The Potential for a Targeted Strength-Training Program to Decrease Asymmetry and Increase Performance: A Proof of Concept in Sprinting.

The global application of horizontal force (F) via hip extension is related to improvements in sprint performance (eg, maximal velocity [v] and power [P]). Little is known regarding the contribution of individual leg F and how a difference between the legs (asymmetry) might subsequently affect sprint performance. The authors assessed a single male athlete for pre-post outcomes of a targeted hip-extension training program on F asymmetry and sprint-performance metrics. An instrumented nonmotorized treadmill was used to obtain individual leg and global sprint kinetics and determine the athlete's strong and weak leg, with regard to the ability to produce F while sprinting. Following a 6-wk control block of testing, a 6-wk targeted training program was added to the athlete's strength-training regimen, which aimed to strengthen the weak leg and improve hip-extension function during sprinting. Preintervention to postintervention, the athlete increased F (standardized effect [ES] = 2.2; +26%) in his weak leg, decreased the F asymmetry (ES = -0.64; -19%), and increased v (ES = 0.67; +2%) and P (ES = 3.2; +15%). This case study highlighted a promising link between a targeted training intervention to decrease asymmetry in F and subsequent improvement of sprint-performance metrics. These findings also strengthen the theoretical relationship between the contribution of individual leg F and global F while sprinting, indicating that reducing asymmetry may decrease injury risk and increase practical performance measures. This case study may stimulate further research investigating targeted training interventions in the field of strength and conditioning and injury prevention.