Effects of Test Modality and Hip Flexion on Resultant Knee Flexor Moments

The valid assessment of knee flexor strength is important because it is a major modifiable risk factor of injuries. Mostly conducted in a seated position, isokinetic knee tests’ accuracy is doubted due to erroneous axis alignment. This study investigated if hip angle (flexed vs. extended) and test modality (discrete vs. reciprocal) affect resultant knee flexor moments. Eight healthy male participants (27 y, 182 cm, 78 kg) performed eight randomly-arranged isokinetic knee flexor tests (60°/s) while capturing their kinematics (100 fps). Test modality (0.439 ≤ ƞp2 ≤ 0.633) and hip angle (0.144 ≤ ƞp2 ≤ 0.268) significantly affected resultant peak moments. Independent of hip angle, reciprocal QH tests revealed significantly lower values than discrete (−17%, d = 1.75) and HH reciprocal tests (−13%, d = 1.56). Seated eccentric tests caused 11% lower peak moments than prone tests (p = 0.005, d = 0.59). Reciprocal QH tests in supine position and reciprocal tests in seated position should be interpreted with caution as peak moments are underestimated. Discrete knee flexor tests in seated and prone position demonstrated similar resultant peak moments. Prone reciprocal HH tests appeared to be a suitable option to reduce the testing time needed.