Relationship of Surface Mechanomyography to Force Production in an Assessment of Gastrocnemius Muscle Contraction
Authors: Linderman Shannon , Aspenleiter Ryan , Stein Hannah , Berkson Eric 
Published: April 2020

PURPOSEEfficient 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).METHODSHealthy, 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.RESULTSPeak 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.CONCLUSIONSCorrelation 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 dynamometer [HHD, (A)], surface mechanomyography [sMMG, (B)], and electromyography [EMG, (C)].
Greenand
redXs indicate calculated muscle activation and deactivation time points based on 3 standard deviations of a resting calibration trial above the minimum for each modality (Solonik et al., 2010).Figure 1