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Keywords:

  • cross-country skiing;
  • double poling;
  • men;
  • peak oxygen uptake;
  • roller skiing;
  • women

Abstract

  1. Top of page
  2. Abstract
  3. Methods
  4. Results
  5. Discussion
  6. Perspectives
  7. Funding
  8. References

Greater gender differences have been found in exercise modes where the upper body is involved. Therefore, the present study investigated the influence of poling on gender differences in endurance performance by elite cross-country skiers. Initially, the performance of eight male and eight female sprint skiers was compared during four different types of exercise involving different degrees of poling: double poling (DP), G3 skating, and diagonal stride (DIA) techniques during treadmill roller skiing, and treadmill running (RUN). Thereafter, DP was examined for physiological and kinematic parameters. The relative gender differences associated with the DP, G3, DIA and RUN performances were approximately 20%, 17%, 14%, and 12%, respectively. Thus, the type of exercise exerted an overall effect on the relative gender differences (P < 0.05). In connection with DP, the men achieved 63%, 16%, and 8% higher VO2peak than the women in absolute terms and with normalization for total and fat-free body mass (all P < 0.05). The DP VO2peak in percentage of VO2max in RUN was higher in men (P < 0.05). The gender difference in DP peak cycle length was 23% (P < 0.05). In conclusion, the present investigation demonstrates that the gender difference in performance by elite sprint skiers is enhanced when the contribution from poling increases.

During the last decade, research has revealed that the performance of elite male athletes in connection with endurance sports is approximately 10–12% better than that of elite female athletes with similar condition (Joyner, 1993; Schumacher et al., 2001; Coast et al., 2004; Maldonado-Martin et al., 2004; Seiler et al., 2007). Most of the gender difference associated with endurance sports has been attributed to a higher VO2max and lower percentage of body fat in men (Joyner, 1993; Calbet & Joyner, 2010). However, in the case of elite sprint cross-country skiing uphill on roller skis using the skating G3 technique, the gender difference was recently found to be approximately 17% (Sandbakk et al., 2012). Because poling generates much of the propulsion in G3 skating (Millet et al., 1998; Stöggl et al., 2011), this more pronounced gender difference in comparison with other sports may reflect more effective poling in male skiers. Studies on other sports reveal greater work rates in swimming than in running and speed skating (Seiler et al., 2007), which may further support the hypothesis of greater gender differences when the upper body is involved.

In cross-country skiing, the manner in which the arms and legs are employed changes with the terrain and the technique utilized (Smith, 1992). Specifically, with the double poling technique (DP), propulsion is powered exclusively by the poling itself (e.g., Nilsson et al., 2004; Holmberg et al., 2005). Therefore, if the more pronounced gender difference associated with G3 skating is due to poling, this difference should be even greater with DP than with techniques that rely less on poling.

Accordingly, the current investigation was designed to compare gender differences in endurance performance among elite skiers utilizing three different techniques that rely on poling to different extents (from extensively to not at all), i.e., DP, G3 skating and diagonal stride roller skiing, as well as running on a treadmill. Thereafter, the findings on DP were examined in greater detail with respect to physiological and kinematic characteristics. Our hypothesis was that the difference between the performance of the men and women is positively correlated to the contribution of poling, and that the gender differences in performance and kinematics connected with DP cannot be explained by differences in peak oxygen uptake (VO2peak) and percentage body fat alone.

Methods

  1. Top of page
  2. Abstract
  3. Methods
  4. Results
  5. Discussion
  6. Perspectives
  7. Funding
  8. References

Subjects

Eight male and eight female Norwegian elite sprint cross-country skiers volunteered to participate in this study. The background characteristics of these two gender groups, who were similar with regards to sprint skiing performance [International Ski Federation (FIS) points] as calculated by the FIS (FIS, 2010), are documented in Table 1. This study was preapproved by the Regional Ethics Committee in Trondheim, Norway, and all subjects were fully informed of its nature prior to providing their written consent to participate.

