Criterion Validity Of Tri-monitor Activpal Configuration In Determining Knee-flexion Angles During Sitting In Laboratory Setting

Abstract

Prolonged sitting impairs cardiovascular and metabolic health. However, studies in this area have been limited to the laboratory setting, primarily due to the lack of measurement tools to characterize habitual sedentary behaviours. Therefore, quantifying the amount of time that people sit in a knee bent posture, causing arterial kink, may help determine if lower limb sedentary postures play a role in cardiovascular health. ActivPAL sensors located on the thigh and torso have been shown to successfully distinguish sitting from laying postures. An additional activPAL monitor positioned on the shin may be able to determine knee flexion angles and further characterize free-living sedentary behaviours. PURPOSE: Test the hypothesis that a tri-monitor activPAL setup can accurately measure knee flexion angles during sitting compared to motion capture (criterion). METHODS: Nineteen adults (12 ♀, 24 ± 4 years, 23.2 ± 4.0 kg/m2) wore three activPAL monitors (torso, thigh, shin) while 14 motion capture cameras simultaneously collected 15 markers located on body landmarks around the ankle, knee, hip, and shoulders. Each participant completed eight 45-s seated trials followed by 15-s of standing. The trial knee flexion angles (105°, 90°, 75°, 60°, 45°, 30°, 15°, 0°) were determined using a handheld goniometer. Validity was assessed via repeated measures ANOVA, Bland-Altman analyses, and intraclass correlations. RESULTS: Compared to motion capture, the calculated angles from activPALs were not different across 15-75° angles. The activPAL underestimated knee flexion angles at 90-105° (difference: ~5.0°; all, p ≤ 0.02), but overestimated knee flexion angles at 0° (difference: 9.1°, p < 0.001). A fixed bias (-0.3 ± 7.9°, p = 0.665) was not observed but a positive proportional bias was (β = 0.223, p < 0.001). The activPAL angles were highly correlated to those from the motion capture (ICC = 0.98, p < 0.001). CONCLUSION: The activPAL is an accurate measure to determine seated knee flexion angles from 75° to 15° but exhibits an average 5–10° error at knee flexion angles >75° and < 15°. Although there is error at the end ranges of motion, the tri-monitor activPAL configuration may be a useful tool to quantify sedentary knee flexion patterns during free-living conditions.