Dalarna University's logo and link to the university's website

Introduction

Endurance training leads to an improved ability of muscle to utilize oxygen. This is related to an increased density and function of mitochondria. The biogenesis and adaptation of mitochondria is a complex process mediated by various signalling pathways and seems to be highly sensitive to the type of exercise and the local environment in the muscle. Changes in the muslce environment in terms of altered metabolism and substrate accumulation are affected by changes in acid/base balance in response to exercise. Recent studies have shown that changes in acid/base balance may affect the regulation of mitochondrial adaptation to acute exercise; however, how this responds to training and relates to performance adaptations in humans is unclear. Similarly, the effect of acid/base balance on mechanisms underlying mitochondrial biogenesis is unclear. The objectives of this study were to examine the relationship between acid/base balance, mitochondrial biogenesis and adaptation.

Methods

Nineteen recreationally active men undertook a six-week periodised high-intensity interval training programme, a protocol known to produce increases in mitochondrial biogenesis. Participants were matched for aerobic fitness and randomly assigned to one of two different training groups. One group ingested sodium bicarbonate (alkaline) and the other group ingested a placebo prior to each training session. Performance test results, blood samples and muscle biopsies were collected before and after the six week training period and assessed for changes in aerobic fitness, blood metabolites and muscle markers of mitochondrial function and biogenesis. Changes in gene expression associated with mitochondrial biogenesis were also examined. 

Results

After the training period, there were significant (P < 0.05) improvements in TTF, Wmax and LT in both groups, citrate synthase activity in the alkaline group and VO2peak in the placebo group. Improvements were also seen in citrate synthase activity in the placebo group and VO2peak in the alkaline group, however these did not reach significance (P = 0.089 and 0.066 respectively).Despite these significant changes within groups in response to training, there were no significant differences between groups.

Discussion

Both training groups showed substantial changes in performance and physiological measures following the training period, however, suppressing exercise-induced acidosis during training did not significantly improve mitochondrial adaptations or performance in comparison to the placebo condition. However, there was a large degree of individual variation in the response and there were trends towards greater adaptations when exercise-induced acidosis was attenuated.

Purpose: To investigate the relationship between race performance and lean mass (LM) variables, as well as to examine sex differences in body composition in elite-standard cross-country skiers. 

Methods: Thirty-four elite cross-country skiers (18 men and 16 women) underwent a dual-emission x-ray absorptiometry body composition test to determine LM, fat mass, and bone mineral content. For both sexes, performance data were collected from a sprint prologue and a distance race. 

Results: The absolute expression of LM variables [whole body (LMWB), upper body (LMUB), and lower body (LMLB)] was significantly correlated with finishing time in the sprint prologue independent of sex. Distance-race performance was significantly related to LMWB, LMUB, and LMLB in women; however, no correlation was found in men. Men had a significantly higher LM and lower fat mass, independent of expression (absolute or relative), for the whole body, arms, trunk, and legs, except for the absolute fat mass in the trunk. 

Conclusions: The absolute expressions of LMWB, LMUB, and LMLB were significant predictors of sprint-prologue performance in both sexes, as well as of distance-race performance in women only. Compared with women, male skiers have a higher LM in the body segments that are major contributors to propelling forces. These results suggest that muscle mass in the lower and upper body is equally important for race performance; thus, more focus of elite skiers’ training should be directed to increasing whole-body muscle mass to improve their competitive performance capability.

Purpose: This study investigated whether there is a correlation between time-trial performance and competitive performance capacity of male and female junior cross-country skiers and sought to explain sex-specific competitive performance capacity through multiple-regression modeling.

Methods: The International Ski Federation's (FIS) junior ranking points for distance (FISdist) and sprint (FISsprint) competitions were used as performance parameters. A total of 38 elite junior (age 18.5 +/- 1.0 y) cross-country skiers (24 men and 14 women) completed 3 time-trial tests: a 3-km level-running time trial (TTRun), a 2-km moderate uphill (1.2 slope) roller-skiing time trial using the double-poling technique (TTDP), and a 2-km uphill (2.8 slope) roller-skiing time trial using the diagonal-stride technique (TTDiag). The correlations were investigated using Pearson correlation analysis, and regression models were created using multiple-linear-regression analysis. Results: For men, FISsprint and FISdist were correlated with the times for TTRun, TTDP, and TTDiag (all P < .001). For women, FISsprint was correlated with the times for TTRun (P < .05), TTDP (P < .01), and TTDiag (P < .01), whereas FISdist was correlated only with the times for TTDP (P < .01) and TTDiag (P < .05). The models developed for FISdist and FISsprint explained 73.9-82.3% of the variance in the performance capacity of male junior cross-country skiers. No statistically valid regression model was found for the women.

Conclusions: Running and roller-skiing time trials are useful tests for accurately predicting the performance capacity of junior cross-country skiers.

