Why VO2 max Declines in Older Athletes (and what you can do about it)

By Jim Rutberg,
CTS Pro Coach, co-author of “Ride Inside“,
“The Time-Crunched Cyclist”, and
“Training Essentials for Ultrarunning”

Maximum aerobic capacity (VO2 max) declines with age, but what causes capacity to drop? Aging athletes want to stay fit, vital, and active for the rest of their lives. So what, if anything, can you do to slow or stop the decline? Understand the physiological and structural changes associated with declining VO2 max helps determine how older athletes should prioritize different types of training.

Determinants of Maximum Aerobic Capacity

Your maximum aerobic capacity is the maximum amount of oxygen you can take in, transport, and utilize in working tissues, primarily skeletal muscles. Although we could go way down the rabbit hole on this, from a practical standpoint aging athletes should be concerned with four main determinants of aerobic capacity:

Cardiac output

Cardiac output is the amount of blood your heart pumps in a minute. It’s relationship to VO2 (oxygen consumption) can be described by a simplified version of the Fick equation:

Cardiac output = Oxygen consumption / Arteriovenous oxygen gradient

The components of the equation are important. Cardiac output is the product of stroke volume (the amount of blood ejected from your heart’s left ventricle with each beat) and heart rate. Oxygen consumption is expressed as VO₂. And arteriovenous oxygen gradient is the difference between the oxygenation of arterial blood leaving the heart and venous blood returning to it. This represents the amount of oxygen extracted by tissues.

Several factors contribute to reduced cardiac output in older athletes, although it is sometimes unclear which factors are causes versus effects. Stroke volume decreases, perhaps due to reduced elasticity of cardiac muscle and peripheral resistance from reduced elasticity of blood vessels. Maximum heart rate decreases with age, in part due to depressed electrical conductivity in the nervous system. A reduction in arteriovenous oxygen gradient (less oxygen being used) could be due to reduced blood perfusion in working muscles, reduced mitochondrial density, reduced mitochondrial function, or a combination of these factors.

Blood flow to skeletal muscle

Compared with younger athletes, blood flow to skeletal muscles in older athletes decreases at rest, during submaximal exercise, and during maximal exercise.

From Salvatore et al 2022: “Resting blood flow measurements have been indicated to be ~25% lower in older (~63 y) compared to younger individuals (~28 y). This effect of aging extends into submaximal exercise, as lower extremity blood flow may be as much as ~25% lower in older (~63 y) than younger (~27 y) adults (older: 4.8 L/min vs. younger: 6.2 L/min). The effect of aging on blood flow is exacerbated during maximal exercise, where blood flow may be as much as ~29% lower in older (~64 y) compared to younger (~22 y) adults (older: 7 L/min vs. younger 9.9 L/min).”

For cyclists and runners, it’s notable that the original research summarized above looked specifically at blood flow to leg muscles. This included an often-cited study from Proctor which featured the figure below. More broadly, research into the blood flow changes associated with aging indicate that blood flow is reduced to large muscle groups more than to individual small muscles. In other words, blood flow to the leg and hip muscles responsible for power output is reduced more than blood flow to forearm muscles responsible for grip strength.

adapted from Proctor, D N et al. “Reduced leg blood flow during dynamic exercise in older endurance-trained men.” Journal of applied physiology (Bethesda, Md. : 1985) vol. 85,1 (1998): 68-75. doi:10.1152/jappl.1998.85.1.68

Capillary Density

Increased capillary density is one of the important adaptations to exercise. One of the big benefits to all that Zone 2 and easy endurance training is the proliferation of small blood vessels that surround muscle fibers. The density of the capillary network contributes to “muscle diffusing capacity”, or the ability for oxygen to diffuse from blood vessels into muscle fibers.

Although muscle diffusing capacity reduces slightly with age, research indicates it is not a rate limiting factor for oxygen consumption or energy production in working muscles. Even as athletes get older, the capillary network remains more robust than necessary to deliver the oxygen available in the blood.

Mitochondrial density and function

The infrastructure already discussed is aimed at delivering oxygen to mitochondria in skeletal muscle fibers. However, advanced age has a detrimental effect on the size, number, and function of mitochondria. Again, from Salvatore et al 2022: “There was a significant negative correlation between increased age and decreased mitochondrial volume density and oxidative capacity. Therefore, oxidative capacity per mitochondrial volume was also reduced in the older adults (older: ~0.22 vs. younger: ~0.32 mM ATP/s %). This indicates ATP production relative to mitochondrial volume is diminished with aging.”

Synopsis:

The determinants of maximum aerobic capacity are interdependent. Reduced oxidative capacity in mitochondria can result from lower blood blow to muscles, which can be affected by reduced cardiac output. Reduced mitochondrial density reduces ATP production, which reduces power output and stamina. This may make workouts less effective for stimulating physiological adaptations that would maintain elevated cardiac output and VO2 max.

Training to Preserve Maximum Aerobic Capacity in Older Athletes

Older athletes want to know how to target training to slow or stop the age-related decline in maximum aerobic capacity. Some determinants of aerobic capacity are more important to preserve than others. For instance, capillary density in endurance-trained older adults is more than sufficient to deliver oxygen to working muscles. As a result, we don’t need to specifically target training to further the development of capillaries.

