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Thresholds Explained (Pt 2)

So last week we explained 'lactate threshold' and why many magazine articles get it so wrong. If you missed it you can read it by GOING HERE. This week, we look at aerobic/anaerobic thresholds and ventilatory thresholds.

We don't need to take blood (as we do for lactate) to measure these thresholds. They can be calculated by measuring the air going in and out of your lungs. Primarily, there are 3 things we measure, how quickly you're breathing, how much air moves in and out and what the air is made up of e.g. oxygen and carbon dioxide.

The role of carbon dioxide

Carbon dioxide is a waste product produced by muscles and other tissues. It's pretty toxic so when we produce it, we need to get rid of it. Your body has sensors which detects when carbon dioxide level increase, it triggers your breathing rate to speed up so you can exhale it.

When you run harder, you need more oxygen so you breathe harder!

Technically yes, although the main trigger is carbon dioxide. When you start to run, you produce CO2, this triggers breathing and heart rate to go up. The harder you work, the more CO2 you produce, this triggers breathing and heart rate to increase further.

How do we use this to calculate thresholds?

This is very simple. We can measure the increase in breathing rate when you exercise and we can measure how much oxygen your body absorbs. When you breathe faster, you do it for 2 reasons: to get more oxygen in and to remove waste carbon dioxide. If your breathing rate goes up but your body doesn't absorb any more oxygen as a result, then you must be breathing faster for the other reason... to get rid of carbon dioxide.

Calculating thresholds

During a cycle or run testing session, there are 2 key thresholds. The aerobic threshold occurs quite early, this is the point when your breathing rate increases above rest. The best example of this is being able to exercise and hold a full conversation, then as the pace increases, you notice a change in your breathing and can't hold a full conversation. This threshold occurs quite early during an exercise test.

As the exercise test gets harder, your breathing rate increases steadily to match. Eventually you hit a second 'anaerobic threshold' point where your breathing starts to rapidly increase. During a 10k / 5k running race at your fastest pace, your breathing will be fast and hard, but it will remain 'stable'. If you push the pace just a little too much, it becomes 'unstable' and you start to hyperventilate. The only way to change this is to slow down and regain control of breathing.

These 2 thresholds can be measured during a Vo2 max testing session, by using a mask and gas analysis machine. Their description sounds similar to lactate thresholds but we find that the heart rate calculations are generally higher than during a lactate threshold test. Measuring thresholds as above tends to be more accurate for most athletes, when lactate threshold tends to calculate lower than expected and is therefore less practical.

Ventilatory threshold

The test we've outlined above involves the measurement of breathing rate to identify changes, for this reason, they are often refered to as ventilatory thresholds (VT). Next time you are riding with a friend and approaching a hill, listen to their breathing (and your own) and you can identify the 2 thresholds. Start at an easy conversation pace and climb steadily, the conversation will soon stop at VT1. Continue to climb and increase the pace and your breathing will become more laboured but still under control. For the last few minutes, ride at a pace which is harder than you can sustain, you'll sense and hear your breathing rapidly increasing beyond control, this is VT2. On a long, hard climb, most people know where their VT2 is, and instinctively ride/run a few beats below it, to ensure that they don't 'blow!!'.

Next week, we'll talk functional threshold, the final part of the trilogy!

If you'd like a more accurate assessment of your personal strengths and weaknesses, you can book a sports science assessment. We can put together a plan which will be specific to you, the cost for sports science assessment is £75 and you can BOOK HERE.

Marc Laithwaite
The Endurance Store

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