produce more discomfort, displeasure, and a higher direct hypertrophy measures (magnetic resonance
rating of perceived effort than training with moder- imaging, ultrasound, etc.) were isolated from less
ate-to-high loads (101). While training with moderate sensitive indirect measures (dual-energy X-ray ab-
loads seems to produce the greatest practical ad- sorptiometry, air displacement plethysmography,
vantages, preliminary evidence suggests a potential etc.). Nonetheless, there is large interindividual
hypertrophic benefit to employing a combination of variability in the hypertrophic response to differing
loading ranges. This can be accomplished through amounts of RT volume. Although higher volume pro-
a variety of approaches, including varying repeti- tocols enhance muscular adaptations in most indi-
tion ranges within a session from set to set, or by viduals, some appear largely unresponsive to great-
implementing periodization strategies with specific er doses (108).
‘blocks’ devoted to training across different loading
schemes (see the periodization section for further Some evidence indicates that substantially high-
discussion on the topic). er volumes (>20 sets per muscle group per week)
may show a greater dose-response relationship with
Volume muscle hypertrophy (111-114), although these find-
ings are not universal (115,116). It is important to
Overview note that the protocols in studies showing a benefit
to higher volumes comprised a relatively moderate
Broadly speaking, RT volume refers to the amount of number of total sets per week for all exercises com-
work performed in a RT session. RT volume can be bined. Thus, results can only be extrapolated to in-
expressed in several ways including: (a) the num- fer that the potential benefits of higher volumes are
ber of sets performed for a given exercise (102); (b) specific to a limited number of muscles in a given
the total number of repetitions performed per exer- program.
cise (i.e., the product of sets and repetitions) (103);
and (c) volume load (the product of sets, repetitions, Although objective evidence is limited, it is logical
and load either absolute [e.g., kg] or relative [e.g., that the dose-response relationship between RT
%1RM])) (104). Although all these methods are con- volume and muscle hypertrophy follows an inverted
sidered viable ways to express volume, the number U-shaped curve, which is consistent with the con-
of sets performed is most commonly used in the liter- cept of hormesis. In this hypothesis, higher volume
ature that focused on muscle hypertrophy. Evidence RT will confer an increasingly additive hypertrophic
indicates this metric serves as a viable standard to effect up to a certain threshold, beyond which point
quantify training volume for repetition ranges from 6 results would plateau and ultimately could have a
to 20 per set (105), and thus will be used herein to detrimental impact on muscular adaptations due to
form recommendations on the topic. overtraining. A specific upper threshold for volume
has not been determined and undoubtedly would
Evidence from the Literature vary between individuals based on a multitude of
genetic and lifestyle factors. Hypothetically, the
Acute studies show an anabolic advantage to em- upper threshold could also vary between different
ploying higher RT volumes. These findings are muscle groups (117).
supported by multiple lines of acute evidence that
include volume-dependent increases in anabolic in- Gaps in the Literature
tracellular signaling (106-108), MPS (109), and sat-
ellite cell response (110). Recent research indicates that the hypertroph-
ic dose-response relationship to volume in resist-
A robust body of longitudinal evidence identifies RT ance-trained individuals may be dependent on the
volume as a major driver of muscle development. amount of volume previously performed (116,118).
Research shows a dose-response relationship be- These findings suggest a potential benefit to individ-
tween volume and hypertrophy, at least up to a cer- ualizing weekly training volume so that increases in
tain point. A meta-analysis of 15 studies that com- dose are applied incrementally over time. The lim-
pared higher to lower volumes found graded relative ited evidence to date indicates that an increase of
increases in muscular gains (5.4%, 6.6%, and 9.8%) ~20% performed over a given training cycle (e.g.,
when the number of sets per muscle group per week several weeks) may serve as a good starting point
was stratified intoSchoenfeld, B. J., Fisher, J. P., Grgic, J., Haun, C,T., Helms, E T.,
International Journal of Strength and Conditioning. 2021 Phillips, S, M., Steele, J., Vigotsky, A, D.
To date, research has focused on comparing differ- Evidence from the Literature
ent volumes for the duration of a given study period.
