The prevalence of inter-limb asymmetries has been reported in numerous studies across a wide range of sports and physical qualities; however, few have analysed their effects on physical and sports performance. A systematic review of the literature was undertaken using the Medline and SPORT Discus databases, with all articles required to meet a specified criteria based on a quality review. Eighteen articles met the inclusion criteria, relating participant asymmetry scores to physical and sports performance measures. The findings of this systematic review indicate that inter-limb differences in strength may be detrimental to jumping, kicking and cycling performance. When inter-limb asymmetries are quantified during jumping based exercises, they have been primarily used to examine their association with change of direction speed with mixed findings. Inter-limb asymmetries have also been quantified in anthropometry, sprinting, dynamic balance and sport-specific actions, again with inconsistent findings. However, all results have been reported using associative analysis with physical or sport performance metrics with no randomised controlled trials included. Further research is warranted to understand the mechanisms that underpin inter-limb differences and the magnitude of performance changes that can be accounted for by these asymmetries.

INTERLIMB ASYMMETRIES HAVE BEEN A POPULAR TOPIC OF INVESTIGATION IN THE STRENGTH AND CONDITIONING LITERATURE. RECENTLY, NUMEROUS EQUATIONS HAVE BEEN HIGHLIGHTED THAT CAN QUANTIFY THESE BETWEEN-LIMB DIFFERENCES. HOWEVER, NO DISTINCTION WAS PROVIDED ON WHETHER THEIR USE WAS APPLICABLE TO BOTH BILATERAL AND UNILATERAL TESTS. THIS ARTICLE PROVIDES A FRAMEWORK FOR SELECTING THE MOST APPROPRIATE ASYMMETRY EQUATION BASED ON THE SELECTED TEST METHOD, ENSURING ACCURATE CALCULATION AND INTERPRETATION. IN ADDITION, CONSIDERATIONS FOR DATA ANALYSIS HAVE ALSO BEEN INCLUDED AS A GUIDE FOR PRACTITIONERS ON THE RELEVANCE OF MONITORING INTERLIMB DIFFERENCES LONGITUDINALLY.

The countermovement jump (CMJ) is one of the most used performance assessments in strength and conditioning. Although numerous studies discuss the usability of different metrics in this test, this is often performed within the context of a specific aim. However, to our knowledge, no information currently exists providing practitioners with some over-arching recommendations on which metrics to choose when the purpose of using the test differs. This article discusses how the metrics selected to monitor during CMJ testing may differ when aiming to use it as a proxy for athletic performance, as part of neuromuscular fatigue monitoring, or as part of a test battery for return to performance in injured athletes.

ASYMMETRY DETECTION HAS BEEN A TOPIC OF INTEREST IN THE STRENGTH AND CONDITIONING (SC) LITERATURE WITH NUMEROUS STUDIES PROPOSING MANY DIFFERENT EQUATIONS FOR CALCULATING BETWEEN-LIMB DIFFERENCES. HOWEVER, THERE DOES NOT SEEM TO BE A CLEAR DELINEATION AS TO WHICH EQUATION SHOULD BE USED WHEN QUANTIFYING ASYMMETRIES. CONSEQUENTLY, THE AUTHORS HAVE UNCOVERED 9 DIFFERENT EQUATIONS THAT POSE CONFUSION AS TO WHICH METHOD THE SC SPECIALIST SHOULD USE DURING DATA INTERPRETATION. THE AIM OF THIS ARTICLE IS TO IDENTIFY THE DIFFERENT EQUATIONS CURRENTLY BEING USED TO CALCULATE ASYMMETRIES AND OFFER PRACTITIONERS A GUIDE AS TO WHICH METHOD MAY BE MOST APPROPRIATE WHEN MEASURING ASYMMETRIES.

Bishop, C, Lake, J, Loturco, I, Papadopoulos, K, Turner, A, and Read, P. Interlimb asymmetries: the need for an individual approach to data analysis. J Strength Cond Res 35(3): 695–701, 2021—It has been shown that the magnitude of interlimb asymmetries varies depending on the test selected; however, literature relating to whether asymmetries always favor the same limb is scarce. The aim of this study was to determine whether interlimb asymmetries always favored the same side for common metrics across unilateral strength and jumping-based tests. Twenty-eight recreational sport athletes performed unilateral isometric squats, single-leg countermovement jumps, and single-leg broad jumps with asymmetries in peak force compared across all tests, and eccentric and concentric impulse asymmetries compared between jumps. Mean asymmetries for all tests were low (≤−5.3%), and all interlimb differences for jump tests favored the left limb, whereas asymmetries during the isometric squat favored the right limb. Despite the low mean asymmetry values, individual data highlighted substantially greater differences. Levels of agreement for asymmetries were computed through the Kappa coefficient and ranged from slight to substantial (<0.01–0.79), although concentric impulse asymmetries for jump tests was the only comparison with result in substantial levels of agreement. With asymmetries rarely being present on the same side across tests, these results show that a more individual approach to reporting asymmetries is required, which should help practitioners when designing targeted training interventions for their reduction.