title: Metabolic Power Requirement of Change of Direction Speed in Young Soccer Players: Not All Is What It Seems.
abstract: OBJECTIVE
  The aims of this study were to 1) compare the metabolic power demand of straight-line and change of direction (COD) sprints including 45° or 90°-turns, and 2) examine the relation between estimated metabolic demands and muscular activity throughout the 3 phases of COD-sprints.
  
  
  METHODS
  Twelve highly-trained soccer players performed one 25-m and three 20-m sprints, either in straight-line or with one 45°- or 90°-COD. Sprints were monitored with 2 synchronized 100-Hz laser guns to assess players' velocities before, during and after the COD. Acceleration and deceleration were derived from changes in speed over time. Metabolic power was estimated based on di Prampero's approach (2005). Electromyography amplitude (RMS) of 2 lower limb muscles was measured. The expected energy expenditure during time-adjusted straight-line sprints (matching COD sprints time) was also calculated.
  
  
  RESULTS
  Locomotor-dependant metabolic demand was largely lower with COD (90°, 142.1±13.5 J.kg(-1)) compared with time-adjusted (effect size, ES = -3.0; 193.2±18.6 J.kg(-1)) and non-adjusted straight-line sprints (ES = -1.7; 168.4±15.3 J.kg(-1)). Metabolic power requirement was angle-dependent, moderately lower for 90°-COD vs. 45°-COD sprint (ES = -1.0; 149.5±10.4 J.kg(-1)). Conversely, the RMS was slightly- (45°, ES = +0.5; +2.1%, 90% confidence limits (±3.6) for vastus lateralis muscle (VL)) to-largely (90°, ES = +1.6; +6.1 (3.3%) for VL) greater for COD-sprints. Metabolic power/RMS ratio was 2 to 4 times lower during deceleration than acceleration phases.
  
  
  CONCLUSIONS
  Present results show that COD-sprints are largely less metabolically demanding than linear sprints. This may be related to the very low metabolic demand associated with the deceleration phase during COD-sprints that may not be compensated by the increased requirement of the reacceleration phase. These results also highlight the dissociation between metabolic and muscle activity demands during COD-sprints, which questions the use of metabolic power as a single measure of running load in soccer.
authors.affiliation: Laboratory of Exercise Physiology and Rehabilitation, EA 3300, Faculty of Sport Sciences, University of Picardie, Jules Verne, 80025 Amiens, France.|National Sports Medicine Programme, Excellence in Football Project, Aspetar-Orthopaedic and Sports Medicine Hospital, Doha, Qatar.
authors.forename: Karim
authors.initials: K
authors.lastname: Hader
authors.affiliation: Sport Science Department, Aspire Academy, Doha, Qatar.
authors.forename: Alberto
authors.initials: A
authors.lastname: Mendez-Villanueva
authors.affiliation: Sport Science Department, Aspire Academy, Doha, Qatar.
authors.forename: Dino
authors.initials: D
authors.lastname: Palazzi
authors.affiliation: Laboratory of Exercise Physiology and Rehabilitation, EA 3300, Faculty of Sport Sciences, University of Picardie, Jules Verne, 80025 Amiens, France.
authors.forename: Saïd
authors.initials: S
authors.lastname: Ahmaidi
authors.affiliation: Sport Science Department, Myorobie Association, Montvalezan, France.|Performance Department, Paris Saint Germain Football Club, Saint-Germain-en-Laye, France.|Institute of Sport, Exercise and Active Living, College of Sport and Exercise Science, Victoria University, Melbourne, Australia.
authors.forename: Martin
authors.initials: M
authors.lastname: Buchheit
mesh_terms: D000293:Adolescent; D054874:Athletic Performance / Q000502:physiology*; D001696:Biomechanical Phenomena; D004576:Electromyography; D004734:Energy Metabolism; D006801:Humans; D008297:Male; D009132:Muscles / Q000502:physiology; D012420:Running / Q000502:physiology*; D012916:Soccer / Q000502:physiology*