However, the amount of volume performed does not Research shows that MPS remains elevated for ~48
have to remain consistent over time. It has been pro- hours after RT and then returns to baseline levels
posed there may be a benefit to periodizing volume (53). The post-workout duration of MPS is truncat-
so that the number of sets per muscle progressively ed in resistance-trained individuals, who display a
increases over a defined training cycle (119). Con- more elevated peak response that persists over a
ceivably, such a strategy would help to maximize somewhat shorter timeframe (120). This divergent
the dose-response effects on hypertrophy while mit- MPS response between trained vs. untrained indi-
igating the potential for overtraining. This hypothesis viduals has led some researchers to speculate that
warrants objective exploration. more frequent stimulation of a muscle via multiple
weekly sessions would maximize the area under the
Consensus Recommendations MPS curve and thus promote a superior hypertroph-
ic response (121).
A dose of approximately 10 sets per muscle per
week would seem to be a general minimum pre- However, despite a seemingly sound logical ration-
scription to optimize hypertrophy, although some ale, longitudinal research generally does not support
individuals may demonstrate a substantial hyper- a hypertrophic benefit to higher frequency training,
trophic response on somewhat lower volumes. Ev- at least under volume-equated conditions in lower-
idence indicates potential hypertrophic benefits to to moderate-volume programs. Acute data show no
higher volumes, which may be of particular rele- differences in MPS rates between volume-matched
vance to underdeveloped muscle groups. Accord- low frequency (10 sets of 10 repetitions performed
ingly, individuals may consider specialization cycles once per week) and high frequency (2 sets of 10
where higher volumes are used to target underde- repetitions performed five times per week) routines
veloped muscles. In this strategy, more well-devel- as assessed by deuterium oxide (122). It should be
oped muscles would receive lower doses so that the noted that MPS in the training conditions did not dif-
overall number of weekly sets for all muscle groups fer from the non-exercise control, thus calling into
remains relatively constant within the athlete’s target question whether deuterium oxide was sufficient-
range. Although empirical evidence is lacking, there ly sensitive to determine anabolic changes in be-
may be a benefit to periodizing volume to increase tween-group protocols.
systematically over a training cycle. Conceivably,
programming would culminate in a brief overreach- Meta-analytic data of studies that directly compared
ing phase at the highest tolerable volume for a given higher versus lower RT frequencies found similar in-
individual, and then be followed by an active recov- creases in muscle size in volume-equated programs
ery period to allow for supercompensation (93). It irrespective of whether muscle groups were trained
may be prudent to limit incremental increases in the 1, 2, 3, or 4+ days per week (123). Alternatively,
number of sets for a given muscle group to 20% of subanalysis of studies whereby volume was not
an athlete’s previous volume during a given training equated showed a small but statistically significant
cycle (~4 weeks) and then readjust accordingly. benefit for higher training frequencies up to 3 days
per week. However, these effects were likely driv-
Frequency en more by training volume and not frequency per
se, as the groups that trained with higher frequency
Overview also trained with a higher volume. Thus, although
frequency does not seem to influence hypertrophy
Frequency refers to the number of RT sessions as a standalone variable, alterations in the number
performed over a given period of time. The quan- of weekly RT sessions may help to manage volume
tification of frequency is generally considered on a for an optimal anabolic effect.
