Aging and Athletic Performance: A Deep Dive into Physiological Changes

Aging and Physiology in Athletes

Initial Considerations: Aging vs. Behavior

An interesting point to consider is whether the physiological changes observed with age are due to the aging process itself or changes in behavior. A study on rats, whose lifespans allow for quicker observation of aging processes (one rat month equates to approximately two to three human years), revealed two key decreases in physical activity.

  • The first decrease corresponds to the age when humans typically leave school, suggesting a potential behavioral shift influencing physiological adaptations.

  • The second decrease occurs around the human age of 50.

Even in human data, a decline in physical activity participation is noticeable around age 50. It raises the question of whether this decline is due to aging or a more sedentary lifestyle accelerating the aging process.

Physiological Changes with Aging

Body Composition

As we age, inevitable changes occur in body composition. Body weight tends to decrease, largely due to a decline in muscle mass. This decline typically starts around age 40 for men and later for women (around age 70). This difference is attributed to:

  • Initial differences: Men generally have higher muscle mass than women.

  • Hormonal changes: Men experience a decline in testosterone levels.

  • Muscle fiber type: Men have a higher proportion of type two (fast-twitch) muscle fibers, which are more prone to loss with aging, while women have more type one (slow-twitch) muscle fibers, which tend to be maintained.

The ultimate result is a decline in muscle mass and a corresponding change in body weight.

Muscle Strength and Functional Strength

A decline in muscle strength corresponds to the decline in muscle mass (sarcopenia). This is due to both a reduction in the number and size of muscle fibers and an increase in slow-twitch muscle fibers. Even with a decline, individuals who train regularly maintain a higher level of strength compared to sedentary individuals.

Functional strength, the ability to perform everyday activities like standing up from a chair, is maintained until about age 70 in the absence of physical activity. After that, functional impairment may occur, limiting participation in daily activities.

The change in muscle strength is related to distinct changes in muscle fiber types. Exercise helps maintain muscle mass and the proportion of muscle fiber types. Recreationally trained or untrained individuals experience a significant shift towards more slow-twitch muscle fibers.

Cardiovascular System

For the same exercise intensity, middle-aged athletes tend to have lower leg blood flow compared to younger athletes. This is likely due to changes in peripheral circulation, including:

  • A decrease in capillary density.

  • Potential changes in mitochondrial volume. These factors affect the ability to extract oxygen from the blood into the muscles.

There's also a decrease in heart rate (approximately one beat per year) due to a decline in sympathetic nervous system activity. Additionally, maximum stroke volume decreases due to:

  • An increase in total peripheral resistance, which reduces venous return and end-diastolic volume.

  • A decrease in ventricular contractility.

Combining these factors, maximum cardiac output (the amount of blood moving around the body per minute) is reduced.

Respiratory System

Maximum respiration declines with age, typically peaking between ages 20 and 30 and gradually declining thereafter. This decline is probably due to decreased elasticity in lung walls and tissues. Trained individuals have a higher starting point of maximal respiration and experience a slower decline compared to untrained individuals.

VO2 Max and Endurance Performance

Aging leads to changes in oxygen delivery and extraction, ultimately resulting in a decline in VO2 max (maximum aerobic capacity). A higher initial VO2 max, achieved through training, leads to a higher maintained level with age. Individuals with a sedentary lifestyle may see their VO_2 max drop below the line of dependence, increasing mortality risk.

VO_2 max and the line of dependence:

  • VO2 max: a measure of the maximum amount of oxygen that an individual can utilize during intense or maximal exercise.

  • Line of dependence: the level of aerobic fitness required to live independently. If the athlete's VO2 max value goes under the line of dependence, there is an increased mortality risk.

Impact of Continued Training

A study of well-trained distance runners showed that the decline in VO2 max over 20 years was not drastic. There was an increase in body fat, however. Maintaining exercise is crucial for offsetting negative health implications. The specificity of training is also important. Runners who maintained high specificity in their training experienced less decline in VO2 max compared to those who stopped training altogether.

The decline in VO_2 max is not dramatic if you maintain a regular training schedule. It can be less than 10% in twenty years for well maintained athletes.

Conclusion

While physiological changes occur with aging, exercise is the best way to offset aging and promote longevity. The saying "use it or lose it" is very relevant to aging and physiology.

VO2 max equation: VO2 = Stroke Volume * Heart Rate * (Arterial O2 - Venous O2)

The single greatest remedy to offset aging and maintain athletic performance is high specificity exercise.