Effects of alternating exposure to cold and heat for 14 days on cold tolerance in winter

People are exposed to heat regularly due to their jobs or daily habits in cold winter, but few studies have reported whether parallel heat and cold exposure and diminish cold acclimation. This study was conducted to investigate the effects of alternating exposure to cold and heat on cold tolerance in eight young males. A daily acclimation program to cold and heat, which consisted of 2-h sitting at 10 °C air in the morning and 2-h running and rest at 30 °C air in the afternoon, was conducted for 14 consecutive days. Eight male subjects participated in a cold tolerance test (10 °C [ ± 0.3], 40%RH[ ± 3]) before (PRE) and after (POST) completing the alternating exposure program. During the cold tolerance test, subjects remained sitting upright on a chair for 60 min. Rectal temperature (T_re) was lower in POST than in PRE during the 60-min cold tolerance test (P = 0.027). During the cold tolerance test, systolic, diastolic, and mean arterial blood pressures in POST were lower than those in PRE (P = 0.006, P = 0.005, and P = 0.004). No significant differences in skin temperatures between PRE and POST were found for the cold tolerance test. There were no significant differences in energy expenditure during cold exposure between PRE and POST. Subjects felt less cold in POST than in PRE (P = 0.013) whereas there was no significant difference in overall thermal comfort between PRE and POST. These results suggest that cold adaptation can still occur in the presence of heat stress.     

The effect of local heating on blood flow in the finger and the forearm skin

Blood flow of the finger and the forearm were measured in five male subjects by venous occlusion plethysmography using mercury-in-Silastic strain gauges in either a cool-dry (COOL: 25 degrees C, 40% relative humidity), a hot-dry (WARM: 35 degrees C, 40% relative humidity), or a hot-wet (HOT: 35 degrees C, 80% relative humidity) environment. One hand or forearm was immersed in a water bath, the temperature (Tw) of which was raised every 10 min by steps of 2 degrees C until it reached 41 degrees or 43 degrees C. While the other hand or forearm was kept immersed in a water bath (Tw, 35 degrees C), blood flow in the heated side (BFw) was compared with the corresponding blood flow in the control side (BFc). Under WARM or HOT conditions, finger BFw was significantly lower than finger BFc at a Tw of 39-41 degrees C in the majority of subjects. When Tw was raised to 43 degrees C, however, finger BFw became higher than BFc in nearly half of the subjects. In the COOL state, finger BFw did not decrease but increased steadily when Tw increased from 37 degrees to 43 degrees C. In the forearm, BFw increased steadily with increasing Tw even in WARM-HOT environments. No such heat-induced vasoconstriction was observed in the forearm. From these results we conclude that in hyperthermic subjects, the rise in local temperature to above core temperature produces vasoconstriction in the fingers, an area where no thermal sweating takes place.     

The effect of cold and heat waves on mortality in Urmia a cold region in the North West of Iran

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The effect of mild whole-body cold stress on isometric force control during hand grip and key pinch tasks

Prolonged exposure to cold can impair manual performance, which in turn can affect work task performance. We investigated whether mild whole-body cold stress would affect isometric force control during submaximal hand grip and key pinch tasks. Twelve male participants performed isometric hand grip and key pinch tasks at 10% and 30% of maximal voluntary contraction (MVC) for 30 and 10 s respectively, in cold (8 °C) and control (25 °C) conditions. Finger temperature decreased significantly by 18.7 ± 2.1 °C and continuous low-intensity shivering in the upper trunk increased significantly in intensity and duration during cold exposure. Rectal temperature decreased similarly for the 8 °C and 25 °C exposures. Force variability (FCv) was <2% for the hand grip tasks, and <3% for the key pinch tasks. No significant changes in FCv or force accuracy were found between the ambient temperatures. In conclusion, isometric force control during hand grip and key pinch tasks was maintained when participants experienced mild whole-body cold stress compared with when they were thermally comfortable.     

The effect of muscularity on thermal responses,muscle performance,and dexterity during whole body exposure to 10 °C

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The study evaluated the effects of exposure to cold air (10 °C) on thermal responses, muscle performance and dexterity of muscular subjects and their matched lean counterparts.