## 4 Discussion
The generation of high power outputs during DP is partially influenced by VO2 peak, but also related to the fractional utilization of VO2 peak, efficiency, and anaerobic capacity. Therefore, one possible explanation for improved DP performance could be the increased energetic flux resulting from the enhanced oxidative capacity within the working muscles, possibly supplemented by an increased maximal strength, and anaerobic capacity--assuming that there was an increase in lean body mass [72]. The significance of dynamic strength is uncertain. For instance, upper-body 1 RM measurements were imprecise in distinguishing between national and world-class athletes in their capacity to generate high power outputs on DP ergometers. [1; 6; 73; 74]. One of the limitations of the study was that participants were relatively young and included both genders, leading to a heterogeneous group. This diversity might influence the results due to variations in maturation, with younger individuals in the LL and control group potentially affecting outcomes differently compared to those in the HL group. Therefore, these findings might not be directly applicable to more homogeneous groups of elite or world-class senior athletes. Moreover, the study utilized a per-protocol design rather than intent-to-treat, due to organizational reasons. Therefore, a reduced sample size (n = 8) and varying sample size within the different groups diminished the statistical power, possibly impacting the significance levels. Additionally, the decrease in study population size during the intervention, due to illness, limited the number of participants in different groups for robust analysis, which means that a single outlier impacts the calculation. This situation underscores the inherent challenges of conducting applied research in elite sports, where such specific populations are rarely accessible. Despite these obstacles, the data collected remain valuable, providing unique insights into a group that is seldom studied, thus contributing significantly to our understanding of high-performance sports. The study's findings demonstrate significant improvements in VO2 peak-DP among elite youth cross-country skiers following a 10-week resistance training intervention. This suggests enhanced peak aerobic capacity with potential implications for enhancing endurance performance in cross-country skiing. While both HL and LL protocols resulted in significant increases in upper-body strength, HL showed superior improvements compared to LL in strength. This indicates a dose-response relationship to load magnitude for strength development. Interestingly, these strength gains, particularly pronounced in the HL group, significantly enhanced DP performance. Thus, endurance athletes could benefit from prioritizing high-load protocols with ample volume (e.g., 20 sets per major muscle group per week) while emphasizing effort (proximity to failure) to maximize their upper-body endurance performance. However, future investigation is warranted to ascertain whether this improvement extends to DP efficiency, as observed in previous research. Examining the interplay between increased energy delivery and potential improvements in efficiency will contribute to a more comprehensive understanding of the performance adaptations resulting from resistance training.