# Reliability of a Portable Fixed Dynamometer During Different Isometric Hamstring Assessments
## 1 Introduction
Researchers have reported acceptable reliability of this technology for within- (CV = 6.67-9.50%; ICC = 0.75-0.91) [16; 20; 26] and between-session reliability (CV = 6.27-10.58%, ICC = 0.68-0.91) for peak force during a range of kneeling, lying, standing and seated positions [16; 20; 26; 27]. [PERSON] et al. [27] also measured RFD, during a seated (30\({}^{\circ}\) knee flexion) hamstring curl; however, the results were not reported as reliable (CV = 26.3-35.1%, ICC = 0.59-0.75), potentially due to the low sampling frequency (80 Hz) of the strain gauge used, which will not provide an accurate value for RFD, given that human skeletal muscle is capable of producing >10 maximum isometric forces per second [28; 29]. Therefore, technology with higher sampling frequencies is required during hamstring assessments to gain accurate RFD measures. As evident by the current research reviewed in this manuscript, isometric hamstring strength has been tested in a range of different positions. It has been consistently noted that testing hamstring strength at long muscle lengths may reflect the larger work of the hamstring during the late swing phase and initial contact during running and sprinting [30]. However, the authors acknowledge that testing hamstrings at different angles, ranges of motion and muscle lengths emphasizes different muscles of the hamstring complex. For example, the biceps femoris muscle has been shown to be maximally activated between 15\({}^{\circ}\) and 30\({}^{\circ}\) of knee flexion (from full knee extension), whereas the semi-membranous and semi-tendinous muscle were maximally activated at angles between 90\({}^{\circ}\) and 105\({}^{\circ}\)[31]. Furthermore, it might be that a short to long muscle length approach to the testing of the hamstrings may better align with early- to late-stage rehab, given the location or the severity of the hamstring strain. With the literature reviewed in mind, there is a need for a low-cost, high-accuracy, and high-utility alternative for measuring hamstring strength during a range of different positions that can be utilized during early to late stages of rehabilitation, as well as for tracking hamstring strength and asymmetry in healthy athletes. Additionally, many of these previously mentioned technologies only report peak force, with a small portion also presenting RFD at low sampling frequencies. These metrics may not be suitable to track for those in early-stage rehab; for example, metrics that provide insights into other aspects of force capability, such as contraction duration, mean force and impulse, may be more appropriate. Once an athlete has progressed into mid- and late-stage rehab, maximal and explosive strength variables may be of more interest to the practitioner, such as peak force and RFD. Therefore, the aim of this study was to evaluate the intra- and inter-session reliability of a commercially available, portable, low-cost and high-resolution portable fixed dynamometer for measuring different force-time variables, during a range of different hamstring assessments, which can be utilized through all stages of rehabilitation.