(13) ARE ALL POTENTIAL ENERGIES CREATED EQUAL? INFLUENCES OF MASS AND HEIGHT ON IMPACT AND ATTENUATION FORCES DURING DROP LANDINGS

 Impact and attenuation phases of landing are important characterizations of landing technique but have not been investigated related to drop landings using manipulations of height compared to external load.

Purpose: Therefore, the purpose of this study was to determine how impact and attenuation impulses were influenced by various external loads compared to various drop heights with no external load.

Methods: 13 healthy young adults performed drop landings from 0.6 m with increasing kettlebells loads (16kg, 28kg, and 40kg) in addition to drop landings from 0.6 m, 0.9 m, and 1.21 m with no external load. Bilateral vertical ground reaction forces (vGRF) were used to calculate impulses from initial impact to peak vGRF, and from peak vGRF to the end of the landing when vertical velocity reaches 0 m/s. Linear regression lines for loaded trials (LOAD) and bodyweight trials (BW) were fitted separately, to impact and attenuation impulses with respect to potential energy (PE) at the top of the box (PE= system mass*gravity*box height). Paired samples t-test was used to compare the coefficients between the two tasks for each dependent variable. Effect sizes are provided for statistically significant results.

Results: No significant differences were seen between the slope (BW: 0.07 ± 0.05, LOAD: 0.07 ± 0.11) or intercept (BW: 41.87 ± 33.52, LOAD: 59.58 ± 55.42) derived from impact impulses with respect to PE in the BW compared to the LOAD landings (BW: p >0.05). However, there were significant differences with large effects between attenuation impulses in BW compared to LOAD for the slope (BW: 0.36 ± 0.18, LOAD: 1.61 ± 0.83, p< 0.05, ES: 2.08) and intercept (BW: 211.56 ± 109.76, LOAD: -224.63 ± 410.68, p< 0.05, ES: 1.45).

Conclusions: These preliminary results suggest impact impulse changes with respect to PE at a similar rate for both LOAD and BW drop landings, while the attenuation impulse increases more rapidly with LOAD compared to BW drop landings. The type of PE, whether manipulated through mass or height, does not seem to influence the impact phase but does influence the attenuation phase. The attenuation phase is the larger contributor to total eccentric impulse ( >80%), thus manipulating external load during drop landings provides a more potent mechanism of increasing eccentric force production compared to increasing box height. PRACTICAL APPLICATIONS: The PE during landing from 0.9 or 1.21 m is greater than the heaviest landing from 0.6 m. Thus, even though the relationship between force and PE is steeper for LOAD landings, the practicality of inducing high eccentric force demands may be easier with BW landings from greater heights because it would require heavier loads than was available in the current study to equate PE between a BW landing from 1.21 m and a LOAD landing from 0.6 m.

Acknowledgements: None