On the other hand, mitochondria appear to remain responsive to training in aging athletes. Your body may not be quite as quick or efficient at producing and maintaining mitochondria compared to a younger athlete, but you can do it. This is the reason most older athlete training plans include a lot of Zone 1 and Zone 2 training. Accumulating lots of time at easy and moderate aerobic intensities stimulates the development and maintenance of healthy mitochondria.

Strength training is important for older athletes, in part because more muscle means more opportunity for maintaining a higher mitochondrial density. You need mitochondria to have the machinery to use oxygen to produce ATP, and without muscle you can’t have mitochondria. Remember, however, that older athletes face challenges to build and maintain existing muscle mass. Muscle protein synthesis (MPS) becomes less efficient with age, although some of this decline is counterbalanced by fitness-related improvements in MPS. Nevertheless, the importance of muscle mass to healthy, mobility, and maximum aerobic capacity are good reasons behind recommendations for older athletes to incorporate strength training 2-3 times per week and to consume 1.6 – 2.0 grams of protein per kilogram of bodyweight per day.

Affecting the Cardiovascular Determinants of VO2 max

Improving mitochondrial density and function is one way older athletes can preserve maximum aerobic capacity. That’s at the muscle end of the process. Can older athletes improve the starting point by increasing cardiac output? In relatively untrained individuals, yes. Normal adaptations to endurance training include increases in stroke volume because of increased plasma volume, strengthening of the heart muscle, and nervous system adaptations. And, as discussed, aerobic training increases mitochondrial density and capillary density, which in turn increase the arteriovenous gradient. In other words, it’s never too late to start exercising!

Experienced and life-long endurance athletes face a slightly different scenario. If you have already achieved a lot of the structural adaptations to endurance exercise (stronger heart muscle, increased capillary and mitochondrial densities), you’re less likely to further increase cardiac output as you get older. If anything, you are fighting the gradual stiffening of blood vessels, the loss of elasticity in cardiac muscle, and the lower conductivity of electrical signals in your nervous system. These things affect relatively untrained or inexperienced older athletes, too, but they still have room to improve before these factors limit their performance.

Lifestyle Habits to Preserve Maximum Aerobic Capacity in Older Athletes

Older athletes have limited avenues to preserve maximum aerobic capacity through training alone. However, recovery and lifestyle habits offer opportunities.

• Recovery scheduling: In these podcasts (Part 1, Part 2), coach Joe Friel and CTS Coach Adam Pulford discuss workout structures that include a 9-day training week (one hard day, two easy days x 3) for athletes who can decouple their training week from their calendar week. For those who can’t, a 5-2 structure (two hard workouts and five easy workouts across seven days) may be advantageous. In the context of older athletes, it’s important to prioritize recovery so athletes can adapt to training stress and continue executing high quality training.
• Sleep: This goes hand-in-hand with prioritizing the quality and duration of recovery between training sessions. All athletes should focus on 7-9 hours of high-quality sleep per night, and it’s no less important for older athletes.
• Stress management: Hopefully, older athletes have moved into a less stressful period, compared to the height of their career and child-raising years. That’s not true for everyone, of course. Nevertheless, reducing lifestyle stress improves sleep and post-exercise recovery, and preserves immune system function. These improve workout quality and reduce missed training days due to illness.
• Nutrition: In addition to consuming adequate protein, as mentioned previously, it’s important to consume adequate total calories and carbohydrate to support your activity level.
• Weight management: Because VO2 max is often expressed in milliliters of oxygen per kilogram per minute (ml/kg/min), losing weight increases VO2 max. Rather than losing weight to change the math equation, you’re better off aiming for a healthy body composition that prioritizes lean muscle mass. Usually, when we prioritize building muscle (strength training) and mitochondria (aerobic training), body composition changes occur along the way.

Final Word

Maximum aerobic capacity will decline with age. With consistent aerobic and strength training you can preserve VO2 max by maintaining – or even improving – muscle mass and mitochondrial density/function. In contrast, there isn’t as much that experienced older athletes can do to restore age-related losses in cardiac output. However, good lifestyle and recovery habits may help older athletes get the most out of the capacities they still have.

References:

Betik, Andrew C, and Russell T Hepple. “Determinants of VO2 max decline with aging: an integrated perspective.” Applied physiology, nutrition, and metabolism = Physiologie appliquee, nutrition et metabolisme vol. 33,1 (2008): 130-40. doi:10.1139/H07-174

Kim, Chul-Ho et al. “The Effect of Aging on Relationships between Lean Body Mass and VO2max in Rowers.” PloS one vol. 11,8 e0160275. 1 Aug. 2016, doi:10.1371/journal.pone.0160275

Parry-Williams, Gemma et al. “The heart of the ageing endurance athlete: the role of chronic coronary stress.” European heart journal vol. 42,28 (2021): 2737-2744. doi:10.1093/eurheartj/ehab095

Proctor, D N et al. “Reduced leg blood flow during dynamic exercise in older endurance-trained men.” Journal of applied physiology (Bethesda, Md. : 1985) vol. 85,1 (1998): 68-75. doi:10.1152/jappl.1998.85.1.68

Ribeiro, Ana Sofia Fernandes et al. “Cardiac System during the Aging Process.” Aging and disease vol. 14,4 1105-1122. 1 Aug. 2023, doi:10.14336/AD.2023.0115

Salvatore SS, Zelenski KN, Perkins RK. Age-Related Changes in Skeletal Muscle Oxygen Utilization. Journal of Functional Morphology and Kinesiology. 2022; 7(4):87. https://doi.org/10.3390/jfmk7040087