Reliability and smallest detectable change determination for serratus anterior muscle strength and endurance tests

The purposes of this study were to determine inter-tester reliability, one-week test-retest reliability and smallest detectable difference (SDD) of serratus anterior muscle strength and endurance tests. Asymptomatic subjects were tested on an apparatus designed by the investigators. During strength testing, subjects performed isometric contractions recorded by a hand-held dynamometer. For endurance testing, subjects held a dumbbell of 15% of their body weight and performed repetitions until they became fatigued. Intraclass correlation coefficients (ICC) for the strength test revealed good inter-tester reliability (ICC2,3 = .90-.93) and good one-week test-retest reliability (ICC2,3 = .83-.89). For the endurance test, ICCs showed good inter-tester reliability (ICC2,1 = .71-.76) but moderate one-week test-retest reliability (ICC2,1 = .59-.62). The SDDs at 68% confidence level ranged from 22.7 to 39.2 newtons for the strength test, and 11 to 20 repetitions for the endurance test. In summary, the technique used in the study is reliable for quantifying the SA muscle strength.