The effect of different onset thresholds on isometric hamstring force-time variables using force plates

Ripley, Nicholas; Fahey, Jack; Comfort, Paul

Abstract

Introduction. There is an increasing frequency of single joint isometric assessments using force plates within team sports to inform training decisions; however, limited methodological consistency has been identifi ed within the literature , including onset threshold (muscle contraction initiation). Purpose: The purpose of this study was to determine the eff ect of diff erent onset thresholds on force-time characteristics during a 90:90 isometric hamstring assessment. Methodology: Twenty female soccer players (age: 20.7 ± 4.7 years; height: 168.7 ± 5.9 cm; body mass: 64.4 ± 6.7 kg) completed three maximal trials per limb. Five thresholds assessed, including fi ve standard deviations (SD) of system weight (SW, which included limb weight and any pre-tension) (SW 5SD), SW plus 15 N (SW 15N), and 10-, 20-, and 30% of SW. Results: Moderate relative reliability and excellent absolute reliability for force at 100 ms (F100) and 200 ms (F200), and rate of force development (RFD) was observed for SW 5SD and SW 15N , out-performing percentage-based thresholds. 10-, 20-and 30% of SW resulted in increased F100, F200, and RFD values, with large eff ects observed (η² p ≥ 0.166). Conclusions: SW 5SD and SW 15N were identifi ed as the most reliable and consistent methods for assessing time-related force variables. Practical implications: Sport scientists, strength and conditioning coaches, and medical staff who regularly use isometric hamstring assessments to monitor training and return to sport objectives are recommended to use either SW 5SD and SW 15N thresholds to ensure valid and accurate results on the hamstrings force generating that can be used to inform training.

• Journal Article Type: Article
• Acceptance Date: Apr 26, 2025
• Publication Date: Jul 14, 2025
• Deposit Date: Jul 15, 2025
• Publicly Available Date: Jul 17, 2025
• Journal: Journal of Applied Sports Sciences
• Print ISSN: 2534-9597
• Electronic ISSN: 2535-0145
• Publisher: Pensoft Publishers
• Peer Reviewed: Peer Reviewed
• Volume: 9
• Issue: 1
• Pages: 24-39
• DOI: https://doi.org/10.37393/JASS.2025.09.01.3