Bilateral Comparison And Reliability Of Ground Reaction Forces During Single Leg Hop Test

Abstract

PURPOSE: To compare single leg horizontal hop ground reaction forces (GRF) between the dominant (DOM) and non-dominant (NDOM) limbs and to determine the reliability GRF based variables. METHODS: After a standardized warm-up, 20 (10 men, 10 women) physically active (Tegner score = 6.5 +/- 1.7, range 4-9) young adults (21.7 +/- 2.1 yrs) performed three DOM and three NDOM single leg horizontal hops in random order during two sessions 72 hours apart. In addition to recording hop distance, GRF were used to calculate 10 variables using the vertical (vGRF) and anterior-posterior (apGRF) GRF: peak, peak to ground off (GO), impulse, average force, and impulse time. Reliability was assessed across session one trials (intrasession) and between sessions one and two (intersession) using intraclass correlation coefficients (ICC) and standard error of measurement. Separate two factor analysis of variance were conducted to assess interactions between limb (DOM, NDOM) and direction (vGRF, apGRF) using the session one three trial average. The relationship between hop distance and GRF variables were established using correlational analyses. RESULTS: No significant hop distance difference was found (t19 = -.840, P =.412) between the NDOM (1.07 ±.12 % ht, 95% CI: 1.03 - 1.09)(and DOM (1.06 ±.11 % ht, 95% 1.02 - 1.08) limbs. Similarly there were no significant limb differences (interactions or main effects) for any of the GRF variables (P>.05). A significant direction main effect was observed for peak (vGRF>aGRF, PaGRF, P<.001), average force (vGRF>aGRF, PvGRF, P.75) with the exception of intrasession vGRF peak to GO (both limbs). Four GRF variables significantly related to hop distance: DOM vGRF impulse (r =.480, P =.032), DOM aGRF peak (r =.524, P =.018), DOM aGRF impulse (r =.677, P =.001) and NDOM aGRF impulse (r =.765, P<.001). CONCLUSION: Equal hop distances and underlying GRF may be expected between DOM and NDOM in healthy individuals. Except vGRF peak to GO, all GRF based variables were reliable. Further research is needed to determine if GRF analyses increases the sensitivity of the single leg hop test in identifying performance deficits, and/or injury predisposition.