weekly basis, although any time period can be used
for prescription. From a hypertrophy standpoint, fre- Gaps in the Literature
quency is most commonly expressed as the number
of times a muscle group is trained on a weekly basis. The interplay between training frequency and vol-
ume is an important aspect to consider. An exam-
ination of the current research seems to indicate
an upper threshold for volume in a given session,
beyond which hypertrophy plateaus. This would be
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International Journal of Strength and Conditioning. 2021 Hypertrophy in an Athletic Population: Position Stand of the IUSCA
consistent with the hypothesis that muscle has a lim- longer rest periods (126). Researchers have spec-
ited capacity to synthesize proteins from an exercise ulated these transient systemic fluctuations play an
dose; hence, at some point, a high number of sets important role in regulating exercise-induced muscle
per session exceeds the anabolic capacity of the development (127,128), and may even be more crit-
muscle to synthesize proteins so that any addition- ical to the process than chronic changes in resting
al volume results in “wasted sets” (121). However, hormonal concentrations (129). However, research
no attempts have been made to quantify a specif- casts doubt on the relevance of acute hormonal fluc-
ic threshold in this regard. Scrutiny of existing data tuations to hypertrophic adaptations; it appears that
suggests that it may be appropriate to limit volume any anabolic effects, if they do indeed occur, would
to approximately 10 sets per muscle per session; be modest and likely overshadowed by other factors
when weekly volume exceeds this amount, splitting (130). Indeed, McKendry et al. (131) found that the
the volume across additional training sessions may early phase myofibrillar MPS rate and anabolic intra-
help to maximize anabolic capacity. Therefore, the cellular signaling response (p70S6K and rpS6) were
greatest benefit of manipulating training frequen- blunted with 1- versus 5-minute rest intervals follow-
cy may be in its effect on the distribution of weekly ing multi-set lower body resistance exercise despite
training volume. However, further research is need- significantly higher post-exercise testosterone con-
ed to provide more objective evidence on the topic. centrations in the shorter rest condition.
Consensus Recommendations Evidence from longitudinal studies generally fails
to support an anabolic benefit for employing short
Significant hypertrophy can be achieved when train- rest intervals; in fact, there may be a possible hyper-
ing a muscle group as infrequently as once per week trophic advantage for the use of somewhat longer
in lower- to moderate volume protocols (~≤10 sets rest intervals in resistance-trained individuals (132).
per muscle per week); there does not seem to be Detrimental effects of short rest intervals conceiva-
a hypertrophic benefit to greater weekly per-muscle bly may be explained by a reduction in volume load
training frequencies provided set volume is equated. from peripheral fatigue. In other words, less work
However, it may be advantageous to spread out vol- can be performed on subsequent sets when exer-
ume over more frequent sessions when performing cising with limited inter-set recovery. In support of
higher volume programs. A general recommenda- this theory, Longo et al. (133) demonstrated an im-
tion would be to cap per-session volume at ~10 sets paired hypertrophic response with 1- versus 3-min-
per muscle and, when applicable, increase weekly ute periods following 10 weeks of multi-set knee
frequency to distribute additional volume. extension exercise. However, the differences neu-
tralized when additional sets were performed in the
Rest interval short rest condition to equate volume-load. Recent
sub-group moderation analysis of rest intervals on
Overview muscle mass outcomes in young adults revealed
similar ES for intervals 90 seconds (g = 0.59 [95% CI
between sets of the same exercise, or between dif- 0.28 to 0.74]) (134).
ferent exercises in a given session. Evidence shows
that the duration of the inter-set rest period acutely Gaps in the Literature
affects the RT response, and these responses have
been speculated to influence chronic hypertrophic It is conceivable that the effects of rest interval du-
adaptations (124). Henceforth, leading organiza- ration are influenced by the exercise type and mo-
tions commonly recommend relatively short inter-set dality. In particular, recovery is impaired to a great-
rest intervals (30 to 90 seconds) for hypertrophy-ori- er extent during multi- versus single-joint exercise.
ented training (125). Senna et al. (135) found a significantly greater
drop-off in the number of repetitions performed in a
Evidence from the Literature 10RM bench press across 3 sets when employing
1- versus 3-minute rest intervals (mean difference of
Prevailing rest interval recommendations for hyper- 3 repetitions). Alternatively, a relatively similar repe-
trophy are largely based on acute research showing tition reduction was observed in the chest fly in both
significantly greater post-exercise anabolic hormone 1- and 3-minute rest conditions (mean difference
(testosterone, insulin-like growth factor and growth of less than 1 repetition). These findings suggest a
hormone) elevations when employing shorter versus potential benefit to using shorter rest periods in sin-
Copyright: © 2021 by the authors. Licensee IUSCA, London, UK. This article is an
open access article distributed under the terms and conditions of the 10
Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).Schoenfeld, B. J., Fisher, J. P., Grgic, J., Haun, C,T., Helms, E T.,
International Journal of Strength and Conditioning. 2021 Phillips, S, M., Steele, J., Vigotsky, A, D.
gle joint exercise, as this conceivably may help to (143-148), seemingly as a result of the interaction
enhance muscle buffering capacity (136) and thus between architectural variances and factors related
have a positive effect on performance when train- to biomechanics. This has led some researchers to
ing with moderate- to higher repetition ranges; at the speculate that hypertrophy-oriented training should
very least, it will make workouts more time-efficient. incorporate a variety of exercises to promote growth
of specific muscles (149,150).
