Fatigue of voluntary contractions in normal and myasthenic human subjects

Secher, N. H.; Petersen, Sune Høirup

doi:10.1111/j.1748-1716.1984.tb07507.x

Cited by 7 publications

(4 citation statements)

References 9 publications

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“…Nevertheless, the pattern of exercise changed dramatically with partial neuromuscular blockade in that the smooth rotating movement of the crank could not be kept up but was disintegrated into separate 'kicks' by alternating use of the left and right leg. The recruitment pattern may be comparable to the pattern seen during sustained static exercise in experiments with tubocurarine (Secher, R0rsgaard & Secher, 1978; Leonard, Mitchell, Mizuno, Rube, Saltin & Secher, 1985) as well as in myasthenic subjects fatigued by static exercise (Secher & Petersen, 1984). Under these conditions a forceful contraction cannot be maintained for more than approximately half a second.…”

Section: Discussionmentioning

confidence: 62%

Cardiovascular, ventilatory and catecholamine responses to maximal dynamic exercise in partially curarized man.

Galbo

Kjær

Secher

1987

The Journal of Physiology

101

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SUMMARY1. In ten young men the ventilator, cardiovascular, catecholamine and metabolic responses to maximal dynamic leg exercise on a stationary bicycle were followed during partial neuromuscular blockade with tubocurarine. Maximal exercise was performed when the drug effect was at its maximum as well as during the subsequent reduction in the effect allowing a gradually increasing work intensity. The results were compared with those obtained during submaximal and maximal exercise performed without tubocurarine. Partial neuromuscular blockade decreased hand-grip strength to 41±+ 1-1 % (s.E. of mean) and the maximal work load to 27 + 2-4% of control values. Voluntary effort was maximal and the rate of perceived exertion was high at all levels ofexercise with tuboeurarine indicating a maintained intense central nervous motor command.2. During maximal action of the drug oxygen uptake was 1-67 + 0-11 1/min while only 0-91 + 0-13 1/min (P < 0-01) at the same work intensity without neuromuscular blockade. This difference may reflect a dominant reliance on fast-twitch muscle fibres when work was performed under the influence of tubocurarine.3. Compared at a given oxygen uptake ventilation was higher during work with tubocurarine than during control exercise (e.g. 55 + 4-2 and 40 + 2-2 1/min, respectively (P < 0-01), at a mean oxygen uptake of 1 9 1/min), while heart rate did not differ significantly (146 + 4-4 and 139 + 3-0 beats/min). With decreasing drug effect both variables increased towards the maximum values of 138 ± 4-5 1/min and 183 + 3.9 beats/min, respectively, achieved in control experiments at an oxygen uptake of 3-8 ± 0-2 1/min. Like heart rate the mean arterial blood pressure increased with increasing work load and was similar at a given oxygen uptake with and without tubocurarine. 4. During maximal exercise at peak tubocurarine effect plasma adrenaline and noradrenaline concentrations were smaller than during control maximum, 1-6 + 0-27 versus 3-4 +0-55 nmol/l (P < 0-01) and 7-5 + 1-3 versus 12-6 + 1-8 nmol/l (P < 0-05), respectively. However, comparisons at identical oxygen uptake rates revealed that catecholamine responses were markedly enhanced during tubocurarine treatment.Also, blood lactate concentrations were smaller at peak tubocurarine action than H. GALBO AND OTHERS during control maximum, 19+0042 mmol/l and 641+0-49 mmol/l (P < 001). In contrast the concentration of free fatty acids was higher in tubocurarine experiments: 0.5 + 0-07 against 0-3 + 0-03 mmol/l (P < 0-01) in agreement with the view that lactate inhibits the release of free fatty acids.5. The higher ventilations and plasma catecholamine values at given oxygen uptake rates in tubocurarine compared to control experiments suggest that activity in motor centres in the central nervous system (central command) has a role in regulation of these variables. On the other hand ventilation, heart rate, arterial blood pressure and, less so, catecholamine concentrations were much smaller than during control maximal exercise, and increased as abs...

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Section: Discussionmentioning

confidence: 62%

Cardiovascular, ventilatory and catecholamine responses to maximal dynamic exercise in partially curarized man.

Galbo

Kjær

Secher

1987

The Journal of Physiology

101

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“…The slow rate of rise of tension seen in the weak graded voluntary muscle was also reported by Secher & Petersen (1984). However, in a myasthenic patient they saw a brisk force development at all contraction intensities.…”

Section: Discussionmentioning

confidence: 75%

Heart rate at the onset of static exercise in man with partial neuromuscular blockade.

Secher¹

1985

The Journal of Physiology

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In human subjects the length of the first complete cardiac cycle after the onset of static finger or hand muscle contractions was recorded. Graded contractions as well as maximal contractions in which muscle fatigue was provoked by ischaemia were studied. Maximal finger muscle contractions were also weakened by partial neuromuscular blockade with either decamethonium or tubocurarine. The change in R‐R interval at the onset of exercise was variable and in part dependent on the length of the last R‐R interval before the onset of exercise. The largest decreases were seen when the preceding R‐R interval was long. During graded submaximal and maximal contractions a correlation was demonstrated between the change of the R‐R interval at the onset of exercise and the contraction intensity. At the onset of the weakest contractions a 3% prolongation of the R‐R interval was seen while the strongest contractions were associated with a shortening of 8%. At the onset of all maximal contractions, whether fatigued due to ischaemia or weakened by decamethonium or tubocurarine, a decrease in R‐R interval was seen independent of the force developed. When compared at the same resting R‐R interval, contractions performed with hand muscles elicited a greater shortening of R‐R interval than contractions with finger muscles. The results suggest that the initial change in heart rate at the onset of static muscle contractions is related to the voluntary effort rather than to the force developed, the state of the working muscles or to the type of muscle fibres involved. It may thus be elicited by 'cortical irradiation' rather than by a 'muscle‐heart reflex'. Its size depends on the length of the preceding R‐R interval, the intended contraction intensity and the muscle mass involved.

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“…2006), and in response to repeated maximal isometric and dynamic contractions with a finger (Mosso 1904), the hand (Secher et al. 1983, Secher & Petersen 1984), and the arm (Asmussen & Mazin 1978). During whole body maximal exercise, arterial deoxygenation reduces the near‐infrared spectroscopy (NIRS)‐determined cerebral O 2 haemoglobin saturation ( S C O 2 ) (Nielsen et al.…”

mentioning

confidence: 99%

Cerebral oxygenation decreases during exercise in humans with beta‐adrenergic blockade

et al. 2009

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Fatigue of voluntary contractions in normal and myasthenic human subjects

Cited by 7 publications

References 9 publications

Cardiovascular, ventilatory and catecholamine responses to maximal dynamic exercise in partially curarized man.

Cardiovascular, ventilatory and catecholamine responses to maximal dynamic exercise in partially curarized man.

Heart rate at the onset of static exercise in man with partial neuromuscular blockade.

Cerebral oxygenation decreases during exercise in humans with beta‐adrenergic blockade

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