Objectives To investigate inter and intra-rater reliability of hand held (HHD) and externally fixed (EFD) dynamometry for shoulder internal (IR) and external rotation (ER) strength and their correlation to isokinetic testing. Design Within participant, inter and intra-rater reliability study. Participants Twenty active, healthy male and female participants underwent testing by two examiners. Outcome measures Intra-class coefficients (ICC), percentage standard error of measurement (%SEM), and percentage minimal detectable change (%MDC) were calculated for inter-rater, intra-day and intra-rater, inter-week reliability. Maximum and average of three repetitions were compared to the isokinetic results at three speeds (60°/sec, 180°/sec, 240°/sec) for both concentric and eccentric contractions. Results Inter and intra-tester values demonstrated good to high agreement (HHD, ICC range = 0.89–0.97, %SEM = 4.80–8.60%, %MDC = 13.29–23.70%; EFD, ICC = 0.88–0.96, %SEM = 6.60–11.00%, %MDC = 18.40–30.04%). HHD and EFD showed moderate to very strong correlations to the isokinetic testing (HHD, r = 0.45–0.86; EFD, r = 0.49–0.83). Conclusions The results of this study indicate that both EFD and HHD are suitable for clinical practice and research. Hand-held dynamometry is preferred due to its higher intra- and inter-rater reliability and smaller MDC and lower SEM.