Age-related widening of sex differences in upper-body strength and double poling performance in U16-U23 cross-country skiers and biathletes

Introduction Sex differences in the performance of elite cross-country skiers are reported enlarged in techniques with a higher upper-body contribution, such as double poling (DP) and G3 skating. However, little is known about the development of upper-body strength, aerobic power, and DP performance throughout adolescence and early adulthood. Therefore, this study examined age- and sex-related differences in upper-body characteristics and their associations with DP performance. Methods Ninety-eight competitive cross-country skiers and biathletes (47 males, 51 females) from the U16 to U23 age categories completed a 15-s DP ergometer sprint test (DPP 15s ), and an incremental DP ergometer test to volitional exhaustion (DPP peak ). Maximal strength was assessed using one-repetition maximum tests in the bench press (1RM press ) and bench pull (1RM pull ). Maximal oxygen uptake (VO 2max ) was determined during treadmill running with poles. Age- and sex-related differences were analyzed using two-way MANOVAs followed by separate two-way ANOVAs. Partial Pearson correlations were used to examine associations between maximal strength, DP performance, and aerobic power while controlling for age and sex. Results Males demonstrated higher values across all performance measures, which generally increased with age. Significant age × sex interactions were observed for absolute 1RM pull (η²=0.13, p=0.010), 1RM press (η²=0.12, p=0.010), DPP peak (η²=0.14, p=0.003), VO 2peak during DP (η²=0.14, p=0.003) and VO 2max (η²=0.11, p=0.018), indicating larger absolute sex differences in older age groups. No significant age × sex interactions were observed for DPP 15s (η²=0.05, p=0.228) or body-mass normalized measures, except for VO 2peak during DP (η²=0.11, p=0.019). 1RM was moderately to strongly associated with DPP 15s , DPP peak and VO 2peak during DP (r =0.50–0.61), whereas associations were weaker after normalization to body mass (r =0.13–0.39). Aerobic power showed strong associations with DPP peak (r=0.73–0.82). Conclusion Absolute sex differences in upper-body performance increased across age-groups and were more pronounced than previously reported for lower-body performance. However, body-mass normalized differences were largely stable across age groups. Upper-body strength was consistently associated with DP performance after accounting for age and sex, highlighting its potential relevance for DP performance development in youth athletes. However, the cross-sectional design precludes attribution of these age-related differences to maturation, training, or other developmental factors.