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High volume of endurance training impairs adaptations to 12
weeks of strength training in well-trained endurance athletes
Running head: “Concurrent training adaptations”
Bent R. Rønnestad1, Ernst Albin Hansen2, and Truls Raastad2
1Lillehammer University College, Lillehammer, Norway
2Norwegian School of Sport Sciences, Oslo, Norway
Corresponding author:
Bent R. Rønnestad
Lillehammer University College
PB. 952, 2604 Lillehammer
Norway
E-mail: bent.ronnestad@hil.no Phone: +47 61288193 Fax: +47 61288200
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Abstract
The purpose of the present study was to compare the effect of 12 weeks of strength training
combined with a large volume of endurance training with the effect of strength training alone
on strength training adaptations. Well-trained cyclists with no strength training experience
performed heavy strength training twice a week in addition to a high volume of endurance
training during a 12-week preparatory period (S+E; n=11). A group of non strength-trained
individuals performed the same strength training as S+E, but without added endurance
training (S; n=7). Thigh muscle cross-sectional area, 1 repetition maximum (1RM) in leg
exercises, squat jump performance, and peak rate of force development (RFD) were
measured. Following the intervention period, both S+E and S increased 1RM strength, thigh
muscle cross-sectional area, and squat jump performance (p<0.05), and the relative
improvements in S were greater than in S+E (p<0.05). S increased peak RFD while S+E did
not, and this improvement was greater than in S+E (p<0.05). To the best of our knowledge,
this is the first controlled study to demonstrate that the strength training response on muscle
hypertrophy, 1RM strength, squat jump performance, and peak RFD is attenuated in well-
trained endurance athletes during a period of concurrent endurance training.
Key words: CONCURRENT TRAINING, CYCLING, HYPERTROPHY, JUMPING
ABILITY, WEIGHT TRAINING
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INTRODUCTION
In accordance with the principle of training specificity, strength training and endurance
training induce quite different muscular adaptations. Consequently, endurance athletes have
historically been reluctant to include heavy strength training as a part of their normal training.
However, during the last decade, endurance athletes have been encouraged to add strength
training to their normal endurance training to further improve endurance performance (e.g.
Hoff et al. 1999; Millet et al. 2002; Rønnestad et al. 2010; 2011; Sunde et al. 2010; Turner et
al. 2003). These recommendations are based on studies in which some endurance athletes
performed strength training in addition to their normal endurance training, while others
formed a control group that simply continued the normal endurance training. In most of these
studies increased strength and endurance performance, together with no change in body mass
were reported (e.g. Hoff et al. 1999; Millet et al. 2002; Støren et al. 2008; Sunde et al. 2010).
Several authors suggested that the normal muscle hypertrophy response to strength training
was absent in these studies (e.g. Hoff et al. 1999; Støren et al. 2008; Sunde et al. 2010),
although no measurements of cross-sectional area (CSA) of the strength-trained muscles were
included. Lack of hypertrophic response to strength training indicates attenuated strength
training adaptations. However, without a control group performing the identical strength
training program as the endurance athletes, but without performing the endurance training, it
is difficult to conclude whether a high volume of endurance training in fact inhibits strength
training adaptations.
The pioneering work of Hickson (1980) revealed that concurrent strength and endurance
training attenuated the increase in maximal muscle strength compared with a group
performing strength training only. A number of subsequent investigations have either
confirmed (e.g. Bell et al. 2000; Dudley and Djamil 1985; Kraemer et al. 1995) or
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contradicted (e.g. Häkkinen et al. 2003; Leveritt et al. 2003; McCarthy et al. 1995; 2002) this
finding. A closer look at studies finding attenuated strength gains from concurrent strength
and endurance training reveals that the examined muscles were exposed to at least six training
days per week, and this was observed in both untrained and moderately trained muscles (e.g.
Bell et al. 2000; Dudley and Djamil 1985; Hickson 1980; Kraemer et al. 1995). In the studies
finding no strength gain attenuation, fewer training days were performed, suggesting that
strength gains may be attenuated when endurance training frequency and/or volume is too
high. In line with this, no muscle fibre hypertrophy was reported in the few studies on
endurance athletes in whom biopsies were performed (Aagaard et al. 2011; Bishop et al.
1999; Hickson et al. 1988). Unfortunately, neither of these studies included a group
performing strength training only. Furthermore, it should be noted that the fibre area of both
muscle fibre type I and type II has been found to vary significantly within the m. vastus
lateralis, meaning that fibres in the deep parts of the muscle are larger than those located
superficially (Lexell and Taylor 1989). In addition, the size relationship between type I and II
fibres varies within the muscle (Lexell and Taylor 1989). This means that analyses of muscle
fibre area should preferably be accompanied by multiple-site measures at the whole muscle
level (e.g. using MRI, CT, or DEXA). Nutrition is another factor that can potentially influence
the adaptations to strength training. Energy deficit is known to have a negative effect on
muscle hypertrophy (Houston 1999; Lambert et al. 2004), and may partly explain the
attenuated strength training adaptations observed in untrained subjects when concurrent
training is performed at a high training frequency. However, determining dietary intake is
challenging and is consequently rarely performed in longitudinal studies. In the present study
dietary intake was determined by a weighted food intake method.
