Monitoring locomotor load in soccer: is metabolic power, powerful?

Buchheit M, Manouvrier C, Cassirame J and Morin JB. Monitoring locomotor load in soccer: is metabolic power, powerful? Int J Sport Med, In press, 2015.

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Figure 1. Oxygen uptake (VO₂), speed and metabolic power estimated from locomotor demands (P_GPS) during the warm-up and the 3 exercise bouts in a representative player. VO₂max: maximal oxygen uptake reached during an incremental test to exhaustion.

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Abstract

The aim of the present study was to examine the validity and reliability of metabolic power (P) estimated from locomotor demands during soccer-specific drills. Fourteen highly-trained young soccer players (15.4±1.6 yr) performed a soccer-specific circuit with the ball (3 x 1-min bouts, interspersed with 30-s passive recovery) on two different occasions. Locomotor activity was monitored with 4-Hz GPS units, while oxygen update (VO₂) was collected with a portable gas analyzer. P was calculated using either net VO₂responses and traditional calorimetry principles (P_VO2, W.kg^-1) or locomotor demands (P_GPS, W.kg^-1). Distance covered into different speed, acceleration and P zones was recorded. Players covered 30 times more distance >20 W/kg (P_GPS) than >14.4 km.h^-1. While P_GPS was 29 ± 10 % lower than P_VO2 (Cohen’s d<-3) during the exercise bouts, it was 85 ± 7 % lower (d<-8) during recovery phases. The typical error of the estimate between P_GPS vs P_VO2 was moderate: 19.8%, 90% confidence limits: (18.4;21.6). The correlation between both estimates of P was small: 0.24 (0.14;0.33). Very large day-to-day variations were observed for acceleration, deceleration and >20 W.kg^-1 distances (all CVs >50%), while total distance, average P_VO2 and P_GPS showed CVs <10%. ICC ranged from very low- (acceleration and >20 W.kg^-1 distances) to-very high (P_VO2). To conclude, P_GPS largely underestimates the energy demands of soccer-specific drills, especially during the recovery phases. Together with its moderate agreement with calorimetry-related P estimations, the poor reliability of P_GPS >20 W.kg^-1 questions its value for monitoring purposes in soccer.