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Losnegard, T., Mikkelsen, K. L., Rønnestad, B. R., Hallén, J., Rud, B.,
Raastad, T. (2011). The effect of heavy strength training on muscle
mass and physical performance in elite cross country skiers.
Scandinavian Journal of Medicine & Science in Sports, 21, 389-401.
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onlinelibrary.wiley.com: http://dx.doi.org/10.1111/j.1600-0838.2009.01074.x
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onlinelibrary.wiley.com: http://dx.doi.org/10.1111/j.1600-0838.2009.01074.x
THE EFFECT OF HEAVY STRENGTH TRAINING ON MUSCLE MASS
AND PHYSICAL PERFORMANCE IN ELITE CROSS-COUNTRY SKIERS
T. Losnegard1, K. Mikkelsen1, B. R. Rønnestad2, J. Hallén1, B. Rud1 and T. Raastad1
1The Norwegian School of Sport Sciences, Oslo, Norway
2 Lillehammer University College, Lillehammer, Norway
Abstract
Aim: to investigate the effect of supplementing high volume endurance training with heavy
strength training on muscle adaptations and physical performance in elite cross-country
skiers. Eleven male (18-26 years) and eight female (18-27 years) were assigned to either a
strength group (STR) (n=9) or a control group (CON) (n=10). STR performed strength
training twice a week for 12 weeks in addition to their normal endurance training. STR
improved 1RM for seated pull-down and half squat (19 ± 2% and 12 ± 2% respectively),
while no change was observed in CON. Cross-sectional area increased in m. triceps brachii
for both STR and CON, while there was no change in m. quadriceps cross-sectional area.
VO2max during skate-rollerskiing increased in STR (7 ± 1 % ), while VO2max during running
was unchanged. No change was observed in energy consumption during rollerskiing at
submaximal intensities. Double-poling performance improved more for STR than for CON.
Both groups showed similar improvement in rollerski time-trial performance. In conclusion,
12 weeks of supplemental heavy strength training improved strength in leg and upper body
muscles, but had little effect on muscle cross-sectional area in thigh muscles. The
supplemental strength training improved both VO2max during skate-rollerskiing and double-
poling performance.
Introduction
Cross-country skiing, including both sprint skiing and traditional races, is a typical endurance
sport with high reliance on maximal aerobic power. However, the introduction of sprint skiing
and mass start competitions has increased the importance of other physiological factors
affecting top speed on skis, such as muscular strength and the ability to generate high power
(Stöggl et al. 2007a, b). Consequently, heavy strength training has gained interest both in
science and in the practice of cross-country skiing athletes. In fact, a strong correlation has
been reported between maximal power output measured in a 4 repetition maximum (RM)
rollerboard test and sprint skiing tests in cross-country skiing (Stöggl et al. 2007a). Further, a
strong correlation has also been found between maximal speed and performance in short
duration tests in running and cross-country skiing (Rusko et al. 1993, Stöggl et al. 2007a, b). In
addition to potentially having a role in maximal power generation and top speed on skis,
heavy strength training may also reduce the energy cost of skiing. However, this has only
been investigated during double pooling in an ergometer, which may be different from skiing
(Hoff et al. 1999; 2002; Østerås et al. 2002).
It has been suggested that supplementing endurance training with maximal strength training
does not increase muscle mass in cross-country skiers (Hoff et al. 1999; 2002; Østerås et al.
2002, Nesser et al. 2004, Welde et al. 2006). However, muscle mass was not measured in
these studies; the suggestion was inferred from the fact that no change in bodyweight was
observed. In general, strength training 2-3 times per week for 10-12 weeks, with training
loads above 60% of 1RM and 2-6 series per exercise, normally results in a considerable
increase in muscle strength and cross-sectional area of the trained muscle groups (Rhea et al.
2003, Campos et al. 2002, Peterson et al. 2004, Wernbom et al. 2007). A 40% improvement in
1RM is normally seen in untrained subjects after a strength training program lasting 12 weeks
(Kraemer et al. 2002). However, high volume endurance training may be antagonistic to the
normal strength training adaptations on muscle size and strength, possibly causing strength
gain to be reduced when strength and endurance training are performed in parallel. In fact,
studies have reported only 10-40% improvement in 1RM when strength training and
endurance training were combined. (Hickson et al. 1988, Hoff et al. 1999; 2002, Bishop et al.
1999, Bell et al. 2000, Millet et al. 2002). Elite cross-country skiers may reach a volume of
60-90 hours endurance training per month in the pre-season. Training generally includes
disciplines that focus on the endurance training, including running, bicycling and rollerskiing.
Only parts of this training include arm muscles. Thus, performing strength training during a
period of high volume endurance training may negatively affect the strength gain particularly
in leg muscles.
Supplementing endurance training with strength training does not appear to compromise the
normal increase in VO2max inflicted by endurance training (Hickson et al. 1988, Bell et al.
2000, Hoff et al. 2002). Enhanced upper body capacity, both strength and aerobic, has been
recognised as an important strategy to increase complex performance in field tests in cross-
country skiing (Shorter et al. 1991, Terzis et al. 2006, Gaskill et al. 1999, Mahood et al. 2001,
Nesser et al. 2004). However, the effect of strength training on changes in performance and
VO2max during whole body efforts, like skate-skiing, has not been examined in elite athletes.
Improved work economy on a double pooling ergometer has been reported after a period of
heavy strength training (Hoff et al. 1999; 2002; Østerås et al. 2002). However, the effect of
strength training on work economy and energy consumption in skate-rollerskiing on treadmill,
or in the field, has not been investigated. The aims of this study were therefore to examine the
effect of supplementing high volume endurance training with strength training on:
1. Cross sectional area of thigh and arm muscles
2. VO2max during running and skate-rollerskiing, and energy consumption in submaximal
skate-rollerskiing
3. Rollerski performance during a time-trial, double-poling performance on a poling
ergometer, and performance in sprint-rollerskiing.
