Men and women have different morphology and physiology that lead to sex differences in performance and fatigability. Although women continue to increase their participation and performance in sport, the research used to guide training principles has been heavily reliant on male athletes. One reason a woman s physiology differs is because of the fluctuating hormones throughout the menstrual cycle. Estrogen and progesterone, are hormones known to influence metabolism as well as basal body temperature regulation, potentially impacting a women s training, performance and fatigue. Race-specific performance can be effectively measured by time-trials, and time trial (TT) performance is influenced by pacing strategy. Pacing strategy is a learned skill and less experienced athletes are likely to have a variable pacing strategy which may reduce performance. Therefore, the purpose of this study was to determine the influence of sex, menstrual cycle phase, age and pacing strategies on 3km track TT performance after a high intensity interval training (HIIT) session in cross-country (XC) skiers. Thirty female and nine male XC skiers completed 3 days of testing/training: a 3km track TT on Day 1 (pre-HIIT) and Day 3 (post-HIIT), and a HIIT session composed of 4-8x 800m on Day 2. An overall improvement in performance from pre- to post-HIIT TTs was observed (p<0.01). Significant differences were not observed in TT performance after HIIT between sexes (p=0.16) or menstrual cycle phases (p=0.26). There was a trend for greater improvement in TT performance after HIIT in younger (u18) athletes compared to older (18+) athletes (p=0.06). Pacing strategy of u18 athletes did not differ between those who did or did not improve their performance, although all u18 athletes improved pacing strategy in the Post-HIIT TT. Most 18+ athletes did not improve pacing strategy; however, those who did were significantly more likely to also improve their TT performance
