The present approach for the assessment of top-level soccer players match performance through video analysis allowed us to assess instantaneous metabolic power, thus redefining the concept of "high intensity" on the basis of actual metabolic power rather than on speed alone.

body mass) was ≈20 % larger, and its angle of application in respect to the horizontal ≈10° smaller, for Bolt, as compared to MLS. Finally, we estimated that, on a 10 % downsloping track Bolt could cover 100 m in 8.2 s. Conclusions The above approach can yield useful information on the bioenergetics and biomechanics of accelerated/decelerated running.Keywords Acceleration · Deceleration · Metabolic power · Mechanical power · Soccer energy expenditure Abbreviations a(t)Acceleration at time t a f Forward acceleration aLaAlactic oxygen debt C 0 Energy cost of running at constant speed on flat terrain (J kg −1 m −1 ) COMCentre of mass C r Energy cost of running (J kg −1 m −1 ) C sr Energy cost of sprint running (J kg −1 m −1 ) Ean Anaerobic energy ED Equivalent distance: distance covered running at constant speed on flat terrain, for a given energy expenditure EDI Equivalent Distance Index: ratio between ED and actual distance covered EM Equivalent body mass ES Equivalent slope = tan (90 − α) F Force F acc Force acting on the subject during accelerated running: M g′ F cost Force acting on the subject during constant speed running: M g gAcceleration of gravity g′ Vectorial sum of af and g: g ′ = a 2 f + g 2 AbstractPurpose To estimate the energetics and biomechanics of accelerated/decelerated running on flat terrain based on its biomechanical similarity to constant speed running up/ down an 'equivalent slope' dictated by the forward acceleration (a f ).Methods Time course of a f allows one to estimate: (1) energy cost of sprint running (C sr ), from the known energy cost of uphill/downhill running, and (2) instantaneous (specific) mechanical accelerating power (P sp = a f × speed).Results In medium-level sprinters (MLS), C sr and metabolic power requirement (P met = C sr × speed) at the onset of a 100-m dash attain ≈50 J kg −1 m −1 , as compared to ≈4 for running at constant speed, and ≈90 W kg −1 . For Bolt's current 100-m world record (9.58 s) the corresponding values attain ≈105 J kg −1 m −1 and ≈200 W kg −1 . This approach, as applied by Osgnach et al. (Med Sci Sports Exerc 42:170-178, 2010) to data obtained by video-analysis during soccer games, has been implemented in portable GPS devices (GPEXE © ), thus yielding P met throughout the match. Actual O 2 consumed, estimated from P met assuming a monoexponential VO 2 response (Patent Pending, TV2014A000074), was close to that determined by portable metabolic carts. Peak P sp (W kg −1 ) was 17.5 and 19.6 for MLS and elite soccer players, and 30 for Bolt. The ratio of horizontal to overall ground reaction force (per kg Communicated by

Team sports are characterised by frequent episodes of accelerated/decelerated running. The corresponding energy cost can be estimated on the basis of the biomechanical equivalence between accelerated/decelerated running on flat terrain and constant speed running uphill/downhill. This approach allows one to: (i) estimate the time course of the instantaneous metabolic power requirement of any given player and (ii) infer therefrom the overall energy expenditure of any given time window of a soccer drill or match. In the original approach, walking and running were aggregated and energetically considered as running, even if in team sports several walking periods are interspersed among running bouts. However, since the transition speed between walking and running is known for any given incline of the terrain, we describe here an approach to identify walking episodes, thus utilising the corresponding energy cost which is smaller than in running. In addition, the new algorithm also takes into account the energy expenditure against the air resistance, for both walking and running. The new approach yields overall energy expenditure values, for a whole match,≈14% smaller than the original algorithm; moreover, it shows that the energy expenditure against the air resistance is≈2% of the total.

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A previous approach to estimate the time course of instantaneous metabolic power and O consumption in team sports has been updated to assess also energy expenditure against air resistance and to identify walking and running separately. Whole match energy expenditure turned out ≈14% smaller than previously obtained, the fraction against the air resistance amounting to ≈2% of the total. Estimated net O consumption and overall energy expenditure are fairly close to those measured by means of a portable metabolic cart; the average difference, after a 45 min exercise period of variable intensity and mode, amounting to ≈10%. Aerobic and anaerobic energy yields, metabolic power, energy expenditure and duration of High (HI) and Low (LI) intensity bouts can also be estimated. Indeed, data on 497 soccer players during the 2014/2015 Italian "Serie A" show that the number of HI efforts decreased from the first to the last 15-min periods of the match, without substantial changes in mean metabolic power (≈22 W·kg) and duration (≈6.5 s). On the contrary, mean metabolic power of the LI decreased (5.8 to 4.8 W·kg), mainly because of a longer duration thereof, thus underscoring the need for longer recovery periods between HI.