Methods
Subjects
Eleven male and eight female competitive cross-country skiers completed the study. The
inclusion criteria were finishing top 30 for senior women and top 70 for senior men in the
Norwegian Cross-Country Skiing Championships. A criterion for junior skiers was top 15 in
the Norwegian Championships for juniors. The participants were self-selected into a strength
group (STR) (n=9; 2 jr and 7 sr) or a control group (CON) (n=10; 2 jr and 8 sr). None of the
skiers performed strength training systematically before entering the study. A total of 11
females and 14 males started the study, but six participants were excluded from the study due
to injuries, illness or inability to complete the required number of strength training sessions
(minimum 85% adherence). The athletes’ physical characteristics are shown in Table 1. The
study was approved by the Regional Ethics Committee of Southern Norway and performed
according to the Declaration of Helsinki. The subjects gave their written consent before study
participation.
(Table 1 near here)
Intervention
The strength training program lasted for 12 weeks from the beginning of June to the end of
August, a basic preparatory training period for cross-country skiers. STR performed two
strength workouts per week in June and August, and one workout per week in July. Exercises
were performed in the same order at each training session: half squat, seated pull-down,
standing double-poling, and triceps press (Figure 1). Subjects performed a general aerobic
warm up for 10 minutes followed by three submaximal series (10-6-3 reps) with increasing
loads (40, 60 and 80% of 1RM) in half squat, before beginning the maximal half squat sets.
For the other exercises, one warm up set per exercise (3 repetitions, 80% of 1RM) was
performed before the maximal sets. Rest between sets was set to 2-3 minutes. The training
sessions lasted approximately 45 minutes. When a subject could successfully execute three or
four sets with the prescribed load, the load was increased by 2.5-5% at the next session.
Standing double-poling was performed with 10RM load throughout the intervention period
because it was difficult to perform this exercise with correct technique with higher loads. The
upper body exercises targeted specific muscles used in cross-country skiing. All upper body
exercises utilised a handlebar specifically designed to imitate the grip on poles in cross-
country skiing. Free weights were used in the half squat during training.
(Figure 1 near here)
The strength training program was designed as a “daily undulating periodised program”, with
progression in intensity (Table 2). These methods to vary the strength training load have been
shown to be effective in increasing strength (Willoughby 1993, Rhea et al. 2002). The aim of
the strength training regime was to increase cross sectional area of targeted muscles, and
further increase strength as described in previous studies (Campos et al. 2002, Kraemer et al
2002). Training for low back and abdominal muscles was optional for both groups. The
normal endurance training was managed by the athletes themselves or after consulting with
their coach. Subjects recorded each training session throughout the 12 weeks using a training
log that was sent by e-mail to the project coordinator. Subjects were individually supervised at
the three first strength training sessions by an investigator in order to ensure proper technique
and appropriate work load.
(Table 2 near here)
Testing procedures
Prior to the pre-test at the start of the intervention, all subjects completed one familiarisation
trial on the rollerski treadmill, double-poling ergometer and in the strength tests. All subjects
were familiar with the VO2max running test and outdoor rollerskiing. The entire battery of
tests, including a rest day, was conducted over four days (Table 3). All test procedures,
including the order of tests, were identical at pre- and post-test. During the test days athletes
were allowed to drink a sports drink ad libitum, and a light meal was consumed between tests
on the heaviest test day (test day 3).
(Table 3 near here)
Testing of counter movement jump performance (test day 1)
Counter movement jumps (CMJ) were executed on a force platform (SG 9, Advanced
Mechanical Technology Inc., Newton, MA) and force data was processed through a low pass
filter at 1050 Hz. The subjects warmed up with 5-min cycling on an ergometer at 60-70% of
maximal heart rate (HRmax). The CMJ started from a standing position with hands placed on
the hips and the counter movement was performed as one rapid movement down to a self-
selected depth. Subjects used their own shoes at pre- and posttest. Jump height was calculated
from the vertical reaction force impulse during take off. Subjects performed four jumps at pre
and at post-test, and the best result was used in the data analysis (CV<5%).
Work economy and VO2max during skate-rollerskiing (test day 1)
Oxygen consumption was measured by an automatic system (Oxycon Pro Jaeger Instrument,
Germany) which was calibrated according to the instruction manual before each test. Oxygen
and CO2 analyzers were calibrated with room air and certified calibration gases at 180 kPa
(5.55% CO2 and 94.45% N2). The flow turbine (Triple V, Erich Jaeger GmbH, Hoechberg,
Germany) was calibrated with a 3.00 l 5530 series calibration syringe (Hans Rudolph, Inc.,
Kansas City, USA). Heart rate (HR) was measured by Polar S610i™ (Polar electro OY,
Finland) and blood lactate concentration was measured in unhaemolysed blood from capillary
fingertip samples (YSI 1500 Sport, YSI Incorp., Yellow Spring Instr. Co., Inc., USA).
Swenor skating rollerskis (Swenor, Sarpsborg, Norway) with type 1 wheels were used during
warm up and testing. The same pair of rollerskis was used during pre and post tests and the
same pair was also used during warm up to ensure stabilization of the friction in the wheels.
Swix Star poles (Swix, Lillehammer, Norway) with a tip customized for treadmill rollerskiing
were used. The V1 skating technique with optional hangarm, was used for both submaximal
and VO2max testing.
Work economy and VO2max tests during rollerskiing, were performed on a treadmill with belt
dimensions of 3 x 4.5 m (Rodby, Sodertalje, Sweden). After a 15-min warm up (60-70% of
HRmax) on the treadmill the subjects completed 3 x 5-min bouts with a 2-min break between
each effort. The speed on the treadmill at submaximal tests was set to 3 m·s-1 for men and 2.5
m·s-1 for women, with inclines of 4, 5, and 6 degrees for both genders. Oxygen consumption
and HR were averaged between 2.5 and 4.5 minutes. Blood plasma lactate concentration was
measured immediately after each 5-min effort. Eight minutes after the last submaximal effort,
the participants performed a VO2max test. The subjects started at 5 or 6° inclination, and the
speed was set to 3 m·s-1 for men and 2.5 m·s-1 for women. With constant speed, inclination
was increased by one degree every minute until 8°, and thereafter the speed was increased
with 0.25 m·s-1 until exhaustion. Respiratory exchange ratio >1.1 and skiing to exhaustion
were used as criteria to indicate that VO2max was reached. Oxygen consumption was measured
continuously and averaged over one minute, and the highest oxygen value was taken as
VO2max.
