Using a Stretch Sensor to Evaluate Muscle Contraction Timing During a Neuromuscular Control Screening Activity

Abstract

PURPOSE: Stretch sensors are wearable devices that when applied over a muscle group, can measure the physical output of muscle deformation resulting from a muscle contraction. Electromyography (EMG) is the clinical standard for assessing the electrical signal identifying muscle activation. The well-established challenges in EMG data collection and analysis methods limit utility for wearable wide-spread neuromuscular control screening. The purpose of this study was to investigate the ability of stretch sensors to detect timing patterns of muscle contraction and compare time events to those collected through traditional clinical EMG. METHODS: 4 healthy subjects (mean age: 23.29 ±3.45 y) completed 5 repetitions of a unilateral partial squat with a stretch sensor and an EMG unit simultaneously applied to the dominant leg quadriceps muscle. Paired T-test and linear regression analyses assessed differences in key muscle contraction time events (Figure 1) for the stretch sensor (SS) and EMG. RESULTS: Relative times of peak contraction (r2= 0.99, mean relative error (RE)= 0.04), activation (r2= 0.98, RE= 0.14), and deactivation (r2= 0.92, RE= 0.35) displayed excellent correlation between the EMG and SS. Duration of ascent (p= 0.103, EMG: 1.14 ±0.46 s, SS: 1.36 ±0.27 s) and descent (p= 0.079, EMG: 1.38 ±0.49 s, SS: 1.14 ±0.37 s) squat phases and total contraction time (p= 0.95, EMG: 2.55 ±0.83 s, SS: 2.49 ±0.30 s) did not differ significantly between EMG and SS. Average within-subject variation was not significantly different for EMG timing of ascent (p= 0.56) and descent (p= 0.15) phases, and total contraction (p= 0.08). CONCLUSIONS: Our findings reveal similarities in time signatures between SS and EMG for assessing quadriceps activation during a standard neuromuscular screening activity. This suggests the potential for utility of SS evaluation of muscle activation timing. This study was supported in part by figur8 IncFigure 1:: Example of relative muscle contraction timing for stretch sensor and EMG signals during a repeated partial squal task. A 6 th order lower-pass Butterworth filter (3 Hz) and rectified TKEO function were applied to a raw EMG data. Threshold of activation/dectivation was defined as 3 standard deviations of a resting calibration trial.