What role does heat play in exercise? Part 1: Resistance exercise.

Using a within-subjects design, each participant will undertake a training intervention with one upper limb randomly assigned to cool resistance training. Cool training will attenuate exercise-induced heat accumulation with immersion in cool water (14°C) preceding (10 min) and interspersed between exercise sets (cool-trained limb is immersed in the cold water for ~2 min between sets). The contralateral (control) upper limb will train the same but without cooling. The intervention consists of 6 weeks of training with each limb training 3 times per week (~30 min each session), supervised by Masters and Honours research students. The upper limb will perform unilateral bicep curls (six sets of 4 repetitions at ~85% of 1 Repetition Maximum (1RM), spaced 3 min apart) with exercise loads being progressed during the 6-week period, increasing ~5% 1RM when arms were able to complete more than 4 repetitions on the final set. Measurements: Pre- and post-intervention: Testing will take place before the initiation of training and at least 48 hours after completing training, respectively, using 4 assessments. First, dynamic strength will be assessed by the 1RM across a full range of motion. The 1RM will also be used to provide relative training intensities. Second, isometric torque will be assessed using a Maximial Voluntary Contraction (MVC) at a standardised joint angle with the elbow joint at 90° flexion. This static method of strength assessment is less impacted by improved coordination in dynamic 1RM tests. Third, twitch interpolation will be done in the same position (90° flexion) to determine physical contractile characteristics of the muscle (i.e., rate of force development and decay). Fourth, force production will be assessed also using isokinetic dynamometry (60°/s) at the elbow joint to determine the general ability to produce force during elbow flexion. Anthropometry will be assessed to measure tissue adaptations to exercise training. This entails (i) eight-electrode multi-frequency bioelectric impedance analysis, (ii) girth and skinfold thickness of limb segments at the point of maximal circumference and ultrasound assessment of each upper arm, and (iii) dual-energy X-ray absorptiometry as an additional measure of change in upper limb muscle mass and whole-body composition. Acute Training: Blood flow measures (duplex ultrasound and near-infrared spectroscopy), perceptual measures, including rating of perceived exertion, perceived body temperature and associated thermal comfort will be assessed in both the warm and the cool arms during training. This is to determine the physiological and perceived strain of training with and without exercise induced heat strain.