Vertical Force measures to Predict Unilateral and Bilateral Jump Height

Abstract

Vertical jumps are regularly implemented in assessments of leg strength and power given the clear relationship between power and jump height. While many investigations have had various successes predicting jump height using complex methodologies, a simplistic method for identifying variables that predict jump height would prove useful to develop training programs. PURPOSE: To analyze the vertical ground reaction force during single leg vertical jumps (SLVJ) and bilateral vertical jumps (BVJ) with the aim of predicting jump height. METHODS: 17 physically active adults (9M, 8F; age = 24 ± 5yrs; mass = 71.0 ± 12.5kg; height = 1.74 ± 0.10m) performed 5 unilateral and 7 bilateral jumps with each foot on an independent force plate. Two sacral markers were tracked with an 8-camera motion capture system to determine jump height. Peak vertical ground reaction forces (vGRFs), minimum vGRFs, rate of force development, rate of force reduction, loading rate, and impulse were calculated and extracted from the propulsion and landing phases of each jump trial. All variables were entered into a stepwise regression to identify which variables predicted vertical jump height. Variables were retained if the model was statistically significant at the p<.05 and variables were extracted if the model increased to p=.10. RESULTS: A model consisting of rate of force reduction during landing, minimum vGRF during landing, peak vGRF during propulsion and the rate of force development during propulsion explained single leg jump height on the right leg (r-squared = .94+/- .02). Rate of force reduction was the only significant predictor of single leg jump height on the left leg (r-squared = .76+/- .03). Finally, bilateral jump height was explained using a combined model of peak vGRF during propulsion, minimum force during landing and the propulsive impulse (r-squared = .89+/- .03). CONCLUSIONS: This study provides evidence that jump height of SLVJ and BVJ can be accurately predicted by calculating loading rates, impulse, and extracting peak and minimum values from vertical ground reaction forces. Differences between right SLVJ and left SLVJ may result from different neural control strategies used to complete each jump. Lastly, these variables may identify aspects of jump height that could be implemented during training to improve jump performance.