(27) THE IMPACT OF A COUNTERMOVEMENT AND LOAD ON THE FORCE-TIME CHARACTERISTICS OF THE HEXAGONAL BARBELL JUMP IN RESISTANCE-TRAINED MEN

Purpose: To compare the force-time characteristics of the hexagonal barbell jump performed from a static start (HEXJ-S) or with a countermovement (HEXJ-CM). Methods: 20 resistance-trained men (age = 23.5 ± 3.0 years, height = 175.1 ± 8.7 cm, body mass [BM] = 79.6 ± 11.8 kg, relative one repetition maximum back squat = 1.90 ± 0.28 kg/kg) participated in two separate testing sessions. Subjects completed maximal strength testing and were familiarized with the HEXJ-S and HEXJ-CM during the first session. During the second session, subjects performed unloaded HEXJ-S and HEXJ-CM repetitions as well as loaded repetitions with loads equal to 20, 40, 60, 80, and 100% of their BM. The HEXJ-S repetitions were performed from the ground where the subjects squatted down to the barbell, assumed a knee angle of approximately 90°, and held a quiet standing period of at least one second before receiving a countdown prior to each jump. In contrast, the HEXJ-CM repetitions started from a standing position with the hexagonal barbell held at arm’s length. Two HEXJ-S repetitions were performed prior to two HEXJ-CM repetitions at each load. All jumps were performed on a force platform and the force-time data were used to determine propulsion net relative mean force (NetRelMF), duration (Dur), and net impulse (NetIMP). The average performance between repetitions at each load was used for statistical comparison. A series of 2 (type) x 6 (load) repeated measures ANOVA with Bonferroni post hoc tests were used to examine the differences in each variable between the jump types and loads. Hedge’s g effect sizes were calculated to examine the magnitude of the differences. Results: There was a significant type x load interaction effect for NetRelMF (p < 0.001) and NetIMP (p = 0.003) but not for Dur (p = 0.318). Post hoc analysis revealed significantly greater NetRelMF during the HEXJ-CM compared to the HEXJ-S at every load (all p < 0.001, g = 0.94-2.13). In contrast, NetIMP was greater during the HEXJ-S compared to the HEXJ-CM at every load (p < 0.05) except BM (p = 0.074) with trivial-small differences (g = 0.10-0.49). There was a significant type main effect (p < 0.001) showing longer load-averaged Dur during the HEXJ-S compared to HEXJ-CM. Conclusions: Propulsion NetRelMF, Dur, and NetIMP were significantly impacted by the jump type and external load. Greater NetRelMF magnitudes and shorter Dur times were produced during the HEXJ-CM. Significantly greater NetIMP magnitudes were produced during the HEXJ-S. Practical Applications: HEXJ-CM may provide a superior training stimulus for propulsive rapid force production compared to the HEXJ-S due to greater forces being produced over shorter durations. HEXJ-S may produce greater propulsion NetIMP; however, the impulses may be characterized by lower NetRelMF produced over longer durations. Practitioners should note that using percentages of BM has its shortcomings and that individuals may respond differently to the prescribed loads. Acknowledgements: None