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It has been suggested that training-induced changes in the ability to develop force during high
shortening velocities and rate of force development (RFD) are more attenuated than changes
in the ability to produce high force during low shortening velocities, when strength training is
combined with endurance training (Dudley and Fleck 1987, Rhea et al. 2008). Vertical jump
power can be assessed in a reliable way during vertical jumping (Samozino et al. 2008). It is
important to note that this assessment is not based solely on the recording of maximal
jumping height, and thus maximal jumping height must not be considered a surrogate measure
per se of maximal leg extension power. In trained rugby players as well as in untrained
subjects there has been observed superior improvement in vertical jump performance after
strength training alone compared to concurrent strength and endurance training (Hennessy &
Watson 1994, Hunter et al. 1987). In the present study we further explored these observations
and investigated the effect of combining strength training with a high endurance training
volume on changes in vertical jump ability, and isometric RFD characteristics of the muscle.
To the best of our knowledge, no studies investigating the effect of supplementing the
endurance training with strength training, in not-strength trained but well trained endurance
athletes, have compared the strength training adaptations with a not-strength trained control
group performing strength training only. Consequently, the purpose of the present study was
to investigate the effects of 12 weeks of strength training combined with a high volume of
endurance training in previously non strength-trained endurance athletes with the effects of
strength training alone on muscle CSA, 1RM, RFD, and vertical jump performance. We
hypothesised that combining strength training with a high volume of endurance training
would reduce strength training adaptations in all parameters investigated in the present study.
METHODS
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Participants
Twelve well-trained cyclists [classified according to the criteria suggested by Jeukendrup et
al. (2000)] and nine recreationally active individuals volunteered for the study, which was
approved by the Southern Norway regional division of the National Committees for Research
Ethics. All participants signed an informed consent form prior to participation. None of the
participants had performed any strength training during the preceding 6 months. One of the
cyclists and two of the recreationally active individuals did not complete the study due to
illness. Their data are not included.
Experimental design
The cyclists (S+E; n=11 [all men], age 27±2 years, height 183±2 cm, body mass 76.1±2.8 kg)
performed heavy strength training in addition to their usual endurance training. The
recreationally active individuals (S; n=7 [all men], age 26 ±2 years, height 180±3 cm, body
mass 75.7±3.4 kg) performed the same strength training regimen as S+E, but performed at
most one endurance training session per week in addition to the strength training. The
intervention was completed during the cyclists’ preparation phase prior to the competition
season. Tests were conducted before (pre-intervention) and after the 12-week intervention
(post-intervention). Prior to the pre-intervention test, two familiarization sessions were
conducted with the purpose of instructing the participants in proper technique and testing
procedure.
Training
Endurance training for S+E consisted primarily of cycling. Endurance training duration was
calculated based on recordings from heart rate monitors (Polar, Kempele, Finland). During the
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12-week intervention period S+E performed a total of 119±13 hours of endurance training,
corresponding to 9.9±1.1 hours pr. week.
Heavy strength training performed by S+E and S targeted leg strength and was performed
twice a week. On days where both strength and endurance training were scheduled for S+E,
the cyclists were encouraged to perform strength training in the first training session of the
day and endurance training in the second session. A review of the cyclists’ training diaries
confirmed that the cyclists largely complied with this guideline. Based on the assumption that
it is the intended rather than actual velocity that determines the velocity-specific training
response (Behm and Sale 1993), the heavy strength training was conducted with emphasis on
maximal mobilization in the concentric phase (lasting around 1 s), while the eccentric phase
was performed more slowly (lasting around 2-3 s).
At the start of each strength training session, participants performed a ~10-min warm-up at
self-selected intensity on a cycle ergometer, followed by two to three warm-up sets of half
squat with gradually increasing load. The performed exercises were: half squat, leg press with
one leg at a time, standing one-legged hip flexion, and ankle plantar flexion. Both intervention
groups were supervised by an investigator at all sessions during the first two weeks and
thereafter at least once every second week for the remainder of the intervention period.
During the first three weeks, participants trained with 10RM sets in the first session in the
week and 6RM sets in the second session. During the next three weeks, sets were adjusted to
8RM and 5RM for the first and second weekly sessions, respectively. During the final 6
weeks, sets were adjusted to 6RM and 4RM, respectively (Table 1). Participants were
encouraged to increase their RM loads as their strength evolved throughout the intervention
period and assistance was permitted during the last repetition. The number of sets in each
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exercise was always three, with 1.5-2 min rest between sets. Adherence to the strength
training program was high, with S+E and S completing 97±1% and 92±2% of the prescribed
strength training sessions, respectively.
(Insert Table 1 about here)
Testing
Testing was completed as follows: day 1) measurement of thigh muscle CSA; day 2)
measurement of squat jump height, RFD, and 1RM. The participants were instructed to
refrain from intense exercise the day preceding testing, and to consume the same type of meal
before each test. They were not allowed to eat during the hour preceding the test or to
consume coffee or other products containing caffeine during the preceding three hours.
Testing at pre- and post-intervention was overseen by the same investigator and conducted on
the same equipment with identical subject/equipment positioning and performed at the same
time of day to avoid influence of circadian rhythm. The post-intervention strength test was
conducted 3-5 days after the last strength training session.
