Heating of the whole body by immersion in water for short periods (Vernon, 1924) or of a limb by application of hot fomentations (Hall, Schamp, Brown & Davis, 1944; Hall, Munoz & Fitch, 1947) has been shown to reduce the strength and duration of voluntary rhythmic and sustained contractions. More recently, Nukada & Muller (1955) and Nukada (1955) showed that when a limb was immersed for a short period in water ranging from 10 to 400 C (rhythmic contractions) and from 20 to 400 C (sustained contractions) the duration of contractions to fatigue steadily increased from the higher to the lower water temperatures. These experiments on human subjects have led all these observers to the conclusion that the influence of temperature on the performance of muscular contraction is due to alterations in the proportion of blood flowing through the muscle and the skin of the exercised limb.The possibility that the temperature of the muscle might be associated with the duration or strength of contraction has been dismissed by these workers, but the evidence of Ellis & Beckett (1954) and Hadju (1951) casts some doubt on the validity of such a conclusion. Working with isolated muscle preparations, they showed that both strength and duration of contractions, in the absence of a blood supply, depend on muscle temperatures.Lind & Samueloff (1957) measured in man the duration of successive sustained contractions when the interval between the contractions was varied and when the arm was kept in water at 18 or 340 C throughout the experiment. They found that contractions were always longer in water at 180 C when the interval between contractions was 20 or 40 min.The present experiments were designed to discover (a) whether there was a further deterioration in muscular performance when the forearm was heated in water above 340 C, and (b) if further improvement occurred in the strength and duration of contractions when the water was cooler than 180 C. Blood flow, muscle temperatures and action potentials were measured on the exercised

No abstract

The influence of temperature on the amplitude and frequency components of the EMG power spectra of the surface EMG recorded over the forearm muscles was examined in five male and five female subjects during brief and fatiguing isometric contractions of their handgrip muscles. Brief (3 s) isometric contractions were exerted at tensions ranging between 10 and 100% of each subject's maximum strength while fatiguing contractions were exerted at tensions of 25, 40, and 70% of their maximum strength. The temperature of the muscles during those contractions was varied by placing the forearms of the subjects in a controlled temperature water bath at temperatures of 10, 20, 30, and 40 degrees C. The results of these experiments showed that the center frequency of the power spectra of the surface EMG was directly related to the temperature of the exercising muscles during brief isometric contractions. During fatiguing isometric contractions, the amplitude of the EMG increased while the center frequency of the EMG power spectra decreased for all tensions examined.

No abstract

No abstract

Three subjects walked continuously on a treadmill for periods of 1 hr or more at 180, 300, or 420 kcal/hr in a range of cool and hot climates from corrected effective temperature (CET) 10–32 C. At each rate of work rectal thermal equilibrium was practically independent of the influence of environment over a wide range of climates (“prescriptive” zone); the upper limit of the prescriptive zone appeared to be associated with the minimal bodily thermal gradient compatible with the transfer of adequate amounts of heat from the core to the periphery without placing the thermoregulatory system under disproportionately increased strain, in terms of circulatory response and elevated body core temperature; as such, this seems to be one possible criterion by which thermal environmental limits for everyday work may be assessed. The upper limits of prescriptive zones for work at an energy expenditure of 300 kcal/hr is CET 27.4 C and those for the lower and higher rates of work, respectively, were CET 30.2 C and 26.9 C. Submitted on June 15, 1962

SUIMMARY1. The cardiovascular responses to sustained hand-grip contractions at 20, 30 and 50 % maximal voluntary contraction (MVC) were measured in subjects who were engaged in treadmill walking at three different rates with oxygen intakes of 11, 1-7 and 2-8 1./min. The increments in heart rate and blood pressure at tensions of 20 and 30 % MVC were similar at all rates of walking, but the response to a contraction at 50 % MVC was lower at the hardest work rate than at the two easier rates.2. When two or more muscle groups contracted at the same relative tension, the increments in heart rate and blood pressure were the same, whether they contracted separately or together.3. When two or more muscle groups contracted simultaneously at different relative tensions, the increments in heart rate and blood pressure were the same as when the muscle group, at the higher relative tension, contracted separately at that tension.4. The blood flow to a muscle engaged in sustained contraction was increased when a second muscle group contracted at a higher relative tension.

SUMMARY1. When diluted human plasma is perfused through a frog heart, a marked augmentation of the heartbeat is produced which is very similar in action to that of low concentrations of adenosine triphosphate (ATP) on the heart. 2. It was established that the substance in the plasma responsible for the heart stimulation was ATP. The following tests were used: (a) the diluted plasma emitted light from firefly lantern extract characteristic of the light signal produced by a solution of ATP; (b) the stimulatory effect on the frog heart and luminescent effect upon the firefly extract were abolished by incubation of the plasma solution with the enzyme apyrase, which converts ATP to adenosine monophosphate (AMP); AMP does not stimulate the heart or cause light to be emitted from firefly extract; (c) the stimulatory substance in the plasma was eluted through a column of Sephadex G-25 in the same pattern as ATP; and (d) simultaneous assay of plasma solutions on frog heart and firefly extract produced the same quantitative result as that produced by a solution of ATP.3. The amount of ATP in plasma from the venous blood of resting subjects ranged from 0*19 to 0 95 ,ug/ml. (mean 0-63 ,tg/ml., S.D. + 0 25); up to half of the ATP detected could be attributed to blood platelet damage. Simultaneous arterial and venous samples of blood from four subjects at rest had mean concentrations of 0-19 ,ug/ml. (0-07-0-26 ,ug/ml.) and O70 ,ug/ml. (0.57-0.84 ,tg/ml.) respectively.