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At least 1,279 records · Page 71Linked to original sources
PubMed1979

Isometric muscle contraction response during recovery from reduced intramuscular temperature.

This study was done to determine the effects of a 30-minute cold water bath on intramuscular temperature and plantar flexion strength, immediately after treatment and during a 3-hour posttreatment recovery period. Twenty persons were tested twice, receiving treatment once and serving as controls once. Measurements were taken prior to the treatment period, immediately after treatment and then every 30 minutes for 3 hours. The dominant leg was submerged in water at 10 C for 30 minutes. Plantar flexion strength was measured with a cable tensiometer and intramuscular temperature was measured with a hypodermic thermistor probe. Intramuscular temperature significantly decreased immediately posttreatment on the experimental days and then increased significantly during the recovery period. Significant increases in strength were noted during the recovery period. A definite relationship exists between intramuscular temperature and plantar flexion strength.

Adult↗
PubMedDate not supplied

Effect of dehydration and a few regimes of rehydration on human performance.

The present study was prompted by the controversy about the effect of heat-induced dehydration on human performance, and the popular Indian belief that it is not advisable to take water immediately after prolonged exertion in the sun. The points investigated were: (i) the effect of dehydration on some aspects of physical and mental performance, and (ii) variation in the post-dehydration performance caused by the timing of rehydration. Dehydration amounting to 2% of body weight did not impair mechanical efficiency while 3% dehydration reduced the endurance time for isometric contraction of extensors of the forearm. The maximum isometric tension and mental performance, measured by proof reading and a choice reaction time experiment, were not affected. The studies suggested that once dehydration had been produced, rehydration or its timing did not make any difference. Analysis of the results in terms of the sequence in which the experiments were done suggested the influence of psychological factors on the performance measured.

Adult↗
PubMedDate not supplied

[Application of the Doppler examination to the study of changes in the venous circulation of muscles during exercise].

The authors use Doppler examination to study the functional hyperaemia of healthy muscle during muscle contraction. In the leg, isometric contraction of the gastrocnemii produces: 1) a flush effect, rapid but transient (1 to 2 sec.); 2) next a speed intermediate between that at peak and that at rest; 3) finally, a post-contractile hyperaemia. In the case of isotonic contractions, the same type of tracing is oberved more clearly for dorsal flexion of the foot (dorsiflexion) than for plantar flexion (extesion), and this occurs whether the mode of movement is active or passive. In the normal untrained subject, fatigue due to repetition of movement occurs very quickly, whatever the conditions, and results in a diminution of the venous flush. But in the trained subject, this effect does not appear, or not till much later.

Adolescent↗
PubMed1990

Contractions to 5-hydroxytryptamine in human coronary artery and human saphenous vein.

Isometric contractions were obtained to 5-hydroxytryptamine receptor agonists in human saphenous vein and human coronary artery. Based on the interaction with the 5-HT2 receptor antagonist ketanserin, both 5-HT1 and 5-HT2 receptors are involved in contractions of human saphenous vein, but the predominant subtype involved in contractions of human coronary artery is the 5-HT1 receptor.

Coronary Vessels↗
PubMed1980

Strength of isometric and isokinetic contractions: knee muscles of men aged 20 to 86.

Maximum isometric and isokinetic torques of the knee flexor and extensor muscles were measured at three knee joint positions in 72 normal, health men in three age groups from 20 to 86 years. The isokinetic contractions were performed at a speed of 36 degrees per second. The isometric contractions were sustained for five seconds. Strength of the men in the older age groups was significantly less than that of the youngest group. The strength of the isokinetic contractions was significantly less than that of the isometric contractions for all joint positions. The men in the oldest age group generally took longer than the younger men to reach peak torque during the isometric contractions. The torque values provide base-lines for evaluating patients with knee joint disabilities.

Adult↗
PubMed2004

Is the blood flow response to a single contraction determined by work performed?

Nine healthy volunteers performed a series of single handgrip isometric contractions to test the hypothesis that the blood flow response to a contraction is determined solely by the tension-time index (isometric analog of work). Contractions were performed in duplicate at 15, 30, and 60% of maximal voluntary contraction (MVC) at durations of 0.5, 1, and 2 s. Forearm blood flow (FBF) was measured beat by beat by using Doppler ultrasound. Peak FBF responded in a graded fashion to graded increases in peak tension with contraction time held constant (35, 56, and 90 ml/min for 15, 30, and 60% MVC for 1 s, respectively). When tension was kept constant, peak FBF responded in a graded fashion to graded increases in duration (77, 90, and 97 ml/min for 60% MVC for 0.5, 1, and 2 s). With a constant tension-time index, peak FBF responded in a graded fashion to graded increases in peak tension (48, 56, and 77 ml/min for 15% MVC/2 s, 30% MVC/1 s, and 60% MVC/0.5 s). Similar trends were also observed for total postcontraction hyperemia. Blood flow increased regardless of whether the change in tension-time index was accomplished by an increase in tension or duration of contraction. However, with a constant tension-time index, the change in blood flow was related to the peak tension developed. Our results suggest that the blood flow response to a single muscle contraction is not determined solely by the work performed (tension-time index) but also by the number of muscle fibers recruited.

Adult↗
PubMed1984

The relationship between action potential duration and force of contraction in rat myocardium.

Intracellular action potentials and peak force (F) of isometric contractions were recorded from ventricular trabeculae of adult rats at 26 degrees C. The duration of the action potentials was measured at 50% of the amplitude (APD50) and at 10% of the amplitude (APD10). The effect of a variety of experimental interventions on the three variables was studied. APD50 reflects the duration of the plateau phase which is typically about 30 ms in rat myocardium. APD10 reflects the sum of the duration of the plateau phase and of the slow final repolarization phase (phase 3') and is about 80 ms. During paired-pulse stimulation, strong contractions coincided with shortened APD50 and prolonged APD10, i.e. a negative APD50-F and a positive APD10-F relationship was obtained. Addition of Sr2+ to the medium caused an increase of F and prolongation of APD50 and APD10. Nifedipine caused a decrease of F and a shortening of APD50 and APD10. Substitution of extracellular NaCl by LiCl caused an increase of F but a shortening of APD50 and APD10. An increase of [Ca2+]o caused an increase of F whereas APD50 was almost constant and APD10 increased. A simple model is proposed which explains the results, assuming that: the effect of paired-pulse stimulation is related to time dependent intracellular Ca2+ transport; Sr2+ and nifedipine act mainly on isi; NaCl substitution inhibits Na+/Ca2+ exchange; and [Ca2+]o affects both isi and Na+/Ca2+ exchange.

Action Potentials↗