Thigh muscle cross-sectional area
Magnetic resonance tomography (MR) (Magnetom Avanto 1.5 Tesla, Siemens AG, Munich,
Germany) was used to measure thigh muscle CSA. Participants were scanned in supine
position. The feet were fixed and elevated by a pad placed on the back of the knees to prevent
the muscles on the back of the thighs from compressing against the bench. The machine was
centered 2/3 distally on the femur and nine cross-sectional images were sampled starting at
the proximal edge of the patella and moving towards the iliac crest, with 35 mm interslice
gaps. Each image represented a 5 mm thick slice. The images were subsequently uploaded to
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a computer for further analysis. The images of the thigh muscles were divided into knee
extensor and knee flexor/adductor compartments using a tracer function in the software. The
CSA of the thigh muscles was measured from the five most proximal images and the average
CSA of these five images was used for statistical analysis.
Squat jump height
On the second test day, the participants performed a 10-min warm-up on a cycle ergometer.
Squat jump performance was tested on a force plate (SG-9, Advanced Mechanical
Technologies, Newton, Mass., USA, sampling frequency of 2 KHz). The hands were kept on
the hips throughout the jump, knees were flexed to 90º, and the participants were instructed to
execute a maximal vertical jump from a standing static flexed position (held in 3 seconds
before take-off). No downward movement was allowed prior to the maximal vertical jump,
and the force curves were inspected to verify this. Vertical jumping height was calculated
from the impulse from the ground reaction force. Each participant performed four attempts,
with 1 minute rest between each jump. The participants were blinded to the results. The best
jump from each participant was used in data analysis (CV<3%).
Peak rate of force development
After five minutes of rest, peak RFD was measured during isometric half squat in a custom-
built rack that was bolted to the floor located over a force plate (SG-9, Advanced Mechanical
Technologies, Newton, Mass., USA, sampling frequency of 2 KHz). The knee angle during
the half squat was 90°. To ensure similar position during all tests, each participant’s squat
depth and placement of the feet was carefully monitored and marked on the rack and on the
force plate, respectively. Verbal encouragement was given throughout the test and each action
was sustained for approximately 3 s. The participants were instructed to perform the muscle
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activation as quickly and forcefully as possible. The participants were blinded to the results.
Four attempts were performed with 2-min recovery between each attempt. Custom made
software was used for the subsequent analysis of peak RFD (N·s-1), which was defined as the
peak slope of the force-time curve (MATLAB R2007a, version 7.4, MathWorks, Nitick,
Massachusetts, USA). Peak RFD was determined as the peak average slope in moving 2.5 ms
time intervals (in the range from 20% to 80% of maximal voluntary force). A 2nd order
lowpass digital Butterworth filter was used with a cut off frequency of 50 Hz. The average of
the three highest values of peak RFD was used in the statistical analysis.
1RM
After five minutes of rest, maximal strength of the leg extensors was measured as 1RM. 1RM
was first measured in half squat and thereafter in leg press. 1RM in half squat was measured
using a Smith machine. The average of the 1RM in the two exercises was used in statistical
analysis. To ensure similar knee angles during all tests, the participant’s knee flexion depth
(to 90°) was carefully monitored and marked on a scale on both the leg press machine and the
Smith machine. Thus, each participant had to reach his individual depth marked on the scale
for the lift to be accepted. In both exercises participants performed a standardized warm-up
protocol consisting of 3 sets with gradually increasing load (40%, 75%, and 85% of predicted
1RM) and decreasing number of repetitions (10, 7, and 3, respectively). Similarly, the
placement of the feet was monitored for each participant to ensure identical test positions
during both tests. The first 1RM attempt was performed with a load approximately 5% below
the predicted 1RM load. Both 1RM exercises included a preceding eccentric phase. After each
successful attempt, the load was increased by 2%-5% until the participant failed to lift the
same load after 2-3 consecutive attempts. The rest period between each attempt was 3 min.
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Dietary intake
In the 6th training week, the participants recorded their daily dietary intake for a 4-day period
(Wednesday to Saturday) using a weighted food intake method, which is recognized as a valid
method (Bingham 1987) when participants are not supervised 24 hours a day. The participants
were given food record journals and digital food weighing scales (Vera 67002; Soehnle-
Waagen GmbH & Co, Murrhardt, Germany; precision 1 g). They were also given detailed
verbal and written guidelines about how to carry out this method. Dietary assessment data
were analyzed using a nutrient analysis program (Mat på data 5.1; LKH, Oslo, Norway).
Statistics
All data in the text, figures, and tables are presented as mean±SE. To test for differences
between groups at pre-intervention, unpaired Student’s t-tests were used. Pre- and post-
intervention measurements for each group were compared using paired Student’s t-test. To
test for differences in relative changes (from pre- to post-intervention) between the groups,
unpaired Student’s t-tests were performed. Student’s t-tests were performed in Excel 2003
(Microsoft Corporation, Redmond, WA, USA). Correlation analyses (Pearson product-
moment correlation coefficient) was performed using GraphPad InStat (GraphPad Software,
Inc. CA, USA). All analyses resulting in p≤0.05 were considered statistically significant.
