Test-retest reproducibility and validity of the back-leg-chest strength measurements

BACKGROUND: A single measure to characterize overall muscle strength is advantageous because it saves time and costs of evaluation. For this reason, the back-leg-chest (BLC) strength might be an appropriate single measure in characterizing total body strength. OBJECTIVE: To assess the test-retest reproducibility and smallest real difference (SRD) of the BLC dynamometer in healthy adults and adolescents and to examine whether handgrip, knee-extensor and knee-flexor strength predict BLC strength in healthy adults. METHODS: Forty-five adults and 58 adolescents were recruited. In a first session back-leg-chest strength, handgrip strength, and additionally, in adults, isometric knee -extensor strength, and knee-flexor strength were measured. In a second session, 2-5 days later, BLC strength was measured again for test-retest reproducibility. RESULTS: Inter-session correlations of BLC strength were high (all r's and ICC's > 0.92). Bland-Altman-plots showed high agreement. The SRD and SRD% were between 14-26, and 19% and 26% respectively. Strength variables (handgrip, knee extensor, and knee-flexor strength) explained 87% of the variance in BLC strength. A stepwise linear regression showed that dominant knee extensor and flexor strength were the most important significant predictors of BLC strength (r(2) = 0.86). CONCLUSIONS: This study demonstrated that the BLC dynamometer has reasonably high test-retest reproducibility and hence may serve in some pertinent situations to be an appropriate tool for clinical, basic and applied research.