Transcript Document

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
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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. 97:84138, 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... “
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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.
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
4000
Incremental Protocol
VO2 (mL/min)
3500
VO2max
100% VO2max
3000
2500
80% VO2max
60% VO2max
2000
40% VO2max
1500
1000
20% VO2max
500
0
0
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4
6
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10
12
14
16
18
20
Time (min)
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).
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.
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. 55:42D47D, 1985 with permission.
• 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.
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.
• 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.
• 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.
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.
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.
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.
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.
Limiting factors for max oxygen
uptake