| Aging is associated with an increase in obesity and muscle adiposity which may confer insulin resistance. Aerobic exercise improves insulin resistance thereby reducing the risk to type 2 diabetes mellitus; however, it is unclear whether these improvements are related to changes in muscle fat content. The purposes of the present investigation were: (1) to determine the lipid content of different muscles in older adults using novel MRI methodology, (2) to examine the effect of exercise on muscle lipid content as well as muscle and lipid area, (3) to determine if there is an association between skeletal muscle adiposity and insulin sensitivity. A total of eight (2 men, 6 women), non-obese (BMI - 27.0 ± 5.0 kg·m−2 ), healthy (2 hour - OGTT glucose −118.7 ± 24.2 mg·dl−1), older adults (68.1 ± 2.4 years) underwent a 16-week intervention to determine the effect of aerobic exercise on physical fitness, body composition, insulin sensitivity and skeletal muscle lipid content. Following training, body composition did not change, while physical fitness improved by ∼7% (36.8 ± 6.6 to 39.0 ± 6.5 ml·kgFFM−1·min−1; p < 0.05). Insulin mediated glucose disposal increased (p < 0.05) by 10% from 10.60 ± 2.19 to 11.56 ± 2.05 mg·kgFFM −1·min−1, with the non-oxidative portion of glucose disposal exhibiting a trend towards increase. Gastrocnemius skeletal muscle lipid content was higher prior to training compared to tibialis anterior (7.10 ± 5.84 vs. 2.45 ± 1.43 g·dl−1 ; p < 0.05) and exhibited a 40% increase following training. A significant correlation was found between tibialis anterior muscle lipid content and insulin sensitivity before training (r = 0.88; p < 0.05). No association was seen between the change in insulin sensitivity and the change in lipid content of the Gastrocnemius, Soleus or Tibialis Anterior. The results of the current investigation point to a muscle specific (Gastrocnemius) training induced increase in lipid content and an association between insulin sensitivity and muscle lipid content of the Tibialis Anterior. However, the results need to be interpreted with caution given the small sample size, lack of a control group, and relatively healthy status of the volunteers. |
