Effects of Aerobic and Resistance Training on Accumulation of Old, Modified Proteins in Young and Older Adults

• Skeletal muscle protein synthesis rate [ Time Frame: Approximately 14 weeks for the endurance or resistance training groups and approximately 28 weeks for the combined group ] [ Designated as safety issue: No ]
  The investigators will determine the rate of incorporation of stable isotope amino acid tracers in skeletal muscle proteins during several hours of rest. The measurement will be an average resting muscle protein synthesis rate (% new muscle protein per hour) and will be performed at baseline and following 12 weeks of exercise training.
  
  

The loss of muscle mass and function with age leads to high social and economic costs. Lifestyle interventions that can help maintain muscle mass and function can be beneficial to improve health and decrease the costs associated with loss of independence in the elderly. Muscle proteins accumulate damage during aging, which is suggested to lead to loss of function. The biological processes that remove damaged proteins and synthesis new proteins appear to be decreased with aging. Exercise is known to increase the processes that remove older and synthesis newer muscle proteins and may be an effect lifestyle intervention to improve muscle quality and function. Additionally, specific types of proteins appear to decay with age including contractile and mitochondrial proteins. Different types of exercise training can increase the making of specific proteins. The investigators will examine the ability for aerobic and resistance training to increase the quality of mitochondrial and contractile proteins between younger and older people.