title: Lower-limb activity during the power serve in tennis: effects of performance level.
abstract: OBJECTIVE
  The aim of the present study was to investigate the differences in lower-limb activity during the tennis power serve between players of different performance levels.
  
  
  METHODS
  Thirty-two participants distributed in three groups (beginner, B; intermediate, I; elite, E) performed countermovement jumps to measure leg power (P(max)) and 15 power serves from a force platform. Lateral, horizontal, and vertical forces (Fx, Fy, and Fz) were sampled simultaneously with EMG signals from six leg muscles. Racquet-ball impact height (I(height)) and maximum velocity of the ball (V(max) were measured with video analysis and radar, respectively. The total duration of the serve was fractioned into four phases: preparation (Pre), eccentric (Ecc), concentric (Con), and suspension (Sus).
  
  
  RESULTS
  Pmax was similar in the three groups. The duration of Pre was longer (P < 0.05) in E than in B, whereas Con was shorter (P < 0.05). Vmax (169.4 +/- 11.3 vs 107.2 +/- 6.1 kmxh, P < 0.001), I(height) (149.2 +/- 2.7 vs 142.6 +/- 4.7% of standing height, P < 0.05), and Fz(max) (2.12 +/- 0.36 vs 1.68 +/- 0.33 of body weight, P < 0.01) were higher in E than in B. I(height) was correlated (r = 0.85, P < 0.001) with Fz(max) in E. Peaks EMG occurred earlier (P < 0.05) in E (79 +/- 17% of Con) than in other groups (B: 94 +/- 11% and I: 94 +/- 15%).
  
  
  CONCLUSIONS
  The vertical forces and coordination in lower extremities during the tennis serve were different between players of different skill levels but with the same P(max). This may partly explain the differences in serve efficiency.
authors.affiliation: UPRES-EA 3759, Faculty of Sports Sciences, Montpellier, France. olivier.girard@univ-montp1.fr
authors.forename: Olivier
authors.initials: O
authors.lastname: Girard
authors.forename: Jean-Paul
authors.initials: JP
authors.lastname: Micallef
authors.forename: Gregoire P
authors.initials: GP
authors.lastname: Millet
mesh_terms: D000293:Adolescent; D000328:Adult; D001696:Biomechanical Phenomena; D004576:Electromyography; D005602:France; D006801:Humans; D035002:Lower Extremity / Q000502:physiology*; D008297:Male; D018482:Muscle, Skeletal; D013647:Task Performance and Analysis; D013715:Tennis