Ventilatory Thresholds & Training Zones
Sample report showing thresholds, with corresponding HR and Power
The most important question I’m asked about metabolic assessment is “how can I use this information?” As it should be. Fitness talk is awash with metrics and variables to analyze. Informed practitioners and clients should always be asking what is the utility of these numbers.
Let’s begin with everyone’s favorite metric du jour, “Zoning”. There are several different models for zones, for simplicity we will be referring to the 5-Zone model most commonly used by applications like TrainingPeaks in this discussion. The zoning model is used to more easily illustrate where exercise training should occur. What the models do not do is correspond to specific physiologic landmarks.
When we perform a metabolic assessment with a gas analyzer like the VO2 Master I use, there are only three landmarks observed. Those are 1st Ventilatory Threshold (VT1), 2nd Ventilatory Threshold, and Maximum Ventilation (VO2max). The question becomes what are these and how can they be used to guide your training?
1st Ventilatory Threshold
VT1 as implied by the name is the first change we observe during metabolic assessment. The primary trend we are looking for is a change in the rate of ventilation. This inflection point is associated with a change in metabolism. In its simplest terms VT1 is the point exercise moves from “moderate” to “heavy or hard”. On the physiologic side of things it reflects a change in primary fuel source from fats to carbohydrates (fuel sources and their contribution to different intensities will be addressed in a follow-up post). This is an important distinction, most people have ample fat stores for extended exercise. “Zone 2 Training” is very popular at the moment, in designing a five zone training program we are looking to have the upper band of zone 2 to be roughly in line with VT1. This ensures you are able to sustain long bouts at the prescribed intensity as well as maximize fat metabolism.
Raw data of Exercise Test used to determine thresholds
2nd Ventilatory Threshold
VT2 is the point at which exercise becomes unsustainable. Breathing becomes much more rapid while often becoming shallower. Aerobic carbohydrate metabolism is no longer the primary energy source and a move to anaerobic metabolism occurs here. This is extremely important in establishing training zones. Often this is the point that separates Zones 4 & 5. Zone 5 being the maximal intensity that can only be held for brief periods of time. Other notable breakpoints will cluster around this point. Commonly used metrics like Functional Threshold Power (FTP) should be just before VT2 is reached. Maximal Lactate Steady State (MLSS, closely related to the formerly popular Lactate Threshold) also occurs just before this point. In our practice we use mNIRS of Muscle Oxygenation Inflection point as a guide to confirm VT2 or when exercise suddenly becomes unsustainable. This is seen in our analysis as a sharp sudden drop in oxygenation of the muscle, indicating that demand for oxygen is outstripping supply
Illustration of changes observed in Muscle Oxidation (SMO2) during graded exercise test
VO2max or Maximum Ventilation
VO2max is the upper limit at which the body can process oxygen. No further aerobic energy contribution can be gained above this limit. Any further increases in intensity are almost purely anaerobic. In designing a training program this is important to know. For instance if training for sprinting power the prescription should be above the observed VO2 max to train the metabolism used in an event.
The importance of assessment
There are many formulas used to find training zones. They are however all based on regression equations using large, diverse groups of people. No one model or formula can say exactly where your individual threshold will be. The Zone 2 or VT1 formula, for instance, is usually calculated as 65%-75% of max Heart Rate. Using the 220-Age formula puts VT1 anywhere between 124-143 beats per minute. A 20 bpm difference! Depending on training status that can be the difference of VT1 and VT2. Inaccurate estimation of zones can limit your ability to properly train and find the benefits of personalized exercise prescription.
This is MDB Wellness difference. Rest easy and train smarter with personalized solutions. Catering specifically to you or your clients needs. There is no one formula that can provide results for everyone.