Table 1. Anthropometric characteristics, annual training time and level of sprint performance (expressed as FIS points) in our eight male and eight female elite sprint cross-country skiers
ParameterMenWomen
  1. All values presented are means ± standard deviation.

  2. a

    P < 0.001 in comparison to the corresponding value for the women.

Age (year)25.8 ± 2.224.1 ± 2.4
Body height (cm)183.8 ± 5.1a 168.0 ± 2.8
Body mass (kg)83.3 ± 7.2a 60.1 ± 4.7
Body mass index (kg/m2)24.6 ± 0.6a 21.3 ± 1.4
Body fat (%)8.5 ± 2.3a 14.5 ± 2.0
Fat-free body mass (kg)76.1 ± 6.0a 51.3 ± 3.2
VO2max (L/min) in running5.8 ± 0.5a 3.6 ± 0.4
Annual training (h)673 ± 96686 ± 65
FIS points49.9 ± 12.049.0 ± 14.3

Overall design

Initially, performance in four different exercise modes were compared: DP, G3 skating, and diagonal stride (DIA) roller skiing techniques on a treadmill [in which order of the influence of poling has been reported to gradually decrease (Stöggl et al., 2011)] as well as treadmill running (RUN), where no poling is involved. Thereafter, the findings concerning DP were examined in greater detail with respect to physiological and kinematic parameters. Finally, body composition was determined. All tests were performed within 3 weeks in a randomized order during the dry land training period (August and September), when skiers mainly use running and roller skiing in their daily training. The subjects performed two familiarization sessions in all techniques before the study started. There were at least 2 days between tests, and standardized training 48 h before testing.

Instruments and materials

The roller skiing tests were performed on a 6 × 3 m motor-driven treadmill (Bonte Technology, Zwolle, the Netherlands). The nonslip rubber surface of the treadmill belt allowed the subjects to use their own ski poles (equipped with special carbide tips and with a mean length, expressed as a percentage of body height, of 83 ± 2% in the case of the DP and DIA techniques and 90 ± 2% with G3 for both genders). The subjects were secured to the treadmill with a safety harness during testing. To exclude possible variations in rolling resistance, all skiers used the same prewarmed pair of Pro-ski classic roller skis (for DP and DIA) or Swenor skating roller skis (for G3) with standard wheels and the Rottefella binding system (Rottefella AS, Klokkartstua, Norway). Treadmill running was performed on a motorized treadmill (Woodway GmbH, Weil am Rein, Germany). Both treadmills' inclination and speed were calibrated using the Qualisys Pro Reflex system and the Qualisys Track Manager software (Qualisys AB, Gothenburg, Sweden).

In order to calculate work rate with roller skiing techniques, the rolling friction force (F f) of the roller skis were assessed utilizing the towing test described previously by Sandbakk et al. (2010). The rolling friction coefficient (μ) was then determined by dividing F f by the normal force (F n) inline image. In the current study, we found μ-values of 0.028 and 0.023 for the classic and skating roller skis. These values were employed to calculate work rate.

Respiratory parameters were measured employing open-circuit, indirect calorimetry with an Oxycon Pro apparatus (Jaeger GmbH, Hoechberg, Germany) after calibration with standardized procedures, as presented in earlier studies (Sandbakk et al., 2010; 2012). Heart rate (HR) was assessed with a monitor designed specifically for this purpose (Polar RS800, Polar Electro OY, Kempele, Finland) and the 5 μL of blood taken from the fingertip was assayed for lactate concentration (BLa) with the Lactate Pro LT-1710t apparatus (ArkRay Inc., Kyoto, Japan), as validated by Medbø and co-workers (2000).

For the examination of kinematic parameters, two synchronized 50-Hz Sony video cameras (Sony Handycam DCR-VX2000E, Sony Inc., Tokyo, Japan) were fixed to the front and side of the treadmill and the recordings made analyzed utilizing the Dartfish Pro 4.5 program (Dartfish Ltd, Fribourg, Switzerland).

