I. Purpose:
To summarize the physiological events occurring during treadmill or bicycle
exercise of progressively increasing intensity.
II. Theory:
There is little doubt concerning the primary metabolic processes which
contribute to high intensity short duration exercise (phosphagen depletion and/or
anaerobic (fast glycolysis) or in longer duration performance (oxidation). The
transition period from low intensity aerobic exercise to high intensity anaerobic
exercise has generated much discussion in recent years. A determination of the
adjustments, which are respiratory related and an identification of the phases
which occur during transition can assist in understanding the ongoing metabolic
processes involved.
There are three exercise transition phases which can be identified in the
progression from low to high intensity exercise. The current lab will measure
gas exchange parameters (VO2, VCO2, FEO2, FECO2, RQ, VE) and heart rate
response, while making reference to typical changes in blood lactate (LA). The
actual measurement of LA levels would be useful but are beyond the scope of this
laboratory procedure.
Phase I (Refer to Figure 1 for a representation of typical values and changes one may
expect)
A greater amount of oxygen is being extracted by the tissues resulting in a
gradually decreasing fraction of oxygen (FEO2) in the expired air with increasing
levels of relatively low intensity exercise. There are also linear increases in
oxygen uptake (VO2), minute ventilation (VE), and heart rate (HR). When greater amounts of CO2 are produced, expired fraction (FECO2) and volume of CO2 produced (VCO2) also increase. Physiologiss agree that the first phase primarily involves aerobic metabolism since LA assessed during this period remains near resting levels (1-2 mM)
Phase II:
The exercise intensity continues to increase and reaches a point between
40% and 60% VO2MAX, VO2 and HR continue to rise linearly and there is an initial
rise in LA to twice resting values (about 2 mmol/liter). The body attempts to
compensate for the higher levels of LA (H+ accumulation) and CO2, the respiratory
center is stimulated to increase VE; the combined effect of a higher VE and a higher
level of CO2 in the blood produces a higher VCO2. The LA rises to a value lower
than approximately 4 mmol/liter by the end of this second phase, this respiratory
compensation appears reasonably effective.
The extra increase in VE results in a lower extraction of oxygen per volume of per
volume of air ventilated and there is a corresponding rise in FEO2 since the body
does not consume more oxygen than is needed to replace the ATP utilized.
Therefore, the onset of Phase II is characterized by a nonlinear increase in VE and
VCO2, and an increase in FEO2 without a corresponding decrease in FECO2, plus a
rise in blood LA from approximately 1 to 2 mmol/liter. This onset of blood LA
accumulation corresponds to the anaerobic threshold described by Wasserman,
Whipp, Royal & Beaver (1973) known today as the lactate threshold (LT).
Phase III:
Further increases in exercise intensity to about 65-90% VO2MAX, the linear
rise in VO2 and the HR continues until near-maximal work loads at which time they
begin to plateau. Blood LA is around 4 mmol/liter at the onset of phase III and
then increases more rapidly until the subject attains their VO2MAX. There is also a
further increase in VE and a continuous rise in VCO2 in an attempt to compensate
for the marked rise in LA. The 2nd change in VE indicates the hyperventilation
cannot compensate adequately and there is a drop-off in FECO2, while FEO2
continues to rise. The onset of Phase III is thus characterized by a sharp rise in
blood LA from a level of about 4 mmol/liter, onset of blood lactate accumulation
(OBLA), a decrease in FECO2, a marked hyperventilation. The phase III onset, with
its “break-away” ventilation (respiratory compensation), appears to correspond to
the anaerobic threshold noted by MacDougall (1978) and Green, Daub, Painter,
Houston & Thomson (1979).
Historically, both the onset of Phase II and Phase III have been referred to
by different authors as the anaerobic threshold. Skinner and McLellan have
suggested that since the initial rise in lactate and the non-linear increases in VE
and VCO2, which characterize the onset of Phase II, are related to the recruitment of slow twitch fibers and to an imbalance between the rate of pyruvate production
and pyruvate oxidation and are related less to anaerobiosis that this be designated
the aerobic threshold. Similarly, since the sharp rise in lactate and the “break-
away” VE seen at the onset of Phase III are related more to anaerobiosis and the
increasing recruitment of fast twitch fibers with their predisposition to hypoxia,
Skinner and McLellan suggest that this point be termed the anaerobic threshold
(we will call this the OBLA).
III. Equipment Needed:
A. Gas analysis and volume measurement equipment
B. Bicycle ergometer or treadmill
C. Heart rate monitor
IV. Procedures:
A. Subject should be trained (healthy) and accustomed to high intensity exercise.
B. Subject will be outfitted for oxygen uptake and heart rate measurement (Polar Heart Rate Monitor) and will begin walking on the treadmill at the stipulated speed (Bruce Treadmill Protocol). Each stage will last for three (3) minutes.
C. All values for completing the recording form will be collected every thirty (30) seconds. Heart rate and Rating of Perceived Exertion (RPE) will be measured every minute.
D. This recording process should continue until the subject reaches maximal effort. Collect the values during the last minute of exercise during the final stage if the subject cannot continue until the end of the stage.
V. Questions:
1. Construct a series of graphs with time on the horizontal axis and VO2, VCO2, VE, FECO2, FEO2, HR and RPE.
2. Describe and discuss whether or not your participant attained a VO2max or VO2peak.
3. Can you identify the ventilatory/lactate threshold? Are your results in agreement with the examples provided? Explain why the values were or were not in agreement with the lab theory.
4. Can you identify the respiratory compensation/OBLA threshold/lactate turnpoint? Are your results in agreement with the examples provided? Explain why the values were or were not in agreement with the lab theory.
5. What is your participants’s VO2MAX? What was the relative intensity (%VO2MAX) and heart rate (% Hrmax) at which the ventilatory threshold occurred? Which relative intensity did the respiratory compensation/OBLA threshold occur?
6. How accurate are these non-invasive measures, based on your data, in identifying both the ventilatory/lactate and respiratory compensation/OBLA thresholds?
7. Based upon the above findings (#’s 1-5) describe to your patient/participant their findings in “layman” terms. Secondly, develop an age-appropriate exercise prescription to develop cardiovascular fitness that is scientifically- supported and that has a basis from your current test result.
