Association between Changes in Muscle Quality with Exercise Training and Changes in Cardiorespiratory Fitness Measures in Individuals with Type 2 Diabetes Mellitus: Results from the HART-D Study

INTRODUCTION: Type 2 diabetes mellitus (T2DM) is associated with a reduction in muscle quality. However, there is inadequate empirical evidence to determine whether changes in muscle quality following exercise are associated with improvement in cardiorespiratory fitness (CRF) in individuals with T2DM. The objective of this study was to investigate the association between change in muscle quality following a 9-month intervention of aerobic training (AT), resistance training (RT) or a combination of both (ATRT) and cardiorespiratory fitness (CRF) in individuals with T2DM. MATERIAL AND METHODS: A total of 196 participants were randomly assigned to a control, AT, RT, or combined ATRT for a 9-months intervention. The exposure variable was change in muscle quality [(Post: leg muscle strength/leg muscle mass)-[(Pre: leg muscle strength/leg muscle mass)]. Dependent variables were change in CRF measures including absolute and relative VO(2peak), and treadmill time to exhaustion (TTE) and estimated metabolic equivalent task (METs). RESULTS: Continuous change in muscle quality was independently associated with change in absolute (β = 0.015; p = 0.019) and relative (β = 0.200; p = 0.005) VO(2peak), and TTE (β = 0.170; p = 0.043), but not with estimated METs (p > 0.05). A significant trend was observed across tertiles of change in muscle quality for changes in absolute (β = 0.050; p = 0.005) and relative (β = 0.624; p = 0.002) VO(2peak) following 9 months of exercise training. No such association was observed for change in TTE and estimated METs (p > 0.05). DISCUSSION: The results from this ancillary study suggest that change in muscle quality following exercise training is associated with a greater improvement in CRF in individuals with T2DM. Given the effect RT has on increasing muscle quality, especially as part of a recommended training program (ATRT), individuals with T2DM should incorporate RT into their AT regimens to optimize CRF improvement. TRIAL REGISTRATION: Clinicaltrials.gov NCT00458133