RESULTS
Comparison of groups at baseline
There were no significant differences between S+E and S at baseline with respect to body
mass, BMI, thigh muscle CSA (Figure 2), 1RM (Figure 3), squat jump height (Figure 4), or
peak RFD (Figure 5).
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Training load, strength, thigh muscle cross-sectional area, and body mass
The S group increased their average weekly training load in the strength exercises from the
first training week to the last training week to a greater extent than the S+E group in both
absolute and relative terms (from 108±3 kg to 159±3 kg for S vs. from 109±5 kg to 147±6 kg
for S+E, p < 0.05; Figure 1). The mean 1RM in half squat and leg press increased by 35±4%
in S and 25±2% in S+E (p<0.01; Figure 2). The relative increase in 1RM was larger in S than
in S+E (p<0.05; Figure 2). Thigh muscle CSA (sum of flexors and extensors) increased in
both groups, but more in S than in S+E (8.0±0.8% vs. 4.3±0.7%, respectively, p<0.05; Figure
3). Body mass increased from pre- to post-intervention in S by 1.6% (from 75.7±3.4 kg to
76.9±3.3 kg, p<0.05), while there was no change in body mass in S+E.
(Insert Figure 1 about here)
(Insert Figure 2 about here)
(Insert Figure 3 about here)
Squat jump performance and RFD
Both S and S+E increased squat jump performance, but the increase in squat jump
performance was larger in S than in S+E (13.0±2.0% vs. 6.2±1.6%, respectively p<0.05;
Figure 4). There was no change in peak RFD in S+E, while S increased peak RFD by 15±5%
during isometric half squat (p<0.05; Figure 5). The relative increase in peak RFD was larger
in S than in S+E (p<0.05).
(Insert Figure 4 about here)
(Insert Figure 5 about here)
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Dietary intake
No difference in intake of total energy, protein, carbohydrate, or fat was observed between
groups (Table 2).
(Insert Table 2 about here)
DISCUSSION
The primary finding in this study was that endurance athletes who combined strength training
with a high volume of endurance training experienced attenuated strength training
adaptations, measured as changes in 1RM, thigh muscle cross sectional area, jump
performance, and rapid force generation compared with a group of recreationally active
individuals performing a similar amount and type of strength training only.
1RM and thigh muscle CSA
During the 12-week intervention period, leg strength in S+E increased by ~25%. This result is
in accordance with other studies reporting 16-35% increase in 1RM muscle strength after 10
to14 weeks of heavy strength training in endurance athletes (runners, cross-country skiers,
and cyclists) (Bishop et al. 1999; Hickson et al. 1988; Johnston et al. 1997; Losnegard et al.
2011; Millet et al. 2002). The observed improvement in 1RM in S+E is in the lower range of
the expected strength improvement when individuals with no prior strength training
experience perform 10-12 weeks of strength training (Kraemer et al. 2002). In the previous
studies, the strength training adaptations of endurance athletes has not been directly compared
with adaptations in individuals performing the exact same strength training without any
endurance training. Consequently, it has been difficult in those studies to conclude whether
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strength training adaptations was attenuated when endurance athletes combined a high volume
of endurance training with strength training. In the present study, strength training without
concurrent endurance training resulted in a superior increase in 1RM compared with
concurrent strength and endurance training. The present finding of attenuated adaptation in
1RM strength in the endurance athletes agrees with findings for active individuals, although
not endurance athletes, who added a high frequency of endurance training (≥3 sessions per
week) to strength training (Bell et al. 2000; Hennessy and Watson 1994; Hickson 1980;
Kraemer et al. 1995). Importantly, it seems that a smaller endurance training volume (≤2
sessions a week) does not attenuate the 1RM adaptations to strength training (Glowacki et al.
2004; Häkkinen et al. 2003; McCarthy et al. 2002). The order of training sessions on days
where both strength training and endurance training were performed may potentially influence
the attenuated response to strength training in S+E. In the present study, the strength training
was performed as the first training session of the day and endurance training as the second
session. It has been observed that, in untrained subjects, improvement in endurance
performance was greater when, in the same session, the endurance training preceded the
strength training (Chtara et al. 2005). However, similar interactions are not reported for the
adaptation in muscle strength and power (Chtara et al. 2008, Gravelle & Blessing 2000).
Importantly, strength- and endurance training was not performed during the same session in
the present study, but separated by 4 to 6 hours.
The observed attenuated strength gain in the endurance athletes may largely be explained by
impaired muscle hypertrophy. It has frequently been observed that endurance athletes who
add heavy strength training to their endurance training do not gain body mass (e.g. Aagaard et
al. 2011; Hoff et al. 2002; Millet et al. 2002; Storen et al. 2008; Sunde et al. 2010). In the
absence of size measurements of the strength trained muscles, no changes in body weight has
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often been interpreted as no change in muscle size. This relationship has been demonstrated in
studies that have included analyses of muscle fibre area (Bishop et al. 1999; Hickson et al.