Another consideration to take into account is the
ability for individuals to adapt to the use of shorter Evidence from the Literature
rest periods. Evidence shows that bodybuilders are
able to train with a higher percentage of their 1RM Although direct experimental research is limited, ev-
across sets of a multi-set protocol compared to pow- idence suggests that combining different exercises
erlifters when performing multi-set protocols with can enhance development of a given muscle. For ex-
short rest (137). Considering that bodybuilders rou- ample, Fonseca et al. (151) reported that a combina-
tinely employ shorter rest periods (80), these find- tion of various lower body exercises (Smith machine
ings suggest that consistently training in this fash- squat, leg press, lunge, and deadlift) performed for
ion may facilitate preservation of volume load and 12 weeks elicited more uniform hypertrophy of the
thus enhance workout efficiency. Controlled studies quadriceps femoris compared to volume-equated
lend support for this hypothesis, showing that sys- performance of the Smith machine squat alone. Sim-
tematically reducing rest interval length over a 6- to ilarly, a 9-week study by Costa et al. (152) found that
8-week training program produces similar hypertro- a group that performed varied exercise selection ex-
phy to performing sets with a constant rest interval perienced more complete development at different
(138,139) sites along the muscles of the extremities compared
to a group that performed non-varied exercise se-
Consensus Recommendations lection, although differences were relatively modest.
These results suggest that there may be a potential
As a general rule, rest periods should last at least benefit to varied exercise selection.
2 minutes when performing multi-joint exercises.
Shorter rest periods (60-90 secs) can be employed Combining multi- and single-joint exercise appears
for single-joint and certain machine-based exercis- to confer a synergistic effect to foster complete
es. Optimal rest interval duration would also be influ- development of the musculature. Brandao et al.
enced by the set end point, as longer rest intervals (153) found that performance of the bench press
are likely needed when sets are performed to mus- (multi-joint exercise) led to the greatest increase in
cular failure. cross-sectional area of the lateral head of the triceps
brachii whereas performance of the lying triceps ex-
Exercise Selection tension (single-joint exercise) elicited the greatest
increase in the long head over a 10-week training
Overview period; the combination of the single- and multi-joint
exercises produced the greatest overall increase
Exercise selection refers to the inclusion of specific in cross-sectional area of the triceps brachii as a
exercises in a RT program. Exercise selection in- whole. Similar conclusions can be inferred indirectly
volves several factors including the modality (free- from the literature for the thigh musculature. For ex-
weights, machines, cable pulleys, etc.), the num- ample, multi-joint lower body exercise preferentially
ber of working joints (single- versus multi-joint), the hypertrophies the vasti muscles of the quadriceps,
planes of movement, and the angles of pull. with suboptimal growth of the rectus femoris (154).
On the other hand, performance of the leg exten-
It is well established that muscles have varied at- sion results in preferential hypertrophy of the rectus
tachments, hence providing a diverse ability to carry femoris (155). It seemingly follows that including
out movement in three-dimensional space. Research both types of exercise in a routine would help to
indicates that many of the body’s muscles contain optimize quadriceps development. Similarly, back
subdivisions of individual fibers that are innervated squat training results in minimal hypertrophy of the
by separate motor neurons (140,141). Moreover, hamstrings (154,156,157); thus, targeted single-joint
some muscles are composed of relatively short, hamstrings exercise is needed to fully develop this
in-series fibers that terminate intrafascicularly (142). muscle complex.
