LAUSR

BACKGROUND Currently jump-landing ground reaction forces have only been quantified in the vertical direction as a stimulus for bone development. This study quantified the full-spectrum of jump-landing force magnitudes (body weight's) and rates of strain (body weights per second) of bilateral multidirectional jumps (star jump and stride jump) with reactive jump-landings (i.e. jumping immediately after initial jump-landing) among premenopausal women. It was also of interest to quantify the influence of instruction on the magnitude and rate of the jump-landing ground reaction forces. METHODS Twenty-one women [Mean (SD): 43.3(5.9)yr; 69.4(9.6)kg; 167(5.5)cm; 27.5(8.7)% body fat] performed a jump testing session 'with instruction' followed by a jump testing session performed one week later with 'instruction withdrawn'. FINDINGS The resultant magnitudes (3.90 to 5.38, body weights) and rates of strain (192 to 329, body weights per second) for the jump-landings, performed on a force plate, exceeded previously determined osteogenic thresholds (>3body weight's and >43body weights per second, respectively). An instruction effect was observed for resultant (↑8% and ↑12%; P ≤ .01) and vertical (↑8% and ↑7%; P ≤ .01) ground reaction force's (Newtons and body weight, respectively) indicating learning/practice effects for these exercises. A jump-landing effect was observed, with larger peak rates of strain (↑29%; P < .0001, body weight per second) and peak forces (↑12% to ↑48%; P ≤ .01, body weights) for the second jump-landing (post-reactive jump). INTERPRETATION These multidirectional bilateral jumps represent a unique training stimulus for premenopausal women and achieve osteogenic thresholds thought pre-requisite for bone growth and could be utilized in the development of osteogenic exercise programs.