Effect of Barefoot Strength Training on Time to Stabilization and Ankle Inversion During Single-Leg Drop Landing in NCAA Division I Female Volleyball Players

When volleyball players land from a jump, there is a large energy transfer that occurs throughout the kinetic chain. Time to stabilization (TTS) is a measure that represents the ability to control ground reaction forces (GRF) upon landing. Ankle inversion (INV) angles upon landing also represent the risk of ankle injury due to forceful inversion of the ankle joint. Prior research has found differing risk for injury when accounting for volleyball sport-specific limb dominance and inter-limb asymmetries. A joint is weakened when exposed to repetitive landing movements, putting it at a higher risk of injury due to continual absorption of GRF upon landing. Lowering TTS and INV can reduce the risk of injury in jumping athletes. PURPOSE: The aim of this study was to investigate the effects of four weeks of BF strength training on TTS and INV angles upon landing in collegiate volleyball players. METHODS: In an experimental repeated-measures design, ten (n=10) females from a NCAA Division I volleyball program performed BF strength training three times per week for four weeks during offseason training. Participants performed a total of 12 BF workouts. During pre- test and post-test data collection, participants were recorded using OpenCap while completing three single- leg drop landings per limb onto a force plate. TTS and INV variables were objectively analyzed as lead and trail limbs according to a three-step volleyball spike approach. RESULTS: A paired samples t-test found a significant decrease in TTS in the lead limb after four weeks of BF strength training (P=0.035, ES=0.594). No significant difference was found in TTS in the trail limb (P=0.24, ES=0.213) and INV in the lead limb (P=0.288, ES=0.168) or trail limb (P=0.470, ES=0.022). Although not statistically significant, all values decreased in both limbs from pre-test to post-test with stronger trends towards significance in the lead limb. CONCLUSION: The results suggest that BF training may be implemented in training sessions for suggested improvements in ankle stability. If BF training has the potential to improve TTS and the ability to control GRF upon landing, then it may be an appropriate tool to reduce risk for injury. However, further research is still warranted to investigate the effects of BF training on TTS and INV with the recommendations made.