Department of Kinesiology, Nutritional Science, and Institute on Aging, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA
Address for correspondence: Li Li Ji, Ph.D., 2000 Observatory Drive, Madison, WI 53706. Voice: 608-262-7250; fax: 608-262-1656.
ji{at}soemadison.wisc.edu
Aging is associated with increased free radical generation in
the skeletal muscle that can cause oxidative modification of
protein, lipid, and DNA. Physical activity has many well-established
health benefits, but strenuous exercise increases muscle oxygen
flux and elicits intracellular events that can lead to increased
oxidative injury. The paradox arises as to whether exercise
would be advisable to aged population. Research evidence indicates
that senescent organisms are more susceptible to oxidative stress
during exercise because of the age-related ultrastructural and
biochemical changes that facilitate formation of reactive oxygen
species (ROS). Aging also increases the incidence of muscle
injury, and the inflammatory response can subject senescent
muscle to further oxidative stress. Furthermore, muscle repair
and regeneration capacity is reduced at old age that could potentially
enhance the accrual of cellular oxidative damage. Predeposition
of certain age-related pathologic conditions may exacerbate
the risks. In spite of these risks, the elderly who are physically
active benefit from exercise-induced adaptation in cellular
antioxidant defense systems. Improved muscle mechanics, strength,
and endurance make them less vulnerable to acute injury and
chronic inflammation. Many critical questions remain regarding
the relationship of aging and exercise as we enter a new millennium.
For example, how does aging alter exercise-induced intracellular
and intercellular mechanisms that generate ROS? Can acute and
chronic exercise modulate the declined gene expression of metabolic
and antioxidant enzymes seen at old age? Does exercise prevent
age-dependent muscle loss (sarcopenia)? What kinds of antioxidant
supplementation, if any, do aged people who are physically active
need? Answers to these questions require highly specific research
in both animals and humans.
