The reproducibility of fatigue-related indices of the shoulder rotator muscles: A clinical perspective

BACKGROUND: Extensive research has been conducted related to muscle fatigue, but little attention has been given to shoulder rotator muscles. Many different formulas have been used to calculate fatigue. Therefore, there is a need for establishing a reliable fatigue assessment protocol to further assess shoulder rotators using a suitable fatigue formula. OBJECTIVE: To study the reproducibility of two different isokinetic set-ups for assessing shoulder rotators fatigability properties and explore a possible clinical implication when different fatigue calculation formulas are used. METHODS: Forty sedentary subjects took part in this study. They were randomly assigned to either the “45∘ group” or the “90∘ group”, where the upper limb was either abducted to an angle of 45∘ or 90∘ in the frontal plane, respectively. All participants completed two testing sessions, consisting of 30 maximal concentric contractions on dominant shoulder IR and ER muscles at 180∘/s. Relative reproducibility, absolute reproducibility and fatigue indices were assessed. RESULTS: ER was different (p< 0.05) between trials (5%). Relative reproducibility was high for both muscles (ICC 0.97–0.99). Absolute reproducibility remained homogeneous with a SEM of 4–6% while the MDC varied between 11% and 16%. Fatigue formulas estimated no difference between trials (0–2%) for any muscle groups. CONCLUSIONS: Based on this study of reproducibility, both abduction set-ups may be used for assessing fatigue performance without indicating a superiority for either.