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Stronger for Longer:
Concurrent Strength Training
The effect of concurrent strength and endurance training on strength
development and force production:
What the research says and intervention strategies to maximise strength
gains
INTRODUCTION
It is a requirement of numerous sports that participants are able to achieve
high levels of strength and force production whilst also possessing elite
endurance capabilities.
In order to achieve these outcomes in the most efficient manner, many teams
and individuals train for strength and endurance concurrently.
However, from a physiological point of view, strength and endurance training
represent opposite forms of preparation, with strength training consisting of a
small number of muscular contractions performed on a high resistance load
creating near maximal to maximal force, and endurance training consisting of
repeated sub- maximal contractions with a low resistance load (4).
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STRENGTH TRAINING
•
ENDURANCE TRAINING
•
Small number of muscular
contractions
Large number of repeated
contractions
•
High resistance load
•
Low resistance load
•
Near maximal to maximal force
•
Lower force outputs
Further to this, the adaptive responses of skeletal muscle to strength and
endurance training are in conflict as strength training leads to muscle fiber
hypertrophy and is associated with an increase in contractile proteins and
increased maximal contraction force. In contrast, endurance training would
normally not cause muscle fiber hypertrophy but rather an increase in
capillary density, mitochondrial volume density, and oxidative enzyme activity
(7).
Nelson (15) explains that adaptations to exercise are generally considered to
be specific to the training stimulus.
As these two types of training are
performed in such different ways and have almost opposite resulting
adaptations, it would be thought that if strength and endurance were trained
concurrently there would be an interference affect on strength development
and maximal force production when both strength and endurance training are
trained concurrently.
It is imperative that the strength and conditioning professional appreciates the
science behind concurrent strength and endurance training and its effects on
strength development and force production in order to understand how to
employ techniques to minimize any potential deleterious effects of concurrent
training and to ensure that their athletes are not being disadvantaged by the
methodology of training being employed.
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LITERATURE REVIEW
Over the last thirty years, numerous studies have been conducted to
determine if there is a harmful effect on strength development or force
production as a result of concurrent strength and endurance training.
The majority of studies have found that there is some degree of impairment in
strength development when it is trained concurrently with endurance (2, 8, 9,
10, 11, 12, 15).
A small number of studies have shown that concurrent strength and
endurance training may lead to little or no impairment to the expected results
of performing strength training on its own (13, 14, 17), with further research
also presenting the idea that the interference effects of concurrent training
may only be seen when evaluating strength development and force
production at high velocities as a result of the neuromuscular adaptations of
concurrent training (1, 6).
However, the view generally accepted in the professional strength and
conditioning environment is that there is some level of impaired strength and
power gains as a result of concurrent training.
In a 10-week study by Hickson (9), participants were placed into either a
strength training or concurrent strength and endurance-training group. The
results of this study found that both groups of participants increased their
force production capabilities over the ten-week period, however, whilst the
strength training group continued to improve their force production over the
entire ten- week period the concurrent group began displaying a decrease in
force production over the last two weeks of the training program, presenting
that:

Note
Simultaneous training of strength and endurance can lead to a
reduced capacity to develop strength over time.
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Another study, this time by Nelson et al
(15), looked at the effect on strength
production of including endurance
training on the same day that strength
training is performed. The study
involved one group following a strength
only regime 4 days a week for 20 weeks
while a second group performed the same routine but also had endurance
training included on the same days they had their strength sessions.
The results found that:
Although both groups improved their force production capabilities, the
strength only training group showed superior improvements.
Similar results were found by Kraemer et al (11) in a study that tested the
compatibility of high intensity strength and endurance training on hormonal
and skeletal muscle adaptations. The study consisted of thirty- five healthy
men being matched and assigned to one of four training groups that either
performed high intensity strength and endurance training, high intensity
endurance training, upper body only strength and endurance training, or high
intensity strength training. From this investigation it was concluded that the
combination of strength and endurance training results in an attenuation of the
performance improvements and physiological adaptations typical of single
mode training, with the group that trained solely for strength showing
improved strength gains than those of the concurrent group.
Hunter et al (10) also observed the effects of concurrent strength and
endurance training on strength development by having subjects perform either
a strength-training program or a strength-training program that included
endurance based running component. The results of their study further
supported the notion that concurrent training does interfere with force
production with the data showing that:
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The group which trained purely for strength made superior gains in a 1
RM squat when compared to the group that had the running component
included in their regime.
This study also presented the idea that the impairment to strength
development that occurs as a result of concurrent training may be specific to
the muscle groups that are involved in the endurance training.
This assumption is based on the results presenting no
discernible difference in the 1 RM bench press results of
the two groups, but a large discrepancy being found
between the two groups’ results in the 1 RM squat due
to the fact that running was performed as the endurance
component of this study.
In a similar study, Hennessy and Watson (8) looked at the effects of three
preseason-training programs (endurance, strength, and combined strength
and endurance) on endurance, strength, power, and speed.
They found that all training programs led to positive gains in endurance and
upper body strength but gains in lower body strength, power production,
and speed were compromised in the group that trained for both speed
and endurance.
The results of the study by Kraemer et al (11) further strengthens this
hypothesis as results of that study found that all of the groups increased their
1RM for leg press, military press and bench press, however, the increases in
1 RM for the leg press were considerably higher in the strength trained group
than in the concurrent training group that also performed a lower limb
endurance training component.
