Presentation on theme: "The concept of VO2max BASSETT, DAVID R. JR.; HOWLEY, EDWARD T Maximal oxygen uptake: classical versuscontemporary viewpoints. Medicine & Science in Sports."— Presentation transcript:
The concept of VO2max BASSETT, DAVID R. JR.; HOWLEY, EDWARD T Maximal oxygen uptake: classical versuscontemporary viewpoints. Medicine & Science in Sports & Exercise: Volume 29(5) May 1997 pp 591-603
Debate Over the past 10 years there has been a debate about the underlying tenants of VO2max –The O2 plateau –O2 delivery and limitation of VO2max –O2 uptake and limitation of VO2max –Muscle factors as the primary limiters of VO2max
Classical View of VO2max What is VO2max –Maximal rate at which body can take up and utilize O2 –Originally described by Hill in 1923 –Plotted Running speed vs O2 requirement –Determined there was a VO2max that was limited by cardiovascular and respiratory systems
Data from Hill’s VO2 experiments
Plots of Running Speed vs VO2, Ve and RQ (RER) Figure 2-Relationship between speed of running and (a) oxygen intake, (b) lung ventilation, and (c) respiratory quotient. Original graph from. Hill, A. V., C. N. H. Long, and H. Lupton. Muscular exercise, lactic acid and the supply and utilisation of oxygen-parts VII-VIII. Proc. Roy. Soc. B. 97:84- 138, 1924.
Hill argued –“In running the oxygen requirement increases continuously as the speed increases, attaining enormous values at the highest speeds; the actual oxygen intake, however, reaches a maximum beyond which no effort can drive it...The oxygen intake may attain its maximum and remain constant merely because it cannot go any higher owing to the limitations of the circulatory and respiratory system... “ –Hill, A. V. and H. Lupton. Muscular exercise, lactic acid, and the supply and utilization of oxygen. Q. J. Med. 16:135-171, 1923 This has since been referred to as the “plateau” in VO2 at max
Figure 3-Relationship of oxygen uptake to work rate during a discontinuous maximal exercise test, showing that some subjects achieve a plateau whereas others do not. Original data from reference 3. Åstrand, I., P.-O.Åstrand, and K. Rodahl. Maximal heart rate during work in older men. J. Appl. Physiol. 14:562-566, 1959.reference 3
The VO2 plateau Now, it appears as though not all subjects achieve a VO2 plateau –Depends on mode of testing and criteria for plateau E.g. 50, 80 or 150 ml/min And time of averaging
Robergs, R.A. AN EXERCISE PHYSIOLOGIST’S “CONTEMPORARY” INTERPRETATIONS OF THE “UGLY AND CREAKING EDIFICES” OF THE VO2MAX CONCEPT. Journal of Exercise Physiologyonline.2001; 4(1), 1.
Limits on VO2max Another point of controversy regards the question of what limits VO2max –Central or peripheral –Heart, lungs, capillaries or muscle –In general, it is believed that VO2max is limited by the ability of the cardiovascular system to deliver blood, and hence O2, to the tissues
TABLE 2. Summary of previous studies examining maximal oxygen uptake in leg versus combined arm-and-leg exercise. Adapted from Shipe(65).(65)
Role of Muscle Mass It is necessary to use the largest muscle mass possible to elicit a true VO2max Exercise using small muscle masses do not elicit VO2max –Since VO2 is directly proportional to work, it might be expected that using more muscle mass would elicit proportionally more O2 consumption Max work is limited using large muscle mass vs small
Figure 5-Evidence that the heart's capacity to supply blood flow to active muscle is limited. When heavy exercise is performed with the legs, the addition of arm work causes a reduction in both leg blood flow and leg oxygen uptake (not shown). During combined arm-and-leg work, the muscle's capacity to vasodilate exceeds the ability of the heart to supply blood flow. Data of reference 62. Secher, N. H., J. P. Clausen, K. Klausen, I. Noer, and J. J. T. Central and regional circulatory effects of adding arm exercise to leg exercise. Acta. Physiol. Scand. 100: 1979 as shown in reference 58. Rowell, L. B. Human Circulation: Regulation During Physical Stress. New York: Oxford University Press, 1986.reference 62 reference 58
Blood flow limitation When adding arm exercise to leg –Blood flow is reduced to legs –Total body O2 may increase with workload, but reduction in blood flow will ultimately limit exercise capacity with legs –Cardiac output increases just the same Therefore the ability of the circulation to vasodilate outstrips the ability of the heart to pump sufficient blood
Figure 6-Illustration showing experimental set-up for performing isolated muscle contractions of an isolated muscle mass. Only 2 to 3 kg of muscle are active, and blood flow and oxygen uptake values in the region are incredibly high. This demonstrates that if blood flow is not limiting, extremely high values of oxygen uptake can be obtained. From reference 59. Saltin, B. Hemodynamic adaptations to exercise. Am. J. Cardiol. 55:42D- 47D, 1985 with permission. reference 59
Another way to look at blood flow is to realize the muscle has a tremendous capacity to accommodate blood flow –O2 uptake can reach 300-400 ml/kg/min –Argues against skeletal muscle limitations to VO2max –When large muscle masses are utilized, blood flow is reduced and again VO2max is limited
What about VO2max adaptations? What are the adaptations resulting in increased VO2max with training? –Primarily due to……?
