INTRODUCTION: The (positive) mechanical external work (Wext) is the work performed by the muscle-tendon unit to accelerate and lift the body center of mass (Peyré-Tartaruga et al. 2021). It has historically been investigated in steady locomotion, where it was able to explain most of the absolute metabolic cost and its variations (Peyré-Tartaruga et al. 2021). In recent years the mechanical approach has been applied also to unsteady locomotion (e.g. shuttle and sprint running) typical of team sports (Zamparo et al. 2019; Pavei et al. 2019) albeit still using optoelectronic systems, which is a standard for computation, but an unfeasible approach during team sports training or competitions. METHODS: We used a GPS-tracking system to calculate the mechanical external work performed by various players during official football matches. According to Pavei et al. (2019), positive mechanical work was calculated as the sum of the work to accelerate forward, which can be derived by the velocity profile obtained by the GPS, the speed fluctuations and lift at each support. The players of a football club of the Italian second division (Serie B) where monitored during the whole football season 2020-2021 (42 games) with a GPS-tracking system (gpexe pro2, sampling at 18.18 Hz). Only players that completed the whole match (90 minutes), goalkeeper excluded, were analysed. RESULTS: A total of 203 tracks from 20 players were analysed. The positive mechanical work range over the whole 90 minutes was 7.9-15.7 KJ/kg with an average value of 10.8 KJ/kg (1.3 KJ/kg, SD). When expressed as mechanical power (in relation to the whole match time) 1.9 W/kg (0.2 W/kg, SD). The positive mechanical work was different among roles, with center back 9.7 KJ/kg (1.0 KJ/kg, SD), wide back 10.9 KJ/kg (0.7 KJ/kg, SD), midfielder 12.3 KJ/kg (0.9 KJ/kg, SD) and attacker 11.3 KJ/kg (0.7 KJ/kg, SD). CONCLUSION: We showed for the first time the feasibility to calculate mechanical external work in a competition setting with a GPS-tracking system. The mechanical external work performed by the players reflects the muscle-tendon work that needs to be done in order to move the body. Hence, it accounts for accelerative and constant speed movements and could be a useful metric to monitor the work done by the (muscle-tendon unit of the) players, not just during the match but also during training. Although also the mechanical internal work has been shown to have an impact on the total mechanical work performed by the muscle-tendon unit in both shuttle and sprint running (Zamparo et al. 2019; Pavei et al. 2019), its computation is still challenging for the nowadays tracking systems, and only a fusion with video analysis or multiple magneto inertial measurement units could overcome those intrinsic limitations.
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