This chapter provides a comprehensive examination of the multifaceted role of muscular asymmetry in athletic performance, biomechanical efficiency, and injury risk. Muscular asymmetry refers to differences in strength, torque, activation patterns, or morphological characteristics between the dominant and non-dominant sides of the body, and it is particularly evident in sports that involve unilateral loading patterns. Current literature indicates that low levels of asymmetry may serve an adaptive function in certain sporting contexts, whereas larger imbalances can disrupt movement economy, increase joint loading, and elevate the likelihood of musculoskeletal injuries. This chapter explores the neuromuscular and morphological foundations of asymmetry, including motor unit activation, agonist–antagonist ratios, and muscle–tendon mechanics, and discusses their influence on mechanical efficiency and movement coordination.

Furthermore, the validity and reliability of various assessment methods—such as isokinetic dynamometry, electromyography (EMG), functional performance tests, and wearable sensor technologies—are evaluated, with particular emphasis on the commonly cited asymmetry threshold of 10–15% as a potential risk marker. From a performance perspective, the chapter highlights how asymmetries in strength and power influence sprinting, jumping, change of direction, kicking, and throwing mechanics. Regarding injury risk, evidence linking quadriceps–hamstring imbalance, rotator cuff strength asymmetries, and deficits in hip–pelvis control with increased injury incidence is discussed. Finally, the chapter addresses training and rehabilitation strategies—including unilateral strength training, neuromuscular control exercises, and targeted corrective programs—and provides practical recommendations for practitioners. Overall, this chapter underscores the central role of muscular asymmetry in both performance optimization and injury prevention within contemporary sports science.