Aerobic Capacity

Endurance training results in a higher aerobic capacity. Aerobic capacity is a term used synonymously with VO2max, or maximal oxygen consumption. These terms refer to the highest rate of oxygen transport and use by your body during maximal physical exertion.

VO2max is expressed through the Fick equation, which multiplies heart rate (HR) by stroke volume (SV) by arteriovenous oxygen difference (a-v O2 difference):

VO2max (mL / kg / min) = HR (beat / min) x SV (mL / beat) x (a-v O2 difference)

VO2max can be expressed in absolute terms as liters per minute (L/min), but is typically expressed relative to body weight so that comparisons among individuals can be made. Relative VO2max is therefore expressed as milliliters per kilogram per minute (mL/kg/min).

The higher your VO2max, or aerobic capacity, the faster you’re able to move over long distances. This is because a higher VO2max means a higher stroke volume—that is, for each heartbeat your heart will pump a greater amount of oxygenated blood to your muscles. Some of the top male endurance athletes in the world have recorded VO2max scores over 80 or even 90. For example, Greg LeMond’s VO2max was 92.5. Steve Prefontaine’s was 84.4. Mountain runners Matt Carpenter and Kilian Jornet have measured 92.0 and 89.5, respectively, and track runners Jim Ryun and Steve Scott measured 81.0 and 80.1, respectively. Some top female endurance athletes have recorded scores over 70. For example, 1984 Olympic marathon champion Joan Benoit Samuelson had a VO2max of 78.6;  marathoner Rosa Mota had one of 67.2. By comparison, anything above 55 for 20-29 year old men, above 52 for 30-39 year old men, above 50 for 40-49 year old men, above 49 for 50-59 year old men, or above 44 for men over 60 represent scores in the top 10 percentile of the male population, according to the norms provided by the American College of Sports Medicine. Likewise, anything above 49 for 20-29 year old women, above 45 for 30-39 year old women, above 42 for 40-49 year old women, above 37 for 50-59 year old women, or above 34 for women over 60 represent scores in the top 10 percentile of the female population.

Although an individual’s aerobic capacity is based to an extent on genetics, it is also highly malleable. Endurance training can substantially raise one’s VO2max. And per the reversibility principle, a lack of endurance training can lower one’s VO2max. And, as you can see from the norms mentioned above, it decreases with age. Moreover, being born with a high VO2max does not necessarily make a champion runner, cyclist, swimmer, triathlete or other type of endurance athlete. If that were the case, we might as well just all go to the lab to get our VO2max tested and turn in the results to race organizers. Obviously, there are many factors involved in being successful at endurance events, including mental skills, nutrition, and race tactics, just to name a few. Even when it comes to VO2max, two athletes that vary in their aerobic capacities may still possess equivalent effective aerobic capacities when taking into account economy of motion. In other words, Athlete A may achieve a 5K run time of 17 minutes with a VO2max of 62 and fair running economy while Athlete B may achieve that same 5K time with a VO2max of 58 and excellent running economy.

The bottom line is that laboratory recorded numbers are only a starting point. The key is knowing how to use those numbers to effectively train because endurance training will lead to better performance through many central and peripheral physiological adaptations, including an increased VO2max, increased stroke volume (i.e. amount of blood pumped with each heartbeat), increased capillary density in skeletal muscle, improved blood lipid profile, and increased lean body mass.

The following table shows VO2max norms for men and women (ACSM’s Guidelines for Exercise Testing and Prescription: Seventh Edition 2006, p. 79).