Firing rate and recruitment order of toe extensor motor units in different modes of voluntary conraction.

Grimby, Lennart; Hannerz, Jan

doi:10.1113/jphysiol.1977.sp011699

Cited by 288 publications

(109 citation statements)

References 27 publications

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“…We have been able to provide evidence to support this suggestion and have identified that different recruitment patterns also occur between different muscles. A number of examples where the size principle does not hold true have previously been reported for cats (Hoffer et al, 1981;Grimby and Hannerz, 1977;Kanda et al, 1977), jumping in the bushbaby (Gillespie et al, 1974) and humans (Gillespie et al, 1974;Grimby and Hannerz, 1977;Hoffer et al, 1981;Kanda et al, 1977;Nardone et al, 1989;Wakeling, 2004;Wakeling et al, 2006). Our results are the first example to be found in the rat and highlight an area of research where our current understanding is limited.…”

Section: Task-specific Recruitment Of Motor Unitsmentioning

confidence: 64%

Variations in motor unit recruitment patterns occur within and between muscles in the running rat (Rattus norvegicus)

Hodson-Tole

Wakeling

2007

Journal of Experimental Biology

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SUMMARY Motor units are generally considered to follow a set, orderly pattern of recruitment within each muscle with activation occurring in the slowest through to the fastest units. A growing body of evidence, however, suggests that recruitment patterns may not always follow such an orderly sequence. Here we investigate whether motor unit recruitment patterns vary within and between the ankle extensor muscles of the rat running at 40 cm s-1 on a level treadmill. In the past it has been difficult to quantify motor unit recruitment patterns during locomotion; however, recent application of wavelet analysis techniques has made such detailed analysis of motor unit recruitment possible. Here we present methods for quantifying the interplay of fast and slow motor unit recruitment based on their myoelectric signals. Myoelectric data were collected from soleus, plantaris and medial gastrocnemius muscles representing populations of slow, mixed and fast fibres, respectively, and providing a good opportunity to relate myoelectric frequency content to motor unit recruitment patterns. Following wavelet transformation, principal component analysis quantified signal intensity and relative frequency content. Significant differences in signal frequency content occurred between different time points within a stride (P<0.001). We optimised high- and low-frequency wavelets to the major signals from the fast and slow motor units. The goodness-of-fit of the optimised wavelets to the signal intensity was high for all three muscles (r2>0.98). The low-frequency band had a significantly better fit to signals from the soleus muscle (P<0.001), while the high-frequency band had a significantly better fit to the medial gastrocnemius(P<0.001).

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Section: Task-specific Recruitment Of Motor Unitsmentioning

confidence: 64%

Variations in motor unit recruitment patterns occur within and between muscles in the running rat (Rattus norvegicus)

Hodson-Tole

Wakeling

2007

Journal of Experimental Biology

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“…It has been argued that the inputs from polysynaptic descending and segmental inputs would be mediated through common interneurons whose synaptic distribution on spinal motoneurons would be different to that of the Ia input (Binder 1989;Heckman and Binder 1993;Powers and Binder 1985). Variations in the recruitment order in human soleus motoneuron pool have been also observed under voluntary or reflex activation (Davies et al 1993) as well as in toe extensor motor units during phasic or tonic voluntary contractions (Grimby and Hannerz 1977). According to this, the possibility for reversal of the recruitment sequence in the oculomotor system could be found in saccadic versus sustained firings.…”

