Contraction time and voluntary discharge properties of individual short toe extensor motor units in man.

Grimby, Lennart; Hannerz, Jan; Hedman, Björn

doi:10.1113/jphysiol.1979.sp012732

Cited by 71 publications

(54 citation statements)

References 19 publications

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“…Other motor units fired at only [25][26][27][28][29][30] Hz. This is in accordance with the finding that the longest contraction times in the muscles studied were more than twice the shortest ones (Buchtahl & Schmalbruch, 1970;Sica & McComas, 1973 (Borg et at., 1978;Grimby et al, 1979). Muscle fibres with long contraction times can be assumed to fuse completely at 20 Hz.…”

Section: Discussionmentioning

confidence: 99%

“…We have previously studied the voluntary firing rates and recruitment order Grimby & Hannerz, 1977), axonal conduction velocity (Borg, Grimby & Hannerz, 1978) and contraction time (Grimby, Hannerz & Hedman, 1979) of single human motor units and found a continuum between two extreme types of motor units. One type were motor units with a maximum rate of about 30 Hz and a minimum rate for continuous firing of about 10 Hz which was low enough to be maintained voluntarily for apparently unlimited periods of time.…”

Section: Introductionmentioning

confidence: 99%

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The fatigue and voluntary discharge properties of single motor units in man

Grimby

Hannerz

Hedman

1981

The Journal of Physiology

186

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1. The discharge properties of single motor units during prolonged maximal voluntary effort have been studied using electromyographic recordings, mainly in the short big toe extensor muscle but also in the anterior tibial muscle. 2. The required selectivity of the e.m.g. recordings was achieved in the short big toe extensor muscle after previous mechanical lesions to the terminal nerve twigs and muscle fibres and consequent collateral sprouting, and in the anterior tibial muscle with the use of a high impedance wire electrode. 3. During the first few hundred milliseconds of sustained maximal effort the motor units fired at rates ranging from about 30‐60 Hz, and the tension was the same as that obtained on electrical tetanization of the nerve to the toe extensor muscles above 50 Hz. 4. During prolonged maximal effort the firing rates and the proportion of motor units firing successively decreased. Motor units initially firing at 30 Hz continued to fire tonically but at 15‐20 Hz. Motor units initially firing at 60 Hz ceased to fire tonically but could still be made to discharge phasically. The period of time during which all motor units responded tonically could be increased from some seconds up to 20 sec by long‐term training. 5. Motor units with a limited endurance fired at a lower tension in the early than in the late stages of maintained contraction. 6. It is suggested that motoneurones innervating slow twitch muscle fibres respond continuously to prolonged voluntary drive at rates sufficient for full fusion but that the threshold of motoneurones innervating fast twitch muscle fibres increases so that they finally mainly fire phasically thus protecting the peripheral excitation and contractile mechanisms from excessive exhaustion.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

The fatigue and voluntary discharge properties of single motor units in man

Grimby

Hannerz

Hedman

1981

The Journal of Physiology

186

View full text Add to dashboard Cite

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“…Two type I fibers from P TA coexpressed the fast and slow isoforms of MyLC 2 14,17 This range was similar to the fusion range of normal slow fibers. 13 Thus, in our patients, lowthreshold P TA slow fibers were stimulated mainly within the lower half of the fusion range of similar fibers in normal subjects.…”

Section: Emg Recordings During Voluntary Contractionsmentioning

confidence: 92%

Firing rate of the lower motoneuron and contractile properties of its muscle fibers after upper motoneuron lesion in man

1997

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“…The finding that lower threshold motor units discharge at lower initial rates fits with the theoretical organizational properties of a motoneurone pool, as these motor units possess longer contraction and half relaxation times (Bakels & Kernell, 1993;Kernell et al, 1999) and would therefore summate and fuse at lower firing rates compared to higher threshold units with shorter contraction and half relaxation times (Grimby et al, 1979). It is has been hypothesised previously that this level of organization helps to achieve efficient gradation of force across a wide variety of contraction strengths ).…”

Section: Recruitment Threshold and Discharge Characteristicssupporting

confidence: 72%

In-vivo function of human plantar intrinsic foot muscles

Kelly¹

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This thesis investigates the in-vivo function of the plantar intrinsic foot muscles. Though much speculation has been made of the function of these muscles, scant detail exists pertaining to their function. This thesis provides a novel description of the function of these muscles in providing active support for the longitudinal arch (LA) during postural tasks and locomotion. Furthermore, the following chapters provide evidence of an active mechanism to stiffen the LA, primarily provided by the graded activation of these muscles in response to increasing load. This mechanism may have important implications for how energy is stored and released within the foot. Chapter one provides a general overview of the existing literature pertaining to the function of these muscles. Chapters two, three, four and five contain the individual manuscripts from each experiment performed as part of this thesis. Chapter six provides a summary of the findings from the thesis and some general suggestions for the direction of future research in this field.Chapter two investigates the role of the plantar intrinsic foot muscles in providing postural support for the foot during quiet standing. Intra-muscular electromyographic (EMG) activity was recorded from abductor hallucis (AH), flexor digitorum brevis (FDB) and quadratus plantae (QP) while participants performed two balance tasks of graded difficulty. Each task was performed while standing on a force plate, allowing appraisal of any relationship between loading, postural sway and intrinsic foot muscle activity. Intrinsic foot muscle activation increased in response to postural demand, with these muscles displaying highly correlated inter-muscular activation patterns in response to medial postural sway. Contrary to previous thoughts, these muscles are clearly important in postural control and are recruited in a highly co-ordinated manner to stabilise the foot and maintain balance, particularly during single leg stance, in the medio-lateral direction.The purpose of Chapter three was to investigate if the neurophysiological properties of the largest intrinsic foot muscle (abductor halluces) are matched to its suggested postural function. A highly selective, quadrifilar arrangement of fine wire EMG electrodes was employed to describe the discharge properties of AH motor units during ramp and hold isometric contractions, as well as during a submaximal, constant force, fatiguing contraction. Abductor hallucis motor units displayed small rate coding ranges, relatively low peak discharge rates and were largely resistant to fatigue. This muscle is comparatively fatigue resistant and appears to rely predominantly on recruitment to generate force, optimizing the use of slow twitch, fatigue resistant fibres to generate moderate to large amounts of force for sustained periods of time. These properties appear well matched to AH's postural function that involves providing stabilisation of the LA during weight-bearing tasks. 3Chapter four examined the potential for the intrinsic foot muscles ...

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Contraction time and voluntary discharge properties of individual short toe extensor motor units in man.

Cited by 71 publications

References 19 publications

The fatigue and voluntary discharge properties of single motor units in man

The fatigue and voluntary discharge properties of single motor units in man

Firing rate of the lower motoneuron and contractile properties of its muscle fibers after upper motoneuron lesion in man

In-vivo function of human plantar intrinsic foot muscles

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