Metabolic Power Requirement of Change of Direction Speed in Young Soccer Players: Not All Is What It Seems
Purpose The aims of this study were to 1) compare the metabolic power demand of straight line and change of direction (COD) sprints including 45deg or 90deg 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 45deg or 90deg 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 (90deg, 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 90deg COD vs. 45deg COD sprint (ES 1.0; 149.5+ 10.4 J.kg 1) Conversely, the RMS was slightly (45deg, ES +0.5; +2.1% 90% confidence limits 3.6) for vastus lateralis muscle (VL) to largely (90deg, 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. Conclusion 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.
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