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Does stretching affect performance?
Published in David G. Behm, The Science and Physiology of Flexibility and Stretching, 2018
Some researchers have compared a mechanomyogram (MMG) signal with the force or EMG signal to parcel out the EMD associated with excitation–contraction coupling and MTU viscoelastic properties. An MMG monitors changes in the muscle shape by sensing vibrations and oscillations of the muscle fibres at the resonant frequency of the muscle. With a higher signal-to-noise ratio than the surface EMG, it is purported to be able to monitor muscle activity from deeper muscles. After five sets of 45 seconds of passive stretching, the excitation–contraction (E-C) coupling aspect of the EMD (Δt: EMG–MMG) was prolonged for approximately 15 minutes, whereas the MTU viscoelasticity (Δt: MMG–tetanic force) was prolonged for up to 2 hours (45). It is necessary to remind the reader that research is almost never unanimous. A study from our lab also found force deficits up to 2 hours after stretching two muscles for three sets of 45 seconds each. However, although there were significant voluntary force deficits (10%), the evoked twitch and tetanic force deficits (1–4%) were non-significant over that same period (46). However, peak tetanic force has also been reported to be depressed for 2 hours after five repetitions of 45-second static stretches with 15 seconds of rest between stretches (41). Changes in evoked twitch forces represent changes in E-C coupling (muscle action potential leading to the release and sequestration of calcium from the sarcoplasmic reticulum) and tetanic forces represent changes in myofilament kinetics. Hence, five repeats of 45 seconds of stretching in this one study damaged the myosin and actin cross-bridges, which would affect not only peak force but also probably the rate of force development.
Passive stretching-induced changes detected during voluntary muscle contractions
Published in Physiotherapy Theory and Practice, 2020
Haris Begovic, Filiz Can, Suha Yağcioğlu, Necla Ozturk
So far, it has been clear, when a muscle is contracting; muscle fibers undergo changes in transverse diameter causing lateral displacement, which generates oscillation recordable by an accelerometer, the mechanomyogram (MMG) (Orizio et al., 1999). The MMG signal stands for motor unit recruitment and firing rate during voluntary muscle contraction, which shows linearity at low frequency rate (Orizio et al., 2003). Therefore, measuring an acceleration of the muscle fibers during contracting has been widely implemented for the EMD analysis (Begovic et al., 2014; Esposito, Limonta, and Cè, 2011), in synch to other sensors such as EMG to detect electrical changes and load-cell to detect the magnitude of the force/torque output. The synchronization of all these sensors enables simultaneous detection of the signals where EMG first appears, followed by MMG reflecting muscle fiber oscillation and force output detected by load cell.