Author(s): PETERSEN, A., CHANDRASIRI, S., STOREY, A., GARNHAM, A., HADIYAN, H., HAMEED, A., NELSON, A., Institution: VICTORIA UNIVERSITY, Country: AUSTRALIA, Abstract-ID: 1410

INTRODUCTION:
Whole-body or localised heating can increase the anabolic and strength responses to resistance exercise. However, it is unknown whether concurrent whole-body heating can improve performance or muscle mass adaptations during long-term resistance training. We therefore investigated the effects of whole-body heat stress applied concurrently during resistance training on muscle mass, strength, speed, agility, force and anabolic signalling in males.
METHODS:
Eighteen recreationally active males were assigned to HEAT (n = 8, age = 23.3 ± 3.1 years, body mass (BM) = 75.6 ± 14.5 kg, height = 175.6 ± 8.8 cm) or CON (n = 10, age = 21.0 ± 2.7 years, BM = 76.0 ± 11.3 kg, height = 177.2 ± 9.6 cm). Each group undertook 10 weeks of full body resistance training three days per week. CON trained at 23°C, relative humidity 25%, while HEAT trained at 40°C, relative humidity 30%. Strength (1RM leg and bench press), speed (5 and 10 m sprint), agility (T-test), peak force (during squat jump and ballistic push up) and body composition (DXA scan) were assessed at pre-, mid- (week five) and post-intervention. Vastus lateralis muscle biopsies were taken before, 1 h and 48 h after intensity-matched training sessions conducted pre- and post-intervention. Core body temperature and vastus lateralis muscle temperature were measured during the second training session via ingestible telemetric capsule and indwelling thermistor, respectively.
RESULTS:
Despite the much higher environmental training temperature for HEAT, peak core body temperature and peak muscle temperature were not significantly different between CON (38.0 ± 0.2°C; 36.0 ± 0.5°C) and HEAT (38.2 ± 0.1°C; 36.8 ± 0.6°C). Leg press 1 RM increased similarly in both CON (50.25 ± 13.99 kg, p<0.05) and HEAT (32.75 ± 5.89 kg, p<0.05) while bench press 1RM showed no improvement in either group. No improvements were observed in 5 m or 10 m sprint time, agility, or peak force generated during a squat jump or ballistic push up in either group. Total body lean mass and appendicular lean mass increased in CON only by 3.2% and 2.8%, respectively. Upper body lean mass increased and lower body lean mass was unchanged, with no differences between groups. Type I and Type II muscle fibre cross-sectional areas increased in CON only. Myonuclear density increased only in CON, whereas the increase in satellite cell content was not different between HEAT and CON. Markers of the mTOR signalling pathway (total and phospho- Akt, mTOR, p70S6k, 4E-BP1, rpS6) were largely similar between HEAT and CON.
CONCLUSION:
These results indicate that, despite no effects on core or muscle temperature, resistance training in a hot environment impaired muscle hypertrophy but had no effect on performance adaptations.