The relationship between active and passive flexibility of the knee flexors

Abstract

Background. Hamstrings flexibility measurements are of both, research and clinical relevance for evaluation of the training progression, prognosis of acute hamstrings injuries and monitoring recovery from such injuries. The active knee extension test and the passive knee extension test are widely used for hamstrings flexibility evaluation. However, they are based on different neurophysiological mechanisms. Objective. The aim of this study was to assess the relationship between results of both tests: Active knee extension test and passive knee extension test. Methods. 314 generally healthy and physically active subjects (204 women and 110 men), aged 18-45, participated in this study. Each subject performed 3 trials of the active knee extension test and the passive knee extension test for both lower extremities and the range of motion was measured. To make the passive knee extension test more objective the force gauge was used for ensuring constant force in each repetition. The correlations between both tests were assessed using the Pearson coefficient (r). Additionally, the ICCs for intra-rater reliability were calculated. Results. All of the outcomes revealed a significant (p < 0.01) positive, moderately high correlation (r values ranged from 0.67 to 0.73). Presented versions of both tests yield excellent intra-rater reliability – the ICCs (3.1) ranged from 0.98 to 0.99. Although moderately high levels of correlation, in our opinion, both tests can be used interchangeably only for general hamstring flexibility evaluation, but in more specific assessment the suitable test should be chosen, considering passive versus active nature of the movement. Conclusions. The PKET and the AKET are useful and reliable tools for evaluation the flexibility of hamstrings. There is a significant positive, moderately high correlation between results of both tests. In our opinion, AKET is a sufficient test for a simple clinical evaluation in everyday practice and it’s recommended special for people with little experience. Additionally, in more specific clinical assessment due to the different neurophysiological mechanisms, they are based on, the choice of the tests should take into account whether the purpose of the analysis is passive versus active form of the movement.