Accelerometry as a measure of subject compliance in unilateral lower limb suspension

Human unilateral lower limb suspension (ULLS) is a commonly used model to study the effects of disuse and unweighting of human skeletal muscle. ULLS requires subjects to ambulate on crutches with an elevated shoe on the weight-bearing limb or a strap on the unloaded limb for prolonged periods of time (i.e., 4-5 wk). Ensuring compliance during ULLS participation is critical to the integrity of the study.

The purpose of this study was to determine the accuracy of an accelerometer to detect steps taken while walking and to measure the effectiveness of an accelerometer to monitor compliance during ULLS.

There were 10 subjects (26.2 +/- 3.6 yr; 170.9 +/- 6.9 cm; 68.0 +/- 9.6 kg) who participated in two conditions: normal walking and ULLS (left leg was unweighted via an elevated shoe on the contralateral limb) at various speeds. Additionally, subjects completed an obstacle course to simulate daily activities. During these activities, subjects wore a planar accelerometer on their left ankle to measure acceleration. The mean peak axial acceleration (MPAA) of the leg in the swing phase of walking was determined by the accelerometer and a step was detected during ULLS if the MPAA was greater than or equal to the minimum MPAA observed during walking. From this, the sensitivity of the accelerometer was determined. During ULLS, the number of steps detected by the accelerometer with an MPAA--the minimum MPAA during walking was computed and the specificity of the accelerometer was determined.

The sensitivity of the accelerometer during walking was 96% and the specificity during ULLS was 97%.

An accelerometer is an accurate tool to quantify the number of steps taken during walking and it may be used to measure subject compliance during ULLS.