Body composition (test day 1)
The subject’s bodyweight was measured before each treadmill test (Seca, model 708 Seca,
Germany). After the treadmill test magnetic resonance tomography (MR) was performed. MR
(MR GE Signa HD 1.5 T) was performed with the feet strapped and elevated on a pad. The
machine was centered 2/3 distal at femur. Nine cross-sectional images were taken in a regular
manner from patella against iliac crest (5 mm cross-section with spacing 35.5 mm) to measure
cross-sectional area of m. quadriceps. Both legs were measured and mean value of the two
legs was used in the data analysis. During the scanning of muscles in the dominant arm, the
arm was stretched behind the head, and the body was placed so that the dominant arm was
centered in the middle of the machine. Nine cross-sectional images from caput humeri against
elbow joint were taken (5 mm cross-section with spacing 30 mm) to measure cross-sectional
area of m. triceps brachii. Only the dominant arm was analysed. The images were then
conveyed to a computer for further analyses. The circumference of m. quadriceps and m.
triceps brachii was measured on all images, and average circumference from the nine images
is used in results. Changes in body composition were measured by Dual Energy X-ray
Absorptiometry (GE Medical system, Madison WI). The participants were not allowed to eat
or drink the last two hours before each DEXA scan.
VO2max during running (test day 2)
Oxygen consumption during treadmill (Woodway GmbG, Weil am Rein, Germany) running
was measured with the same equipment as during rollerski treadmill testing. After a
standardised 20-min warm up, subjects ran at a constant 10.5% incline, while speed was
increased incrementally each minute until exhaustion. Women ran from 8-12.5 km·h-1, while
men ran from 10-14.5 km·h-1 (with individual variations). Respiratory exchange ratio >1.1 and
running to exhaustion were used as criteria to indicate that VO2max was reached. Oxygen
consumption was measured continuously and the highest oxygen value averaged over one
minute was taken as VO2max.
100 meter sprint skiing test (test day 3)
Subjects warmed up for 10 minutes by running (~65 % of HRmax) and then 10 minutes on the
testing rollerskies (65-75 % of HRmax). Testing was conducted on an even, straight and flat
asphalt road with Swenor skating skis with wheel type 1. All participants used the same
physical pair of skis, but used their own boots and skating poles fitted with rollerski tip. The
participant’s time and speed over 100 meters was measured with photocells every 20 meters
(JBL Systems, Oslo, Norway). Maximal velocity (Vmax) was defined as the subjects highest
speed (m·s-1) during the 100 meter test. Subjects performed two trials in both directions on the
road in a freely chosen skating technique. The mean of the best result for each direction were
used for further analyses. A wind gauge (Sports Anemometer, Gill instruments Limited,
Hampshire, England) detected wind speed. At pre-test, two subjects performed with wind at >
2 m·s-1, while the other subjects performed at < 2 m·s-1. At post-test, the wind was < 2 m·s-1
for all subjects. The road was dry on all test days while temperature was between 11-18
degrees.
1 RM strength tests (test day 3)
The 1RM tests for seated pull-down and half squat exercises (Figure 1) were performed after
the sprint skiing test. In both exercises, the subjects performed 3 sets of exercise-specific
warm up with gradually increasing load (10 repetitions at 40%, 6 repetitions at 75%, and 3
repetitions at 80% of expected 1RM). The first attempt for both exercises was performed with
a load approximately 5% below the expected 1RM. After each successful attempt, the load
was increased by 2–5% until the subject failed to lift the load after 2–3 consecutive attempts.
The rest period between each attempt was 2-4 minutes. The order of tests was the same in all
testing sessions. All 1RM testing was supervised by the same investigator and conducted on
the same equipment with identical equipment positioning for each subject. The 1RM half
squat was performed in a Smith machine (Tecnogym 2SC multipower, Gambettola, Italy). At
the familiarisation session the correct depth (90° knee angle) was noted for reproduction. The
position of the feet was marked and the correct depth was controlled with an elastic band. The
movement over the knee joint was standardized in sagittal plane by moving the knees over
toes. For the seated pull-down, a Tecnogym Radiant (Tecnogym, Gambettola, Italy)
apparatus was used. The movement started with the handlebar positioned at the same height
as the forehead. The participants then pulled the handlebar down to the hip bone. Elbows were
held slightly lateral to simulate a double poling pull, and the wire was parallel to the back
support on the bench. In order for the 1RM to be accepted, the handlebar had to be pulled
completely down in one continuous motion with hands parallel (figure 1).
Double-poling performance (test day 3)
Double-poling performance was tested on a custom-built ergometer based on Concept II
rowing ergometer (Concept Inc., Morrisville, VT., USA), to simulate double-poling in cross-
country skiing (Holmberg and Nilsson 2008). This test was carried out after the sprint skiing
test and the 1RM tests. Therefore, only a specific warm-up of 5 minutes double-poling at
~60% of HFmax was performed in addition to two 20-second efforts at approximately 80% of
maximal power. After the specific warm-up, subjects performed two 20-second bouts at
maximal effort, separated by two minutes rest. The best mean power output results were used
for further analyses. Before the 5-min double-poling test, the subjects had a recovery exercise
for 5 minutes on a cycle ergometer at 100 watt and 60 RPM. The power during the first 90
seconds of the 5-min double-poling test was fixed to avoid over-pacing and individually set,
based on preliminary tests. Thereafter, the subjects regulated the power themselves. The
resistance of the ergometer was constant for the whole duration of the test. The goal of the test
was to produce as much work as possible over 5 min. During the post-test, the same
procedure was followed, with the power during the first 90 s being set to the average power
found at pre-test. This was to avoid a learning effect from pre- to post-test. The double-poling
cycle rate was calculated using video analysis (Sony DCR-TRV900E, Tokyo, Japan).
