But eight years from now, when the first of this group reaches the conventional retirement age of 65, public policy makers will find that a significant number of these new elderly will emulate their parents by abandoning the garden, tennis court, or walking course. They will find that their physical inactivity will decrease, and with unhealthy dietary habits, find themselves at risk for cardiovascular disease and other debilitating disorders.
Although it has been known for quite some time that various behavioral and environmental factors can influence one's regular physical activity level, recent research findings suggest biological mechanisms may also play a role in one's activity patterns. In addition, several studies in humans and animals have found indications that there is a genetic control of one's inherent physical activity level. However, to date there has been no study to suggest potential genetic factors related to one's physical activity level as one ages. Therefore, a new study has been undertaken to investigate the likelihood that physical activity level regulation with aging is controlled, in part, by genetic factors.
A New Study
The authors of "Genetic Influence on Age-Related Changes in Daily Physical Activity Level" are Michael J. Turner, J. Timothy Lightfoot, Mark T. Lindley, and Amber M. Lowe, all from the Department of Kinesiology, University of North Carolina Charlotte, Charlotte, NC; and Steven R. Kleeberger, at the Pulmonary Pathobiology Laboratory, National Institute of Environmental Health Sciences, Durham, NC. They will present their findings at the American Physiological Society conference, Experimental Biology 2003, being held April 11-15, 2003, at the San Diego Convention Center, San Diego, CA.
Methodology
Five female mice (five weeks old) from 10 different inbred strains (A/J, AKR/J, Balb/cJ, C3H/HeJ, C57Bl/6J, C57L/J, C3Heb/FeJ, CBA/J, DBA/2J and SWR/J) were housed in a university vivarium with 12-hour light/dark cycles and were provided with unrestricted amounts of water and food.
At ten weeks of age, all mice were housed individually. Within each mouse cage was a running wheel interfaced with a magnetic sensor and computer that counted revolutions of the running wheel. Past studies have shown that mice gradually increase voluntary wheel running activity from age 3 weeks to 8 weeks with peak activity occurring between 55 and 65 days, after which activity levels begin to decline. Every 24 hours, the distance run by each mouse was determined by multiplying the perimeter of the running wheel by the number of wheel revolutions. Additionally the total time each mouse runs on a 24 hours basis was determined. Data collection was completed when the mice were 36 weeks old.
Two-way ANOVA with repeated measures was performed to compare the strains' weight, daily distance, duration, and velocity of physical activity.
Results
Significant differences were observed between the 10 strains of female mice during the 26-week physical activity period for two of the physical activity measurements (distance per day and duration per day). During the first 13 weeks of the study period (early period), SWR/J increased their distance run when compared to A/J, CBA/J, C3Heb/FeJ, and C57L/J mice (p<0.05). However, only AKR/J female mice were different from the SWR/J mice with respect to the distance run during the last 13 weeks (late period) of the study period (p<0.05). For duration of activity per day, the A/J, Balb/cJ, CBA/J, C3H/HeJ, C3Heb/FeJ, and C57L/J were significantly different from the increase in duration of physical activity for the SWR/J female mice during the early study period. During the last 13 weeks of the study period, the C3H/HeJ, C57L/J and SWR/J mice were significantly different in their duration of physical activity when compared to the AKR/J and Balb/cJ female mice.
Additionally, the CBA/J and C57Bl/6J female mice were significantly different from the AKR/J mice in duration of activity per day during the second half of the study period. Interclass correlations and the coefficient of genetic determination, as described above, were used to estimate the broad-sense heritability for physical activity level during this portion of the lifespan for female mice. The broad-sense heritability with interclass coefficients ranged between 0.23 and 0.43 and the coefficient of genetic determination ranged between 0.13 and 0.27 for the three PA variables.
Conclusions
Genetic influence appears to participate in the alterations observed with daily physical activity level from age three to nine months in 10 strains of female mice. These findings suggest the commonly stated "age-related" decline in physical activity level with aging is due, in part, to genetic influences on physiological alterations. Future research will attempt to isolate the specific genes participating in these observations and quantify the influence of genetics throughout the end of life.
Recent research findings reveal that exercise capacity (maximal ability to perform work) is a strong predictor for the risk of death in men, both healthy and with cardiovascular disease. These findings, adding to the understanding that biological factors have a role in age-related physical activity decline, will make a significant contribution to the effort to create a healthier, aging, population.
The American Physiological Society (APS) is one of the world's most prestigious organizations for physiological scientists. These researchers specialize in understanding the processes and functions underlying human health and disease. Founded in 1887 the Bethesda, MD-based Society has more than 10,000 members and publishes 3,800 articles in its 14 peer-reviewed journals each year.
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