Swimmers’ shoulder side asymmetry at rest and after aerobic load

Purpose. The aim of our study was to evaluate shoulder joint flexibility, shoulder muscle peak isometric force, and sub­ maximal force differentiation ability after warm­up exercises, as well as to compare the peak isometric force and submaximal force differentiation ability before and after a 4.5­km free­style swimming trial in swimmers and triathletes. Methods. Overall, 15 qualified young male swimmers, 15 triathletes, and 14 controls participated. Their shoulder active range of motion (ROM) in internal rotation (IR), external rotation, flexion, extension, abduction were measured. The peak force and the ability to reproduce the submaximal forces of IR and extension muscles were compared before and after 4.5­km free­style swimming in aerobic regimen. Results. Swimmers and triathletes presented larger ROM in flexion and abduction in both arms, and in IR in the non­dominant shoulder than controls. IR and extension muscle isometric peak forces were higher in swimmers and triathletes compared with controls. Strength side asymmetry was not observed in any group. Only triathletes’ IR force was higher in the dominant than in the non­dominant shoulder. The submaximal force reproduction error did not differ among the groups. The peak forces and submaximal force reproduction errors did not change after the 4.5­km swim but caused IR and extension muscles peak force side asymmetry, with stronger muscles in the dominant shoulder. Conclusions. Free­style swimming at 4.5 km in aerobic regimen induced shoulder IR and extension muscle peak force side asymmetry without any decrease of their absolute values or significant worsening in the submaximal force reproduction error.