Rollerski time-trial (test day 4)
The double-poling rollerski time-trial (1.1km) and skate-rollerskiing time-trial (1.3km) were
performed outdoors on an uphill road. The same physical pair of rollerskis used by each
subject at pre-test was also used at post-test. The rollerskis were new at pre-test and stored in
a dark, dry room during the intervention period. Swenor skating skis wheel type 2 without
blocking mechanism were used for both the skate-rollerskiing and double-poling tests.
Subjects warmed up with 20 min rollerskiing and 15 min running at 60-70% of HRmax. The
final 5 min of the warm-up were again done on rollerskis at an individual intensity. For both
time-trials, subjects started individually at 30-sec intervals. The skate-rollerskiing test was
performed first, with freely-chosen technique. After completion, subjects were transported by
car back to the start. After a 45-min break characterised by low-intensity activity the double-
poling time-trial commenced. The road was dry on both pre- and posttest, while temperature
was 9-13 degrees for pretest and 10-16 degrees at posttest.
(Table 4 near here)
Statistics
All results are reported as means and standard error (SE) unless otherwise stated. Paired t-test
was used for detecting significant changes from pre-test to post-test within groups and
unpaired t-test was used to detect significant differences between groups in relative changes.
Pearson’s Product Moment Correlation Analysis was used for correlation analyses, and sub
analysis of correlations for men and women separately, were included to reveal sex
differences. Statistical calculations were performed with Microsoft Excel and GraphPad
software. A p-value ≤ 0.05 was considered statistically significant. A p-value < 0.10 was
considered a tendency.
Results
Endurance training during the intervention period
Training registration from the subjects training diary showed no difference in average weekly
endurance training volume between the two groups (STR: 15.2 ± 1.1 hours) (CON: 15.3 ± 0.7
hours) during the 12-week intervention period.
Strength tests
STR increased 1RM strength in seated pull-down and half squat more than CON (Figure 2, p
< 0.01). STR’s increase was 19 ± 2% for seated pull-down and 12 ± 2% for half squat (both p
< 0.01). CON tended to increase 1RM in seated pull-down (5 ± 3% p = 0.08). The change in
counter movement jump (CMJ) performance tended to be different between groups (p = 0.10)
with a 6.2 ± 2.7% (p < 0.05) decrease in CON and no change in STR (1.7 ± 2.4%, NS)
(Figure 3).
(Fig. 2 and 3 near here)
Muscle cross-sectional area and lean body mass (LBM)
Cross-sectional area (CSA) in m. triceps brachii tended to increase more in STR than in CON
(p = 0.10), with a 5.5 ± 2.1% (p < 0.01) increase for STR and a 1.5 ± 0.7% (p = 0.05) increase
for CON (Figure 4). CSA remained unchanged in m. quadriceps for both groups. The increase
in leg LBM was significantly greater in CON than in STR (p < 0.05). Total LBM and leg
LBM increased in CON (1.8 ± 0.5%, p < 0.01 and 1.9 ± 0.9%, p = 0.05) (Figure 5). No
statistical changes between groups in upper body LBM were seen. STR increased upper body
LBM (3.0 ± 1.1%, p < 0.05), while CON showed a tendency towards increased upper body
LBM (1.8 ± 0.9%, p = 0.07). Total body weight remained unchanged throughout the
intervention period in both groups.
(Fig 4 and 5 near here)
VO2max during skate-rollerskiing and running
VO2max relative to body mass during treadmill skate-rollerskiing increased significantly more
in STR than in CON (p < 0.05) (Figure 6). VO2max during skate-rollerskiing increased by 7 ±
1% for STR (p < 0.01) and 2 ± 2% for CON. At the pre-test, both groups had a significantly
higher VO2max during running than during skate-rollerskiing (p < 0.05), while at post-test
there was no difference between running and skate-rollerskiing VO2max in STR, but a
tendency towards higher VO2max during running in CON (p = 0.07). VO2max relative to body
mass during running remained unchanged in both groups.
(Fig 6 near hear)
Submaximal treadmill rollerski test
VO2 during submaximal rollerskiing on treadmill was unchanged in both groups at all
inclines. The respiratory exchange ratio was, however, reduced in STR at all inclines (p <
0.05), while no change was observed in CON. There were no statistically significant
differences between groups in HR or La-. Average HR was reduced in STR at 4° (6.6 ± 2.7
bpm), 5° (6.9 ± 2.2 bpm), and 6° (4.7 ± 2.0 bpm), inclines (all p < 0.05), while blood lactate
concentration was decreased at 5° incline (0.5 ± 0.1 mmol l-1, p < 0.05). In CON, blood
lactate concentration was decreased at 4° incline (0.2 ± 0.5 mmol l-1, p < 0.05).
(Table 5 near here)
Rollerski time-trial performance
Rollerski time-trial performance did not change significantly between the two groups from
pre-test to post-test. STR improved double-poling performance (-7.4 ± 2.6%, p < 0.05) and
slightly improved (though not significant) skate-rollerskiing performance (-3.7 ± 2.2%, p =
0.14) (Figure 7). CON showed significant improvement in both double-poling and skate-
rollerskiing performance (-6.0 ± 1.7% and -3.3 ± 0.9%, both p < 0.05).
(Figure 7 near hear)
Double-poling performance
Average power relative to body weight (W·kg-1) during the 5-min double-poling test increased
more for STR than CON (p < 0.05, Figure 8). There were no changes in poling frequency
over the intervention period within or between groups. Average poling cycle frequency at pre-
test was 48.2 ± 1.1 RPM in STR and 47.8 ± 0.9 RPM in CON. In addition, no significant
correlations were found between poling frequency and average force, 1RM results, gender or
any anthropometric data. No statistically significant changes between groups were observed
in average power in 20-second performance. Results from the 20-second test showed an
increased power output in both STR (8.3 ± 2.0%) and CON (6.2 ± 1.8%) (both p < 0.001).
