Effects of high or moderate intensity training on inflammation and endothelial function in insulin resistance.

Abstract

Exercise training improves insulin resistance (IR) via numerous mechanisms including improved endothelial function and reduced systemic inflammation. However, it is unclear whether high intensity interval training (HIIT) offers superior benefit when compared with continuous moderate intensity training (CMIT) in a clinical population. This thesis reports findings from a clinical trial designed to determine the effects of short-term high or moderate intensity training on inflammation and endothelial function in overweight/obese adults with IR. Furthermore, the thesis provides a report on factors associated with IR in this population. Clinical examinations (body composition), blood tests [serum insulin and serum C-reactive protein (CRP), plasma glucose] and physiological tests (microvascular function and aerobic fitness tests) were undertaken on consenting individuals who volunteered to participate in the study. Study participants were stratified into IR and insulin sensitive (IS) groups based on their homeostatic model assessment (HOMA-IR) scores. The IR and IS groups were each further randomized into control (CNT), HIIT or CMIT sub-groups. The HIIT and CMIT sub-groups underwent baseline measures and exercise training for 10 consecutive days, followed by a repeat of baseline measures. The CNT sub-group was tested at baseline and post follow-up without taking part in the exercise intervention. When compared with CMIT, HIIT produced a greater improvement in markers of IR [(HOMA-IR); 32% vs. 9% by CMIT] and endothelial function [(PORHmax and MV); 37.59% and 27.45%, respectively, vs. 8.24% and -25.71%, respectively, by CMIT]. These improvements occurred without changes in body fat or aerobic fitness. Cohen’s (d) effect sizes indicated that the improvements produced by HIIT were large, while those of CMIT were unclear, suggesting that HIIT may be the ideal mode of training when the primary goal is to improve IR and endothelial function in overweight/obese adults. Cross-sectional analysis of baseline data indicated that the acute-phase inflammatory protein, CRP, was strongly associated with IR in black Africans. However, this association was only significant in males. Suggesting that CRP has potential clinical application as a maker of systemic inflammation in this population. The gender of the patient, however, must be taken into consideration.