Reducing horizontal force asymmetry may improve sprint performance

Traditionally, most coaches have emphasized development of vertical force production for enhancing sprinting speed. However, with accumulating new research, coaches are becoming increasingly aware of the important contribution that horizontal force production plays in sprinting speed. However, resistance training to enhance force production is often approached with the primary use of bilateral exercises. Some researchers hypothesize that asymmetry  in horizontal force production among lower limbs may limit maximal sprinting speed and potentially increase injury risk among athletes. Thus, identifying asymmetries and making interventions to strengthen the weaker limb may improve sprinting speed.

A new single-subject case study published ahead of print in the International Journal of Sports Physiology and Performance investigated the effects of reducing lower limb horizontal force asymmetry on markers of sprint performance in an adult male team-sport athlete. Unilateral horizontal force, peak velocity and peak power were measured periodically on a non-motorized treadmill throughout a 6-week control-block of testing. A subsequent 6-week training intervention was then used to strengthen the weaker limb and reduce asymmetry between limbs. A combination of unilateral exercises and plyometrics were used to improve strength and power in the weaker limb with an emphasis on horizontal force. Bilateral work was also implemented though no unilateral work was performed for the stronger limb. Symmetry and sprint performance markers were then re-evaluated following the 6-week intervention.

The results showed that the training program reduced lower limb horizontal force asymmetry by 19% (moderate effect size). In addition, maximal velocity sprinting speed also meaningfully improved by 2% (moderate effect size). Finally maximal power production substantially improved by 15% (very large effect size). The authors conclude that this case example provides support for targeted training programs that aim to decrease horizontal force asymmetry in athletes for improving sprint performance. Certainly, more research is needed with larger samples to further evaluate the effectiveness of this strategy for improving performance and reducing injury risk.

Reference:

Brown, S. R., Feldman, E. R., Cross, M. R., Helms, E. R., Marrier, B., Samozino, P., & Morin, J. B. (2017). The Potential for a Targeted Strength Training Programme to Decrease Asymmetry and Increase Performance: A Proof-of-Concept in Sprinting. International Journal of Sports Physiology and Performance, 1-13.