Exercise scientists generally consider the best indicator of cardiovascular fitness to be the body’s ability to take in and utilize oxygen. The measurement of this ability is known as maximal oxygen consumption, or V. O2max. The most widely accepted predictor of cardiovascular fitness is one’s HR response to submaximal work.
Once again, because numerous pharmacological agents can affect HR, it is important to identify the medications that a participant is taking and determine whether or not medication is impacting HR and or BP. Appendix C contains a list of pharmacological agents and their effects on cardiorespiratory responses to exercise. For participants who are taking medications that alter HR responses, it is unreliable to use submaximal HR as a predictor of V. O2max.
Maximal oxygen consumption may be defined as the maximal rate at which the body can take up, distribute, and use oxygen in the performance of large-muscle-mass exercise. For muscular work lasting more than 6 min at rates for which anaerobic sources of energy are not exceeded, there exists a highest level of work at which the body reaches its maximum capacity to supply oxygen. Levels of V. O2max are observed after the participant’s workload is increased progressively until it exceeds the capacity of the oxygen uptake and requires anaerobic sources of power in the final spurt. When oxygen uptake can no longer increase despite the fact that work can continue at higher levels for a short time because of anaerobic power sources, the participant has reached a plateau for maximal oxygen uptake (aerobic capacity). Every person has a measurable upper limit of oxygen uptake, which correlates with his or her ability to do aerobic work.
Factors Affecting V. O2max
A person’s V. O2max level depends on body build and composition and is affected by the following factors:
1. Sex. Comparatively, the typical female will have a lower V. O2max than the typical male.
2. Age. Maximal oxygen uptake (V. O2max) decreases by 10% per decade in men and women regardless of age and exercise activity (Hawkins & Wiswell,
3. Size. A person’s maximal oxygen uptake is directly proportional to height and body surface area.
4. Weight. Maximal oxygen uptake is proportional to a person’s weight.
5. Lean body mass. V. O2max correlates 0.63 with body mass, 0.85 with fat-free body mass, and 0.91 with active muscle tissue.
6. Bed rest. Enforced bed rest of 3 weeks reduces maximal oxygen uptake by approximately 17%.
7. Altitude. At an altitude of 4,000 m V. O2max is reduced by approximately 26%. The reduction increases as altitude increases.
8. Geography. V. O2max is reduced for residents of temperate or tropical areas as compared with those living in circumpolar regions.
Maximal oxygen uptake is not affected by the following:
1. Ingestion of a small meal (up to about 750 kcal)
2. Exposure to heat stress up to 90 ºF
3. Whether the participant warms up before exercise (duration of warm-up exercise can vary)
4. Speed of exercise (rate of work can be slow, moderate, or fast)
5. Repetition (retests at intervals of 20-30 min show similar results)
Maximal oxygen uptake can increase with physical conditioning or decrease with inactivity. The limiting factors may be one or both of the following:
1. The capacity of the respiratory and circulatory systems to take up and transport oxygen, a process that is dependent on alveolar ventilation, diffusing capacity of the lungs, and capacity of the blood flow for transporting oxygen from the lungs to the capillaries
2. The capacity of the working muscles to receive and use oxygen