(Figure 8 near hear)
100 meter sprint-rollerskiing
No statistically significant difference between groups was observed in 100 meter sprint-
rollerskiing (Table 6). In addition, there were no statistically significant differences within or
between groups after 20, 40, 60, or 80 meters and max velocity. STR tended, however, to
improve 100 m time by -1.3 ± 0.7% (p = 0.1).
(Table 6 near hear)
Correlation between basic tests and performance parameters
Correlation analyses from baseline (n=25) showed a strong correlation between 1RM seated
pull-down and several performance parameters (all p < 0.01, Figure 9, a-d). Performance on
the double-poling ergometer (average power at 20 s and 5 min) correlated with 1RM seated
pull-down performance (r = 0.70 and r = 0.87 respectively). A correlation was also observed
between double-poling and skate-rollerskiing time-trial performances and seated pull-down
performance (r = -0.81 and r = -0.81 respectively). In addition, strong correlations between
1RM half squat and skate-rollerskiing time-trial performance (r = -0.82), and 1RM half squat
and 100 meter sprint-rollerskiing performance were observed (r = -0.89) (both p < 0.01,
Figure 9. e-f). Separate correlation analysis for men and women demonstrated high to
moderate correlations for women and moderate to low correlations for men (Figure 9). We
were not able to observe any statistically significant correlation between changes in 1RM
results and changes in any of the performance tests.
(Figure 9 near hear)
Discussion
Supplementing high volume endurance training with heavy strength training resulted in
increased muscle strength in both upper body and legs. However, CSA increased only in the
upper body, while no changes were detected in leg muscles. Surprisingly, for STR, VO2max
increased significantly during skate-rollerskiing, but did not change during running.
Supplementing normal endurance training with heavy strength training for 12 weeks
improved performance in 5-min double-poling on the ergometer. However, no differences
between groups in the time-trial test or sprint-rollerskiing performance were detected.
The increases in 1RM seated pull-down (19 ± 2%) and half squat (12 ± 2%) for STR concur
with similar studies on endurance athletes (10-40% increase over 12 weeks) (Hickson et al.
1988, Hoff et al. 1999; 2002, Bishop et al. 1999, Bell et al. 2000, Millet et al. 2002). The
cross-country skiers had not performed strength training systematically before, and the half
squat exercise, in particular, was unfamiliar to the participants. In general, “untrained”
athletes can expect to increase muscle strength by approximately 40% and “moderately
trained” athletes by 20% after 12 weeks of heavy strength training, measured as 1RM in the
training exercises (Kraemer et al. 2002). The relatively low strength gains observed in our
skiers may be due both to the high volume of endurance training, which may have reduced the
effect of strength training on the legs, and the relatively low volume of leg strength training
(one exercise 1-2 sessions per week).
Counter movement jump height was reduced in CON and unchanged in STR. Reduced jump
height during a period of heavy endurance training involving leg muscles has also been
observed in other studies (Millet et al. 2002). Our results suggest that this “negative” effect of
high volume endurance training can be counteracted by adding heavy strength training on leg
muscles. Peak leg extensor force and vertical jump height is normally highly correlated, and a
concomitant increase in jumping performance with increased leg strength has been reported in
several studies investigating heavy strength training (Kraemer et al. 2002). However, in the
present study, the maintained jump height can be interpreted as a positive effect of strength
training because of the reduced jump height observed in CON.
Strong correlations were seen between CSA in m. quadriceps and 1RM half squat (r = 0.80, p
< 0.01), and between CSA in m. triceps brachii and seated pull-down (r = 0.91, p < 0.01).
This indicates that an increase in muscle CSA is an important factor for achieving further
strength gains. However, CSA in m. quadriceps did not change in either CON or STR and the
changes in 1RM half squat did not correlate with changes in CSA. The increased strength may
alternatively be explained by improved muscle quality, improved lifting technique and
improved use of agonists, and synergists, including stabilising muscles around spine and hip.
Length alteration could also explain increased strength if the length of knee and hip extensors
is more optimal for force generation in the critical phase of a half squat (Alegre et al. 2006).
In similar studies, CSA in fibre and/or muscle circumference was unchanged (Hickson et al.
1988, Johnston et al. 1997) or increased (Bell et al. 1991, Sale et al. 1990). In the present
study, STR performed a strength training program that normally results in increases in both
strength and CSA (Kraemer et al. 2002, Campos et al. 2002). Thus, it seems plausible that the
large volume of endurance training on leg muscles reduced the effectiveness of heavy strength
training on strength gain and muscle growth. In this study, only one exercise involving leg
muscles was included. However, feedback from the athletes indicated that it would be
problematic to increase the strength training volume on leg muscles. Especially problems with
performing endurance training the day after heavy strength training were reported. Adding
more leg exercises to the program could therefore have interfered more with the endurance
training and compromised the quality of training. However, if the subjects had been more
experienced with strength training, these issues might not have occurred. It is therefore likely
that a higher volume of strength training can be tolerated in skiers with more strength training
experience. The half squat exercise also resulted in four dropouts. Two subjects had problems
with the legs (“heavy legs”) and two subjects had back pain related to the half squat exercise
and could therefore not complete the 12 weeks of strength training.
CSA in m. triceps brachii increased in both groups, and tended to increase more in STR than
in CON (p=0.1). DEXA results indicated a greater increase in upper body muscle mass for
STR than for CON, a finding consistent with the changes in 1RM seated pull-down. Increased
muscle mass has therefore contributed to the strength gain in the upper body. These findings
are also consistent with the fact that seated pull-down, in contrast to half squat, is less
sensitive to changes in technique and therefore probably more related to changes in CSA.
