Changes On Non-exercise Physical Activity Are Related To Improvements In Mitochondrial Function Independently Of Structured Intentional Exercise

Abstract

Whether exercise interventions increase or reduce non-exercise physical activity (NEPA) is controversial. Few studies have examined this potential effect on relevant physiological outcomes, particularly in the context of randomized controlled trials. PURPOSE: To determine the effects of a structured exercise program on NEPA, and the independent association between NEPA and both cardiorespiratory fitness (VO2max) and mitochondrial capacity within skeletal muscle. METHODS Thirty-seven older (age=69±5yrs) obese (BMI=35±3kg/m2) adults were randomized to one of the following 6-month interventions: Health education (CON: n=12), diet induced weight-loss (DIWL: n=12, or Weight-loss and exercise (WLEX: n=15). CRWL and WLEX participants had a goal of 10% weight-loss through calorie restriction. Subjects in the WLEX group completed a supervised combined aerobic and resistance exercise program. We quantified components of PA by a multisensory device. VO2max was determined by cycle ergometry. Maximal oxidative phosphorylation (OXPHOS) and maximal uncoupled respiration (ETS) of permeabilized myofibers from biopsies was evaluated by high-resolution respirometry. Repeated measures analysis was performed to compare differences between the three groups pre and post intervention. Adjusted correlations to weight loss (WL) between NEPA and VO2max, ETS and OXPHOS were performed. RESULTS: After the intervention WLEX increased significantly NEPA compared with the other groups (NEPA: WLEX= 89.6±84.5 min/day; DIWL= 3.7±42.4 min/day; CON= -10.5±63.6 min/day; F= 8.87 for time x group interaction, P<0.001). Change in NEPA was positively correlated with change in mitochondrial capacity (OXPHOS, r = 0.453 and r= 0.468; P<0.05 for both) and absolute VO2max (r= 0.453, P<0.05). Both DIWL and WLEX experimented a significant WL (WLEX= -10.1±5.0 min/day and DIWL= -7.2±5.5 min/day; P<0.05). CONCLUSIONS: In addition to the beneficial effects of structured intentional exercise on cardiorespiratory fitness and mitochondrial capacity within muscle, exercise programs in older obese adults may also increase non-exercise physical activity, which in turn appears to independently correlate with improved aerobic capacity. These results highlight the concurrent effect of exercise and NEPA to improve health outcomes.