The Effect of Energy Status on Distance Running Performance Across a Competitive Season in Female Cross-country Runners

Abstract

Female cross-country runners are at a higher risk for chronic energy deficiency (ED). Cross-sectional evidence demonstrates the negative effects of ED on surrogate markers of performance. The association between chronic ED and distance running performance in female cross-country runners across a season is unclear. PURPOSE: To examine competitive 5km time trial performance across a season in female cross-country runners categorized by energy status. METHODS: 18 female cross-country runners (19.5 ± 0.3 yrs, 54.6 ± 1.4 kg, 61.2 ± 1.7 mL/kg/min) participated in this prospective observational study across a 10-12 week competitive season. Outcome measures were assessed pre and post-season. Resting energy expenditure (REE) was measured using indirect calorimetry and compared to the Harris Benedict predicted REE (REE/pREE) as a marker of ED. Performance was assessed during an outdoor 5km time trial. Fasting blood samples were assayed for total triiodothyronine (TT3). Repeated measures ANOVA were performed to compare log TT3 and 5km time trial outcomes across the season among participants grouped by tertiles (n=6 each group) of pre-season REE/pREE (severe ED (SED; REE/pREE<0.84), moderate ED (MED; 0.84≤REE/pREE<0.90), and energy replete (ER; REE/pREE≥0.90)). RESULTS: There was a significant group effect (p=0.004), however no time or interaction effects (p>0.49) were observed for the 5km time trial. Pre-season the SED group was 4.1s (p=0.005) slower vs the MED group, while no differences were observed between the ER and the SED or MED groups (p>0.1). Post-season the SED group was 3.7s (p=0.002) and 2.6s (p=0.023) slower vs the MED and ER groups, respectively. For log TT3 there were no significant time or group effects (p>0.15), however a trend toward a significant interaction effect (p=0.097) was observed. Pre-season log TT3 was lower (p=0.043) in the SED vs MED groups, a trend to significance (p=0.067) was observed between the SED and ER groups, with no difference between the ER and MED groups. Log TT3 was not different between groups post-season (p=0.36). CONCLUSIONS: We provide evidence of decrements in 5km time trial performance in severely ED female cross-country runners. Early detection of severe ED utilizing REE may be a strategy for preventing suboptimal distance running performance across a competitive season.