# Reliability of a Portable Fixed Dynamometer During Different Isometric Hamstring Assessments
## 4 Discussion
With regard to the supine 90:90 hamstring assessment, peak force, mean force and impulse all had moderate to excellent relative consistency (ICC = 0.74-0.95), whereas the only between-session variable that did not have acceptable absolute consistency was impulse (CV = 15.4%). Once again, peak RFD was reported to have unacceptable absolute consistency (CV = 17.0-23.9%), whereas relative consistency was deemed good (ICC = [PERSON]). Previous researchers have determined the reliability of the supine 90:90 hamstring assessment measured via a force plate. [PERSON] et al. [16] reported good within-session reliability (CV = 5.32-7.33%, ICC = [PERSON]) and moderate between-session reliability (CV = 7.52-10.23%, ICC = 0.70-0.80) for peak force measured via a force plate (sampling frequency)--1000 Hz) in female soccer players. Better between-session reliability was reported by [PERSON] et al. [21], as measured via a force plate (CV = 4.34-5.48%, ICC = 0.95) in elite male soccer players. Both research groups only reported peak force measures. Similar within- and between-session results were reported in this study (CV = 3.0-6.7%, ICC = 0.95-0.99). [PERSON] et al. [18] also reported reliable between-session peak force as measured via a force plate (CV = 2.84%, ICC = 0.98); however, they also reported on rapid force-generating measures. Interestingly, the authors observed acceptable absolute reliability for average RFD over 100 and 200 ms, with moderate relative reliability (CV = 4.40-8.33%, ICC = 0.61-0.64), which is largely different from the results observed in this study (CV = 17.0-22.0%, ICC = 0.83-0.88). These differences may be due to several different reasons. First, the metrics, though both are rapid force-generating measures, are not calculated the same; peak RFD was reported in this study rather than its average at certain epochs. Second, instructions given to athletes may have differed; however, [PERSON] et al. did not report on the instructions given to their participants [18]. Third, the differences in technology, i.e., force plates measuring at 1000 Hz, compared to a portable fixed dynamometer measuring at 1200 Hz may account for the differences. Lastly, the populations differed between studies, with resistance-trained males being used in this study as compared to female soccer players. The third assessment performed was the 90:20 hamstring assessment, which had similar within- and between-session reliability to the standing hip extension and 90:90 hamstring assessment. Once more, peak force, mean force and impulse all had acceptable to excellent reliability (CV = 2.6-11.7%, ICC = 0.90-0.99) across trials and testing occasions, with peak RFD having unacceptable absolute consistency (CV = 19.2-36.3%) and moderate to good relative consistency (ICC = 0.64-0.88). To the authors' knowledge, only one other research group has determined the reliability of the 90:20 hamstring assessment measured via force plate technology (500 Hz) [22]. The authors only reported between-session absolute reliability (CV = 7.3-11.0%) for peak force, which was similar to our results (CV = 6.3-8.9%). Other research groups have investigated similar knee and hip angles during an isometric hamstring assessment in a lying and seated position [16; 19; 20; 21; 25; 27]. For example, [PERSON] et al. [21] determined the reliability of a lying hamstring assessment with a knee angle of 30\({}^{\circ}\), measured via a force plate (1000 Hz). The authors reported good to excellent within-session reliability for peak force during this position (CV = 4.84-6.31%, ICC = 0.86-0.93). [PERSON] et al. (2017) determined the between-session reliability of a seated handstring isometric assessment at long muscle lengths (knee flexion = 30\({}^{\circ}\), hip flexion = 90\({}^{\circ}\)) measured via a load cell. They also reported good to excellent reliability (CV = 9.1-9.6%, ICC = 0.88-0.90) for peak force and poor reliability for peak RFD (CV = 26.3-35.1%, ICC = 0.59-0.75), which was similar to the results of this study.