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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A 2x3 mixed ANOVA revealed significant interactions for bench press IPF (p=0.03) and IPFa (p=0.04). Post-hoc comparisons revealed significant increases in bench press IPF (p=0.01,g=0.45) and IPFa (p=0.017,g=0.90) in 3D only following training (T1-T2), whereas bench press IPF (p<0.001,g=0.08) and IPFa (p<0.001,g=0.16) decreased in 5D only following training cessation (T2-T3). No differences were observed in isometric squat metrics for any time point. CONCLUSIONS: Upper body isometric maximal strength is better preserved with 3D of training cessation whereas lower body isometric maximal strength is preserved similarly with 3D or 5D of training cessation in strength athletes. The expression of maximal strength relative to upper body performance capabilities appears to dissipate more rapidly than the lower body after removing the training stimuli. Therefore, sport scientists and strength and conditioning practitioners who use training cessation to promote acute recovery may consider implementing divergent periods of training cessation for the upper and lower body to best preserve performance for maximal strength.

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...