1988). However, it should be noted that muscle fibre area is found to vary significantly within
the m. vastus lateralis (Lexell and Taylor, 1989). This variability suggests that analysis of
muscle fibre area should preferably be accompanied by multiple-site measurements at the
whole muscle level (e.g. using MRI or CT) in order to obtain more reliable measures of
changes in muscle size. It must, however, be mentioned that changes in whole muscle CSA
are influenced by changes in muscle architecture (e.g. Aagaard et al. 2001; Blazevich et al.
2007) and therefore, changes in muscle CSA may not per se reflect the corresponding changes
in physiological CSA and hence in maximal force generating capacity. However, the
importance of measuring adaptations at the whole muscle level is underlined by the findings
of Aagaard et al. (2011), who added a lower-body strength training program, similar to the
program used in the present study, to the normal endurance training in elite cyclists. No
change in muscle fibre area from m. vastus lateralis was found despite an increase in lean
body mass (Aagaard et al. 2011). In that study, total body mass did not change even though
total lean body mass increased. Because only lower-body strength training was performed, it
is likely that the observed changes in lean body mass occurred in the muscles engaged in the
strength training exercises. Similarly, a recent study conducted with cross-country skiers
found increased muscle CSA in m. triceps brachii with no change in total body mass after 12
weeks of concurrent strength and endurance training (Losnegard et al. 2011). Interestingly, in
the latter study a muscle hypertrophy of 5% was observed (Losnegard et al. 2011) and after 16
weeks of concurrent strength and endurance training in elite cyclists lean body mass increased
with 3% (Aagaard et al. 2011). These results suggest an impaired hypertrophic response to the
performed strength training when compared to expected changes in normal active subjects
(e.g. Wernbom et al. 2007). However, because those studies did not include a control group
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performing the same strength training program as the endurance athletes, the exact impact of
endurance training on the strength training adaptations could not be assessed. Participants in
the present study performed a strength training program that was quite similar to what was
performed on m. triceps brachii in the Losnegard et al. (2011) study, and the increase in
muscle CSA was quite similar (~4% for present study; ~5% for Losnegard et al.). The results
from the present study demonstrate that muscle CSA can increase without a change in body
mass. However, since the S group achieved a significantly greater increase in muscle CSA
(~8%) than the S+E group, our results support the hypothesis that a high volume of endurance
training attenuates the hypertrophic adaptations to strength training.
Due to practical challenges with regard to recruiting well-trained endurance athletes for
muscle biopsies, the intracellular mechanisms responsible for the present observation of
attenuated hypertrophic adaptation to strength training was not addressed in the present study.
However, the nutritional data allow some speculations. When assessed halfway in the time
course of training there was no difference between groups in intake of protein, carbohydrate,
and fat. The daily protein intake for both groups was within ACSM`s recommendations for
endurance- and strength-trained athletes (ACSM 2009). However, protein synthesis is an
ATP-dependent process; thus, muscle protein synthesis may be increased during periods of
positive energy balance and attenuated during periods of negative energy balance (Lambert et
al. 2004). In young healthy males it has been observed that energy intake above what is
needed for weight maintenance increases muscle hypertrophy (Rozenek et al. 2002). When
we examined the total energy intake for the two groups, we observed that there was no
difference between the groups even though the S+E group performed ~10 hrs of endurance
training per week in addition to the strength training. It is then likely that the lower activity
related energy expenditure in S resulted in a positive energy balance and thus a more optimal
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environment for muscle hypertrophy. The fact that body mass increased for S but not for S+E
during the intervention period supports such a scenario. Furthermore, it has been shown that a
small positive energy balance ensures a positive anabolic hormonal milieu (Houston 1999).
The carbohydrate intake in S+E during the nutritional registration was lower than
recommended by the ACSM (2009). Whether this was an underestimate or not remains
unclear, but no change in total body weight during the 12 weeks intervention period suggests
at least that that the total energy intake was adequate for weight maintenance. However, low
muscle glycogen may impair the intracellular signalling pathways responsible for
hypertrophy, and may thus potentially contribute to the observed attenuation of strength
training adaptations in S+E (Hawley 2009). Because gains in body mass may compromise
performance in the majority of endurance sports, we suggest that the above observations of
energy intake in the present study are likely to be generalizable to other populations of
endurance athletes. We therefore suggest that the often observed attenuated hypertrophic
response when a high volume of endurance training is added to strength training might partly
be due to a lack of positive energy balance.
Recent discoveries within molecular sports science suggest that endurance training may
negatively affect intracellular pathways important for myofibrillar protein synthesis (reviewed
in Hawley 2009). Activation of adenosine monophosphate-activated protein kinase (AMPK)
by endurance exercise may inhibit mammalian target of rapamycin (mTOR) signalling and
suppress strength exercise-induced myofibrillar protein synthesis (Hawley 2009, Nader 2006).
Consequently, it may be suggested that the acute intracellular signalling response to
concurrent strength and endurance training, does not promote ideal activation of pathways
responsible for muscle hypertrophy (Coffey et al. 2009). Observations of disparate mRNA
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response to concurrent strength and endurance training underline the importance of local
factors in explaining compromised strength training adaptations to a large volume of
concurrent training (Coffey et al. 2009). Furthermore, high volume endurance training
appears to compromise strength training adaptations only when both modes of training engage
the same muscle groups (Bell et al. 1991; Hennessy and Watson 1994; Kraemer et al. 1995).
