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Document Text Contents
Page 1

HUMAN KINETICS

Brad Schoenfeld, PhD, CSCS, CSPS, FNSCA
Lehman College, Bronx, New York

Science
AND

Development
OF

Muscle
Hypertrophy

Page 2

Library of Congress Cataloging-in-Publication Data
Schoenfeld, Brad, 1962- , author.
Science and development of muscle hypertrophy / Brad Schoenfeld.

p. ; cm.
Includes bibliographical references and index.
I. Title.
[DNLM: 1. Muscle Development--physiology. 2. Exercise. 3. Physical Fitness. WE 500]
QP303
612.7'6--dc23

2015035559

ISBN: 978-1-4925-1960-7

Copyright © 2016 by Brad Schoenfeld

All rights reserved. Except for use in a review, the reproduction or utilization of this work in any form or
by any electronic, mechanical, or other means, now known or hereafter invented, including xerography,
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E6681

Page 112

Science and Development of Muscle Hypertrophy

102

any definitive conclusions as to what, if any,
effects aerobic intensity has on hypertrophy
during concurrent training.

Volume and Frequency
Volume may have the biggest impact on the
hypertrophic interference associated with
concurrent training, potentially related to
overtraining symptoms induced by a catabolic
hormonal environment and chronic muscle
glycogen depletion (493). This contention is
supported by research showing attenuations
in maximal strength with frequencies of more
than 3 sessions per week but not less than 2
sessions per week (238). Pooled data from
Wilson and colleagues (831) revealed a sig-
nificant negative correlation between muscle
hypertrophy and the volume (duration and
frequency) of aerobic exercise during con-
current training. With respect to the specific
components of volume, inverse correlations
were especially strong for the duration of exer-
cise (r = .75), whereas frequency displayed a
relatively weak correlation (r = .26).

The effect of varying aerobic frequencies on
muscular adaptations was directly studied in
the context of a concurrent training program
(344). Subjects performed a 3-day-a-week
resistance protocol and supplemented it with
0, 1, or 3 days of aerobic endurance training.
Results showed an inverse dose–response
relationship between increases in limb girth
and aerobic frequency (4.3%, 2.8%, and 1%
for the 0-, 1-, and 3-day-a-week conditions).
These findings indicate that the frequency of
aerobic endurance training should remain low
if muscle hypertrophy is the primary desired
outcome.

Mode
Although aerobic exercise can be carried out
using a variety of modalities, running and
cycling have primarily been studied in the
context of concurrent training. The meta-anal-
ysis by Wilson and colleagues (831) revealed
that running had a particularly negative effect
on the hypertrophic adaptations associated
with resistance training, whereas cycling did
not appear to cause a significant detriment.
The authors speculated that running-related
impairments on muscle growth could be
related to excessive muscle damage caused
by its high eccentric component. Conceiva-
bly, this could inhibit recuperative abilities
and thus blunt the postexercise adaptive
response. Alternatively, they proposed that
cycling has greater biomechanical similarities
to multijoint free weight exercise compared
to running and therefore may have provided
a greater transfer of training. Counterintui-
tively, Panissa and colleagues (556) reported
that high-intensity aerobic cycling negatively
affected strength to a greater degree than
high-intensity treadmill running when per-
formed immediately prior to a resistance train-
ing bout. Over time, this would likely have a
detrimental impact on hypertrophy as a result
of chronic reductions in mechanical tension.

Scheduling
Depending on the scope of the training
program, aerobic endurance exercise can be
performed either in the same session with
resistance training or on alternate days. Sev-
eral studies have examined how the order of
aerobic and resistance exercise performed in
the same session affects intracellular signaling
responses. Coffey and colleagues (151) inves-
tigated the acute effects of a combined session
of knee extension resistance exercise and
moderate-intensity cycling. Cycling before
resistance exercise resulted in a heightened
phosphorylation of Akt but a reduction in
IGF-1 mRNA; alternatively, reversing the order
of performance elevated concentrations of
MuRF-1 mRNA. Follow-up work by the same
lab revealed that performing a high-intensity
sprint cycling bout prior to knee extensions

KEY POINT
If hypertrophy is the desired outcome, the
frequency of aerobic endurance training
should remain low and a lengthy interven-
ing recovery period should be inserted be-
tween aerobic and resistance bouts. Perhaps
even better, the two should be performed on
separate days.

