This investigation aimed to compare the response of older adult and young men to 14 day bed-rest and subsequent 28 day rehabilitation. Sixteen older (OM: 55-65 years) and seven young men (YM: 18-30 years) were exposed to 14-day bed rest (BR) followed by 14-day rehabilitation (R), and 400-day of R. Quadriceps muscle volume, force and explosive power of leg extensors, single fiber isometric force, peak aerobic power, gait stride length, and several metabolic were measured before and after BR and after R.