Lab #4: Metabolic Thresholds
Lactate Threshold. The determination of the anaerobic threshold (AT), more correctly
termed lactate threshold (LT), is very important for many reasons. By definition, LT occurs
when lactate production in the tissues exceeds the rate of removal thereby causing abrupt
increases of lactate in the blood. This is a significant event because it signals the increasing
predominance of anaerobic pathways over oxidative means to regenerate ATP. In other words,
LT can be considered the maximum point where steady-state exercise can be performed because
it is impossible under anaerobic conditions, which has major implications to long-term
endurance exercise performance. In fact, LT is the best predictor (NOT VO2max) of prolonged
(> 60 min) exercise performance. With this in mind, LT can be used to develop an exercise
prescription for an individual, or to develop a training program for an athlete. It can also be used
to determine cardiorespiratory fitness, or as a diagnostic tool of the severity of cardiovascular
and pulmonary disease and exercise tolerance in the clinical setting. Therefore, since these
examples rely on the correct determination of LT, the validity of the methods that are employed
to determine LT is equally important.
The traditional standard criterion method for detecting LT involves measuring the rise in
either arterial or venous lactate concentrations or the drop in arterial bicarbonate ion (HCO3-).
Since HCO3- concentrations can easily be affected by hyperventilation prior to exercise,
measuring arterial lactate concentrations is considered to be a more direct way to determine LT.
Researchers have stated that the time when an observed systematic increase in lactate
concentration occurs above baseline, warm-up values is criteria for accumulation in the blood.
The accumulation of lactate and LT has also been shown to be dependent upon the rate of
increase in workload as well as stage time during the exercise test. This may be due to an
increase recruitment pattern of fast twitch motor units.
Other terms that have been used to describe this point have been “anaerobic threshold”
and OBLA (onset of blood lactate accumulation). The term OBLA is still used commonly today
and is most represented by a value of 4 mmol/L of blood. Anaerobic threshold has lost some
favor over the years because of the bias it has to a total switch-over to anaerobic metabolism
above the point it occurs, which is not the case. Thus, the term lactate threshold is more correct
in describing events at this point. Since blood samples are needed to determine the lactate
threshold, this procedure has been described as an invasive procedure. To attempt to circumvent
the invasiveness of this procedure, some researchers have developed other non-invasive ways to
quantify LT. The more common non-invasive ways to predict LT has been the ventilatory
threshold (VT) and heart rate (HR) threshold.
Ventilatory and HR thresholds. Past researchers have mentioned that the LT can be detected
non-invasively by employing the use of various ventilatory and gas exchange indices. These
indices included minute ventilation (VE), ventilatory equivalent for oxygen (VE/VO2), ventilatory
equivalent for carbon dioxide (VE/VO2), end tidal carbon dioxide (FETCO2), and respiratory
exchange ratio (RER). The point at which the changes in gas exchange patterns occur has been
termed the ventilatory threshold (VT).
The point of VT is best determined by the criteria developed by Caiozzo et al. (1982).
These researchers used the gas exchange variables VE/VO2 and VE/VCO2 to assist in the
selection of the point of VT. At the start of exercise, VE/VO2 decreases initially as the rise in
VO2 meets the rise in VE. As exercise continues, VE begins to increase more than VO2 until the
point where VE sharply increases and breaks away from VO2. VE/VO2 will show a systematic
increase when this occurs and will not be followed by a concomitant rise in VE/VCO2. The
reason for this is that VCO2 continues to rise linearly with VE for a period of time until VE rises
greater than VCO2. The point where VE/VO2 abruptly increases in a nonlinear fashion is
identified as the VT. Caiozzo et al. (1982) also stated that VE/VO2 was the best index for
Traditionally, it is generally thought that heart rate (HR) increases in a linear fashion with
increasing intensity during incremental exercise. However, recent research on heart rate
responses during incremental exercise has suggested that the heart rate-VO2 relationship is quite
variable among subjects of similar backgrounds. This variability was found to be dependent on
exercise protocol, left ventricular function, and cardiovascular health status. The breakpoint that
occurs in HR has been related to the occurrence of the LT with variable results.
The purposes of this lab is to quantify the ventilatory threshold as a % of VO2max using
the ventilatory equivalents method and V slope method and compare the results of these
methods. In addition, we will also identify the HR threshold or HR breakpoint as a % of
VO2max and compare this value to the ventilatory threshold value.
The equipment used will be a Lode Excalibur cycle ergometer, Quinton EKG system, and
the Physio-Dyne MAX-1 metabolic gas analyzer.
Perform a maximal exercise test on at least 5 subjects. Prep the subjects for the EKG and
hook them up to the Physio-Dyne. For gas exchange analysis, collect and print data out at 15 sec
intervals. Record heart rate data every 15 sec until max.
For the determination of VT by the ventilatory equivalents method, graph both VE/VO2 &
VE/VCO2 over VO2. Next, perform a bisegmental regression analysis of the ventilatory
equivalents in Prism to identify the point where VE/VO2 begins to increase abruptly with
increasing VO2. This point should be followed by an increase in VE/VCO2 in approximately 2
minutes. This adds to the sensitivity of VT identification. The V slope method is performed by
graphing VCO2 over VO2 and then identifying a breakpoint response with bisegmental
regression analysis. Also, perform this same analysis using VE graphed over VO2. For the HR
threshold analysis, run the same bisegmental analysis on HR over VO2 and identify a breakpoint
Using the expired gas analysis data, organize the data in 15 sec intervals on the print out
and input into the Prism graphing program. Graph each of VE, VE/VO2, VE/VCO2, VCO2, and
HR against VO2 (L/min). Put VE/VO2 & VE/VCO2 on one graph with VO2 and identify the VT
using the bisegmental regression analysis option on Prism to identify the breakpoint. Do the
same for HR, VE, & VCO2. You need to report the absolute (L/min) and relative (% of
VO2max) value at which these breakpoints occur. Analyze all of the data and report the results
for all subjects in a table format; however, you need only to graph the results for one subject.
1. Comment on the physiological reasons that determine the lactate (LT) and ventilatory
thresholds (VT). What are the ways we can use to quantify the LT from a
methodological standpoint? Is one better than others? What is the best way to quantify
the VT? Are blood lactate levels similar to muscle lactate values? Can we relate blood
lactate levels to muscle?
2. Can we substitute the VT for the LT? Why or why not? What is the agreement between
the two according to the research literature? (intro)
3. Comment on the physiological reasons for the breakpoint in HR (Hoffman, Conconi).
Does this breakpoint correspond to LT? Why or why not? Does the exercise protocol
influence LT, VT, and HR threshold? (intro).
4. In the results/discussion, comment on and discuss the findings in the lab. Were these
findings expected? Did the methods for determining VT differ? Why or why not? Did
the HR threshold differ from VT? Was this expected based on comparisons between HR
threshold and LT in the research literature? Give reasons for the similarities or
differences and compare the results to past research findings.
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Beaver, W. et al. A new method for detecting the anaerobic threshold by gas exchange. Journal
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Caizzeo, V. et al. A comparison of gas exchange indices used to detect the anaerobic threshold.
Journal of Applied Physiology, 53:1184-1189, 1982.
Chwalbinska-Moneta, J. et al. Threshold for muscle lactate accumulation during progressive
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Conconi, F. et al. Determination of the anaerobic threshold by a noninvasive field test in
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Francis, K. et al. The relationship between anaerobic threshold and heart rate linearity during
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Hofmann, P. et al. Heart rate performance curve during incremental cycle ergometer exercise in
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Hughson, R. and Green, H. Blood acid-base and lactate relationships studied by ramp work
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