Squat jump and peak RFD
The finding of improved jump performance in the S+E group is in agreement with previous
studies involving distance runners and soccer players adding strength training to their normal
training (Rønnestad et al. 2008; Spurrs et al. 2003; Turner et al. 2003). Increased jumping
ability is an expected adaptation when individuals with no prior strength training experience
complete a period of strength training (e.g. Cormie et al. 2010). However, since none of the
cited studies included a control group performing the same strength training program without
concurrent endurance training, it is difficult to determine whether or not adaptations were
impaired by the concurrent endurance training. An impaired adaptation with concurrent
endurance training was found in the present study: the S group achieved a significantly greater
increase in vertical jump performance than the S+E group. This finding has been corroborated
by other studies, in which no improvement in vertical jump performance was observed after
adding strength training to a high volume of endurance training (Losnegard et al. 2011; Millet
et al. 2002). Vertical jump performance has been shown to accurately evaluate power
development in the lower limbs extensor muscles (Samozino et al. 2008). It has been
suggested that the ability to develop high power output and RFD is more inhibited by
combining strength training with high volume endurance training than the ability to produce
high force during low muscle shortening velocities; such as for example during a 1RM lift
(Dudley and Djamil 1985; Dudley and Fleck 1987; Häkkinen et al. 2003; Kraemer et al. 1995;
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Rhea et al. 2008). Indeed, Häkkinen et al. (2003) did not find any improvement in RFD in the
group performing concurrent training despite increased muscle size and 1RM strength, while
the group performing only strength training improved peak RFD. However, others have
observed increased RFD in response to concurrent strength and endurance training in
endurance trained athletes (Aagaard et al. 2011). In the present study, S+E did not improve
peak RFD, while S increased peak RFD by 15%. The lack of improvement in peak RFD as
well as less increase in 1RM, likely explains the inferior improvement in vertical jump ability
in S+E compared to S. This notion is partly supported by the findings of a correlation between
relative changes in 1RM and relative changes in vertical jump ability in the present study
(r=0.46, p=0.05). Unfortunately, the present study did not include measurement of muscle
activation, so it is difficult to speculate on the influence of neural adaptations. Häkkinen et al.
(2003) suggested that lack of improvement in RFD after concurrent strength and endurance
training was due to lack of improvement in rapid voluntary neural activation. On the other
hand, endurance training by itself may induce fibre atrophy (Kraemer et al. 1995, Widrick et
al. 1996) and reduce the maximum shortening velocity of the type II fibres and is known to
reduce peak tension development in all fibre types (Fitts et al. 1989). Consequently, both
neural and muscular adaptations may explain the impaired ability to rapid force generation
when combining a large volume of endurance training with strength training.
A limitation of the present study is that there may be differences in genes between endurance
athletes and recreationally active individuals which might affect strength training adaptations.
The fibre type distribution in the two intervention groups was not measured. If there were a
greater percentage of type I fibres in the endurance trained cyclists than in the recreational
active participants, this could affect the outcome of the study possibly due to a lower
hypertrophic response in type I fibres (e.g. Hather et al. 1991). No measurement of fibre type
20
distribution was performed in the present study, which must be kept in mind when the present
results are interpreted.
In conclusion, the present data expands on previous findings of attenuated strength training
adaptations when a relatively high volume of endurance training is combined with strength
training. To the best of our knowledge, this is the first controlled study to suggest that the
effect of strength training on muscle hypertrophy, 1RM strength, squat jump performance,
and peak RFD is attenuated in well-trained endurance athletes during a period of concurrent
endurance training.
Acknowledgements
The authors express their thanks to the participants for their time and effort.
There is no conflict of interest. No funding was received for this work.
21
References
Aagaard P, Andersen JL (2010) Effects of strength training on endurance capacity in top-level endurance athletes. Scand J
Med Sci Sports 20 Suppl 2:39-47
Aagaard P, Andersen JL, Bennekou M, Larsson B, Olesen JL, Crameri R, Magnusson SP, Kjaer M (2011) Effects of
resistance training on endurance capacity and muscle fiber composition in young top-level cyclists. Scand J Med Sci Sports.