Body mass was determined on a Kistler force plate (Kistler 9286AA, Kistler Instrument Corp., Winterthur, Switzerland) and body height using a calibrated stadiometer (Holtain Ltd, Crosswell, UK). The percentage of body fat was estimated from skinfold measurements at four different sites (Holtain Skinfold caliper PE025, Holtain Ltd, Crosswell, UK), with calculations for the men and women according to Durnin and Womersley (1973).

Test protocols and measurements

Performance tests

Roller skiing and running performances (i.e., peak speed during the test protocols) were tested using incremental increases in the speed of the treadmill maintained at a constant incline (5% for the DP and G3 techniques, 12% for DIA, and 10.5% for RUN). In the former two cases, the initial speed of 3.9 m/s was increased by 0.6 m/s after 1 min of skiing and thereafter by 0.3 m/s every minute until exhaustion. In the cases of DIA and RUN, the initial speed of 2.5 m/s was elevated 0.3 m/s every minute until exhaustion. The inclines and speeds in the roller ski tests were chosen on the basis of where these techniques are used during races and experiences from pilot testing and earlier studies involving this type of test (Sandbakk et al., 2011c; 2012). RUN was used to represent pure leg work as skiing without poles involves technical difficulties to ensure the performance of a good maximal test. The 10.5% incline for RUN was regarded the most relevant incline for testing elite skiers according to earlier studies (Ingjer, 1991; Sandbakk et al., 2011a).

Exhaustion was defined as the time-point at which the subject was no longer able to keep the forefoot in front of a marker on the treadmills. Peak speed, was calculated as V f + [(t·T −1Vd], where V f was the speed associated with the final workload, t the duration for which this maximal workload was maintained, T the duration of each individual level of workload, and V d the difference in the speeds at which the last two workloads were performed (Holmberg et al., 2005).

Physiological measurements

For the tests involving the DP and RUN, physiological measurements were also performed. The maximal level of effort was considered to have been attained when a plateau in VO2 was achieved, despite increasing intensity of exercise, and a peak BLa > 8 mmol/L occurred (Basset & Howley, 2000). VO2, HR, and ventilation were monitored continuously and the averages of the three consecutive 10-s intervals associated with the highest values designated as maximal and peak values. BLa was assayed 1 min and 3 min after completion of the tests and the highest of these values designated as peak BLa.

Calculations of work rate

Peak work rate was calculated as the sum of power against gravity (Pg) and friction (Pf) for the roller ski tests, whereas only Pg was considered for RUN.

  • display math
  • display math

with m being the mass of the skier, g the gravitational acceleration, α the incline of the treadmill, v the peak belt speed, and μ the frictional coefficient.

Kinematic parameters

The DP cycle time was defined as the average period between two pole plants for six cycles of poling; the cycle length as the speed multiplied by the cycle time; and the cycle rate as the reciprocal of cycle time. These parameters were assessed both at the same absolute submaximal speed (4.4 m/s) and during the final 30-s workload on the treadmill.

Scaling models

For evaluation of performance, work rate and oxygen uptake were normalized to total body mass. In addition, these parameters were normalized for fat-free body mass to determine whether differences in fat mass could explain any gender differences observed. In all cases, the best power fit for the variables of interest was plotted against body mass according to y = a + b(mass)s. In agreement with Batterham and coworkers (1999), when work rate and VO2 were plotted against total and fat-free body mass, a mass exponent of 1 provided a good fit.