Section: Eye Movement Modality and Recruitment Ordermentioning

confidence: 88%

Recruitment Order of Cat Abducens Motoneurons and Internuclear Neurons

Pastor

González-Forero

2003

Journal of Neurophysiology

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Abducens neurons undergo a dose-dependent synaptic blockade (either disinhibition or complete blockade) when tetanus neurotoxin (TeNT) is injected into the lateral rectus muscle at either a low (0.5) or a high dose (5 ng/kg). We studied the firing pattern and recruitment order in abducens neurons both in control and after TeNT injection. The eye position threshold for recruitment of control abducens neurons was exponentially related to the eye position and velocity sensitivities. We also found a constancy of recruitment threshold for different eye movement modalities (spontaneous, optokinetic, and vestibular). Exponential relationships were found, as well, for eye velocity sensitivity during saccades and for position and velocity sensitivities during the vestibulo-ocular reflex. Likewise, inverse relationships were found between recruitment threshold or position sensitivity with the antidromic latency in control abducens neurons. These relationships, however, did not apply following TeNT treatment. Neuronal firing after TeNT appeared either disinhibited (low dose) or depressed (high dose), but the relationships between neuronal sensitivities and recruitment still applied. However, the pattern of recruitment shifted toward the treated side as more inputs were blocked by the low-and high-dose treatments, respectively. Nonetheless, although the recruitment-to-sensitivity relationships persisted under the TeNT synaptic blockade, we conclude that synaptic inputs are determinant for establishing the recruitment threshold and recruitment spacing of abducens motoneurons and internuclear neurons.

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“…Preferential recruitment of faster muscle fibres during rapid contractions has been shown in various animal studies, including humans (Gillespie et al, 1974;Gollnick et al, 1974;Grimby and Hannerz, 1977;Hoffer et al, 1981;Citterio and Agostoni, 1984;Wakeling et al, 2006;Hodson-Tole and Wakeling, 2008a;Lee et al, 2013). It has been suggested that complete inhibition of slow muscle fibres in a muscle with mixed fibre types would provide resistance to whole muscle shortening and therefore be detrimental to power production for very fast contractions (Josephson and Edman, 1988).…”

Section: Discussionmentioning

confidence: 99%

“…However, the size principle of motor unit recruitment (Henneman et al, 1965a;Henneman et al, 1965b) dictates that slower fibres, with longer relaxation times, are deactivated last. While the size principle adequately describes many recruitment strategies, alternative strategies may also exist (Gillespie et al, 1974;Gollnick et al, 1974;Grimby and Hannerz, 1977;Hoffer et al, 1981;Citterio and Agostoni, 1984;Wakeling et al, 2006;Hodson-Tole and Wakeling, 2008a) when the demands exceed the abilities of the slowest muscle fibres.…”

Section: Introductionmentioning

confidence: 99%

Early deactivation of slower muscle fibres at high movement frequencies

Blake

Wakeling

2014

Journal of Experimental Biology

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Animals produce rapid movements using fast cyclical muscle contractions. These types of movements are better suited to faster muscle fibres within muscles of mixed fibre types as they can shorten at faster velocities and achieve higher activation-deactivation rates than their slower counterparts. Preferential recruitment of faster muscle fibres has previously been shown during high velocity contractions. Additionally, muscle deactivation takes longer than activation and therefore may pose a limitation to fast cyclical contractions. It has been speculated that slower fibres may be deactivated before faster fibres to accommodate their longer deactivation time. This study aimed to test whether shifts in muscle fibre recruitment occur with derecruitment of slow fibres before faster fibres at high cycle frequencies. Electromyographic (EMG) signals were collected from the medial gastrocnemius at an extreme range of cycle frequencies and workloads. Wavelets were used to resolve the EMG signals into time and frequency space and the primary sources of variability within the EMG frequency spectra were identified through principal component analysis. Early derecruitment of slower fibres was evident at the end of muscle excitation at higher cycle frequencies, as determined by reduced low-frequency EMG content, and additional slower fibre recruitment was present at the highest cycle frequency. The duration of muscle excitation reached a minimum of about 150 ms and did not change for the three highest cycle frequencies, suggesting a duration limit for the medial gastrocnemius. This study provides further evidence of modifications of muscle fibre recruitment strategies to meet the mechanical demands of movement.

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Firing rate and recruitment order of toe extensor motor units in different modes of voluntary conraction.

Cited by 288 publications

References 27 publications

Variations in motor unit recruitment patterns occur within and between muscles in the running rat (Rattus norvegicus)

Variations in motor unit recruitment patterns occur within and between muscles in the running rat (Rattus norvegicus)

Recruitment Order of Cat Abducens Motoneurons and Internuclear Neurons

Early deactivation of slower muscle fibres at high movement frequencies

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