The effect of hypoxia and work intensity on insulin resistance in type 2 diabetes - Mackenzie et al. (2012)
Key Points
Exercise and hypoxia have an additive, positive effect on insulin sensitivity
Longer-duration, moderate-intensity exercise in hypoxia is more beneficial than shorter-duration, high-intensity exercise
The sympathetic response to high-intensity exercise might offset its blood glucose-lowering effects
The Breathing Diabetic Summary
We saw in the other Mackenzie et al. (2012) paper that continuous exercise in hypoxia had positive effects on glycemic control. We also saw in their 2011 study that resting or exercising in hypoxia improved the insulin sensitivity of type 2 diabetics. Here, as a continuation of their studies, they investigated whether exercise intensity in hypoxia influenced the impacts on insulin sensitivity.
They had type 2 diabetics perform three different exercise protocols. The first was 60 min of hypoxic exercise at moderate intensity (HyEx60). Then, keeping the total work constant, they increased the intensity but reduced the exercise time to 40 (HyEx40) and 20 (HyEx20) minutes. Thus, the intensity and time were adjusted to ensure that the total work done was the same in all three protocols. Finally, note that their hypoxia protocol was O2 at 14.7%, well within the therapeutic range.
The main outcome of this study was that the longer-duration, moderate-intensity exercises in hypoxia (HyEx60 & HyEx40) had the largest positive impacts on insulin sensitivity. The authors found that the shorter-duration, higher-intensity exercise in hypoxia (HyEx20) lowered blood glucose; however, it also activated the sympathetic nervous system and increased the body’s endogenous production of glucose. Thus, the positive effects of the exercise and hypoxia partially were offset by the stress response that increased the body’s production of glucose.
Overall, this paper shows that moderate-intensity exercise in moderate hypoxia can improve glycemic control in type 2 diabetics by lowering blood sugar and improving insulin sensitivity. For us, this is why Principle 3 emphasizes (1) “easy” breath holds and (2) performing breath holds while walking. By doing easy breath holds, we minimize the sympathetic response, and by performing the breath holds while walking we incorporate some moderate intensity exercise to increase the benefits of hypoxia.
Abstract From Paper
Context: Hypoxia and muscle contraction stimulate glucose transport in vitro.We have previously demonstrated that exercise and hypoxia have an additive effect on insulin sensitivity in type 2 diabetics.
Objectives: Our objective was to examine the effects of three different hypoxic/exercise (Hy Ex) trials on glucose metabolism and insulin resistance in the 48 h after acute hypoxia in type 2 diabetics.
Design, Participants, and Interventions: Eight male type 2 diabetics completed 60 min of hypoxic [mean (SEM) O2 = ~14.7 (0.2)%] exercise at 90% of lactate threshold [Hy Ex60; 49 (1) W]. Patients completed an additional two hypoxic trials of equal work, lasting 40 min [Hy Ex40; 70 (1) W] and 20 min [Hy Ex20; 140 (12) W].
Main Outcome Measures: Glucose rate of appearance and rate of disappearance were determined using the one-compartment minimal model. Homeostasis models of insulin resistance (HOMAIR), fasting insulin resistance index and beta-cell function(HOMA_IR-cell) were calculated at 24 and 48 h after trials.
Results: Peak glucose rate of appearance was highest during Hy Ex20 [8.89 (0.56) mg/kg min, P < 0.05]. HOMAIR and fasting insulin resistance index were improved in the 24 and 48 h after Hy Ex60 and Hy Ex40 (P < 0.05). HOMAIR decreased 24 h after Hy Ex20 (P < 0.05) and returned to baseline values at 48 h.
Conclusions: Moderate-intensity exercise in hypoxia (Hy Ex60 and Hy Ex40) stimulates acute- and moderate-term improvements in insulin sensitivity that were less apparent in Hy Ex20. Results suggest that exercise duration and not total work completed has a greater influence on acute and moderate-term glucose control in type 2 diabetics.
Journal Reference:
R. Mackenzie, B. Elliott, N. Maxwell, G. Brickley, and P. Watt, (2012) The effect of hypoxia and work intensity on insulin resistance in type 2 diabetes, J Clin Endocrinol Metab, 97, 155–162, doi: 10.1210/jc.2011-1843.