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  • 1
    ISSN: 1432-1106
    Keywords: Motor unit types ; Twitch and tetanic tensions ; Potentiation ; Peroneus tertius muscle ; Cat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Motor units of the cat peroneus tertius muscle were systematically analyzed using the criteria established by Burke et al. (1973). On the basis of their speed of contraction and resistance to fatigue, 121 (97%) of 125 motor units examined in ten adult cats could be classified as belonging to one of four types: fast-fatiguable (FF), fast-resistant (FR), fast-intermediate (FI), and slow-resistant (S). Peroneus tertius was found to contain 30% FF motor units, 9% FI units, 39% FR units, and 22% S units. Contraction times of fast motor units (FF, FR, and FI) ranged from 15 to 27 ms and those of S units from 26 to 42 ms. The mean tetanic tensions were 37 g for FF units, 29 g for FI units, 7.5 g for FR units, and 1.1 g for S units. Fast motor units displayed considerable post-tetanic potentiation of twitch tension. Under similar conditions of stimulation, FF units appeared able to potentiate more and faster than FR units.
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  • 2
    ISSN: 1432-1106
    Keywords: Muscle spindle ; Fusimotor ; Afferent ; Intrafusal contraction ; Cat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Responses of secondary endings of muscle spindles of the peroneus tertius muscle of the anaesthetized cat have been recorded during repetitive stimulation of functionally single fusimotor fibres that produced slowing of the discharge. In a sample of 125 pairs of single fusimotor fibres and secondary spindle afferents 5 examples of slowing were seen. The amount of slowing became less at longer muscle lengths. Conditioning the spindle by stimulating the muscle nerve at fusimotor strength, at a length 2.5 mm longer than the test length, and then returning to the test length 3 seconds later led to a greater degree of slowing of the discharge than after conditioning stimulation at the test length. With one exception, responses to muscle stretch were reduced during stimulation of a fusimotor fibre that produced slowing. On two occasions stimulating a fusimotor fibre that produced slowing of the response of one secondary ending, led to excitation of two other endings. Two possible explanations for the generation of slowing responses have been considered. The first is that the slowing is the result of contraction of the region of intrafusal fibre directly underlying the secondary sensory ending. The second, which we favour since it accounts for the facts more adequately, is that slowing is the result of shortening of the region of nuclear chain fibres on which the sensory ending lies, produced by movement in an adjacent nuclear bag fibre.
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  • 3
    ISSN: 1439-6327
    Keywords: Heart Rate ; Body Temperature ; Exercise ; Fréquence cardiaque ; Température corporelle ; Exercice
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Résumé L'évolution comparée de la fréquence cardiaque et de la tempërature corporelle est mesurée chez 23 sujets effectuant des exercices musculaires d'une durée d' 1/2 H, avec un métabolisme d'environ 1 L O2/min, à température très élevée (ts 46 °C; th 35 °C). La relation qui unit ces deux paramètres est linéaire tout au moins pour la partie moyenne du diagramme. Pour les valeurs plus faibles, en-dessous de 100 pulsations/min, la fréquence cardiaque est influencée de façon variable par la température corporelle. Au-delà de 170 pulsations/min, la fréquence cardiaque, approchant de sa valeur maximum, n'est plus fonction de l'hyperthermie. L'amplitude de la réaction cardiaque présente de grandes variations individuelles. En moyenne, une élévation de température interne de 1 °C entraîne une accélération cardiaque de 32,3 pulsations/min, cependant, les extrêmes s'étendent de 21 à 46 pulsations/min. La linéarité de la relation justifie l'emploi de la fréquence cardiaque comme témoin d'une surcharge thermique pendant le travail musculaire à haute température. Le comportement individuel est un reflet de l'aptittide de chaque sujet à supporter les températures élevées.
    Notes: Summary Heart rate and body temperature were measured in 23 men walking on a treadmill during 1/2 an hour in a very hot environment (ta 46 °C; twb 35 °C), with an energy expenditure of about 11 O2/min. A linear relationship was found between the two parameters, at least for the middle part of the diagram. For lower values, below 100 beats/min, heart rate is influenced in a variable manner by the body temperature. Above 170 beats/min, heart rate approaches its highest value, and is hence no more influenced by hyperthermy. From one subject to another, the extent of cardiac reaction varies considerabily. On the average, when body temperature increases by 1 °C, heart rate increases by 32,3 beats/min, but extreme values are 21 and 46 beats/min. The linearity of the diagram justifies the use of heart rate as a reference of a thermal overloading during muscular exercise in hot environment. The individual comportment truly reflects each subject's capacity in bearing hot climates.
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  • 4
    ISSN: 1439-6327
    Keywords: Working capacity ; Hot environment ; Heart rate ; Bodytemperature ; Capacité de Travail ; Ambiance chaude ; Fréquence cardiaque ; Température corporelle
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Résumé Chez 57 sujets les résultats d'épreuves d'ergospirométrie en ambiance normale sont comparés à ceux de cinq épreuves effectuées en chantier à température élevée. On n'observe aucune relation significative entre l'aptitude physique en ambiance normale mesurée par la consommation maximum d'O2, le régime stable limite selon Petit et coll. ou la VO 2/170 et la tolérance à la chaleur estimée en chantier. Un exercise effectué à température ordinaire ne suffit donc pas pour prédire la tolérance à un effort à haute température; il peut cependant servir à une présélection. Les critères de sélection sont ensuite recherchés en étudiant les réactions physiologiques lors d'épreuves d'ergospirométrie en ambiance chaude. Cette dernière consiste en un exercice d'intensité modérée (11 O2/mn), d'une durée prolongée pendant 1/2 h, dans une ambiance très chaude (t s 46 °C;t h 35 °C). Dans ces conditions, la température centrale n'est pas toujours représentative de la contrainte thermique et la fréquence cardiaque paraît constituer un critère préférable parce que plus sélectif et plus limitatif. La valeur absolue de la fréquence cardiaque fournit un témoin synthétique de la contrainte globale entraînée conjointement par le travail musculaire et l'ambiance chaude. L'adaptation à ces deux sollicitations cardio-vasculaires n'est pas nécessairement parallèle et pour chaque individu on peut en préciser les modalités. La fréquence cardiaque mesurée pendant un exercice physique en ambiance normale précise les possibilités circulatoires musculaires. L'évolution du pouls en fonction de rhyperthermie apprécie la tolérance à la contrainte thermique.
    Notes: Summary Working capacity of 57 subjects was assessed comparatively in heat and in normal conditions. No significant relation was found between tolerance to heat estimated in hot environment and working capacity in normal conditions measured either by maximal oxygen intake, either by the “régime stable limite” according to Petitet al. or PWC/170. An exercise in normal environment is insufficient to predict the tolerance to work in heat; meanwhile it can help to make a first selection. Afterwards, an inquiry after selection tests was made studying the physiological reactions during exercise in heat. This exercise consisted in walking slowly ( $$\dot V_{{\text{O}}_{\text{2}} } $$ = 11O2/min) during 1/2 hr, in a very hot environment (td = 46 °C;t w = 35 ° C). In such conditions, the central temperature did not always represent the thermal load; the heart rate seems to be a better criterion because it was more selective and more restrictive. The absolute heart rate synthesizes the global stress caused both by muscular exercise and hot environment. The adaptation to both cardio-vascular solicitations does not necessarily induce parallel responses; but it is possible to precise the modality for everyone. The heart rate measured during muscular exercise in normal conditions precises the circulatory possibilities in muscles. The pulse evolution related to hyperthermy reflects the tolerance to thermal stress.
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