Abstract
Intramuscular pressure (IMP) is the fluid hydrostatic pressure generated within a muscle and reflects the mechanical forces produced by a muscle. By providing accurate quantification of interstitial fluid pressure, the measurement of IMP may be useful to detect changes in skeletal muscle function not identified with established techniques. However, the relationship between IMP and muscle activity has never been studied in vivo in healthy human muscles. To determine if IMP is able to evaluate electromechanical performance of muscles in vivo, we tested the following hypotheses on the human tibialis anterior (TA) muscle: (i) IMP increases in proportion to muscle activity as measured by electrical [Compound Muscle Action Potential (CMAP)] and mechanical (ankle torque) responses to activation by nerve stimulation and (ii) the onset delay of IMP (IMPD) is shorter than the ankle torque electromechanical delay (EMD). Twelve healthy adults [six females; mean (SD) = 28.1 (5.0) years old] were recruited. Ankle torque, TA IMP, and CMAP responses were collected during maximal stimulation of the fibular nerve at different intensity levels of electrical stimulation, and at different frequencies of supramaximal stimulation, i.e., at 2, 5, 10, and 20 Hz. The IMP response at different stimulation intensities was correlated with the CMAP amplitude (r2 = 0.94). The area of the IMP response at different stimulation intensities was also significantly correlated with the area of the CMAP (r2 = 0.93). Increasing stimulation intensity resulted in an increase of the IMP response (P < 0.001). Increasing stimulation frequency caused torque (P < 0.001) as well as the IMP (P < 0.001) to increase. The ankle torque EMD [median (interquartile range) = 41.8 (14.4) ms] was later than the IMPD [33.0 (23.6) ms]. These findings support the hypotheses and suggest that IMP captures active mechanical properties of muscle in vivo and can be used to detect muscular changes due to drugs, diseases, or aging.
Highlights
Functional properties of skeletal muscles change due to training (Duchateau and Baudry, 2011) or aging (Janssen et al, 2002), disuse (Lamboley et al, 2016), malnutrition as well as for a spectrum of acquired and inherited myopathies (Brooke et al, 1989)
The goal of this study was to test the following hypotheses on the human tibialis anterior (TA) muscle in vivo: (i) Intramuscular pressure (IMP) increases in proportion to muscle activity as measured by electrical [compound muscle action potential (CMAP)] and mechanical responses to activation by nerve stimulation. (ii) The onset delay of IMP (IMPD) is shorter than ankle torque electromechanical delay (EMD)
The peak IMP was significantly correlated with the amplitude of Compound Muscle Action Potential (CMAP) for each participant [r median (IQR) = 0.99 (0.05), P < 0.001]
Summary
Functional properties of skeletal muscles change due to training (Duchateau and Baudry, 2011) or aging (Janssen et al, 2002), disuse (Lamboley et al, 2016), malnutrition as well as for a spectrum of acquired and inherited myopathies (Brooke et al, 1989). In vivo evaluation of muscle function has been limited to manual muscle testing, measurement of force production, and electromyography (EMG). EMG is capable of quantifying neuromuscular electrical activity, it does not provide a quantitative measurement of muscle force. Like steroid induced myopathy, the EMG may be normal when there is a reduction in muscle force production. The sensitivity of the available muscle strength tests is limited. To better understand muscle function and weakness, the quantitative assessment of electromechanical properties of individual muscles is necessary. This will provide a more sensitive and robust measure of muscle dysfunction
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