Association between haemoglobin A_1c and whole-body heat loss during exercise-heat stress in physically active men...

What is the central question of this study? Is the impairment in heat dissipation during exercise observed in men with type 2 diabetes related to glycaemic control (indexed by glycated haemoglobin; haemoglobin A_1c )? What is the main finding and its importance? No association was found between haemoglobin A_1c (range: 5.1-9.1%) and whole-body heat loss in men with type 2 diabetes during exercise in the heat. However, individuals with elevated haemoglobin A_1c exhibited higher body core temperature and heart rate responses. Thus, while haemoglobin A_1c is not associated with heat loss per se, it may still have important implications for physiological strain during exercise.

Type 2 diabetes is associated with a reduced capacity to dissipate heat. It is unknown whether this impairment is related to glycaemic control (indexed by glycated haemoglobin; haemoglobin A_1c ) is unknown. We evaluated the association between haemoglobin A_1c and whole-body heat loss (via direct calorimetry), body core temperature, and heart rate in 26 physically active men with type 2 diabetes (43-73 years; HbA_1c 5.1-9.1%) during exercise at increasing rates of metabolic heat production (∼150, 200, 250 W m^-2 ) in the heat (40°C, ∼17% relative humidity). Haemoglobin A_1c was not associated with whole-body heat loss (P = 0.617), nor the increase in core temperature from pre-exercise (P = 0.347). However, absolute core temperature and heart rate were elevated ∼0.2°C (P = 0.014) and ∼6 beats min^-1 (P = 0.049), respectively, with every percentage point increase in haemoglobin A_1c . Thus, while haemoglobin A_1c does not appear to modify diabetes-related reductions in capacity for heat dissipation, it may still have important implications for physiological strain during exercise-heat stress.