Page 113

Role of Aerobic Training in Hypertrophy

103

CONCURRENT TRAINING

Research indicates that concurrent training can have a negative impact on hypertrophic
adaptations. Mitigating aerobic volume, intensity, or both reduces the potential for
any negative consequences associated with the strategy. Non-weight-bearing aer-
obic activities such as cycling appear to attenuate deleterious effects compared to
running, although some evidence is contradictory. There is an absence of research
on the effects of cross-training on various modalities in the context of a regimented
resistance training program. Whether such variation would enhance or hinder results
remains speculative.

The majority of concurrent training studies have been carried out with untrained
subjects, making it difficult to extrapolate conclusions to physically active people. The
few studies that have employed subjects experienced in exercise training indicate
greater interference in those who are well trained. Kraemer and colleagues (389)
investigated the compatibility of aerobic and resistance exercise in a group of army
recruits involved in standard military training for at least 3 days per week for 2 years
before the onset of the study. Subjects were randomly assigned to perform aerobic
endurance exercise, resistance exercise, or concurrent training. The aerobic endur-
ance protocol consisted of a combination of steady-state and high-intensity interval
training. After 12 weeks, subjects in the resistance-only group displayed increases in
Type I, Type IIa, and Type IIc fiber diameters, whereas those in the concurrent group
showed significant increases only in Type IIa fibers. Bell and colleagues (66) found
similar results in a group of physically active university students, at least some of
whom had experience in strength and aerobic endurance training. Subjects performed
12 weeks of cycle ergometry, resistance training, or a combination of both modalities.
Results showed that resistance training only increased both Type I and Type II fiber
cross-sectional area, whereas concurrent training produced increases only in Type II
fibers. Moreover, the magnitude of Type II fiber hypertrophy was markedly greater
in the resistance-only group compared to those who performed concurrent training
(28% vs. 14%, respectively). Taken together, these findings suggest that concurrent
training may be particularly detrimental to those with training experience.

Consideration also must be given to the relatively short duration of most concur-
rent training studies. Hickson (306) found no evidence of interference in a combined
aerobic and resistance protocol until the 8th week of training. This finding indicates
that negative effects on hypertrophy may not manifest for months, but ultimately
long-term increases in muscle size would be compromised.

RESEARCH FINDINGS

blunted phosphorylation of p70S6K compared
to performing resistance exercise first (150).
Moreover, the upregulation of translation
initiation via the PI3K/Akt signaling pathway
may be altered when resistance training is
performed after glycogen depleting aerobic
exercise (160). Combined, these findings sug-
gest greater interference when aerobic exercise
precedes a resistance bout.

Data on the long-term effects of the order
of same-day concurrent training on muscular
adaptations are limited. Multiple studies show
that strength gains are similar regardless of the
sequence of training (138, 153, 264). Hence,
mechanical tension does not appear to be
compromised by the order of performance.
From a hypertrophy standpoint, Cadore and
colleagues (113) found similar increases in

Page 223

213

ABOUT THE AUTHOR

Brad Schoenfeld, PhD, CSCS, CSPS, FNSCA,
is widely regarded as one of the leading
strength and fitness experts in the United
States. The 2011 NSCA Personal Trainer of
the Year is a lifetime drug-free bodybuilder
who has won numerous natural bodybuild-
ing titles, including the All-Natural Physique
and Power Conference (ANPPC) Tri-State
Naturals and USA Mixed Pairs crowns. As
a personal trainer, Schoenfeld has worked
with numerous elite-level physique athletes,
including many top pros. Also, he was elected
to the National Strength and Conditioning
Association’s Board of Directors in 2012.

Schoenfeld is the author of multiple con-
sumer-oriented fitness books, including The
M.A.X. Muscle Plan and Strong and Sculpted

(formerly Sculpting Her Body Perfect). He is a regular columnist for Muscular
Development magazine, has been published or featured in virtually every major
fitness magazine (including Muscle and Fitness, MuscleMag, Ironman, Oxygen, and
Shape), and has appeared on hundreds of television shows and radio programs
across the United States. He also serves as a fitness expert and contributor to
www.bodybuilding.com, www.diet.com, and www.t-nation.com.

Schoenfeld earned his PhD in health promotion and wellness at Rocky Moun-
tain University, where his research focused on elucidating the mechanisms of
muscle hypertrophy and their application to resistance training. He has published
more than 80 peer-reviewed scientific papers and serves on the editorial advisory
boards for several journals, including the Journal of Strength and Conditioning
Research and Journal of the International Society of Sports Nutrition. He is an assis-
tant professor of exercise science at Lehman College in the Bronx, New York, and
heads their human performance laboratory.

Visit his blog at www.workout911.com.

Page 224

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