Acute effects of a dopamine/norepinephrine reuptake inhibitor on neuromuscular performance following self-paced exercise in cool and hot environments

Dopamine/norepinephrine (DA/NE) reuptake inhibitors have been used to manipulate the central mechanisms affecting arousal and motivation during exercise. Eight healthy, physically active males performed 30 min fixed-intensity cycling at 50% Wmax followed by 30 min of self paced time trial (TT) with each section interspersed with a 30 s maximal sprint at 9, 19 and 29 min. The DA/NE re-uptake inhibitor administered was bupropion (BUP) versus a placebo (PLA) in either warm (32 °C, BUP32 or PLA32) or moderate (20 °C; BUP20, PLA20) ambient conditions. Core and skin temperature, heart rate and perceptual responses, neuromuscular and hormonal measures were assessed at multiple times throughout the trials and post exercise. Time trial performance remained unchanged across conditions (12.7-13.1 km) although core temperature was elevated in the fixed intensity section of the trials for BUP32 and BUP20 but continued to rise only in BUP32 during the time trial reaching 38.6 °C (P<0.05). NE increased in all conditions from pre-exercise with BUP32 values peaking at the end of TT to 1245.3±203.1 pg/mL (P<0.05) compared to the other conditions. Neuromuscular responses were similar among conditions although peak force was significantly reduced from pre (262±31 N) to post (202±31 N, P<0.05) exercise along with contraction duration (22%, P<0.05) in BUP20. We conclude that DA/NE re-uptake inhibitors influenced thermoregulation in the heat but not exercise performance. DA/NE re-uptake inhibitors are likely to act centrally to override the inhibitory signals for the cessation of exercise with these drugs acting peripherally to reduce the twitch characteristics of skeletal muscle in cooler conditions.