A compelling body of evidence indicates that skel-
etal muscle hypertrophies in a non-uniform manner
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International Journal of Strength and Conditioning. 2021 Hypertrophy in an Athletic Population: Position Stand of the IUSCA
There appears to be a hypertrophic benefit to work- group gained slightly more lean body mass than a
ing muscles at longer muscle lengths (158). This group with a fixed exercise selection.
suggests that exercise selection should focus on
placing the target muscle in a stretched position. For Logically, it makes sense to keep exercises involv-
example, greater hypertrophy has been demonstrat- ing complex movement patterns (e.g., squats, rows,
ed in the hamstrings when performing the seated- presses, etc.) as regular components of a routine.
versus lying leg curl (159). Similar strategies should This helps to ensure preservation of motor skills in
therefore be employed to maximize the length-ten- these exercises over time. Alternatively, less com-
sion relationship when determining exercise selec- plex exercises (e.g., single-joint and machine-based
tion in program design. exercises) can be rotated more liberally to provide
recurring novel stimuli to the musculature. In support
Gaps in the Literature of this notion, Chillibeck et al. (164) found delayed
hypertrophy in the trunk and legs (observed only at
The use of different exercise modalities may play a post-study, not mid), but not in the biceps brachii
role in the hypertrophic response to RT. In particular, (observed both at mid- and post-study) in a group
machines limit degrees of freedom and thus afford performing leg press, bench press and arm curls.
the ability to better target individual muscles; howev- The authors concluded that the single-joint arm curl
er, this outcome occurs at the expense of stimulating was easier to learn and therefore induced an earli-
various synergists and stabilizers. Alternatively, free- er hypertrophic stimulus compared to the multi-joint
weight exercises are performed in multiple planes exercises.
and therefore more heavily involve the recruitment of
synergists and stabilizer muscles, albeit with a cor- Consensus Recommendations
responding reduction in stimulation of the agonist.
Thus, the advantages of each modality would seem Hypertrophy-oriented RT programs should include
to be complementary and thus promote a synergis- a variety of exercises that work muscles in differ-
tic effect on hypertrophy when combined. However, ent planes and angles of pull to ensure complete
research on the topic is limited. Schwanbeck et al. stimulation of the musculature. Similarly, program-
(160) reported similar increases in biceps brachii ming should employ a combination of multi- and
and quadriceps femoris muscle thickness regard- single-joint exercises to maximize whole muscle de-
less of whether participants used machines or free- velopment. Where applicable, focus on employing
weights over an 8-week study period; the effects of exercises that work muscles at long lengths.
combining modalities was not investigated. Aere-
nhouts et al. (161) showed no benefit to switching Free-weight exercises with complex movement
between machines and free-weights midway during patterns (e.g., squats, rows, presses, etc.) should
a 10-week RT program compared to either modality be performed regularly to reinforce motor skills. Al-
alone; however, hypertrophy was estimated by cir- ternatively, less complex exercises can be rotated
cumference measurements, hence providing only a more liberally for variety. Importantly, attention must
crude estimate of changes in muscle mass. be given to applied anatomical and biomechanical
considerations so that exercise selection is not sim-
Although it appears beneficial to include a varie- ply a collection of diverse exercises, but rather a
ty of exercises in a hypertrophy-oriented routine, cohesive, integrated strategy designed to target the
research is limited as to how frequently exercises entire musculature.
should be rotated across a given training cycle.
Baz-Valle et al. (162) found that session-to-session Set End Point
rotation of exercises had a detrimental effect on hy-
pertrophy. It should be noted that the variation was Overview
achieved via the use of a computer application that
randomly chose exercises from a database; wheth- Set end point can be operationally defined as the
er results would have differed with a more system- proximity to momentary failure, or more specifically,
atic approach remains undetermined. To this point, “when trainees reach the point despite attempting
Rauch et al. (163) investigated a more systematic to do so they cannot complete the concentric por-
approach of autoregulated exercise selection where tion of their current repetition without deviation from
trained individuals selected one of 3 exercises per the prescribed form of the exercise” (165). This is
session for each muscle group based on personal in contrast to a repetition maximum (RM) i.e., “set
preference. Results showed that the autoregulated endpoint when trainees complete the final repetition
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