ABSTRACT
Purpose: The purpose of this study was to examine the relationship among helmet surface temperature (Thl), head top temperature (Thd) and tympanic temperature (Tty) during American football practice in summer. Methods : The subjects were collegiate American football players. Temperatures were measured in August in 1993 and 1994. Thl, Thd and Tty were measured by infrared tympanic thermometers. Environmental temperatures that were measured were dry-bulb temperature (Td), wet-bulb temperature (Tw), globe temperature (GT) and wet-bulb globe temperature (WBGT) . Results: Significant correlations were observed among all measured temperatures (P<0.0001) . High coefficients of correlation were observed among Thl, Thd and GT. The highest relationships were observed between Thl and Thd (r=.727), and between Tty and Td (r=.766) . The coefficient of correlation between Tty and Thl was higher than that between Tty and Thd. Heat stress of the whole body (F1; heat stress factor: Tty, Td, Tw and WBGT, proportion=71.4%) and head environment factor (F2 ; helmet factor : Thl, Thd and GT, proportion=14.3%) were chosen in factor analysis. A close relationship was observed between both factors (r=.773) . Both GT and Thl showed a high correlation with Thd, which suggests the influence of radiant heat through a helmet on the whole body. Conclusion : The temperature in a helmet is a micro environment temperature surrounding the head. Accordingly, the heat load is reduced by taking the helmet off frequently during football practice.
ABSTRACT
A study was conducted to examine the effects of exhaustive enduring exercise training on the skeletal muscle of rats. Twenty-six male Wistar rats were divided into 3 groups : an exhaustive training group (EE), a free-eating control group (Co), and a pair weight group in which body weight was matched to EE (PW) . The rats in EE were forced to run on a treadmill with an inclination of 0-3°, 6 days/week for 4 weeks. At first the rats ran at a constant speed for 60 min. Then we gradually added 2 m/min to the basic speed every minute until they were exhausted. The treadmill speed was 20 m/min during the first, 30 m/min during the second, 35 m/min during the third, and 40 m/min during the final week. The muscle wet weight, the quantity of the muscle protein and the isometric tetanic force were measured with the soleus and extensor digitorum longus (EDL) . Food restriction induced significant decreases in EDL weight. Exhaustive enduring exercise training induced noteworthy decreases in soleus weight, but remarkable gains in EDL weight. It also induced significant changes of the quantity of the muscle protein in the two muscles, which corresponded to the changes in muscle weight. The isometric tetanic force of both muscles was not affected by food restriction. The isometric tetanic force showed a significant decreases in EDL in EE comparison Co. The isometric tetanic force of the soleus did not show a significant decreases. However, its degree of decrease corresponded to that of the muscle protein. These findings illustrate that exhaustive endurance exercise training induces degradation of the soleus and hypertrophy of the EDL. However, it also decrease the muscle force which generats the capacity of the two muscles. We think that this phenomenon depends on the skeletal muscle characteristics, such as fiber type, and eccentric or concentric contraction.