Within- and between-day intrarater reliability and agreement of isometric and isokinetic multi-joint upper- and lower-body strength testing

This study assessed within- and between-day test-retest agreement and reliability of multi-joint isometric and isokinetic dynamometry for both the upper- (chest press; CP and seated row; SR) and lower-body (leg press; LP) using Exerbotics devices. Recreationally active adults (male = 11, female = 3) completed three testing sessions over a three-week period. On each day, participants performed two isometric tests followed by one isokinetic test. Analyses were conducted within a Bayesian posterior estimation framework and all posterior estimates and their precision, along with conclusions based upon them. For isometric testing, within-day limits of agreement were CP ± 39.2N, LP ± 52.7N, and SR ±22.6, and between day limits of agreement were CP ± 46.2N, LP ± 68.4N, and SR ± 31.4N.Intraclass correlation coefficient (ICC) values were CP = 0.939 and 0.937, LP = 0.968 and0.967, and SR = 0.970 and 0.969 for within- and between-day, respectively. For isokinetic testing, the between-day limits of agreement for concentric muscle actions were CP ±34.9N, LP ± 101.0N, and SR ± 24.3N, and eccentric muscle actions were CP ± 50.8N, LP± 162.4N, and SR ± 38.7N. ICC values were CP = 0.954 and 0.931, LP = 0.912 and 0.855,and SR = 0.971 and 0.937, for concentric and eccentric muscle actions respectively. These data suggest good agreement and excellent reliability for multi-joint isometric and isokinetic force measurement.