Knee extensor strength assessed using a vertical squat and a simple geometric model to calculate joint torque: An...

We propose a simple method to measure knee extensor muscle strength using a single-legged vertical squat. The purpose of the present study was to assess the validity of this method in comparison with standard methods of measurement.

A total of 30 healthy adults (mean age 22 years) and 28 healthy older individuals (mean age 69 years) participated in this study. Knee extensor torque at maximum knee flexion during a single-leg squat was calculated by a geometrical model using height, weight and measured leg forward lean angle. Its validity as a measurement of knee extensor strength was assessed by comparing the results with maximum isometric knee extensor strength measured using an isokinetic dynamometer and a handheld dynamometer.

Knee extensor torques calculated by the squat model were highly correlated with those calculated by the isokinetic dynamometer (r = 0.835) and handheld dynamometer (r = 0.884); however, the difference between the squat model and the isokinetic dynamometer measurements, and between the squat model and the handheld dynamometer measurements increased proportionally with increasing muscle strength.

The squat model is a convenient way to measure knee extensor muscle strength quantitatively. However, it might be more suitable for individuals with quadriceps muscle weakness than for those with strong muscles. Geriatr Gerontol Int 2018; 18: 1125-1131.