Surprisingly, STR increased VO2max during skate-rollerskiing, a finding that contradicts
similar studies that found no further changes in VO2max when strength training was added to
endurance training (Hickson et al. 1988, Hoff et al. 2002, Millet et al. 2002). Before the
intervention period, both groups had a significantly lower VO2max in skate-rollerskiing than in
running. After the intervention, VO2max in skate-rollerskiing and running were similar for
STR, but still lower in skate-rollerskiing for CON. This indicates that subjects in this study
had insufficient technical and/or physical capacities to utilise the oxygen delivery to the upper
body before the strength training. Interestingly, a lower O2 extraction has been observed in
arms than in legs in whole body skiing in elite athletes (Calbet et al. 2004). Results from
baseline show a strong correlation between upper body LBM and VO2max during skate-
rollerskiing (r = 0.84). Consequently, it is possible that increased upper body muscle mass
contributes to increased VO2max during skate-rollerskiing without affecting VO2max during
running. An increase in muscle strength and a concomitant improvement in skiing technique,
may have improved the skiers’ upper body VO2max either by increased blood flow or
increased ability to extract oxygen.
No change in VO2 during submaximal rollerskiing was seen for either STR or CON. The
observed change in RER towards higher fat oxidation at a fixed intensity may contribute to
delayed fatigue in long lasting events. However, the observed changes in RER were relatively
small (< 1%), and a small change in RER will not contribute to major changes in work
efficiency as long as VO2 is unchanged. The concomitant reductions in La- and HR may be a
consequence of the higher skate-rollerskiing VO2max. The unchanged work economy in skate-
rollerskiing after strength training in the present study contradicts studies by Hoff et al. (1999;
2002), who showed a large (47-136%) improvement in a time to exhaustion test after heavy
strength training. However, Hoff et al. (1999; 2002) tested performance as time to exhaustion
on a double-poling ergometer. In the present study work economy was tested on a rollerski
treadmill, which more closely simulates actual skiing, an exercise well known by the subjects.
Both groups significantly improved their time in the rollerski double poling time-trial, but
STR’s improvement in skate-rollerskiing was not statistically significant. For reasons that are
not clear, at post-test one subject in STR performed substantially slower in the skate-
rollerskiing time-trial, and performed poorly in several other post-tests. By excluding this
subject’s results from analyses, significant time improvement in skate-rollerskiing was
achieved by STR, and the improvement tended to be greater for STR than CON (p = 0.06).
The improved performance for both groups is probably caused primarily by the regular
endurance training performed during the intervention period. STR’s tendency for superior
improvement can be explained by the increased VO2max in skate-rollerskiing seen during
treadmill testing. Correlation analyses from baseline showed moderate correlation between
1RM seated pull-down and time trial double poling test for the women, while low correlation
was observed for the men. Women in this study had also a significantly lower strength in both
seated pull-down and half squat than men. Based on these correlations it could be
hypothesised that weaker skiers will be more likely to increase performance than stronger
athletes when adding strength training to their normal training routines. However, due to the
low number of skiers in STR we were not able to compared changes in performance between
weak and strong skiers. Interestingly, there was no correlation between relative muscle
strength and performance in the time-trials.
Average power in the 5-min double-poling test increased more in STR than in CON. Results
from baseline tests showed a significant correlation between average power in ergometer and
double-poling performance on rollerskis (r = -0.89). However, the improvement in double-
poling time-trial performance, which had approximately the same duration (~5 minutes), was
not superior in STR. In addition, in the outdoor time-trial test, confounding elements like
weather, surface and unaccustomed rollerskis may give rise to larger variations in
performance. Consequently, it is harder to find intervention effects. On the other hand, the
double-poling technique on the ergometer is different from double-poling on rollerskis. The
strength training intervention, including seated pull-down, is more similar to the ergometer
test and might influence the technique in ergometer double-poling, and thereby more
positively affect ergometer performance than rollerski performance. Surprisingly, no
statistical difference was found between the two groups in the 20-second test. Baseline results
showed a high correlation between 1RM seated pull-down and 20-second double-poling
power, so it was expected that increased upper body strength would improve power in the 20-
second double-poling test. However, it was difficult to maintain good technique on the
ergometer when performing with maximal effort, so technical aspects might explain the lack
of transference from increased strength to performance in this test. In addition, correlation
values from baseline at the 20 seconds test is high mainly due to the women included in this
study. Consequently, strength training might be more adequate regarding performance in this
test for the women because of the lower strength values at baseline.
A high correlation has been reported between maximal power output measured in a 4RM
rollerboard test and sprint-rollerskiing tests (50 m and 1000 m) (Stöggl et al. 2007a). In the
present study, baseline results also showed a high correlation between 1RM seated pull-down
and 100-meter sprint-rollerskiing (r = -0.92, p < 0.01, women: r = -0.65, men: r = -0.57, both
p < 0.05), and between half squat and 100-meter sprint-rollerskiing (r = -0.89 p < 0.01,
women: r = -0.80, p <0.05, men: r = -0.20). Twelve weeks of heavy strength training also
tended to reduce 100 meter time by -1.3 ± 0.7% (p = 0.1). Peak velocity during skate-
rollerskiing is high and increased strength was expected to have more impact on the
acceleration phase than peak velocity. However, no significant improvement was observed in
20 m time or in Vmax (80-100m), a finding that could be explained by the fact that sprinting on
rollerskis is highly technically demanding, especially at maximal speeds (~8.5-9 m·s-1). In
previous studies, strong correlations have also been found between maximal speed and
performance in short duration tests in running and cross-country skiing (Rusko et al. 1993,
Stöggl et al. 2007a, b). In the present study, a moderate correlation was found between 100
meter sprint rollerskiing and performance in the time trial skating test for women (r = 0.62, p
< 0.05), while no correlation was found for men (r = -0.16). Weaker correlations between
maximal speed and time-trial performance observed in the present study might be due to the
uphill terrain, the use the skating technique, and a longer duration in the time-trial tests than in
previous studies.
Perspectives
The results from this study showed increased strength, increased average power in a 5-min
double-poling test, and increased VO2max in a specific rollerski test after adding heavy
strength training to normal endurance training in elite cross-country skiers compared to a
control group that only performed endurance training. However, there were no statistical
differences between groups in the time-trial-tests on roller skies. This indicates that we must
be cautious when we try to translate improvement from one type of exercise into sport
specific performance, even though the exercises include major parts of the sport movements.
