Michael Rosenstein

The effects of arms and countermovement on vertical jumping.

Countermovement and arm-swing characterize most jumping. For determination of their effects and interaction, 18 males jumped for maximal height from a force platform in all four combinations of arm-swing/no-arm-swing and countermovement/no-countermovement. For all jumps, vertical velocity peaked 0.03 s before and dropped 6-7% by takeoff. Peak positive power averaged over 3,000 W, and occurred about 0.07 s before takeoff, shortly after peak vertical ground reaction force (VGRF) and just before peak vertical velocity. Both countermovement and arm-swing significantly (P less than 0.05) improved jump height, but arm-swings effect was greater, enhancing peak total body center of mass (TBCM) rise both pre and posttakeoff. Countermovement only affected the post-takeoff rise. The arm-swing resulted in higher peak VGRF and peak positive power. During countermovement, the use of arms resulted in less unweighting, slower and less extensive TBCM drop, and less negative power. Countermovement increased pretakeoff jump duration by 71-76%, increased average positive power, and yielded large positive and negative impulses. High test-retest reliability was shown for jump descriptive variables. Body weight together with peak posttakeoff TBCM rise effectively predicted peak power (multiple R2 = 0.89, standard error of estimate = 243 W). The results lend insight into which jumping techniques are most appropriate for given sports situations and indicate that a jump test can effectively be used to estimate peak power output.

Cross-validation of three jump power equations

UNLABELLEDnThe vertical jump-and-reach score is used as a component in the estimation of peak mechanical power in two equations put forth by Lewis and Harman et al.nnnPURPOSEnThe purpose of the present study was to: 1) cross-validate the two equations using the vertical jump-and-reach test, 2) develop a more accurate equation from a large heterogeneous population, 3) analyze gender differences and jump protocols, and 4) assess Predicted Residual Sum of Squares (PRESS) as a cross-validation procedure.nnnMETHODSnOne hundred eight college-age male and female athletes and nonathletes were tested on a force platform. They performed three maximal effort vertical jumps each of the squat jump (SJ) and countermovement jump (CMJ) while simultaneously performing the vertical jump-and-reach test. Regression analysis was used to predict peak power from body mass and vertical jump height.nnnRESULTSnSJ data yielded a better power prediction equation than did CMJ data because of the greater variability in CMJ technique. The following equation was derived from SJ data: Peak Power (W) = 60.7x (jump height cm]) +45.3x(body mass [kg])-2055. This equation revealed greater accuracy than either the Lewis or previous Harman et al. equations and underestimated peak power by less than 1%, with a SEE of 355.0 W using SJ protocol. The use of one equation for both males and females resulted in only a slight (5% of power output) difference between genders. Using CMJ data in the SJ-derived equation resulted in only a 2.7% overestimation of peak power. Cross-validation of regression equations using PRESS reveals accurate and reliable R2 and SEE values.nnnCONCLUSIONSnThe SJ equation is a slightly more accurate equation than that derived from CMJ data. This equation should be used in the determination of peak power in place of the formulas developed by both Harman et al. and Lewis. Separate equations for males and females are unnecessary.

Lower limb morphology and risk of overuse injury among male infantry trainees.

The effect of anatomic variation on the risk of overuse injuries has not been adequately evaluated. To determine the association of several common anatomic characteristics (genu varum, genu valgum, genu recurvatum, and lower limb length differences) with risk of overuse injury, we made prospective morphologic measurements of young men prior to beginning 12 week of Army infantry training. The training included frequent running, marching, calisthenics, and other vigorous activities. Lower extremity anatomic landmarks were high-lighted, and front- and side-view photographic slides were taken of the 294 study volunteers. The slides were compute digitized, and the following measures calculated: pelvic width to knee width ratio (to assess genu valgum/varum), quadriceps angle (Q-angle), knee angle at full extension, and lower limb length differences. The cumulative incidence of lower limb overuse injury was 30%. Relative risk of (RR) of overuse injury was significantly higher among participants with the most valgus knees (RR = 1.9). Those with Q-angle of more than 15 degrees had significantly increased risk specifically for stress fractures (RR = 5.4). Anatomic characteristics were associated with several other types of injuries, including pain and nonacute muscle strain due to overuse. This pilot study provides evidence that some lower limb morphologic characteristics may place individuals at increased risk of overuse injuries.