Friday, 15 February 2013

Pushing it to the max!

Well, I'm just back from my VO2 max test on the treadmill at the University of the West of Scotland.  Only about 14 minutes of exercise - but enough to max out my heart rate at 180 bpm.

In order to correctly determine this value you are connected up to a gas analyser that measure how much Oxygen (O2) and Carbon Dioxide (CO2) you are breathing in and out. It's not exactly the most comfortable thing to be connected to, and even 2 hours after the test I can still feel where the nose clips have been pinching!

The start of the test is basically standing still for 3 or 4 minutes whilst the computer collects baseline data, then the treadmill was turned on to 9 km/hour for about 5 minutes allowing me to get warmed up for the test. Then the fun really starts. Each minute the speed is increased by 1km/hour. I managed to complete a minute at 18 km/hr before deciding that flying off the back off the back of the treadmill whilst connected to a very expensive piece of equipment may not be the best idea. Probably a wise decision!

Could I have managed another minute at 19 km/hr? Possibly, but as it turned out I had reached my maximum heart rate anyway and the data had levelled off (reached a plateau) so I'm not sure whether the scientists could have obtained any more useful data.

You're probably wondering what this VO2 max stuff is and why it's important…

Here comes the science!!!

According to
VO2 (or oxygen consumption) is a measure of the volume of oxygen that is used by your body to convert the energy from the food we eat (which is stored in our muscles) into the energy molecules, called adenosine triphosphate (ATP), that your body uses at the cellular level. VO2max (or maximal oxygen consumption) is simply the maximum possible VO2 that a given person can achieve. VO2 and VO2max are important in the context of exercise, because they are a measure of your body's ability to generate ATP, and ATP is the energy source that allows your muscles to continue working while you are exercising. Therefore, by definition, a VO2max measurement is ultimately a measure of your cardiorespiratory fitness level.  

There are a number of what are called 'energy pathways' in the body but to keep things simple, let's consider the two main types of fuel; carbohydrates and fat. The body stores carbohydrate as glycogen and typically we have around 3 hours worth of supply for an intensive exercise like running. We have many, many more hours (days/weeks/months!) supply of fuel in the form of body fat.

The body can process this fuel in one of two ways: aerobic (with oxygen) and anaerobic (without oxygen). You can think of this as a sliding scale as you begin to exercise your body will work aerobically at low intensities and then as you work progressively harder, the anaerobic pathway begins to kick in before becoming the dominant way of producing energy when you are pushing your body to the limit!

When working hard anaerobically your body starts to produce a chemical called lactate and hydrogen ions. As these hydrogen ions build up they create an acid which cause the 'burn' in your muscles. After a while this stops (or inhibits) your muscles from moving - essentially a warning from the body's central nervous system - forcing you to stop before you cause further damage. At this point you've had it and you can no longer keep on going! Not ideal when competing in an endurance race such as triathlon.

The other energy pathway is aerobic - i.e. your body is consuming oxygen together with fat and glycogen stored in your body. We can liken this to burning a candle: the glycogen is the wick and the fat is the candle. Fat stores a great deal more energy than carbohydrate, however, it is a slow burning fuel and is therefore better suited to longer, less intensive exercise.

The reason the VO2 tests are really important are they determine how hard you can work in both your aerobic and anaerobic zones. Essentially the data will provide a heart rate zone (zones 1-4 as mentioned previously in my blog) which helps the athlete to ensure they stay in their aerobic exercise zone, burning as much fat as possible, and not depleting their glycogen stores in the body. Staying aerobic is the goal for long endurance races such as Ironman.

You may have heard of some people hitting 'the wall' in a marathon… this is because over 20 miles or so they have been working too hard for their aerobic system to cope and have slowly but steadily been burning their carbohydrate stores (anaerobically). Once these are gone, that's it and the body starts to break down the protein in the muscles to put glucose back into the bloodstream to ensure the brain's continued survival! The brain is telling the body "(almost) game over" - you're slowing right down, generally to a crawl!!!

Hopefully that now makes a great deal more sense and why I subjected myself to the following tests:

My VO2 max treadmill test - definitely needing to jump off the treadmill at the end of this!

I'm waiting for the full data and analysis on both the bike and run and I'll post it up when I receive it from Zak. Many thanks to everyone there; Zak, John and Chris for the use of the facilities - I hope you get as much out of my data as I will :-)

The data will help to ensure I'm working hard enough on the bike and run so that I build up my aerobic endurance without pushing it too far. 

So what did I get? My VO2max value was 46.6 ml/kg/min - nowhere near the highest recorded value of 90 ml/kg/min of a Norwegian cross country skier, but high enough (according to Heyward et. al.) to put me in the excellent category for my age. Pleased with that!

No comments:

Total Pageviews