Influence of time of day on all-out swimming

The effect of time of day on all-out swim performances was examined. Fourteen subjects performed maximal front crawl swim tests on separate days over 100 m. and 400 m. at 5 different times of day between 06.30 h. and 22.00 h. Performance showed a significant linear trend with time of day in close though not exact association with the circadian rhythm in oral temperature: a goodness of fit test confirmed that the values predicted from linear trend analysis coincided with the measured values (p less than 0.05). The steady improvement throughout the day was 3.5% for 100 m. and 2.5% for 400 m. swims. Trunk flexibility displayed a time of day variation with a trough in the morning and a peak in the afternoon. No significant rhythm was observed in ankle and shoulder flexibility, grip strength or peak expiratory flow rate (p greater than 0.05). It was concluded that maximal swimming trials are best scheduled for the evening and worst in the early morning. Specific fitness factors cannot clearly account for the higher exercise capability in the evening which is strongly related to the circadian curve in body temperature.

Influence of time of day on reactions to cycling at a fixed high intensity

The circadian cycle in all-out competitive performance may be due to changes in motivational drive to tolerate strenuous exercise rather than to rhythms in maximal physiological functions. This experiment explored the hypothesis that a fixed relative loading of high intensity aerobic effort could be sustained for longer in the evening compared with the morning. Eight females cycled to exhaustion at 95% VO2 max at 06.30 h. and at 22.00 h. after a 5 min, moderate load of 40% VO2 max. Oral temperature was 0.4 degrees C higher at 22.00 h. compared with the earlier time. Perceived exertion showed no significant effect of time of day at either work load but exercise tolerance time, total work done and peak lactate production were significantly greater at 22.00 h. (p = 0.05). Perceived exertion at the high load was significantly related to endurance time (r = -0.77) and to the rating at the low work level (r = 0.75). Peak lactate was not significantly correlated with the time to exhaustion (p less than 0.05). It was concluded that superior exercise performance in the evening may be attributed to a greater tolerance for high intensity exercise which is closely associated with the acrophase in body temperature.

Effect of age on angiotensin II receptors from rat brain

1. Angiotensin II receptor binding was studied in specific regions of rat brain at different ages from birth to 14 weeks. 2. The number of specific angiotensin II receptors increased in all regions during the first 2 weeks of life and then decreased to adult levels. Peak numbers of receptors were up to 10 times the adult numbers. 3. The midbrain and thalamus-hypothalamus had maximum numbers of angiotensin II receptors at 2 weeks of age, whereas the rest of the brain regions had maximum number at 1 week. 4. Saralasin-infusion experiments suggested that circulating angiotensin-related peptides could reach brain angiotensin II receptors in 2 week old rats, but not in 6 week old rats. 5. It is postulated that the centrally mediated actions of circulating angiotensin II may be particularly important in the newborn.

The use of Technetium-99m stannous pyrophosphate scintigraphy to identify muscle damage in acute electric burns

High-voltage electric burns are often associated with deep muscle damage in addition to a limited cutaneous burn. Technetium-99m stannous pyrophosphate (99mTc-PYP) scintigrams were evaluated as a diagnostic tool to detect and localize both large and focal areas of skeletal muscle necrosis. Scintigrams were performed in 14 patients between the first and fifth postinjury days and imaging was done over areas of suspected and clinically apparent muscle injury. Muscle damage was identified by an increased cellular uptake of the tagged material. All 14 patients had gross and histologic evidence of muscle necrosis. Muscle necrosis was identified as early as 24 hours and as late as 6 days postinjury. The location and extent of muscle injury was correctly ascertained preoperatively in all patients.

Plasma renin activity, plasma angiotensin II and extracellular fluid volume in patients after renal transplantation

1. Patients with cadaveric renal transplants and plasma creatinine less than 177 micronmol/l who had their own kidneys removed were studied. 2. The renin-angiotensin system appeared to behave in a normal fashion in response to alterations in sodium intake and posture. 3. The renin-angiotensin system had no major role in the establishment or maintenance of hypertension. 4. Mean arterial pressure was directly related to expansion of the extracellular fluid volume.