In addition, it may take more than 12 weeks to utilize the increased strength to improved
performance in a complex exercise, as cross country skiing, and long term experiments,
perhaps over several years, may be needed.
There was a moderate correlation between muscle strength (1RM) and roller ski performance
(time-trial) for the women, while no correlation was observed for the men. The women were
also weaker. Based on correlation analyses it could be argued that weaker subjects, in this
study the women, could benefit from adding heavy strength training to their normal training.
Further, this may indicate that there is a threshold for strength levels necessary for optimal
performance in cross-country skiing and suggests that strong athletes may focus on training
models other than heavy strength training (with the goal of maintaining, not increasing,
strength), while weaker athletes may benefit from increasing muscle strength..
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TABLE 1. Main characteristics of the two groups (mean ± standard deviation). No significant
differences between groups in total or between groups when divided into gender.
STR CON
Women (n=3) Men (n=6) Total (n=9) Women (n=5) Men (n=5) Total (n=10)
Age (year) 21.3 ± 5.1 21.2 ± 2.5 21.2 ± 3.2 22.6 ± 2.4 20.8 ± 2.5 21,7 ± 2.5
Height (cm) 166.0 ± 3.6 182.0 ± 4.3 176.7 ± 8.9 168.6 ± 6.5 178.0 ± 3.6 173.3 ± 7.0
Weight (kg) 60.1 ± 10.1 77.1 ± 3.4 71.4 ± 10.2 60.1 ± 7.5 75.5 ± 7.1 67.8 ± 10.6
VO2max- running
(ml·kg-1·min-1)
61.5 ± 1.1 67.3 ± 5.1 64.7 ± 4.9 57.9 ± 2.8 69.5 ± 4.7 64.6 ± 7.1
VO2max- skating
(ml·kg-1·min-1)
56.8 ± 1.6 64.4 ± 5.1 61.6 ± 5.5 53.1 ± 3.0 68.3 ± 6.1 62.0 ± 9.2
1RM seated
pull-down
26.7 ± 8.0 43.8 ± 2.6 38.3 ± 9.4 27.0 ± 3.3 38.8 ± 3.2 33.5 ± 7.7
1RM half-squat
108.3 ± 25.2 159.2 ± 16.3 139.4 ± 32.9 90.0 ± 11.2 152.0 ± 21.8 121.0 ± 36.7
TABLE 2. Strength training program for STR
Week 1-3 4 5-8 9-12
Workouts per week 2 2 1 2
Sets x repetitions Day 1: 3x6 RM
Day 2: 3x10 RM
Day 1: 3x5 RM
Day 2: 3x8 RM
Day 1: 4x8 RM Day 1: 3x4 RM
Day 2: 3x6 RM
TABLE 3. The entire test-battery including time for each exercise and total time each testday.
TABLE 4. Time at time trial rollerski pre-test (min:sec ± SD). No significant differences
between groups in total or between groups when divided into gender.
STR CON
Women (n=3) Men (n=6) Total (n=9) Women (n=5) Men (n=5) Total (n=10)
DP 6:11 ± 0:57 4:29 ± 0:29 5.13 ± 0:40 6:19 ± 0:39 4:31 ± 0:17 5:25 ± 1:07
Skating 5:59 ± 0:30 4:50 ± 0:19 5.03 ± 1:03 6:14 ± 0:09 4:41 ± 0:19 5:27 ± 0:50
DP: Double poling
Test day Test battery Time (min) Total time (min)
1 1) CMJ
2) Work economy and VO2max during skate-rollerskiing
3) Body composition
10
50
60
120
2 VO2max during running 30 30
Rest-day
3 1) 100 meter sprint skiing test
2) 1RM strength tests
3) Break
4) Double-poling performance
30
30
20
25
105
4 Rollerski time-trial 100 100
TABLE 5. VO2, Respiratory exchange ratio (RER) , heart rate (HR) and blood lactate (La-) at
4°, 5° and 6° inclines with constant speed on the treadmill: 3 m·s-1 for men and 2.5 m·s-1 for
women.
STR (n=9) CON (n=10)
Pre Post % change Pre Post % change
4°
VO2 41.8 (0.8) 41.9 (1.0) 0.1 (1.1) 41.7 (1,3) 41.5 (1.6) -0.4 (1.5)
RER 0.93 (0.2) 0.89 (0.3) -4.7 (1.7)* 0.92 (0.1) 0.90 (0.1) -1.5 (2.2)
HR 164 (2.6) 157 (2.5) -3.9 (1.7)* 161 (2.8) 156 (2.3) -2.0 (1.3)
La- 1.6 (0.2) 1.4 (0.2) -8.3 (10.2) 1.4 (0.1) 1.2 (0.1) -8.7 (3.7)*
5°
VO2 48.5 (1.2) 48.3 (1.2) -0.3 (1.0) 48.2 (1.7) 48.0 (1.6) -0.2 (1.8)
RER 0.96 (0.1) 0.91 (0.2) -4.4 (1.5)* 0.94 (0.2) 0.93 (0.1) -1.4 (1.5)
HR 178 (2.1) 172 (2.2) -3.8 (1.3)* 173 (2.2) 170 (1.7) -1.3 (0.9)
La- 2.7 (0.7) 2.2 (0.3) -17.1 (6.1)* 2.4 (0.3) 2.2 (0.3) -6.6 (4.3)
6°
VO2 53.6 (1.1) 54.8 (1.2) 2.3 (1.4) 54.0 (2.0) 54.4 (1.8) 0.9 (1.8)
RER 0.99 (0.1) 0.93 (0.2) -5.5 (1.3)* 0.99 (0.2) 0.96 (0.2) -2.6 (2.0)
HR 188 (2.2) 183 (1.8) -2.5 (1.1)* 183 (2.0) 181 (1.5) -0.6 (0.6)
La- 4.4 (0.6) 3.8 (0.4) -10.9 (7.6) 4.4 (0.5) 4.2 (0.4) -3.1 (4.7)
(SE) = Standard error. Average VO2 (ml·kg-1·min-1) from 2.5-4.5 min, HR (bpm) from 2.5-
4.5-min and blood plasma lactate concentration (mmol l-1) after each bout. *= Significant
difference within groups (p < 0.05).