The purpose of this study was to: 1) establish the optimal body-mass exponent for maximal oxygen uptake (O₂max) to indicate performance in elite-standard men cross-country skiers; and 2) evaluate the influence of course inclination on the body-mass exponent. Twelve elite-standard men skiers completed an incremental treadmill roller-skiing test to determine O₂max and performance data came from the 2008 Swedish National Championship 15-km classic-technique race. Log-transformation of power-function models was used to predict skiing speeds. The optimal models were found to be: Race speed = 7.86 · O₂max · m ^−0.48 and Section speed = 5.96 · O₂max · m ^{−(0.38 + 0.03 · α)} · e^{−0.003 · Δ} (where m is body mass, α is the section's inclination and Δ is the altitude difference of the previous section), that explained 68% and 84% of the variance in skiing speed, respectively. A body-mass exponent of 0.48 (95% confidence interval: 0.19 to 0.77) best described O₂max as an indicator of performance in elite-standard men skiers. The confidence interval did not support the use of either “1” (simple ratio-standard scaled) or “0” (absolute expression) as body-mass exponents for expressing O₂max as an indicator of performance. Moreover, results suggest that course inclination increases the body-mass exponent for O₂max.

The purpose of the present study was to establish the most appropriate allometric model to predict mean skiing speed during a double-poling roller skiing time-trial using scaling of upper-body power output. Forty-five Swedish junior cross-country skiers (27 men and 18 women) of national and international standard were examined. The skiers, who had a body mass (m) of 69.3 ± 8.0 kg (mean ± s), completed a 120-s double-poling test on a ski ergometer to determine their mean upper-body power output (W). Performance data were subsequently obtained from a 2-km time-trial, using the double-poling technique, to establish mean roller skiing speed. A proportional allometric model was used to predict skiing speed. The optimal model was found to be: Skiing speed = 1.057 · W ^0.556 · m ^−0.315, which explained 58.8% of the variance in mean skiing speed (P < 0.001). The 95% confidence intervals for the scaling factors ranged from 0.391 to 0.721 for W and from −0.626 to −0.004 for m. The results in this study suggest that allometric scaling of upper-body power output is preferable for the prediction of performance of junior cross-country skiers rather than absolute expression or simple ratio-standard scaling of upper-body power output.

Introduction A high maximal oxygen uptake (VO2max) is of importance for success in elite male competitive distance cross-country skiing (Carlsson et al. 2012). However, it is still debatable how VO2max should be expressed to best indicate skiing performance. Therefore, the purpose of this study was to establish the optimal body mass exponent for VO2max to indicate performance in elite-standard male cross-country skiers. Methods Twenty-four elite-standard male cross-country skiers completed an incremental treadmill roller skiing test in diagonal stride technique determining VO2max. Performance data was compiled from a 15-km classic technique race. To predict performance a log-transformation of power-function model: Race speed = β0 • VO2max^β1 • m^β2 was used, where β0 to β2 are constants, and m is body mass. Statistical analyses used R version 2.13.2 (R Development Core Team, New Zeeland) and alpha was 0.05. Results Participants’ VO2max was 5.39 ± 0.57 l/min (mean ± s) and m was 75.5 ± 6.3 kg. Mean race speed was 5.83 ± 0.41 m/s. The model that best predicted performance was: Race speed = 8.829 • VO2max^0.663 • m^-0.355 = 8.829 • (VO2max • m^–0.535 )^0.663, that explains 69.2% of the variance in race speed for the 15-km classic technique race (P < 0.001). For the VO2max-to-mass ratio within the model, the 95% confidence interval (CI) for the body-mass exponent ranged from -0.947 to -0.122. Discussion The optimal body mass exponent for VO2max to indicate performance in elite-standard male cross-country skiers was -0.535. Moreover, the CI for the body-mass exponent does not support the use of simple ratio-standard scaling and absolute expression of VO2max as indicators of 15 km classic ski racing performance in elite-standard men skiers. 

The purpose of this study was to compare peak (VO 2 peak) and maximal (VO 2 max) oxygen uptake, physical performance, and lactate accumulation [la-] in warm versus cold environments. The influence of inhaled air temperature and different warm up modes on these variables as well as arterial oxygen saturation (SaO 2%) and pulmonary function were also studied. Two studies were performed. In study A, 10 males performed maximal exercise tests on a bicycle at +20°C and -12°C. In study B, 8 elite cross-country skiers performed maximal cross-country skiing tests at +13.7°C. Different warm up modes (continuous and intermittent) and different temperatures of the inhaled air (-8°C and +13°C) were used. In study A, we found significantly higher VO 2 peak, peak carbon dioxide (VCO 2 peak), peak ventilation (V E peak) and respiratory exchange ratio (RER) in +20°C compared to -12°C. In study B, we found significantly lower SaO 2% at the end compared to the beginning of the maximal performance test. Time to exhaustion (T ex) was significantly longer using intermittent warm up irrespectively of inhaled air temperature. In conclusion, we found that VO 2 max was affected by different environmental temperatures but not by different temperatures of the inhaled air and that intermittent warm up increased T ex without affecting VO 2 max.