Warm-up exercise in human type 2 diabetes: is high-intensity exercise required?

Abstract

With great interest, we read the innovative study of Rocha and colleagues (7), which concluded that a single high-intensity warm-up (referred to as "priming exercise") enhanced the matching of oxygen (O 2 ) delivery and utilization within skeletal muscle microvasculature in middle-aged people with uncomplicated type 2 diabetes (T2D). As previously suggested (1,9), the authors identify blunted O 2 availability as one of the primary mechanisms that limit V O 2 kinetics in people with T2D and show compelling evidence identifying warm-up exercise as a technique to mediate the blunted O 2 kinetics at the onset of an exercise bout.The purpose of our letter is to suggest cautious interpretation of the need for high-intensity exercise as priming exercise. Participants performed two trials, as suggested for O 2 kinetics research (4), each trial separated by 45 min of rest. Trials consisted of three 9-min bouts of cycling interspersed with 12 min of rest, each bout beginning with 3 min at 10 W and completing the final 6 min at 1) moderateintensity ("unprimed"), 2) high-intensity ("priming" stimulus), and 3) moderate-intensity ("primed"). Oxygen uptake and muscle deoxygenation kinetics were reported from each moderate-intensity exercise. The 45 min of rest between trials was based on seminal work from Burnley and colleagues (2) which concluded that the "priming" effect of prior exercise persists for~45 min.Based on the current experimental approach, it is implausible to distinguish the priming effects of the high-(number 2 above) and moderate-intensity cycling (number 1 above) exercise which concluded 15 and 36 min before initiation of the "primed" moderate-intensity exercise (number 3 above), respectively. Thus the purported priming benefits of highintensity exercise as warm-up may be due to either exercise intensity (moderate or high). This distinction is important for clinical interpretation of these data as prescribing a high-intensity exercise as warm-up could be a significant barrier to participating in exercise among people with T2D, who often have weaker, less powerful, and more fatigable skeletal muscle (3,8).The mechanisms for the "priming" effect of high-intensity cycling exercise were not investigated, but were suggested to be 1) lactic acidosis or 2) augmented flow-mediated vasodilation. The former proposed mechanism (lactic acidosis) was considered by Burnley and colleagues (2), and