Use of motor units in relation to muscle fiber type and size in man

Jakobsson, Finnbogi; Borg, Kristian; Edström, Lars; Grimby, Lennart

doi:10.1002/mus.880111205

Cited by 88 publications

(74 citation statements)

References 27 publications

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“…In contrast, torque relaxation was somewhat prolonged in the unfatigued muscle of the older men (Tables 1 and 2). This age-related slowing of relaxation has been observed in previous studies (29,41) and probably reflects the higher proportion of type I muscle fiber content of the tibialis anterior muscle in older adults [76% in young, 84% in old (22)]. It is unlikely that slowed torque relaxation in the older group was due to deconditioning, because physical activity levels were similar between the groups.…”

Section: Contractile Propertiesmentioning

confidence: 52%

“…Human aging is accompanied by a number of changes in the neuromuscular system that might affect fatigue, including motor unit remodeling (11), reduced maximal motor unit discharge rates (25), and a general shift toward a greater type I fiber composition (22). The extent of these age-related alterations appears to vary by muscle group and level of habitual physical activity (3,21,30).…”

mentioning

confidence: 99%

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Age-related enhancement of fatigue resistance is evident in men during both isometric and dynamic tasks

Lanza

Russ

Kent‐Braun

2004

Journal of Applied Physiology

150

119

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It has been suggested that the effects of old age on the ability to resist fatigue may be task dependent. To test one aspect of this hypothesis, we compared the neuromuscular responses of nine young (26 +/- 4 yr, mean +/- SD) and nine older (72 +/- 4 yr) healthy, relatively sedentary men to intermittent isometric (3 min, 5 s contract/5 s rest) and dynamic (90 at 90 degrees /s) maximum voluntary contractions (MVC) of the ankle dorsiflexor muscles. To assess the mechanisms of fatigue (defined as the ratio of postexercise MVC to preexercise MVC), we also measured isometric central activation ratios (CAR), tetanic torque, contractile properties, and compound muscle action potentials before and immediately after exercise. Because dynamic contractions are more neurally complex and metabolically demanding than isometric contractions, we expected an age-related fatigue resistance observed during isometric exercise to be absent during dynamic exercise. In contrast, older men (O) fatigued less than young (Y) during both isometric (O = 0.77 +/- 0.07, Y = 0.66 +/- 0.02, mean +/- SE; P < 0.01) and dynamic (O = 0.45 +/- 0.07, Y = 0.27 +/- 0.02; P = 0.04) contractions (ratio of postexercise to preexercise MVC), with no evidence of peripheral activation failure in either group. We observed no obvious limitations in central activation in either group, as assessed using isometric CAR methods, after both isometric and dynamic contractions. Preexercise half-time of tetanic torque relaxation, which was longer in O compared with Y, was linearly associated with fatigue resistance during both protocols (r = 0.62 and 0.66, P < or = 0.004, n = 18). These results suggest that relative fatigue resistance is enhanced in older adults during both isometric and isokinetic contractions and that age-related changes in fatigue may be due largely to differences within the muscle itself.

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Section: Contractile Propertiesmentioning

confidence: 52%

mentioning

confidence: 99%

Age-related enhancement of fatigue resistance is evident in men during both isometric and dynamic tasks

Lanza

Russ

Kent‐Braun

2004

Journal of Applied Physiology

150

119

View full text Add to dashboard Cite

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“…We were careful to select only those units that exhibited either large amplitudes or unique shapes. In this way, it is very unlikely that two units with identical complexities in their shape were being recorded at the same time (see Jakobsson et al 1988 (Feinstein, Lindegard, Nyman & Wohlfart, 1955). There is no evidence to suggest that proximal-distal differences exist, particularly for muscles that appear to be functionally homogeneous, such as the TA.…”

Section: Methodological Considerationsmentioning

confidence: 99%

Mechanism for reflex reversal during walking in human tibialis anterior muscle revealed by single motor unit recording.

Serres

Yang

Patrick

1995

The Journal of Physiology

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1. A reversal in the sign of a cutaneous reflex during walking was recently described in the human. Such reversals were most clearly seen in muscles that were active in two parts of the step cycle, such as the tibialis anterior (TA). The current study determined whether the reversal resulted from differential activation of a single group of motor units. 2. Single motor units were recorded from the TA muscle of healthy human subjects while they walked on a treadmill with a splint that limited motion at the ankle joint. The majority of motor units from which recordings were made (43 out of 46) were active in both the swing phase and the transition from swing to stance, indicating that the two bursts of activity from the TA muscle do not represent the activity of two separate populations of motor units.3. The firing behaviour of three motor units was observed during walking steps when stimuli were applied to the posterior tibial nerve during either the swing phase or the transition from swing to stance. The post-stimulus time histograms indicated that the same motor unit was excited during the swing phase, and inhibited during the transition from swing to stance.4. The results support the hypothesis that there are parallel excitatory and inhibitory pathways from cutaneous afferents to single motoneurones of the TA muscle. A shift in balance between the two pathways as a function of the step cycle most probably generates the reflex reversal observed.

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“…One of the main explanations of this increase has been proposed by Jakobsson et al [43] and Lexell [37] , indicating an age-related shift toward a higher percentage of type I fibers. However, this explanation was in conflict with results of Tarpenning et al [14] , showing that the type I and type II fiber area and distribution do not differ between age groups of endurance-trained men.…”

Section: Muscular Twitch and M-wavementioning

confidence: 99%

Age-Related Changes in Neuromuscular Function and Performance following a High-Intensity Intermittent Task in Endurance-Trained Men

Bieuzen¹,

Hausswirth

Louis³

et al. 2009

Gerontology

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Background: Much attention has been focused on the need to design strategies to increase functional capacities in older populations. This has raised several questions regarding the ability of regular endurance training to preserve functional capacity with age. Objective: The purpose of this study was to examine the age-associated changes in neuromuscular function in endurance-trained men before and after a high-intensity, intermittent fatiguing task. Method: Twenty-six healthy endurance-trained male subjects: 16 older (59–79 years) and 10 young (20–34 years) men performed a high-intensity, intermittent fatiguing exercise corresponding to 10 sets of 10 repetitions on a horizontal leg press at 70% of the individual one-repetition maximum. Maximal voluntary contractions and evoked contractions of the knee extensor muscles were performed before and after the exercise. Results: Decreases in maximum voluntary contractions (older: –9.7%; young: –14.3%) and electromyographic activity were not different between groups. Peak twitch torque was reduced only for the older men and no changes in voluntary activation and M-wave properties were recorded in either group. Conclusion: The present study indicates that in endurance-trained men aged 59–79 years, muscle functional capacities are maintained despite losses in strength and contractile function related to the age.

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Use of motor units in relation to muscle fiber type and size in man

Cited by 88 publications

References 27 publications

Age-related enhancement of fatigue resistance is evident in men during both isometric and dynamic tasks

Age-related enhancement of fatigue resistance is evident in men during both isometric and dynamic tasks

Mechanism for reflex reversal during walking in human tibialis anterior muscle revealed by single motor unit recording.

Age-Related Changes in Neuromuscular Function and Performance following a High-Intensity Intermittent Task in Endurance-Trained Men

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