Effect Of Exercise Training On Intermuscular Adipose Tissue And Insulin Resistance In Young And Older Adults

PURPOSE: Intermuscular adipose tissue (IMAT) has unique secretory properties and is associated with metabolic dysfunction and aging. IMAT also decreases in response to exercise training in older adults with obesity, but it remains unclear how exercise influences IMAT among healthy, non-obese older adults in relation to insulin sensitivity. Therefore, the purpose of this study was to determine if IMAT accumulates in skeletal muscle of healthy older adults in the absence of obesity, diabetes, or frailty and its relationship to insulin sensitivity. A secondary purpose was to determine the influence of exercise training on IMAT in young and older adults. METHODS: 29 young (25.0 ± 3.7 yo) and 22 older (70.0 ± 4.0 yo) adults underwent MRI-based measurements of lower leg IMAT and measurements of insulin sensitivity by hyperinsulinemic euglycemic clamp. IMAT and insulin sensitivity measurements were repeated following 12 weeks of exercise training. RESULTS: IMAT abundance was higher in older compared to young adults (521.34 ± 217.04 mm3 vs 278.51 ± 130.88 mm3; p < 0.0001). The glucose infusion rate (GIR) during hyperinsulinemia was similar in young and older adults (13.48 ± 2.94 mg/kg FFM/min vs 14.07 ± 4.19 mg/kg FFM/min; p = 0.38). IMAT was associated with GIR in young (r2 = 0.152; p = 0.049) but not older (p = 0.52) adults. Exercise training reduced IMAT in young (p = 0.014) but not older (p = 0.28) adults. GIR was unchanged by training in young adults (p = 0.49) but increased in older adults (14.07 ± 4.19 mg/kg FFM/min vs 15.61 ± 6.44 mg/kg FFM/min; p = 0.004). Although the post-exercise increase in GIR coincided with decreased IMAT content in most participants, the association did not reach statistical significance (r2 = 0.088, p = 0.054). CONCLUSIONS: These data support previous findings that IMAT increases with age, however, we find IMAT is increased despite absence of obesity, diabetes, or known chronic disease. Although IMAT and insulin sensitivity were associated in young adults, this was not evident in older adults. Exercise improved insulin sensitivity without changing IMAT in older adults, further highlighting the dissociation between these variables in healthy older adults. Therefore, accumulation of IMAT with aging may be an early event preceding the development of insulin resistance. Supported by: R01 K1331194-01A1