doi:10.1111/j.1600-0838.2010.01283.x
Aagaard P, Andersen JL, Dyhre-Poulsen P, Leffers AM, Wagner A, Magnusson SP, Halkjaer-Kristensen J, Simonsen EB
(2001) A mechanism for increased contractile strength of human pennate muscle in response to strength training: changes in
muscle architecture. J Physiol 534:613-623
American Dietetic Association; Dietitians of Canada; American College of Sports Medicine, Rodriguez NR, Di Marco NM,
Langley S. American College of Sports Medicine position stand (2009) Nutrition and athletic performance. Med Sci Sports
Exerc 41:709-731
Behm DG, Sale DG (1993) Velocity specificity of resistance training. Sports Med 15:374-388
Bell GJ, Petersen SR, Wessel J, Bagnall K, Quinney HA (1991) Physiological adaptations to concurrent endurance training
and low velocity resistance training. Int J Sports Med 12:384-390
Bell GJ, Syrotuik D, Martin TP, Burnham R, Quinney HA (2000) Effect of concurrent strength and endurance training on
skeletal muscle properties and hormone concentrations in humans. Eur J Appl Physiol 81:418-427
Bingham SA (1987) The dietary assessment of individuals; methods, accuracy, new techniques and recommendations. Nutr
Abstr Rev 57:705-743
Bishop D, Jenkins DG, Mackinnon LT, McEniery M, Carey MF (1999) The effects of strength training on endurance
performance and muscle characteristics. Med Sci Sports Exerc 31:886-891
Blazevich AJ, Cannavan D, Coleman DR, Horne S (2007) Influence of concentric and eccentric resistance training on
architectural adaptation in human quadriceps muscles. J Appl Physiol 103:1565-1575
Chtara M, Chamari K, Chaouachi M, Chaouachi A, Koubaa D, Feki Y, Millet GP, Amri M (2005) Effects of intra-session
concurrent endurance and strength training sequence on aerobic performance and capacity. Br J Sports Med 39:555-560
Chtara M, Chaouachi A, Levin GT, Chaouachi M, Chamari K, Amri M, Laursen PB (2008) Effect of concurrent endurance
and circuit resistance training sequence on muscular strength and power development. J Strength Cond Res 22:1037-1045
Coffey VG, Pilegaard H, Garnham AP, O'Brien BJ, Hawley JA (2009) Consecutive bouts of diverse contractile activity alter
acute responses in human skeletal muscle. J Appl Physiol 106:1187-1197
Cormie P, McGuigan MR, Newton RU (2010) Adaptations in athletic performance after ballistic power versus strength
training. Med Sci Sports Exerc 42:1582-1598
Dudley GA, Djamil R (1985) Incompatibility of endurance- and strength-training modes of exercise. J Appl Physiol 59:1446-
1451
Dudley GA, Fleck SJ (1987) Strength and endurance training. Are they mutually exclusive? Sports Med 4:79-85
Fitts RH, Costill DL, Gardetto PR (1989) Effect of swim exercise training on human muscle
fiber function. J Appl Physiol 66:465-475
Glowacki SP, Martin SE, Maurer A, Baek W, Green JS, Crouse SF (2004) Effects of resistance, endurance, and concurrent
exercise on training outcomes in men. Med Sci Sports Exerc 36:2119-2127
Gravelle BL, Blessing DL (2000) Physiological adaptation in women concurrently training for strength and endurance. J
Strength Cond Res 14:5-13
Hather BM, Tesch PA, Buchanan P, Dudley GA (1991) Influence of eccentric actions on skeletal muscle adaptations to
resistance training. Acta Physiol Scand 143:177-185
22
Hawley JA (2009) Molecular responses to strength and endurance training: are they incompatible? Appl Physiol Nutr Metab
34:355-361
Hennessy LC, Watson AWS (1994) The interference effects of strength training for strength and endurance simultaneously. J
Strength Cond Res 8:12-19
Hickson RC (1980) Interference of strength development by simultaneously training for strength and endurance. Eur J Appl
Physiol Occup Physiol 45:255-263
Hickson RC, Dvorak BA, Gorostiaga EM, Kurowski TT, Foster C (1988) Potential for strength and endurance training to
amplify endurance performance. J Appl Physiol. 65:2285-2290
Hoff J, Gran A, Helgerud J (2002) Maximal strength training improves aerobic endurance performance. Scand J Med Sci
Sports 12:288-295
Houston ME (1999) Gaining weight: the scientific basis of increasing skeletal muscle mass. Can J Appl Physiol 24:305-316
Hunter G, Demment R, Miller D (1987) Development of strength and maximum oxygen uptake during simultaneous training
for strength and endurance. J Sports Med Phys Fitness 27:269-275
Häkkinen K, Alen M, Kraemer WJ, Gorostiaga E, Izquierdo M, Rusko H, Mikkola J, Hakkinen A, Valkeinen H, Kaarakainen
E, Romu S, Erola V, Ahtiainen J, Paavolainen L (2003) Neuromuscular adaptations during concurrent strength and endurance
training versus strength training. Eur J Appl Physiol 89:42-52
Jeukendrup AE, Craig NP, Hawley JA (2000) The bioenergetics of World Class Cycling. J Sci Med Sport 3:414-433
Johnston RE, Quinn TJ, Kertzer R, Vroman NB (1997) Strength training in female distance runners: Impact on running
economy. J Strength Con Res 11:224-229
Kraemer WJ, Adams K, Cafarelli E, Dudley GA, Dooly C, Feigenbaum MS, Fleck SJ, Franklin B, Fry AC, Hoffman JR,
Newton RU, Potteiger J, Stone MH, Ratamess NA, Triplett-McBride T; American College of Sports Medicine (2002)
American College of Sports Medicine position stand. Progression models in resistance training for healthy adults. Med Sci
