One leg lateral jumps - a new test for team players evaluation.

AIM: We assessed the subject's capacity to accelerate himself laterally in monopodalic support, a crucial ability in several team sports, on 22 athletes, during series of 10 subsequent jumps, between two force platforms at predetermined distance. METHODS: Vertical and horizontal accelerations of the Centre of Mass (CM), contact and flight times were measured by means of force platforms and the Optojump-System®. Individual mean horizontal and vertical powers and their sum (total power) ranged between 7 and 14.5 W/kg. "Push angle", i.e., the angle with the horizontal along which the vectorial sum of all forces is aligned, was calculated from the ratio between vertical and horizontal accelerations: it varied between 38.7 and 49.4 deg and was taken to express the subject technical ability. RESULTS: The horizontal acceleration of CM, indirectly estimated as a function of subject's mass, contact and flight times, was essentially equal to that obtained from force platforms data. Since the vertical displacement can be easily obtained from flight and contact times, this allowed us to assess the Push angle from Optojump data only. CONCLUSIONS: The power developed during a standard vertical jump was rather highly correlated with that developed during the lateral jumps for right (R=0.80, N.=12) and left limb (R=0.72, N.=12), but not with the push angle for right (R=0.31, N.=12) and left limb (R=-0.43, N.=12). Hence standard tests cannot be utilised to assess technical ability. Lateral jumps test allows the coach to evaluate separately maximal muscular power and technical ability of the athlete, thus appropriately directing the training program: the optimum, for a team-sport player being high power and low push-angle, that is: being "powerful" and "efficient".

Sprint running: a new energetic approach.

The speed of the initial 30 m of an all-out run from a stationary start on a flat track was determined for 12 medium level male sprinters by means of a radar device. The peak speed of 9.46+/-0.19 m s(-1) (mean +/- s.d.) was attained after about 5 s, the highest forward acceleration (a(f)), attained immediately after the start, amounting to 6.42+/-0.61 m s(-2). During acceleration, the runner's body (assumed to coincide with the segment joining the centre of mass and the point of contact foot terrain) must lean forward, as compared to constant speed running, by an angle alpha = arctang/a(f) (g = acceleration of gravity). The complement (90-alpha) is the angle, with respect to the horizontal, by which the terrain should be tilted upwards to bring the runner's body to a position identical to that of constant speed running. Therefore, accelerated running is similar to running at constant speed up an ;equivalent slope' ES = tan(90-alpha). Maximum ES was 0.643+/-0.059. Knowledge of ES allowed us to estimate the energy cost of sprint running (C(sr), J kg(-1) m(-1)) from literature data on the energy cost measured during uphill running at constant speed. Peak Csr was 43.8+/-10.4 J kg(-1) m(-1); its average over the acceleration phase (30 m) was 10.7+/-0.59 J kg(-1) m(-1), as compared with 3.8 for running at constant speed on flat terrain. The corresponding metabolic powers (in W kg(-1)) amounted to 91.9+/-20.5 (peak) and 61.0+/-4.7 (mean).

Effects of elastic recoil on maximal explosive power of the lower limbs.

The maximal explosive power during a two legs jump was measured on four competitive athletes [mean age 24(SD 4.3) years; height 1.79 (SD 0.09) m; body mass 68.7 (SD 12.8) kg] at different starting knee angles (70, 90, 110, 130 and 150 degrees). The experiments were performed on a newly developed instrument with which both force and speed could be measured using a force platform and a wire tachometer, respectively, and on a conventional force platform. At the smallest knee angle (70 degrees) the mean power output (W in watts per kilogram) developed during the jump was found not to differ significantly between the two methods (P > 0.1). At the larger knee angles W was 18.4% (90 degrees), 34.5% (110 degrees), 47.4% (130 degrees) and 19.4% (150 degrees) higher using the conventional force platform (P < 0.05 throughout). The difference of W between the two methods was attributed to the recovery of elastic energy due to the counter movement which immediately preceded the jump on the conventional platform, but not on the newly developed instrument. Indeed because of a mechanical arrangement which prevented the subject from moving towards the platforms, eccentric work (W-) could not be performed on the newly developed instrument; whereas W- on the conventional force platform was almost negligible at 70 degrees knee angle [mean 1.7 (SD 2.3 J)] reached a maximum of 13.1 (SD 7.9) J at 130 degrees and decreased again to a mean 4.7 (SD 3.6) J for the largest angle (150 degrees). Furthermore, on the conventional force platform, the force at the onset of the positive speed phase (Fi) was an increasing function of W- (r2 = 0.519, P < 0.001); and the difference of W between the conventional and new instruments was larger the larger the difference of Fi (r2 = 0.391, P < 0.01).