High-intensity Interval Training Prescriptions to Reduce the Risk of Complications Linked to Type 2 Diabetes: the Role of Interval Length on Clinical Benefits and on Physiological Mechanisms

Type 2 diabetes (T2D) prevalence has steadily been rising in the past decades and its complications, including cardiovascular diseases (CVD), are a major public health concern.

To lower CVD risk and to maintain an adequate glycemic control, Diabetes Canada recommends aerobic exercise of high-intensity interval training (HIIT). The leading hypothesis of this study is that longer intervals will favor an anti-inflammatory immune state, and that and that it will be correlated with reduced arterial stiffness and blood pressure.

Type 2 diabetes (T2D) prevalence has steadily been rising in the past decades and its complications, including cardiovascular diseases (CVD), are a major public health concern. Insulin resistance, an important component of T2D, is associated with vascular dysfunctions, which directly contributes to the pathogenesis of CVD, such as atherosclerosis, and hypertension, particularly with the elderly. It is also suggested that glucose variability, measured with continuous glucose monitors (CGM), is an independent risk factor of CVD in T2D individuals, exposing them to an increased risk of premature death. Moreover, in part because of immune dysregulation, women with T2D are at a heightened risk of developing CVD compared to males. Indeed, monocyte inflammatory profile is altered during the aging process and in women with T2D. This, in turn, causes vascular dysfunction which is associated with a pro-thrombotic state, and exacerbates atherosclerosis and arterial stiffening.

To lower CVD risk and to maintain an adequate glycemic control, Diabetes Canada recommends aerobic exercise of high-intensity interval training (HIIT). However, this recommendation is solely based on the improvement of cardiorespiratory fitness in type 2 diabetes individuals (level of evidence: grade B, level 2). Furthermore, most of these studies use exercise protocols with ergocycles, which limit the ecological validity considering that the elderly population prefers to walk. Though, it is essential to evaluate the impact of different walking HIIT protocols on clinical targets such as arterial pressure, glycemic variability/control using ambulatory blood pressure monitors (ABPM) and CGM.

The preliminary data collected in our laboratory shows that a low volume HIIIT program (6 × 1 min) is insufficient to improve glycemic control/variability and ambulatory blood pressure over 24 hours in elderly diabetic women, despite reducing inflammatory gene expression in monocytes. Interestingly, pro-inflammatory monocytes are linked with hyperglycemia and play a crucial role in the atherosclerotic process, while also being associated with arterial stiffening in individuals with kidney failure, a common T2D complication.

These results raise several questions, including the role played by the length of HIIT intervals on clinical targets. While our preliminary results didn't impact ambulatory blood pressure over 24 hours with shorter intervals (6 × 1 min), other studied showed a reduction of this parameter with longer intervals (4 x 4 min). Therefore, the leading hypothesis of this study is that longer high intensity intervals (Wisløff protocol: 4 x 4 min) will reduce ambulatory blood pressure over 24 hours in a greater extent than shorter intervals (10 x 1 min). Indeed, reduced shear stress induced by shorter intervals could damper cellular and molecular responses to exercise bouts, thereby limiting the effects on arterial stiffness and blood pressure in the hours following exercise. Moreover, changes in gene expression do not guarantee changes at the protein level, and proteins are the real effectors of cellular response. Hence, proteomics will be useful to better understand monocyte response to different HIIT protocols and, possibly, the clinical benefits of this training method. Indeed, longer intervals could induce greater variations to the monocytes' proteome, favoring an anti-inflammatory phenotype, and those changes could be associated with reduced arterial stiffness and blood pressure.

The primary objective of this study is therefore to compare the effect of two treadmill HIIT modalities (4x4 min vs. 10x1 min) on arterial stiffness, ambulatory blood pressure over 24 hours and on glycemic variability in elderly women with T2D. The secondary objective is to assess the proteomic changes in monocytes induced by the two HIIT modalities and to correlate them with changes in clinical parameters.

Eligibility Criteria:
Inclusion Criteria:

* With a diagnostic for type 2 diabetes
* Arterial hypertension (controlled at rest)
* Low or no alcohol consumption (≤ 7 alcoholic beverages/week)
* Non-smoking
* Physically active ( \> 60 minutes of structured and scheduled physical activity/week for the previous 3 months)

Exclusion Criteria:

* Insulin therapy
* Use of beta blockers
* Unstable medication in the past 6 months
* Stroke in the past 6 months, or with consequences limiting physical activity practice
* Coronary disease without revascularization, or peripheral artery disease
* Neuropathy, retinopathy of nephropathy diagnostics
* Orthopedic limitations, or medical counter-indication for physical activity practice
* Surgery scheduled during the study period