Effects of Asymmetric and Symmetric Sport Load on Upper and Lower Extremity Strength and Balance: A Comparison Between the Dominant and Non-Dominant Side in Adolescent Female Athletes

The aim of this research was to investigate the effects of primarily asymmetrical (soccer and volleyball) and symmetrical sport load (sprint and swimming) in the upper and lower limbs on dynamic balance and muscle strength and to compare these values in the dominant and non-dominant limbs. This study employed a cross-sectional design, included 45 adolescent female athletes from four sports, divided into asymmetric (ASYM, <i>n</i> = 25) and symmetric (SYM, <i>n</i> = 20) groups. They were assessed for maximal voluntary isometric muscle contraction (MVIC) relative muscular strength using a handheld dynamometer (HHD) for shoulder external rotation (ER) and internal rotation (IR), as well as hamstring and quadricep strength. Upper and lower limb balance were also assessed using the Upper (YBT-UQ) and Lower Quarter Y Balance Test (YBT-LQ) tests. The results showed significantly greater balance in the upper extremities of swimmers and in the lower extremities of the sprinters in both the dominant (DS) and non-dominant (NDS) sides than in other groups (<i>p</i> < 0.0001). However, no significant difference in internal and external shoulder rotator muscles strength between the groups (<i>p</i> > 0.05). Although significant differences were found in hamstring strength on the dominant side and quadricep strength on both sides (<i>p</i> < 0.05), a notable finding was that sprint athletes consistently demonstrated stronger quadriceps muscles as compared to other groups in both the dominant and non-dominant sides. According to the current findings, there are significant differences in upper and lower body balance, hamstring, and quadricep muscle strength among sports. This suggests that athletes of asymmetrical sports may need to improve non-dominant side knee strength and balance symmetry to prevent the risk of injury.