These studies (8, 10, 11) present the idea that the negative effects of
concurrent training on strength development may be limited to the
muscle groups that are involved in the endurance component.
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A method that can therefore be employed when planning a training schedule
for your athlete may be to not train legs on running days (although this is often
not possible due to training schedules etc).
A potential weekly schedule based on this theory may look as such:
AM
MON
TUE
WED
THU
FRI
SAT
Running/
LB
UB
LB
Running/
LB & UB
Training
Weights
Weights
Weights
Training
Weights
(Optional
Extras)
PM
UB
Running/
Weights
Training
Leveritt, Abernathy, Barry, and Logan (12) reviewed what effect concurrent
strength and endurance training had when compared with strength training
alone. They found that the concurrent training of strength and endurance
does appear to inhibit strength development when compared with
strength training by itself.
In their review they contend that skeletal muscle cannot adapt metabolically or
morphologically to both strength and endurance training simultaneously due
to the many adaptations that occur at the muscular level in response to
strength training being different to those observed after endurance training.
They also discuss the concept that residual fatigue from the endurance
component of concurrent training compromises the ability to develop tension
during the strength element of the concurrent training. As such, the repeated
acute reductions in the quality of the strength training sessions then lead to a
reduction in strength over time. Other factors such as muscle damage and
glycogen depletion are also implicated as possible fatigue mechanisms that
can lead to a decreased quality of strength training when being concurrently
trained with endurance.
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In a study that focused more on the hormonal effects of concurrently training
for strength and endurance, Bell, Syrotuik, Socha, Maclean, and Quinney (2)
observed the effects of strength training and concurrent strength and
endurance training on strength, testosterone, and cortisol levels. The study
consisted of 11 subjects (6 male and 5 female) strength training 3 times a
week for 16 weeks, and 22 subjects (14 male and 8 female) strength training
3 times a week as well as endurance training three times a week on alternate
days. The variables that were tested were serum testosterone (T), and urinary
free cortisol (UC).
The results presented that there was no significant
difference in T with either program, however UC was
significantly raised during the duration of the concurrent
training and only returned to baseline levels 8 weeks after
the conclusion of the concurrent training program.
As
such,
these
results
present
the
notion
that
concurrently training for strength and endurance has a negative effect
on muscular adaptations as the concurrent training raises cortisol levels
in the body which in turn can break down stored protein found in the
skeletal muscle to be used as energy which in turn may lead to
decreased strength and force producing abilities.
The results of numerous other studies have shown that the effects of
concurrently training for strength and endurance on strength development and
force production may in fact be minimal, however, these results are
significantly dependent on specific variables or populations.
Read the following article to better understand the effects of variable selection
on the effects of concurrent training

Take 5
Read the article ‘The influence of dependant variable selection’
found in Appendix 1
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In their research on the interaction between concurrent strength and
endurance training, Sale, MacDougall, Jacobs, and Garner (17) assessed two
separate groups. One group (4 men and 4 women) trained one leg for
strength (S) and the other leg for strength and endurance (S + E). The second
group trained one leg for endurance (E) and the other leg for endurance and
strength (E+S). The results of the study found that concurrent strength and
endurance training did not interfere with strength or endurance
development when compared to the results found by the groups that
trained solely for strength or endurance.
A study by McCarthy, Pozniak, and Agre
(14)
examined
the
neuromuscular
adaptations to concurrent strength and
endurance training. In the study, thirty
sedentary healthy males were randomly
assigned to one of three training groups
that either performed 10 weeks of high intensity strength training (S), cycle
endurance training (E), or concurrent strength and endurance training (CC).
In their conclusion, McCarthy, Pozniak, and Agre present findings that
indicate that concurrent performance of both strength and endurance
training does not impair adaptations in strength, muscle hypertrophy,
and neural activation induced by strength training alone.
In an earlier study by McCarthy et al (13), subjects were placed either into a
strength group, that performed strength training exercises for 3 alternate days
a week for a period of 10 weeks, or into a concurrent group that preformed the
strength training program in addition to an endurance training program for the
3 alternate days.
Their results found that there was no difference in the strength gains made
between the two groups.
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However, the authors did note that because the programs were performed
on alternate days the study allowed for full recovery from each session
and this may explain why similar strength results were found for both
groups.
This long recovery period would also explain the discrepancy between this
study and the hypothesis of Leveritt, Abernathy, Barry, and Logan (12) when
they spoke about residual fatigue from the endurance component of
concurrent training compromising the ability to develop tension during the
strength element of the concurrent training.
When looking at the effects of concurrent strength and endurance training it is
important to evaluate at what the speed the production of force is affected as
most athletes are required to produce force at high velocities.
Haikkenen
et
al
(6)
investigated
the
neuromuscular adaptations during concurrent
strength
and
endurance
training
versus
strength training on its own.
The purpose of the study was to observe the
effects of concurrent strength and endurance training (SE) (2 days on each a
week) versus strength training alone (S) (2 days a week) in men [SE; n=11;
38 (5) years, S; n=16; 37 (5) year] over a training period of 21 weeks.
From the results found in this study it was observed that the concept of the
interference effect in strength development and muscle hypertrophy when
strength and endurance training is concurrently performed is not fully
supported.
Of greater importance to athletic performance, these results do suggest
that even low frequency concurrent strength and endurance training
leads to interference in explosive strength development mediated in part
by the limitations of rapid voluntary neural activation of the trained
muscles.
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