Changes in single skinfold thickness in 100 km ultramarathoners

BACKGROUND: Changes in single skinfold thickness and body fat have been investigated in ultraswimmers and ultracyclists, but not in ultrarunners. The present study investigated the changes in single skinfold thickness during a 100 km ultramarathon. METHODS: Firstly, we investigated associations between prerace preparation and prerace body composition and, secondly, changes in single skinfold thickness during a 100 km ultramarathon in 219 male ultramarathoners. Changes in fat mass and skeletal muscle were estimated using anthropometric methods. RESULTS: Kilometers run weekly prerace and running speed during training were negatively associated with all skinfold thicknesses (P < 0.05) except for the front thigh skinfold. During the race, skinfold thickness at the pectoral (−0.1%), suprailiac (−1.8%), and calf (−0.8%) sites decreased (P < 0.05). The subjects lost 1.9 ± 1.4 kg of body mass (P < 0.001), 0.7 ± 1.0 kg of estimated skeletal muscle mass (P < 0.001), and 0.2 ± 1.3 kg of estimated fat mass (P < 0.05). The decrease in body mass was positively related to the decrease in both estimated skeletal muscle mass (r = 0.21, P = 0.0017) and estimated fat mass (r = 0.41, P < 0.0001). CONCLUSION: Firstly, prerace fat mass and prerace skinfold thickness were associated with both volume and speed in running training. Secondly, during the ultramarathon, skinfold thickness decreased at the pectoral, suprailiac, and calf sites, but not at the thigh site. Percent decreases in skinfold thickness for ultrarunners was lower than the percent decreases in skinfold thickness reported for ultraswimmers and ultracyclists.