Changes in Energetic Factors and Performance Following a Competitive Season in Female Distance Runners

Open Access
Author:
Mctavish, Mitchell Scott
Area of Honors:
Kinesiology
Degree:
Bachelor of Science
Document Type:
Thesis
Thesis Supervisors:
  • Mary Jane De Souza, Thesis Supervisor
  • Jinger Gottschall, Honors Advisor
Keywords:
  • female athlete triad
  • distance runners
  • energy availability
  • energetic factors
  • performance
Abstract:
Female long-distance runners are at a higher risk for chronic energy deficiency, defined as inadequate energy intake relative to energy expenditure, and other medical conditions associated with the Female Athlete Triad, to include low energy availability with or without disordered eating, menstrual disturbances, and low bone mineral density. To date, the relationship between chronic energy deficiency and running performance in female long-distance runners has yet to be determined. Purpose: The purpose of this study is two-fold: (1) to characterize the change in energetic factors (REE, fasting concentrations of TT3 and ghrelin, and EA) across a competitive season in female long-distance runners categorized by energy status and (2) to examine distance running performance during a competitive time trial (test race time) from pre- to post-season in female long-distance runners categorized by energy status. Methods: This study was a prospective investigation examining energetic, metabolic, and performance characteristics in 18 female long-distance runners (17-25yr) categorized by energy status across a competitive season. Participants were assessed pre- and post-competitive running season (10-12 weeks). REE was measured by indirect calorimetry using a ventilated hood system. A ratio of the actual REE to the Harris Benedict predicted REE (REE/pREE) was calculated once during each monitoring period. We categorized our participants according to tertiles of REE/pREE: severe energy deficiency (ED) (REE/pREE<0.84) (n=6), moderate ED (0.84≤REE/pREE<0.90) (n=6), and energy replete (REE/pREE≥0.90) (n=6). Fasting blood samples were collected and assayed for total triiodothyronine (TT3) using a chemiluminescence-based immunoassay and total ghrelin using radioimmunoassay. Test race time (min) and running velocity (mph) were determined as indicators of performance via a competitive 5km time trial on an accurately measured outdoor course . Body composition was measured using dual energy x-ray absorptiometry. Energy intake was assessed using 3-day diet logs. Exercising training volume/expenditure was determined using 7-day training logs. Exercise energy expenditure was measured using the Ainsworth compendium. Energy availability was determined as EI minus EEE relative to kg LBM [EA = (EI – EEE)/LBM (kg)]. Maximal oxygen uptake (VO2max) was measured on a treadmill using indirect calorimetry and the modified Astrand protocol. One-way ANOVA with repeated measures were performed to compare REE, fasting TT3 and ghrelin, EA, test race time and running velocity across the competitive season. Paired t-test and one-way ANOVA analyses were performed to confirm time and group effects, respectively. Results: Study participants were 19.5±0.3 yr, weighed 54.6±1.4 kg with 22.9±0.8% body fat (%BF). There were no differences (p<0.05) in body mass, BMI, and LBM among groups at pre- or post-season. The severe ED group had a higher %BF than the energy replete group (p=0.011) at pre-season measurements, and a higher % BF (p<0.05) than both the energy replete and moderate ED groups at post-season. As expected, REE/pREE and REE were lower (p<0.05) in the severe ED group than energy replete runners at pre-season, as well as lower (p<0.05) than the energy replete group and the moderate ED group at post-season. The moderate ED group also demonstrated lower REE/pREE (p<0.05) than the energy replete group at pre- and post-season. At pre-season, the severe ED group had slower test race time and running velocity (p<0.05) than the moderate ED group. No differences in test race time and running velocity were observed (p>0.05) between the severe ED and moderate ED groups vs. the energy replete group at pre-season. At post-season, the severe ED group had a slower test race time and running velocity (p<0.05) than both the moderate ED and energy replete groups. At pre-season, Log TT3 was lower (p=0.043) in the severe ED group vs. the moderate ED group. No changes in EA and fasting TT3 were observed across the season (p=0.005). A time effect was observed for ghrelin within groups (p<0.05). Conclusion: In summary, we provide evidence of an association between severe energy deficiency and decrements in distance running performance. Thus, early detection of poor energy status in female distance runners, using REE testing, may be beneficial in for promoting optimal distance running performance across a season. Future research is necessary to confirm this association in a larger sample of female runners.