isometric strength testing involves assessing the maximum amount of force a muscle group can produce when there is no change in its length and is typically measured using a handheld dynamometer (hhd). reliability is a measure of the consistency or repeatability of a measure and is important when conducting isometric strength testing using hhds. the activ5© is a small and inexpensive hhd which uploads the data immediately via bluetooth to a smartphone app. the reliability of the activ5© as a clinical or research tool has not been investigated. purpose: to investigate the within-day and the between-day reliability of the activ5©, and to investigate the intertester reliability of the activ5© in measuring isometric hip strength in competitive male ice hockey players. methods: part one investigated the reliability of the activ5© in measuring mass both within-day and between-day. testing took place on two consecutive days with the same procedures being followed during each session. standardized weights ranging from 0.5 kg to 22.8 kg were placed on top of the activ5© at 45-step increments and in random order, with three measurements taken at each increment. within-day reliability was established using the intraclass correlation coefficient (icc) by comparing the force data at each increment between trials one and two from session one. between-day reliability was established using the icc by comparing the mean force among the three trials at each increment between sessions one and two. part two investigated the intertester reliability of the activ5©. twenty competitive male ice hockey players (age = 24.4 ± 2.9 years, mass = 89.3 ± 7.8 (kg), and height = 181.6 ± 6.1 cm) performed three maximal isometric contractions in hip extension, hip internal rotation, and hip abduction on their dominant leg. two experienced female testers performed the isometric testing with the isometric force being measured by the activ5© against the tester’s resistance. intertester reliability was assessed using the icc by comparing the mean 8 isometric force of the three trials for each hip joint motion across participants between testers one and two. results. an excellent icc (1.00) was found for both between-day and within-day reliability. high intertester reliability was found for hip internal rotation (icc=.664) and abduction (icc=.622), and very high reliability for hip extension (icc=.786). conclusion: the results from this study suggested that the activ5© had excellent within-day and between-day reliability, and high intertester reliability. future research assessing the reliability of the activ5© using different muscle groups would be of value to investigate if these results can be replicated across other joints.