TABLE 6: Time at 20, 40, 60, 80, 100 meters and maximal velocity (Vmax) for rollerski
skating.
STR group CON group
Pre Post %change Pre Post %change
Time 20 m (s) 3.68 (0.10) 3.66 (0.10) -0.55 (0.64) 3.87 (0.08) 3.87 (0.09) -0.04 (0.77)
Time 40 m (s) 6.32 (0.18) 6.29 (0.17) -0.36 (0.58) 6.62 (0.14) 6.60 (0.16) -0.30 (0.66)
Time 60 m (s) 8.74 (0.25) 8.66 (0.24) -0.88 (0.62) 9.14 (0.21) 9.09 (0.22) -0.51 (1.17)
Time 80 m (s) 11.08 (0.33) 10.95 (0.31) -1.10 (0.67) 11.54 (0.27) 11.48 (0.28) -0.55 (0.51)
Time 100 m (s) 13.36 (0.40) 13.18 (0.38) -1.24 (0.72) 13.89 (0.33) 13.82 (0.34) -0.52 (0.48)
V
max (m·s-
1
) 8.83 (0.26) 9.00 (0.25) 2.02 (1.19) 8.55 (0.21) 8.58 (0.21) 0.38 (0.59)
a) b1) b2)
c) d1) d2)
FIGURE 1. Strength exercises and tests a) standing double-poling, b1) and b2) seated pull-
down (training and 1RM test,) c) triceps press, d) half squat with free weights (training) and
in Smith-machine (1RM test)
0 %
5 %
10 %
15 %
20 %
25 %
Half squat Seated pull-down
Changes in 1 RM
CON
STR *
#
#
*
FIGURE 2. Changes in 1RM half-squat and seated pull-down. * Significant change from pre-
test (p < 0.01). # Significant change between groups (p < 0.01).
27
28
29
30
31
32
33
34
CON STR
Jump height (cm)
Pre
Post
*
FIGURE 3. Changes in Counter-movement jump. * Significant change from pre-test (p <
0.05).
0 %
1 %
2 %
3 %
4 %
5 %
6 %
7 %
8 %
M. quadriceps M. triceps brachii
Change in CSA
CON
STR
*
*
FIGURE 4. Change in cross-sectional area (CSA) of m. quadriceps and m. triceps brachii. *
Significant change from pre-test (p < 0.05)
-4 %
-3 %
-2 %
-1 %
0 %
1 %
2 %
3 %
4 %
5 %
Weight (kg) LBM Total LBM leg LBM trunk
Change
CON STR
*
*
#*
FIGURE 5. Change in weight and lean body mass (LBM) measured with DEXA * Significant
change from pre-test (p < 0.05). # Significant change between groups (p < 0.01).
60
61
62
63
64
65
66
67
68
69
70
Skating Running Skating Running
CON STR
VO
2max
(ml•kg
-1
•min
-1
)
Pre
Post
§
§
* #
FIGURE 6. Change in VO2max during rollerski skating and running. * Significant change from
pre-test (p < 0.01). # Significant change between groups (p < 0.05). § Significantly different
than skating pre-test.
-12 %
-10 %
-8 %
-6 %
-4 %
-2 %
0 % Skating Double poling
Change in duration
CON
STR *
*
*
FIGURE 7. Change in duration in the ski skating and double-poling time-trial tests.
*Significant change from pre- to post-test (p < 0.05).
1.50
2.00
2.50
3.00
3.50
4.00
4.50
20 seconds 5 minutes 20 seconds 5 minutes
CON STR
Watt·kg-1
Pre Post
*
*
*
* #
FIGURE 8. Change in average relative watt (watt·kg-1) in the 20-second and 5-min tests. *
Significant change from pre-test (p < 0.01). # Significant change between groups (p < 0.05).
03:00
04:00
05:00
06:00
07:00
08:00
10 20 30 40 50
1RM seated pull-down (kg)
Time-trial DP (min:sec)
r = -0.81
03:00
04:00
05:00
06:00
07:00
08:00
10 20 30 40 50
1RM seated pull-down (kg)
Time-trial skating (min:sec)
r = -0.81
0
1
2
3
4
5
10 20 30 40 50
1RM seated pull-down (kg)
5 min DP (watt•kg-1)
r = 0.70
0
1
2
3
4
5
10 20 30 40 50
1RM seated pull-down (kg)
20 s DP (watt•kg-1)
r = 0.87
03:00
04:00
05:00
06:00
07:00
08:00
50 75 100 125 150 175 200
1RM half-squat (kg)
Time-trial skating (min:sec)
r = -0.82
10
11
12
13
14
15
16
17
50 75 100 125 150 175 200
1RM half-squat (kg)
100 meter skating (sec)
r = -0.89
FIGURE 9. Correlation between 1RM seated pull-down and a) rollerski double-poling time-
trial (women: r = -0.66, p < 0.05, men: r = 0.13), b) rollerski skating time-trial (women: r = -
0.34, men: r = 0.08), c) 5-minute double-poling on ergometer (women: r = 0.67, p < 0.05 men:
r = 0.28) and d) 20-second double-poling on ergometer (women: r = -0.79, p < 0.05 men: r =
0.45). Figures e and f show correlation between 1RM half squat and rollerski skating
(women: r = -0.62, p < 0.05, men: r = 0.10) and 100-meter rollerski (women: r = -0.80, p <
0.05 men: r = -0.20). All figures show results from baseline (total n=25, men n=14, women
n=11). All values in figures p ≤ 0.01.
▲= women
■ = men
▲= women
■ = men
▲= women
■ = men
▲= women
■ = men
▲= women
■ = men
▲= women
■ = men
