638 MEP164 – Precise instruction increases reliability and hamstring activation at the 90:20 isometric posterior chain test and can help to detect hamstring fatigue and prevent hamstring injuries

AbstractMuscle fatigue and lateral deficit are associated with the risk of hamstring injuries (HSIs) (McCall et al. 2014). Frequent testing of hamstring strength (HSS) can help prevent HSIs. Pilot testing shows that the applied vertical force (Fz) of the 90:20 Isometric Posterior Chain (IPC) Test (Matinlauri et al. 2019) is strongly influenced by a misdirected anterior horizontal force component.We therefore instructed subjects to not only apply vertical force, but to apply vertical and posterior horizontal force onto a force plate and hypothesized better reliability, validity, and hamstring activation.12 subjects (data acquisition in progress; target sample size: n=20) performed the IPC Test under the two different instructions, and tested isometric HSS under identical hip and knee angles on a gold-standard single joint isokinetic device to check for validity of the different instructions. We furthermore placed EMG electrodes on the biceps femoris, semitendinosus and gluteus maximus to evaluate which instruction better adresses the hamstrings' muscular capacities. To evaluate reliability the identical procedure was carried out on two separate days with 2–5 days between the measurements.ICCs of Fz under our new instruction show excellent reliability (r=0.95), whereas Fz under bare vertical instruction, as proposed by Matinlauri et al. (2019), results in r=0.80.Bland-Altman Plots with z-scores show no difference in agreement of the different instructions with gold-standard measurements.Repeated measures ANOVA (all p's non-significant) reveal that our new instruction increases biceps femoris and semitendinosus activation by 4.4% and 4.5%, respectively, whereas gluteus activation decreased by 5.2% compared to Matinlauri et al.'s (2019) instruction.We strongly recommend using our new instruction as it better adresses hamstring's muscular capacities and more reliably detects HSS and muscle fatigue. This efficient test can be implemented in weekly performance testing to evaluate readiness to play and thus prevent HSIs in the long term.Download figure Open in new tab Download powerpoint Abstract 638 Figure 1