Effects of an 8-week high-intensity interval training on body mass index, cardiorespiratory fitness and retinal microcirculation in 40 to 60-year-olds

Introduction: The leading morbidity and mortality factors in today‘s age are cardiovascular diseases (CVD). As the incidence of CVD has risen ever since the end of the 20th century physical activity (PA) has a high standing as a lifestyle habit to minimize cardiovascular risk due to high cardiorespiratory fitness (CRF) being associated with healthy aging. Methods: In this study, 20 participants were split into two groups. The intervention group (IG) received an 8-week high-intensity interval training (HIIT) program, and the control group (CG) just PA recommendations. Effects of the training program were examined with pre- and post-intervention measurements of the body mass index (BMI) cardiorespiratory fitness (CRF) measured by maximal oxygen uptake ( ̇VO2peak), and arteriovenular ratio (AVR) in the microcirculation in the eye. Results: Pre- to post-examinations displayed a significant BMI reduction in both groups (CG: d = -1.39, p=0.002; IG: d = -2.09, p < 0.001), with the effect size bigger in the IG. CRF improved in the IG only with a large effect size of 1.18 (p = 0.005) versus no effect in the controls (d = -0.27, p = 0.415). AVR improved insignificantly in both groups with moderate effect sizes of d= 0.53 (p = 0.125) and d = 0.68 (p = 0.059). Discussion: When comparing the IG to CG, the weight reduction was at a near similar level from controls to trained individuals. AVR did not show any differences between the groups as well. The only significant difference analyzed is the large effect on CRF for the IG easily explainable due to the physiological adaptations such as increased mitochondrial biogenesis, more efficient oxygen uptake and usage in the muscle or improved fat oxidation induced by the HIIT training. Conclusion: Health benefits associated with results from this study are restricted to an increased CRF when comparing IG to CG, however, with the observed weight loss in controls and the IG, cardiovascular risk factors should be altered to a risk reduction for CVD as well.