Changes in insulin resistance and HbA1c are related to exercise-mediated changes in body composition in older adults with Type 2 Diabetes : Interim outcomes from the GREAT2DO trial

OBJECTIVE To investigate changes in body composition after 12 months of high-intensity progressive resistance training (PRT) in relation to changes in insulin resistance (IR) or glucose homeostasis in older adults with type 2 diabetes. RESEARCH DESIGN AND METHODS One-hundred three participants were randomized to receive either PRT or sham exercise 3 days per week for 12 months. Homeostasis model assessment 2 of insulin resistance (HOMA2-IR) and glycosylated hemoglobin (HbA1c) were used as indices of IR and glucose homeostasis. Skeletal muscle mass (SkMM) and total fat mass were assessed using bioelectrical impedance. Visceral adipose tissue, mid-thigh cross-sectional area, and mid-thigh muscle attenuation were quantified using computed tomography. RESULTS Within the PRT group, changes in HOMA2-IR were associated with changes in SkMM (r = −0.38; P = 0.04) and fat mass (r = 0.42; P = 0.02). Changes in visceral adipose tissue tended to be related to changes in HOMA2-IR (r = 0.35; P = 0.07). Changes in HbA1c were related to changes in mid-thigh muscle attenuation (r = 0.52; P = 0.001). None of these relationships were present in the sham group (P > 0.05). Using ANCOVA models, participants in the PRT group who had increased SkMM had decreased HOMA2-IR (P = 0.05) and HbA1c (P = 0.09) compared with those in the PRT group who lost SkMM. Increases in SkMM in the PRT group decreased HOMA2-IR (P = 0.07) and HbA1c (P < 0.05) compared with those who had increased SkMM in the sham group. CONCLUSIONS Improvements in metabolic health in older adults with type 2 diabetes were mediated through improvements in body composition only if they were achieved through high-intensity PRT. Body composition is central to insulin resistance (IR) and type 2 diabetes, projected to affect 435 million adults by 2030 (<a href="http://care.diabetesjournals.org/content/36/8/2372#ref-1" id="x-x-x-x-xref-ref-1-1">1). Lifestyle interventions are recommended to improve body composition (reduce adiposity, increase lean tissue) and, ultimately, to improve metabolic health. One lifestyle component is progressive resistance training (PRT), an anabolic exercise shown to improve body composition, as well as IR and glucose homeostasis in type 2 diabetes (<a href="http://care.diabetesjournals.org/content/36/8/2372#ref-2" id="x-x-x-x-xref-ref-2-1">2–<a href="http://care.diabetesjournals.org/content/36/8/2372#ref-4" id="x-x-x-x-xref-ref-4-1">4). Skeletal muscle hypertrophy is thought to mediate metabolic benefits of PRT by increasing the quality and quantity of skeletal muscle available for glucose storage. Increases in lean tissue have been associated with improvements in IR and glucose homeostasis (<a href="http://care.diabetesjournals.org/content/36/8/2372#ref-5" id="x-x-x-x-xref-ref-5-1">5,<a href="http://care.diabetesjournals.org/content/36/8/2372#ref-6" id="x-x-x-x-xref-ref-6-1">6). In the Graded Resistance Exercise And Type 2 Diabetes in Older adults (GREAT2DO) study, we have shown strong relationships between body composition and homeostasis model assessment 2 of insulin resistance (HOMA2-IR) at baseline, before randomization to experimental (power training) or control (sham exercise) groups (<a href="http://care.diabetesjournals.org/content/36/8/2372#ref-7" id="x-x-x-x-xref-ref-7-1">7). The purpose of this interim report was to investigate changes in body composition after the first 12 months of training in relation to changes in IR or glucose homeostasis. We hypothesized that the experimental group would improve body composition (increased skeletal muscle mass [SkMM] and reduced visceral adipose tissue [VAT], reduced total fat mass [FM], and reduced intramyocellular lipid [IMCL]) compared with the control group. Furthermore, we hypothesized that across the entire cohort, beneficial shifts in body composition would lead to improvements in IR and glucose homeostasis.