Stroke Volume TABLE 3. Physiological mechanisms behind the elevated ˙VO2max seen in elite endurance athletes, compared to normally active control subjects. Adapted from Rowell (58), p. 218.(58)
What limits submaximal performance?
Figure 7-Relative contribution in percent of energy yield from aerobic and anaerobic processes, respectively, during maximal work of different durations. Drawn from data of reference 5. Åstrand, P.-O. and K. Rodahl. Textbook of Work Physiology. New York: McGrawHill, 1970, pp. 303-304.reference 5
As exercise duration progresses, ATP needs are increasingly met by oxidative metabolism VO2max-10 min- 70% aerobic 95% VO2max – 30 min – 90% aerobic 85% VO2max – 60 min – 95% aerobic 80 % VO2max – 120 min – 99% aerobic
Blood Lactate vs Duration Figure 8-Blood lactate values of men after distance races of 1.5-42.2 km. Broken line represents average resting value observed among runners in the laboratory. From reference 14. Costill, D. L. Metabolic responses during distance running. J. Appl. Physiol. 28:251-255, 1970 with permission.reference 14
Blood lactate accumulation is a reliable indicator of anaerobic metabolism As exercise duration increases, blood lactate accumulation decreases
We know that VO2 is proportional to intensity Figure 9-Linear relationship between running speed on the treadmill and oxygen uptake (mL·kg-1·min-1). Adapted from reference 10. Bransford, D. R. and E. T. Howley. Oxygen cost of running in trained and untrained men and women. Med. Sci. Sports Exerc. 9:41-44, 1977.reference 10
And VO2max is a “good” predictor or performance in a heterogeneous population Figure 10-Relationship between maximal oxygen consumption(˙VO2max) and distance running performance. Regression line represents the running times in a 10-mile test race. From reference 18. Costill, D. L., H. Thomason, and E. Roberts. Fractional utilization of the aerobic capacity during distance running. Med. Sci. Sports Exerc. 5:248-252, 1973 with permission.reference 18
Figure 11-Variability in the steady state oxygen uptake at fixed running speeds in 12 highly-trained and experienced male distance runners. From reference 13. Conley, D. L. and G. Krahenbuhl. Running economy and distance running performance of highly trained athletes. Med. Sci. Sports Exerc. 12:357-360, 1980.reference 13
Figure 12-Relationship between 10 km race time (y-axis) and steady-state oxygen uptake at 268 m·min-1 in 12 highly-trained and experienced male distance runners. From reference 13. Conley, D. L. and G. Krahenbuhl. Running economy and distance running performance of highly trained athletes. Med. Sci. Sports Exerc. 12:357-360, 1980.reference 13
So, VO2max will set your upper limit to utilize O2 –This will determine your performance capacity Factors such as economy and lactate threshold (which are trainable over time) will determine how good you will be relative to that capacity
Figure 13-Summary of the major variables related to˙VO2max and the maximum velocity that can be maintained in distance races.