Ankle Plantarflexor Muscle Forces During Loaded Vertical Jumps

Abstract

Hexagonal barbell (HB) loaded jumps are often used in training to increase lower extremity power. The effect of external load on lower extremity kinematics and kinetics during jumping has been described, but how individual muscles accommodate to these loads has not. Given the significant contribution of plantarflexors to acceleration and total power, an understanding of how the ankle musculature individually performs during loaded jumps would be advantageous. PURPOSE: To describe the effects of load on ankle musculature during the concentric phase of loaded HB jumps. METHODS: 10 male collegiate athletes (20.4 ± 2.4 y; 108.8 ± 14.0 kg) performed 5 maximal HB jumps at 0%, 20%, 40% and 60% of their HB deadlift 1-repetition maximum (216.6 ± 10.9 kg). Filtered Ground reaction forces (300 Hz) and 3D lower extremity marker trajectories (6 Hz) were input into a 23 DOF musculoskeletal model and muscle forces were estimated with static optimization. Peak muscle force (xBW) was calculated for the gastrocnemius (GASpeak) and soleus (SOLpeak), as well as time to peak force (ms; GAStime, SOLtime). Analysis of variance and LSD post hoc comparisons were used for analysis (p < 0.05). RESULTS: Significant increases were found in GASpeak across loads (0%: 2.14 ± 0.10 xBW; 20%: 2.47 ± 0.14 xBW; 40%: 2.72 ± 0.12 xBW; 60%: 2.85 ± 0.14 xBW) with significance between each load (all p ≤ 0.038). Significant increases were noted in SOLtime across loads (0%: 71.80 ± 13.03 ms; 20%: 116.83 ± 23.26 ms; 40%: 157.40 ± 24.95 ms; 60%: 177.93 ± 34.50 ms), with significant comparisons between 0% and all other loads and between 20% and heavier loads (all p ≤ 0.038). Significant increases were also found in GAStime across loads (0%: 212.40 ± 11.67 ms; 20%: 243.13 ± 13.19 ms; 40%: 308.90 ± 15.36 ms; 60%: 355.68 ± 25.80 ms). Significant comparisons were noted between nearly all loads (all p ≤ 0.028), with the exception of between 0% and 20%. There was no significant difference in SOLpeak across loads (p = 0.122). CONCLUSIONS: In accordance with muscle force-velocity mechanics, higher loads elicited higher peak muscle forces in the gastrocnemius and increased time to peak force in both muscles. Despite the observation of greater muscle force, the increased time to peak force may indicate diminished transferability of this training to the high-speed movement of vertical jump.