Healthy subjects performing < 30 min exercise twice per week were studied prior to randomization and after of sixteen weeks exercise. They were randomized to sixteen weeks of supervised exercise performed on a stationary bike vs. placebo exercise (a series of flexibility exercises performed at home). Intensity, duration and frequency of exercise were gradually increased to four sessions per week lasting forty minutes each and achieving 80% target heart rate. Participants were weighed perioidically and counseled appropriately when weight changed by > 2 %. Insulin sensitivity and muscle mitochondrial protein synthesis were studied.