Sports Exerc 34:364-380
Kraemer WJ, Patton JF, Gordon SE, Harman EA, Deschenes MR, Reynolds K, Newton RU, Triplett NT, Dziados JE (1995)
Compatibility of high-intensity strength and endurance training on hormonal and skeletal muscle adaptations. J Appl Physiol
78:976-989
Lambert CP. Frank LL, Evans WJ (2004) Macronutrient considerations for the sport of bodybuilding. Sports Med 34:317-
327
Leveritt M, Abernethy PJ, Barry B, Logan PA (2003) Concurrent strength and endurance training: the influence of dependent
variable selection. J Strength Cond Res 17:503-508
Lexell J, Taylor CC (1989) Variability in muscle fibre areas in whole human quadriceps muscle. How much and why? Acta
Physiol Scand 136:561-568
Losnegard T, Mikkelsen K, Rønnestad BR, Hallén J, Rud B, Raastad T (2011) The effect of heavy strength training on
muscle mass and physical performance in elite cross country skiers. Scand J Med Sci Sports 21:389-401
McCarthy JP, Agre JC, Graf BK, Pozniak MA, Vailas AC (1995) Compatibility of adaptive responses with combining
strength and endurance training. Med Sci Sports Exerc 27:429-436
McCarthy JP, Pozniak MA, Agre JC (2002) Neuromuscular adaptations to concurrent strength and endurance training. Med
Sci Sports Exerc 34:511-519
Millet GP, Jaouen B, Borrani F, Candau R (2002) Effects of concurrent endurance and strength training on running economy
and .VO(2) kinetics. Med Sci Sports Exerc 34:1351-1359
Nader GA (2006) Concurrent strength and endurance training: from molecules to man. Med Sci Sports Exerc 38:1965-1970
Rhea MR, Oliverson JR, Marshall G, Peterson MD, Kenn JG, Ayllón FN (2008) Noncompatibility of power and endurance
training among college baseball players. J Strength Cond Res 22:230-234
Rozenek R, Ward P, Long S, Garhammer J (2002) Effects of high-calorie supplements on body composition and muscular
strength following resistance training. J Sports Med Phys Fitness 42:340-347
23
Rønnestad BR, Hansen EA, Raastad T (2011) Strength training improves 5-min all-out performance following 185 min of
cycling. Scand J Med Sci Sports 21:250-259
Rønnestad BR, Hansen EA, Raastad T (2010) Effect of heavy strength training on thigh muscle cross-sectional area,
performance determinants, and performance in well-trained cyclists. Eur J Appl Physiol 108:965-975
Rønnestad BR, Kvamme NH, Sunde A, Raastad T (2008) Short-term effects of strength and plyometric training on sprint and
jump performance in professional soccer players. J Strength Cond Res 22:773-780
Samozino P, Morin JB, Hintzy F, Belli A (2008) A simple method for measuring force, velocity and power output during
squat jump. J Biomech 41:2940-2945
Spurrs RW, Murphy AJ, Watsford ML (2003) The effect of plyometric training on distance running performance. Eur J Appl
Physiol 89:1-7
Storen O, Helgerud J, Stoa EM, Hoff J (2008) Maximal strength training improves running economy in distance runners.
Med Sci Sports Exerc 40:1087-1092
Sunde A, Støren O, Bjerkaas M, Larsen MH, Hoff J, Helgerud J (2010) Maximal strength training improves cycling economy
in competitive cyclists. J Strength Cond Res 24:2157-2165
Turner AM, Owings M, Schwane JA (2003) Improvement in running economy after 6 weeks of plyometric training. J
Strength Cond Res 17:60-67
Wernbom M, Augustsson J, Thomeé R (2007) The influence of frequency, intensity, volume and mode of strength training
on whole muscle cross-sectional area in humans. Sports Med 37:225-264
Widrick JJ, Trappe SW, Costill DL, Fitts RH (1996) Force-velocity and force-power properties of single muscle fibers from
elite master runners and sedentary men. Am J Physiol 271:C676-C683
24
Figures
Fig. 1 Average weekly training load (kg) in the leg exercises during the 12-week training
intervention. S+E = Strength training in addition to a large volume of endurance training, S =
The same strength training program as S+E without a large volume of endurance training.
#Significantly greater increase from the 1st to the 12th training week in S compared with S+E
in both absolute and relative terms (p ≤ 0.05)
25
Fig. 2 Average 1RM load in half squat and leg press before (Pre) and after the 12 week
intervention period (post). For explanation of S+E and S, the reader is referred to Figure 1.
*Greater than at Pre (p<0.05). #The relative change from Pre is greater than in S+E (p<0.05)
26
Fig. 3 Thigh muscle cross-sectional area (CSA) separated into area of knee extensors (upper
panels) and knee flexors (lower panels) before (Pre) and after the 12-week intervention period
(post). For explanation of S+E and S, the reader is referred to Figure 1. *Greater than at Pre
(p<0.05). #The relative change from Pre is greater than in S+E (p<0.05)
27
Fig. 4 Squat jump height before (Pre) and after the 12-week intervention period (post). For
explanation of S+E and S, the reader is referred to Figure 1. *Greater than at Pre (p<0.05).
#The relative change from Pre is greater than in S+E (p<0.05)
28
Fig. 5 Peak rate of force development (RFD) in isometric half squat before (Pre) and after the
12-week intervention period (post). For explanation of S+E and S, the reader is referred to
Figure 1. *Greater than at Pre (p<0.05). #The relative change from Pre is greater than in S+E
(p<0.05)
