Mathematical simulation of energy expenditure and recovery during sprint cross-country skiing

Maximizing recovery time between knock-out races improves sprint cross-country skiing performance

BACKGROUND

In a sprint cross-country (XC) ski competition, the difference in recovery times separating the first and the second semi-final (SF) heats from the final (F) may affect performance. The aim of the current study was to compare the effects of longer vs. shorter recovery periods prescribed between the 3 knock-out races of a simulated sprint XC ski competition involving a prologue (P), quarter-final (QF), SF, and F.

METHODS

Eleven well-trained XC ski athletes completed 2 simulated sprint XC ski competitions on a treadmill involving 4 × 883-m roller-ski bouts at a 4° incline using the gear 3 ski-skating sub-technique. The first 3 bouts were completed at a fixed speed (P_FIX, QF_FIX, and SF_FIX) corresponding to ∼96% of each individual's previously determined maximal effort. The final bout was performed as a self-paced sprint time trial (F_STT). Test conditions differed by the time durations prescribed between the QF_FIX, SF_FIX, and F_STT, which simulated real-world XC ski competition conditions using maximum (MAX-REC) or minimum (MIN-REC) recovery periods.

RESULTS

The F_STT was completed 5.4 ± 5.5 s faster (p = 0.009) during MAX-REC (179.2 ± 18.1 s) compared to MIN-REC (184.6 ± 20.0 s), and this was linked to a significantly higher power output (p = 0.010) and total metabolic rate (p = 0.009). The pre F_STT blood lactate (BLa) concentration was significantly lower during MAX-REC compared to MIN-REC (2.5 ± 0.8 mmol/L vs. 3.6 ± 1.6 mmol/L, respectively; p = 0.027), and the pre-to-post F_STT increase in BLa was greater (8.8 ± 2.1 mmol/L vs. 7.1 ± 2.3 mmol/L, respectively; p = 0.024). No other differences for MAX-REC vs. MIN-REC reached significance (p > 0.05).

CONCLUSION

Performance in a group of well-trained XC skiers is negatively affected when recovery times between sprint heats are minimized which, in competition conditions, would occur when selecting the last QF heat. This result is combined with a higher pre-race BLa concentration and a reduced rise in BLa concentration under shorter recovery conditions. These findings may help inform decision making when XC skiers are faced with selecting a QF heat within a sprint competition.

Energy system contribution during competitive cross-country skiing

Energy system contribution during cross-country (XC) skiing races is dependent on several factors, including the race duration, track profile, and sub-techniques applied, and their subsequent effects on the use of the upper and lower body. This review provides a scientific synopsis of the interactions of energy system contributions from a physiological, technical, and tactical perspective. On average, the aerobic proportion of the total energy expended during XC skiing competitions is comparable to the values for other sports with similar racing times. However, during both sprint (≤ 1.8 km) and distance races (≥ 10 and 15 km, women and men, respectively) a high aerobic turnover interacts with subsequent periods of very high work rates at ~ 120 to 160% of VO_2peak during the uphill sections of the race. The repeated intensity fluctuations are possible due to the nature of skiing, which involves intermittent downhills where skiers can recover. Thus, the combination of high and sustained aerobic energy turnover and repeated work rates above VO_2peak, interspersed with short recovery periods, distinguishes XC skiing from most other endurance sports. The substantially increased average speed in races over recent decades, frequent competitions in mass starts and sprints, and the greater importance of short periods at high speeds in various sub-techniques, have demanded changes in the physiological, technical, and tactical abilities needed to achieve world-class level within the specific disciplines.

Comparison of Peak Oxygen Uptake and Test-Retest Reliability of Physiological Parameters between Closed-End and Incremental Upper-Body Poling Tests

Objective: To compare peak oxygen uptake (VO_2peak) and the test-retest reliability of physiological parameters between a 1-min and a 3-min closed-end and an incremental open-end upper-body poling test. Methods: On two separate test days, 24 healthy, upper-body trained men (age: 28.3 ± 9.3 years, body mass: 77.4 ± 8.9 kg, height: 182 ± 7 cm) performed a 1-min, a 3-min and an incremental test to volitional exhaustion in the same random order. Respiratory parameters, heart rate (HR), blood lactate concentration (BLa), rating of perceived exertion (RPE), and power output were measured. VO_2peak was determined as the single highest 30-s average. Relative reliability was assessed with the intra-class correlation coefficient (ICC_{2, 1}) and absolute reliability with the standard error of measurement (SEM) and smallest detectable change (SDC). Results: The incremental (3.50 ± 0.46 L·min^-1 and 45.4 ± 5.5 mL·kg^-1·min^-1) and the 3-min test (3.42 ± 0.47 L·min^-1 and 44.5 ± 5.5 mL·kg^-1·min^-1) resulted in significantly higher absolute and body-mass normalized VO_2peak compared to the 1-min test (3.13 ± 0.40 L·min^-1 and 40.4 ± 5.0 mL·kg^-1·min^-1) (all comparisons, p < 0.001). Furthermore, the incremental test resulted in a significantly higher VO_2peak as compared to the 3-min test (p < 0.001). VO_2peak was significantly higher on day 1 than day 2 for the 1-min test (p < 0.05) and displayed a trend toward higher values on day 2 for the incremental test (p = 0.07). High and very high ICCs across all physiological parameters were found for the 1-min (0.827-0.956), the 3-min (0.916-0.949), and the incremental test (0.728-0.956). The SDC was consistently small for HR (1-min: 4%, 3-min: 4%, incremental: 3%), moderate for absolute and body-mass normalized VO_2peak (1-min: 5%, 3-min: 6%, incremental: 7%) and large for BLa (1-min: 20%, 3-min: 12%, incremental: 22%). Conclusions: Whereas both the 3-min and the incremental test display high relative reliability, the incremental test induces slightly higher VO_2peak. However, the 3-min test seems to be more stable with respect to day-to-day differences in VO_2peak. The 1-min test would provide a reliable alternative when short test-duration is desirable, but is not recommended for testing VO_2peak due to the clearly lower values.