Differences in Deceleration Mechanics from Mass- vs Velocity-Dominant Impact Momentum

The purpose of this study was to determine how landing mechanics differ when impact momentum is manipulated by drop height (HEIGHT) compared to external loading (LOAD). 15 recreationally trained adults (10 males 5 females, 21.8 ± 3.5 years, 78.4 ± 13.2 kg, back squat 1RM: 127.6 ± 35.9 kg, back squat 1RM relative to mass: 1.61 ± 0.26) performed drop landings with bodyweight from 0.6 m, 0.91 m, and 1.22 m, in addition to externally loaded (via kettlebell) drop landings from 0.6 m with 16 kg, 28 kg, and 40 kg. Vertical ground reaction forces were analyzed for average force and velocity, landing depth, loading impulse, and attenuation impulse. Regression analysis was performed on each variable with respect to impact momentum with an alpha level of 0.01 (Bonferroni correction). The strongest relationships, identified by regressions with an R2 greater than 0.5, were attenuation impulse for both HEIGHT (R2= 0.839) and LOAD (R2= 0.656), and average vGRF with LOAD (R2= 0.617). Moderate relationships, identified by regressions with an R2 between 0.3 and 0.5, were loading impulse with HEIGHT (R2= 0.322), landing depth with HEIGHT (R2= 0.412), and average vGRF with HEIGHT (R2= 0.441). Weak relationships, identified by regressions with an R2 less than 0.3, were loading impulse with LOAD (R2= 0.030), landing depth with LOAD (R2= 0.149), and average velocity with HEIGHT (R2= 0.161). Loading impulse with LOAD and average velocity with LOAD were the only regressions to not be statistically significant, indicating the regression equation did not predict loading impulse better than the average across all trials. Administering the drop landing intensity with HEIGHT and LOAD led to some contrasting responses from the neuromusculoskeletal system, and future research is warranted to determine acute responses and eventual training effects, especially regarding individual joint kinetics.