Bilateral force deficit and sports performance: a guideline to optimize individual training programs

Abstract

Introduction: Bilateral deficit (BLD) occurs when the force produced by the same bilateral contractions is less than sum of the forces produced by single-limb contractions. Studies have shown that the bilateral fraction is related to athletic performance, such that a smaller BLD is beneficial for athletes involved in bilateral movements, while in team sports, a larger BLD is likely to be beneficial. Purpose: This article aims to review and collect literature related to bilateral deficit and its relation to sports performance. Methodology: After a detailed review of the scientific databases Web of Science, PubMed, Science Direct, and Google Scholar regarding the mentioned area, we analyzed relevant scientific articles. Results: It seems there is a relationship between bilateral deficit in the countermovement jump and change of direction, which shows a larger BLD could be beneficial for performing unilateral actions, such as changes of direction or one-legged jumps. Also, it seems unilateral training contributes to the improvement of vertical jumps, linear speed, and change of direction speed, which are crucial elements in team sports such as basketball. We can speculate that the relation of BLD with athletic performance depends on the requirements of the sport. Several studies have shown that BLD changes with resistance training. So, unilateral exercises increase BLD, while bilateral exercises decrease it. Based on these findings, it can be speculated that BLD can be related to physical and motor performance. Bilateral deficit has been shown in different movements and contraction types. It appears to be a more consistent phenomenon in dynamic contractions, with the magnitude being greater in the lower body compared to the upper body movements. Many mechanisms have been proposed to explain the BLD phenomenon. The exact mechanism is still unclear, but to date, the most accepted explanation for the deficit is interhemispheric inhibition—a phenomenon that describes the inhibition of opposite brain hemispheres. Conclusion: In general, determining the role of bilateral deficit in sports performance and underlying mechanisms is the first step towards optimal individualization of training programs. This research also helps clarify whether certain athletes should use predominantly bilateral or unilateral contractions in their training.