Statistical analyses

All data were found to be normally distributed utilizing the Shapiro–Wilks test and are presented as means ± standard deviations. Differences between the men and women were compared utilizing the independent t-test procedure, with adjustment of alpha levels according to Bonferroni. In this context, the values for women were regarded as 100%. To examine whether the mode of exercise influenced the gender differences, we first calculated the combined mean of both the male and female values together for each type of exercise. Thereafter, all data were normalized to the corresponding combined mean, thereby eliminating all variance associated with the mode of exercise. A one-way analysis of variance for repeated measures, with gender as an inter-subject factor and consideration of the interaction between mode of exercise and gender, revealed the impact of the type of exercise on gender differences. The location of relative gender differences between exercise modes was assessed through a contrast analysis. Relationships between variables were analyzed by linear regression and Pearson's product–moment correlation coefficient test. All statistical analyses were processed using the Statistical Package for the Social Sciences (SPSS) 11.0 Software for Windows (SPSS Inc., Chicago, IL, USA), with an α-value of < 0.05 being considered statistically significant.

Results

  1. Top of page
  2. Abstract
  3. Methods
  4. Results
  5. Discussion
  6. Perspectives
  7. Funding
  8. References

Endurance performance in connection with the different modes of exercise

Performance (i.e., peak speed during the different protocols) utilizing the DP, G3, DIA, and RUN techniques were 5.8 ± 0.2, 6.2 ± 0.3, 4.2 ± 0.1, and 4.4 ± 0.2 m/s for men, and 4.9 ± 0.2, 5.3 ± 0.2, 3.7 ± 0.1, and 3.9 ± 0.2 m/s for women. Thus, men were approximately 20%, 17%, 14%, and 12% faster for DP, G3, DIA, and RUN, respectively (Fig. 1, P < 0.05). The mode of exercise influenced the relative gender difference (Fig. 1, P < 0.05).

figure

Figure 1. (a) Relative gender differences in speed and (b) differences from the normalized combined mean (where all variance caused by the mode of exercise has been eliminated) for eight male and eight female performance-matched sprint cross-country skiers in connection with four different types of exercise. From high extensive (left) to no use (right) of poling: peak speed utilizing the double poling (DP), G3 skating, or diagonal stride (DIA) technique during treadmill roller skiing, and treadmill running (RUN). The circles and squares in B indicate the mean values for the women and men, respectively, while the vertical bars indicate the standard deviation. The combined mean for both genders in B is set to a value of 1.00. *Significantly different from DP and #significantly different from G3 (P < 0.05).

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The gender differences in absolute work rates were 67% (mean values: 355 vs 212 W), 62% (372 vs 230 W), 58% (512 vs 324 W), and 54% (374 vs 243 W) for DP, G3, DIA, and RUN, respectively (all P < 0.05). Normalized for total and fat-free body mass, these differences were reduced to 20% and 12% for DP, 17 and 9% for G3, 14% and 6% for DIA, and 12% and 3% for RUN (all P < 0.05).

Within both genders, significant correlations between treadmill roller ski performance and FIS points were found for DP, G3, and DIA (r = 0.76, r = 0.78, and r = 0.69 for men and r = 0.88, r = 0.73, and r = 0.62 for women, all P < 0.05). RUN performance did not correlate significantly with FIS points.

More detailed analysis of the double poling technique

The physiological and kinematic variables for men and women performing DP are compared in Table 2 and Fig. 2. The men demonstrated a 63% higher absolute VO2peak, which was 16% and 8% higher relative to total and fat-free body mass (both P < 0.05). The DP VO2peak in percentage of VO2max in RUN was higher in men (P < 0.05). At submaximal speed, the men executed 17% longer cycle lengths at a 17% lower rate (both P < 0.05), whereas at peak speed, the men exhibited 23% longer cycle lengths (P < 0.05), with no difference in rate. At maximal speed, the gender differences in work per cycle (i.e., peak work rate divided by cycle rate) normalized for lean body mass, and cycle length normalized for body height were also statistically significant (both P < 0.05).

figure

Figure 2. Differences in cycle length and rate between eight male and eight female elite sprint cross-country skiers during 5-min stages of roller skiing on a treadmill using the double poling technique at a submaximal speed (4.4 m/s) and at maximal speed. The values presented are means ± standard deviation (the vertical bars). *Indicates significant differences between the gender groups and #significant differences between submaximal and peak speed within each group.

