Influence of fat percentage on muscle oxygen uptake and metabolic power during repeated-sprint ability of footballers

Abstract

The aim of this study was to analyse the muscle oxygen saturation (SmO 2 ) dynamics during a repeated-sprint ability (RSA) protocol (8 sprints x 20 meters, 20 s recovery) using near-infrared spectroscopy. Twenty-five footballers were grouped according to the levels of body-fat percentage (level 1: <9%; level 2: 9.1–11.5%; and level 3: >11.6%) from the Spanish third division participated. During RSA, energy cost (EC), metabolic power (MP), speed and total time as external load were measured. Desaturation and resaturation rates and muscular oxygen extraction (▽% SmO 2 ) of the gastrocnemius muscle, along with heart rate (HR) were used as indicators of internal load. ▽% SmO 2 was identified as the most sensitive variable to detect the minimal change during RSA. Footballers with a lower fat percentage (level 1) achieved a higher ▽% SmO 2 after the 4th sprint (Δ= –13; p= 0.001) and (Δ= 9.6; p= 0.017) vs level 2 and level 3, respectively. SmO 2 was related to EC (r2= 0.57 p= 0.005), MP (r2= 0.61 p= 0.003), speed (r2= 0.59 p= 0.004) and total time (r2= 0.59 p= 0.004). Therefore, SmO 2 was a better indicator of internal load than HR during RSA. The ▽% SmO 2 can be used as a parameter to explore potential differences in footballers' RSA performance. Besides, we highlighted the relevance of measuring the body-fat percentage, since it is a variable that affects performance by disturbing ▽% SmO 2 , altering the ability to resist repeated high-speed bouts (sprints), a critical variable in football.