Influence of temperature on muscle and vascular adaptation to exercise
Nielsen, Leland James
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In our lab, we have observed that the lower limbs of individuals with spinal cord injury (SCI) are typically colder (up to 10°C) when compared to those of able-bodied individuals. This is a result of a decrease in metabolic rate, blood flow, and muscle activity in the legs. In addition to considerations such as temperature regulation, training people with SCI and other special populations by traditional methods is inherently difficult. Some evidence exists using rat models that warm temperature can enhance the hypertrophy response to resistance training. Increased temperature also increases local blood flow. This research was conducted to determine if temperature influences muscle and vascular adaptations to resistance (study 1) and muscle endurance (study 2) training, respectively, in healthy, able-bodied participants. Subjects performed forearm exercise training with one arm in a warm condition (42-44°C) and one arm in a cool condition (18-20°C). Subjects in study 1 trained 3 times per week for 10 weeks, completing 4 sets of wrist curls at 5-repetition maximum (5-RM) with each arm. Lean tissue mass of the forearm (dual energy x-ray absorptometry) and forearm strength 1RM) was measured before and after training. Subjects in study 2 trained 4 times per week for 5 weeks completing 400 wrist curls per arm over a 20-min span (20 reps per min). The resistance was set at 15% of their 1-RM for each arm and progressed as tolerated. Arterial range, resting diameter, and peak blood flow were measured in the radial artery before and after training. Forearm strength (study 1) increased in both the warm and cool arms with no difference between temperature conditions. Forearm lean tissue mass did not change and there was no temperature effect. In study 2, arterial range, resting diameter, and peak blood flow in the radial artery did not change from pre to post in either arm. Increasing muscle temperature did not enhance muscle strength or muscle hypertrophy following resistance training and did not enhance vascular adaptations following muscle endurance training in able-bodied subjects. Our findings suggest that temperature is not an important factor in altering arterial remodeling or muscular characteristics with training.