PURPOSE Neuromuscular control is an important factor for injury incidence and post‐surgical rehabilitation. Surface Mechanomyography (sMMG) sensors are novel wearable devices that are applied over a muscle group to 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. However, well‐established data collection and analysis challenges limit the utility of EMG for wide‐spread neuromuscular control screening in a clinic environment. The purpose of this study was to investigate the ability of sMMG sensors to detect timing patterns of muscle contraction and compare time events to those collected through traditional clinical EMG during a bilateral squat task. METHODS Eleven healthy, active individuals (mean age= 30.0 ± 10.77 y, 7 males, 4 females) underwent a neuromuscular control assessment with EMG and sMMG sensors simultaneously applied to the right quadriceps. Subjects performed a series of 3 bilateral deep squats. EMG data processed with a low‐pass 6th order Butterworth filter and a TKEO function, and raw sMMG data were used for timing analyses. Statistical analyses included paired T‐test assessments between measurement modalities. RESULTS There was no significant difference in the timing of total duration of quadriceps contraction between EMG (mean= 2.526 ± 0.553 s) and sMMG (mean= 2.527 ± 0.539 s), p= 0.985. The duration of quadriceps contraction during the descent phase of the squat (eccentric contraction, p= 0.773) and the ascent phase (concentric contraction, p= 0.298) did not differ significantly between modalities. CONCLUSIONS Results are consistent with physiologic expectations that myoelectrical activity (measured by EMG) and the physical muscle deformation of muscles (measured by sMMG) occur in extremely rapid succession. Successful sMMG detection of quadriceps contraction is supported by similarity to EMG time signatures. Findings also suggest the ability of sMMG sensors to detect timing of activation for different types of muscle contraction during a functional exercise without the need for complex signal processing (Figure 1). The sMMG sensor may be helpful for assessing quadriceps muscle performance and timing as part of quick, in‐the‐clinic neuromuscular control screenings for injury prevention, rehabilitation, and exercise training. Example of data analysis steps for comparison between electromyography (EMG) and surface mechanography (sMMG) timing during a bilateral squat task

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PURPOSE Efficient gastrocnemii force production is essential for performance of functional activities such as stair ascent/descent and athletic activities involving jumping or running. Appropriate neuromuscular control and timing of gastrocnemius contraction is also important for fatigue and injury prevention. Hand Held Dynamometry (HHD) is the clinical standard for assessing force production during a muscle contraction. However, HHD is unable to provide precise timing data on the muscle activation responsible for force generation or monitor fatigue during an activity. Surface mechanomyography (sMMG) sensors are novel wearable devices that can be applied across a muscle group to provide a measurement of physical muscle output during a contraction. The purpose of this study is 1) to assess the relationship of sMMG’s muscle bulk displacement measurement to force generation and 2) to confirm sMMG detection of gastrocnemius contraction compared to the clinical timing standard of electromyography (EMG). METHODS Healthy, athletic individuals (mean age= 32.56 ±10.57 y, n= 9, 7 males, 2 females) underwent a neuromuscular control assessment of the gastrocnemius. Subjects performed a series of 3 resisted “make‐test” isometric holds with the right leg supported on an exam table and the ankle plantar flexed at 90 degrees against a hand‐held dynamometer with simultaneous EMG and sMMG recording. The third trial was selected for analysis when available. EMG data was processed with a 6th order low‐pass Butterworth filter and a Teager‐Kaiser energy operator function. A threshold for detecting the time points of gastrocnemius activation and deactivation was set at 3 standard deviations of a resting calibration trial above the minimum value for each measurement modality. The relationship of sMMG signal output for physical muscle displacement was compared to muscle contraction force output via HHD and timing measured via EMG using paired T‐tests and a Pearson correlation. RESULTS Peak gastrocnemius muscle bulk displacement detected by sMMG (mean= 7.65 ±2.68 mm) positively correlated with maximum force generation detected by HHD during isometric contraction (mean= 58.43 ±13.12 lb), r2= 0.669. The duration of gastrocnemius muscle contraction during the isometric hold activity did not differ significantly between SMG (mean= 4.71 ±1.17 s) and EMG (mean= 4.53 ±1.17 s), p= 0.273. CONCLUSIONS Correlation between HHD and sMMG support the findings that increased physical muscle bulk displacement of the gastrocnemius was associated with greater force production during a contraction. The similarity to EMG timing reinforces the ability of the sMMG sensor to consistently detect active gastrocnemius contraction without complex signal processing (Figure 1). sMMG sensors may be a useful measurement tool for assessment of gastrocnemius functional performance during neuromuscular control screenings for injury prevention and rehabilitation. Example comparison of signal output during a resisted isometric gastrocnemius hold between a hand‐held dynam...

Electromyography (EMG) is the clinical standard for capturing muscle activation data to gain insight into neuromuscular control, yet challenges surrounding data analysis limit its use during dynamic tasks. Surface mechanomyography (sMMG) sensors are novel wearable devices that measure the physical output of muscle excursion during contraction, which may offer potential easy application to assess neuromuscular control. This study aimed to investigate sMMG detection of the timing patterns of muscle contraction compared to EMG. Fifteen healthy participants (mean age = 31.7 ± 9.1 y; eight males and seven females) were donned with EMG and sMMG sensors on their right quadriceps for simultaneous data capture during bilateral deep squats, and a subset performed three sets of repeated unilateral partial squats. No significant difference in the total duration of contraction was detected by EMG and sMMG during bilateral (p = 0.822) and partial (p = 0.246) squats. sMMG and EMG timing did not differ significantly for eccentric (p = 0.414) and concentric (p = 0.462) phases of muscle contraction during bilateral squats. The sMMG magnitude of quadriceps excursion demonstrated excellent intra-session retest reliability for bilateral (ICC3,1 = 0.962 mm) and partial (ICC3,1 = 0.936 mm, n = 10) squats. The sMMG sensors accurately and consistently provided key quadriceps muscle performance metrics during two physical activities commonly used to assess neuromuscular control for injury prevention, rehabilitation, and exercise training.