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Table 2. Performance, physiological responses and kinematic parameters for eight male and eight female elite cross-country sprint skiers performing incremental treadmill roller skiing (at 5% inclination) employing the double poling technique
ParameterMenWomenDifference (%)
  1. TBM, total body mass; FFBM, fat-free body mass; RER, respiratory exchange ratio; HR, heart rate; BLa, blood lactate concentration. Submaximal speed = 4.4 m/s. All values presented are means ± standard deviation.

  2. a

    Significantly different (P < 0.05) for men and women.

Time to exhaustion (s)408 ± 30198 ± 45206a
Peak speed (m/s)5.8 ± 0.34.9 ± 0.220a
Work rate (W)347 ± 29208 ± 1667a
Work rate (W/kg) TBM 4.2 ± 0.13.5 ± 0.220a
Work rate (W/kg) FFBM 4.6 ± 0.14.1 ± 0.212a
VO2peak (L/min)5.2 ± 0.43.2 ± 0.263a
VO2peak (mL/min/kg) TBM 62.2 ± 1.853.6 ± 3.016a
VO2peak (mL/min/kg) FFBM 68.0 ± 1.662.7 ± 3.28a
% of VO2max in running89 ± 386 ± 33a
Peak ventilation (L/min)195 ± 15133 ± 845a
Peak RER1.10 ± 0.041.09 ± 0.041
Peak HR (bpm)189 ± 5190 ± 60
% of max HR98 ± 198 ± 10
Peak BLa (mmol/L)11.7 ± 2.011.3 ± 2.93
Submaximal cycle rate at (Hz)0.59 ± 0.040.69 ± 0.0417a
Submaximal cycle length (m)7.5 ± 0.46.4 ± 0.317a
Peak cycle rate (Hz)0.72 ± 0.050.74 ± 0.043
Peak cycle length (m)8.1 ± 0.76.5 ± 0.624a

Discussion

  1. Top of page
  2. Abstract
  3. Methods
  4. Results
  5. Discussion
  6. Perspectives
  7. Funding
  8. References

The current investigation was designed to compare gender differences in endurance performance among elite skiers utilizing three different techniques that rely on poling to different extents. The size of gender differences on performance (i.e., peak speed) was associated with the amount of poling contribution. The gender differences ranged from 20% in DP (mostly poling) to 12% in RUN (model for no poling), with 17% and 14% in G3 and DIA. In absolute work rates, these gender differences were 67%, 62%, 58%, and 54% for DP, G3, DIA, and RUN. In DP, we examined the gender differences in more detail. The differences in VO2peak normalized for total (16%) and fat-free (8%) body mass were somewhat smaller than differences in work rates. The work rate differences in DP were mostly due to a longer cycle length with no significant gender difference in cycle rate.

Our comparison of performance associated with DP, G3, DIA, and RUN, ranging from exclusively poling in DP to no poling in RUN, clearly revealed an effect of poling intensity on gender differences. The 20% gender difference in peak speed associated with DP decreased to 17% with G3, 14% with DIA and 12% with RUN. The approximately 10–12% gender differences in performance reported for comparable sports, are not different with those observed with RUN here (Schumacher et al., 2001; Coast et al., 2004; Maldonado-Martin et al., 2004; Seiler et al., 2007). Thus, the 20% gender difference associated with DP was significantly greater.

Work rate is related to an exponential expression of velocity, and the magnitudes of difference in work rate associated with a given performance are, in many cases, more correct representations of the actual gender differences (Seiler et al., 2007). In the current study, gender differences in work rates across exercise modes revealed the same results as the comparisons of peak speed. An additional finding was that the gender differences for RUN almost disappeared (3%) when work rate was normalized for fat-free body mass, whereas these differences increased with the poling contribution. Overall, the calculations of work rate further support our hypothesis that the performance difference between men and women is positively correlated to the contribution of poling.

