Motor unit recruitment patterns 1: responses to changes in locomotor velocity and incline

Hodson-Tole, Emma F.; Wakeling, James M.

doi:10.1242/jeb.014407

Cited by 37 publications

(60 citation statements)

References 47 publications

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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%

“…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). Therefore, it has been speculated that slow muscle fibres are activated, but deactivated before faster muscle fibres (Hodson-Tole and Wakeling, 2008a;Roberts and Gabaldón, 2008;Lee et al, 2013). This is to account for their longer deactivation times, as the time between the end of excitation and the end of muscle shortening represents an increasing portion of the muscle contraction-relaxation cycle at increasing cycle frequencies.…”

Section: Discussionmentioning

confidence: 99%

“…The principal components determined from the EMG frequency spectra differ from those established previously (Wakeling, 2004;Wakeling and Rozitis, 2004;Wakeling et al, 2006;Hodson-Tole and Wakeling, 2008a;Wakeling, 2009;Lee et al, 2011;Lee et al, 2013) as time was retained and the mean was subtracted. In these previous studies the mean was not subtracted in order to evaluate and reconstruct the entire signal, whereas subtraction of the mean in the current study results in the principal components representing variance of the time-varying frequency spectra (Ramsay and Silverman, 2005) and highlight the major shifts in frequency away from the mean.…”

Section: Research Articlementioning

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%

“…It was speculated that alterations in muscle fibre recruitment during running, such that faster fibres remain active after deactivation of slow fibres, might explain the shorter relaxation times as they should not decrease if dominated by slow fibres as dictated by the size principle (Henneman et al, 1965a;Henneman et al, 1965b). Studies have qualitatively indicated such a recruitment pattern in humans (Wakeling, 2004) and rats (Hodson-Tole and Wakeling, 2008a) running at various speeds, while Lee and co-workers (Lee et al, 2013) were unable to confirm a relationship between relaxation rates and muscle fibre recruitment in goats. Despite having been repeatedly suggested, an early derecruitment of slower fibres during muscle relaxation at high cycle frequencies has not yet been Early deactivation of slower muscle fibres at high movement frequencies Ollie M. Blake* and James M. Wakeling demonstrated.…”

Section: Introductionmentioning

confidence: 99%

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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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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Research Articlementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Early deactivation of slower muscle fibres at high movement frequencies

Blake

Wakeling

2014

Journal of Experimental Biology

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Motor unit recruitment for dynamic tasks: current understanding and future directions

2008

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Skeletal muscle contains many muscle fibres that are functionally grouped into motor units. For any motor task there are many possible combinations of motor units that could be recruited and it has been proposed that a simple rule, the 'size principle', governs the selection of motor units recruited for different contractions. Motor units can be characterised by their different contractile, energetic and fatigue properties and it is important that the selection of motor units recruited for given movements allows units with the appropriate properties to be activated. Here we review what is currently understood about motor unit recruitment patterns, and assess how different recruitment patterns are more or less appropriate for different movement tasks. During natural movements the motor unit recruitment patterns vary (not always holding to the size principle) and it is proposed that motor unit recruitment is likely related to the mechanical function of the muscles. Many factors such as mechanics, sensory feedback, and central control influence recruitment patterns and consequently an integrative approach (rather than reductionist) is required to understand how recruitment is controlled during different movement tasks. Currently, the best way to achieve this is through in vivo studies that relate recruitment to mechanics and behaviour. Various methods for determining motor unit recruitment patterns are discussed, in particular the recent wavelet-analysis approaches that have allowed motor unit recruitment to be assessed during natural movements. Directions for future studies into motor recruitment within and between functional task groups and muscle compartments are suggested.

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A Muscle’s Force Depends on the Recruitment Patterns of Its Fibers

et al. 2012

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Biomechanical models of whole muscles commonly used in simulations of musculoskeletal function and movement typically assume that the muscle generates force as a scaled-up muscle fiber. However, muscles are comprised of motor units that have different intrinsic properties and that can be activated at different times. This study tested whether a muscle model comprised of motor units that could be independently activated resulted in more accurate predictions of force than traditional Hill-type models. Forces predicted by the models were evaluated by direct comparison with the muscle forces measured in situ from the gastrocnemii in goats. The muscle was stimulated tetanically at a range of frequencies, muscle fiber strains were measured using sonomicrometry, and the activation patterns of the different types of motor unit were calculated from electromyographic recordings. Activation patterns were input into five different muscle models. Four models were traditional Hill-type models with different intrinsic speeds and fiber-type properties. The fifth model incorporated differential groups of fast and slow motor units. For all goats, muscles and stimulation frequencies the differential model resulted in the best predictions of muscle force. The in situ muscle output was shown to depend on the recruitment of different motor units within the muscle.

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Motor unit recruitment patterns 1: responses to changes in locomotor velocity and incline

Cited by 37 publications

References 47 publications

Early deactivation of slower muscle fibres at high movement frequencies

Early deactivation of slower muscle fibres at high movement frequencies

Motor unit recruitment for dynamic tasks: current understanding and future directions

A Muscle’s Force Depends on the Recruitment Patterns of Its Fibers

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