Monitoring Locomotor Load in Soccer: Is Metabolic Power, Powerful?

Buchheit M., Manouvrier C., Cassirame J., Morin J.-B.

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 uptake (VO2) was collected with a portable gas analyzer.

P was calculated using either net VO2 responses and traditional calorimetry principles (PVO2, W.kg-1) or locomotor demands (PGPS, W.kg-1). Distance covered into different speed, acceleration, and P zones was recorded. Players covered 30 times more distance >20 W/kg (PGPS) than >14.4 km.h-1.

While PGPS was 29 ± 10% lower than PVO2 (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 PGPS vs PVO2 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 PVO2, and PGPS showed CVs <10%. ICC ranged from very low- (acceleration and >20 W.kg-1 distances) to very high (PVO2).

To conclude, PGPS 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 PGPS >20 W.kg-1 questions its value for monitoring purposes in soccer.

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