The current study reported greater gender differences in all roller ski modes than the ∼10% difference between genders in mean speeds during FIS sprint races from 2000 to 2008 (Stöggl et al., 2008). However, the world cup races performed over similar distances from 2010 to 2012 show that gender differences between the top 10 skiers have increased from 12% to 16%. This indicates increasing gender differences among sprint skiers in recent years, probably reflecting a greater degree of specialization for sprint skiing in male skiers. Despite this, performance in the tests employed here does not necessarily reflect the actual difference between genders in sprint skiing competitions; we believe our protocols are highly relevant for examining the gender differences between exercise modes. Furthermore, the validity of the tests are supported by the significant correlations between FIS points and peak speed in all roller ski tests employed, and that performance in a similar test was strongly correlated to sprint time-trial performance in the skating technique (Sandbakk et al., 2011c).

It was also of interest to compare our findings with sports where most of the propulsion is generated by the upper body. With various distances, the gender differences in the mean speeds of world record holders at the end of 2010 were approximately 11% for swimming and rowing, and approximately 13% for kayaking. However, the quadratic influence of velocity on opposing frictional forces and the fact that the boats are deeper in the water with heavier men leads to larger differences in work rate than the time differences indicate in these sports. Seiler et al. (2007) report larger differences in the work rates produced when swimming (approximately 45%) where the upper body is highly involved, compared with running and speed skating (20–30%), where only the legs produce propulsion. Altogether, these data support our findings of a more effective utilization of the upper body in men.

Our more in-depth analysis of DP revealed that in this case the gender differences were associated with higher VO2peak both in absolute values and relative to VO2max in the male sprint skiers. With respect to VO2peak, this gender difference was consistently greater than those observed for comparable endurance sports (Joyner, 1993; Calbet & Joyner, 2010) and might explain, at least in part, the more pronounced gender difference. Previous investigations have attributed differences in performance between men and women to higher levels of hemoglobin and less body fat in the men (Joyner, 1993; Stefani, 2006; Calbet & Joyner, 2010). Overall, this confirms the hypothesis that the gender differences connected with DP cannot be explained by differences in peak oxygen uptake (VO2peak) and the percentage of body fat alone.

In the present examination of DP performance, male skiers executed a longer cycle length (i.e., work per cycle) both at submaximal and peak speeds, whereas the cycle rate differed only at submaximal speed. This demonstrates that cycle length is the key differentiating factor with respect to DP performance by men and women, in agreement with a previous study by Lindinger and colleagues (2009), showing that for male skiers performing the DP technique, increased speed is associated with longer cycle length. In comparison with what we have reported for the same subjects with the G3 skating technique on a similar incline (see Sandbakk et al., 2012), with DP here the gender difference in cycle length were slightly greater.

Perspectives

  1. Top of page
  2. Abstract
  3. Methods
  4. Results
  5. Discussion
  6. Perspectives
  7. Funding
  8. References

This study demonstrates that gender differences in endurance performance and peak aerobic capacity among elite sprint skiers become more pronounced as the contribution from upper-body propulsion (poling)increases. In contrast to previous observations on elite endurance athletes, differences in VO2peak, and fat-free body mass could not totally explain the gender difference in DP performance documented here. In the present case, these differences were also associated with longer cycle length in the male sprint skiers. Whether female skiers have a greater potential than men to develop their poling performance remains to be determined.

Funding

  1. Top of page
  2. Abstract
  3. Methods
  4. Results
  5. Discussion
  6. Perspectives
  7. Funding
  8. References

The study was supported financially by the Mid-Norway Department of the Norwegian Olympic Committee.

References

  1. Top of page
  2. Abstract
  3. Methods
  4. Results
  5. Discussion
  6. Perspectives
  7. Funding
  8. References
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