The aim of the study was to characterize the electromechanical properties of skeletal muscle during isometric loading as well as to assess the potential of estimating intramuscular pressure by electrical and mechanical methods. Simultaneous electromyography (EMG), mechanical myotonometry (MYO, frequency and decrement of decay) and intramuscular pressure (IMP) measurements were conducted at rest and during short-term and long-term isometric contractions in patients with chronic pain in the anterior leg or dorsal forearm. The EMG amplitude and MYO(freq) accounted significantly (24-73%, p < 0.0001) for the variations in the IMP under short-term isometric loading. The IMP, EMG and MYO(freq) increased linearly with the relative muscle load (r = 0.868-0.993, p < 0.05). Mean values of EMG amplitudes at the contraction levels of 75% and 100% maximum voluntary contraction (MVC) and MYO(freq) values at all contraction levels (0-100% MVC) were higher for subjects with pathological values of IMP than for those with IMP values in the normal range. Total changes in IMP and EMG amplitude during 1 min isometric contraction were linearly interrelated (r = 0.747, p < 0.0001). We conclude that both surface electromyography and myotonometry parameters are indicative of intramuscular pressure, but neither of these methods can be used alone to diagnose non-invasively chronic compartment syndrome with acceptable accuracy.

Background Clinical assessment of skin stiffness is unreliable in many applications. The durometer, an industrial device to measure hardness, has previously been applied in scleroderma. The Myoton is a noninvasive handheld device for assessing soft tissue biomechanical parameters. Materials and Methods We evaluated the reproducibility of both devices in six healthy subjects in the volar forearm, dorsal forearm, upper arm, shin, and calf bilaterally. The intraclass correlation coefficient (ICC) was used as a measure of reproducibility among three observers. Results The interobserver intraclass correlation coefficient (ICC) of overall stiffness for the Myoton was 0.74 [95% confidence interval (CI) 0.45‐1.00] and 0.71 [0.39‐1.00] for the durometer. Coefficient of variation (CV) for the Myoton was 6.4% [range 1.3‐12.1] and 7.6% [range 4.4‐13.8] for the durometer. Myoton and durometer values had a Pearson correlation of 0.69. The intraobserver Myoton ICC was 0.89 [0.74‐1.00] and CV 3.1% [range 1.6‐5.0]. The 95% confidence minimal detectable change by the Myoton for a single observer is 32.4 N/m, which is 7.6% of the average subject's overall stiffness. Conclusion The Myoton demonstrated high reproducibility, particularly in the overall stiffness parameter, and merits further investigation to assess disease progression and treatment efficacy.

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