China
Africa
Explore chapters and articles related to this topic
Muscle energetics and electromyography
Published in Kumar Shrawan, Mital Anil, Electromyography in Ergonomics, 2017
Since the ‘size principle’ of Henneman et al. (1965) was first proposed based upon results from cat motor neurones, strong evidence has been presented that in muscle contraction there is a specific sequence of recruitment in order of increasing motor neuron and motor unit (MU) size (Milner-Brown et al., 1973; Freund et al., 1975; Kukulka and Clamann 1981; De Luca et al., 1982). Goldberg and Derfler (1977) also showed positive correlations between recruitment order, spike amplitude, and twitch tension of single MUs in human masseter muscle. It is well documented that motor unit recruitment and the firing frequency (rate coding) depend primarily upon the level of force and the speed of contraction. When low-threshold MUs are recruited, this results in a muscular contraction characterized by low force-generating capabilities and high fatigue resistance. With requirements for greater force and/or faster contraction, high-threshold-fatiguable MUs are recruited (Fruend et al., 1975; Henneman and Mendell, 1981). However, Kukulka and Clamann (1981) and Moritani et al. (1986a) demonstrated in human adductor pollicis that for a muscle group with mainly type I fibers, rate coding plays a more prominent role in force modulation. For a muscle group composed of both type I and II fibers, MU recruitment seems to be the major mechanism for generating extra force above 40-50% of the maximal voluntary contraction (MVC) (Kukulka and Clamann, 1981; De Luca et al., 1982; Moritani et al., 1986a; Moritani and Muro 1987).
Wheels of Motion: Oscillatory Potentials in the Motor Cortex
Published in Alexa Riehle, Eilon Vaadia, Motor Cortex in Voluntary Movements, 2004
Frequency (Hz) FIGURE 7.8 Corticomuscular coherence in the beta frequency band. LFP in the hand area of the monkey primary motor cortex (A) was recorded simultaneously with rectified EMG from the adductor pollicis muscle (B), as the monkey performed precision grips sustained for over l sec (D). In D, the mean time course of finger and thumb displacements producing the grip is shown, along with the mean rectified EMG. During the period of maintained grip, the EMG exhibited distinct oscillatory bursts that were coherent with LFP oscillations at a frequency of about 25 Hz (C). The coherence spectrogram in E (mean of 274 trials), shows that the corticomuscular coherence was largely confined to the duration of constant muscle contraction, not involving movement initiation. (Adapted from Reference l2, with permission.)
A validated combined musculotendon path and muscle-joint kinematics model for the human hand
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2019
Jumana Ma’touq, Tingli Hu, Sami Haddadin
The proposed model includes all extrinsic and intrinsic muscles of the human hand, see Figure 1 and Table 2. The musculotendon path, which describes the full muscle path from origin to insertion including the wrapping and via-points in 3-D space, is implemented for each muscle based on the anatomical descriptions from Lippert (2011) and the human hand dissection description from An et al. (1983). Based on these muscle descriptions, muscles with multiple origins such as in the Adductor Pollicis muscle (AdP), were modeled with several subregions to represent each origin-insertion path. For an arbitrary musculotendinous unit i, its length is modeled as a function of joint angles q and thus denoted as It is calculated as a summation of multiple muscle segment lengths, which connect origin, via-points, and insertion, see Figure 3.
The ‘sensory tolerance limit’: A hypothetical construct determining exercise performance?
Published in European Journal of Sport Science, 2018
Thomas J. Hureau, Lee M. Romer, Markus Amann
Metabo-nociceptors, in addition to metabosensitive muscle afferent feedback, also limit exercise performance, perhaps by contributing to the sensory tolerance limit. This idea is reflected in a study during which muscle pain was induced by hypertonic saline injection into the vastus lateralis of one leg. The performance during a subsequent maximal single-leg hop task executed with the infused (i.e. painful) leg was compromised compared to the same task performed without pain (Deschamps et al., 2014). Interestingly, however, hopping performance of the contralateral (i.e. non-painful) leg was also compromised following hypertonic saline infusion in the other leg (Deschamps et al., 2014). Further studies triggered metabo-nociceptors by occluding blood supply to the fatigued elbow extensors at the end of exercise (tourniquet placed proximally to fatigued muscle) to investigate the impact of ischaemic muscle pain on performance and voluntary muscle activation. Similarly, muscle pain decreased maximal voluntary activation and performance of the fatigued elbow extensors, but also that of the elbow-flexors (Kennedy, McNeil, Gandevia, & Taylor, 2013). These investigators later documented that post-exercise ischaemic muscle pain and related metabo-nociceptive feedback to the CNS not only decreases voluntary activation of the fatigued and painful muscle (adductor pollicis), but also that of an unfatigued proximal muscle within the same limb (elbow flexor) (Kennedy, McNeil, Gandevia, & Taylor, 2014).