PEMES 3153 Exercise Physiology Lab
Ventilatory Threshold and Onset of Blood Lactate
Before coming to Lab read the following in your textbook: p. 124-125 (Lactate Threshold); p. 198-199 (Ventilatory Threshold)
Introduction
The Lactate Threshold (LT) is the point at which blood lactate begins to substantially accumulate above resting concentrations. It is also the point at which lactate production exceeds clearance, which is what cause the resting concentration to start to increase. Typically a value of 1-2 mmol of blood lactate above baseline is an accepted indicator of LT. This marks a metabolic shift towards greater reliance from anaerobic pathways. Shortly after reaching LT a second point of interest occurs, onset of blood lactate (OBLA). A lactate value of 4 mmol signifies OBLA. OBLA represents the maximal intensity one can sustain during prolonged steady state activities without succumbing to premature fatigue (stabilized lactate clearance).
It is therefore advantageous, particularly for endurance athletes, to know the intensity at which the LT or OBLA occurs. This allows optimization of training by performing heavy (slightly above LT or OBLA) and light (below LT or OBLA) training sessions. Blood lactate measurements can be performed inexpensively and in laboratory or field settings. Unfortunately, blood lactate measurements require blood samples. This minor issue could be troublesome for obvious reasons.
An alternative method to LT and OBLA testing ant not requiring blood samples is measuring the Ventilatory Threshold (VT). This requires measuring the volume of air ventilated and can be easily done using various types of spirometers. In this lab you will use a digital spirometer to measure ventilation during progressive exercise.
Measurement
1. Each student will perform a maximal bicycle effort. During the last 12 seconds of each minute your minute ventilation will be measured using the digital spirometer.
2. Follow the protocol below and record the data each minute. It is important to maintain as close to 80 rpm throughout the test. The test is terminated when you cannot maintain at least 60 rpm. If you feel like you are going to have to stop the test prior to the end of the 1-minute stage, tell the others in your group so you can measure your ventilation.
Kg/RPM / Power(Watts) / Ventilation
L per Min / Kg/RPM / Power
(Watts) / Ventilation
L per min
.25/80 / 20 / 2.75/80 / 220
.5/80 / 40 / 3.0/80 / 240
.75/80 / 60 / 3.25/80 / 260
1.0/80 / 80 / 3.5/80 / 280
1.25/80 / 100 / 3.75/80 / 300
1.5/80 / 120 / 4.0/80 / 320
1.75/80 / 140 / 4.25/80 / 340
2.0/80 / 160 / 4.5/80 / 360
2.25/80 / 180 / 4.75/80 / 380
2.5/80 / 200 / 5.0/80 / 400
Analyses
1.) Using Excel, graph the response for each subject of ventilation vs power with ventilation on the left vertical axis and power on the horizontal axis. (Just like Figure 8.14 in your text except with power on the horizontal axis)
2.) For each subject determine the power at which the ventilatory threshold occurred.
3.) For each subject determine the percentage of their maximal power at which the ventilatory threshold occurred.
4.) Based on the results for your group, which group member would be likely to win a 10 mile bike race? Explain your rationale.
5.) Did there appear to be a gender difference in the absolute power at which the ventilatory threshold occurred? Explain why or why there was not a gender difference?
6.) Did there appear to be a gender difference in the percentage of maximal power at which the ventilatory threshold occurred? Explain why or why not there was a gender difference.
5.) Explain why the ventilator threshold can be used as an estimate of the lactate threshold.