Within- and between-session test-retest reliability of pain-free grip strength in individuals with lateral elbow tendinopathy

Abstract

Introduction: Pain-free grip strength is an important clinical outcome measure in lateral elbow tendinopathy (LET). This study examined the test-retest reliability and minimal detectable change (MDC) for pain-free grip strength between- and within-session in individuals with LET. Methods: Data from 27 individuals (16 males) with LET, recruited for a randomised crossover trial examining the effects of biomechanical tape, were used for this study. Participants underwent three testing sessions, biomechanical tape, control tape, and no tape. During each session pain-free grip strength was measured at three timepoints: baseline, immediately after application, and post-exercise. Baseline measures from the first two data collection sessions, completed between 2 and 28 days apart, were used to examine between-session reliability. The baseline and immediately post-application measures (completed 20 to 30 minutes apart) from the no-tape condition, were used to examine within-session reliability. Pain-free grip strength was assessed in two positions: shoulder neutral, elbow at 90°, forearm pronated (flexed position), and shoulder at 90°, elbow extended, forearm pronated (extended position). Participants were asked to cease gripping as soon as they felt pain and the force (N) was recorded. At each timepoint and position, three trials of pain-free grip strength separated by 30 seconds’ rest were measured using a grip force transducer (ADInstruments, NZ). The mean of the three trials was calculated. To determine test-retest reliability, intraclass correlation coefficients (ICCs) with 95%CI were performed using an absolute agreement, two-way random-effects model (ICC2,3). The MDC at the 95% confidence level was calculated by multiplying the standard error of measurement by 1.96 and then by √2. Results: Between-session ICCs (95%CI) were ICC2,3=0.86 (0.69 - 0.94) and ICC2,3=0.93 (0.84 - 0.97) for the flexed and extended positions, respectively. Within-session ICCs (95%CI) were ICC2,3=0.96 (0.92 - 0.98) and ICC2,3=0.97 (0.93 - 0.98) for the flexed and extended positions, respectively. Between-session MDCs were 97.8 N (flexed) and 94.0 N (extended) and within-session MDCs were 49.3 N (flexed) and 63.8 N (extended). Discussion: The reliability of pain-free grip strength was excellent in both testing positions. Researchers and clinicians should expect to see a change of 94 to 98 N between-session and 49 to 64 N within-session, depending on upper limb position, to be confident a true change has occurred. Conflict of interest statement: The authors have no conflict of interest of relevance to this submission.