Metabolically Suppressed Female Runners, Described By Pre-Season RMR Ratio, Exhibit Poorer Running Performance

Female distance runners are at a high risk for chronic energy deficiency (ED). These athletes often present with higher energy expenditure compared to intake during a competitive season. ED during training phases characterized by predominantly high-volume and/or high intensities may compromise performance. Prior studies have related markers of ED, i.e., reduced resting metabolic rate (RMR) ratio and low triiodothyronine (T3) to poor performance. To date, the relationship between pre-season energy status and running performance in female runners across a season is unclear. PURPOSE: To test the hypothesis that energy status as defined by RMR ratio impacts running performance. METHODS: 42 female collegiate distance runners (18-25 yr) were assessed across 10-12 wks. Energy status, body composition and performance (5 km time trial) were assessed pre- and post-competitive season. Runners were categorized into groups based on pre-season measured RMR-to-Cunningham 1991 predicted RMRratio: ED, i.e., metabolically suppressed (SUP: RMRratio < 0.92) (n = 7), and Energy Replete (NSUP: RMRratio ≥ 0.92) (n = 14). Repeated measures ANOVA was used to test effects of group, time, and group*time for analysis of the effect of pre-season RMRratio on performance. Linear regression analysis was used to identify if other energetic factors (T3) predicted performance across the season. RESULTS: 21 runners completed pre and post season performance runs. Runners were 19.6 ± 0.2 yr with a BMI: 20.2 ± 0.4 kg/m2. There were no differences in body mass, BMI, %BF or LBM among energy groups at pre- or post-season. ANOVA revealed a significant group effect (RMRratio), but no effect of time or group*time. SUP had slower time trial performance compared to NSUP (22.4 ± 0.7 vs 20.4 ± 0.5 min) (group: post-hoc t-test p = 0.04). Regression analyses revealed that when controlling for post-season VO2max, pre-season T3 was a predictor of post-season time trial performance (R2 = 0.61, F = 13.7; p = 0.001). CONCLUSION: Female runners with metabolic suppression as described by pre-season RMR ratio < 0.92 exhibited poorer running performance during a season compared to those with adequate (replete) energy status. Early detection of metabolic compensation in runners may be necessary for optimal performance across a season.