How Fit … ?

In The Hitchhiker’s Guide to the Galaxy, we learn that the answer to the Ultimate Question of Life, the Universe, and Everything is 42 which I’m sure is correct. If we ask Strava how fit I am the answer is …

154.

Not bad, eh?

In fact three point six (recurring) times greater than the meaning of everything but notice that back in February when I started tracking my bike riding on Strava my fitness was zero. As far as I can recall I had a pulse and could ride around the block – zero it could not have been.

It looks as though my fitness has improved and in the last couple of months there is the suggestion of a plateau. The dotted line at the right hand end is a prediction of what would happen if I quit exercise. In broad terms I wouldn’t argue with all that but what does the 154 represent? If you are a 152 am I fitter than you?

There are a number of metrics in Strava and other fitness and training apps for which you can find an explanation but not a definition or a formula. Strava’s explanation from their glossary is …

While fitness is a complicated concept, it can be simplified to an accumulation of training. The Fitness Score is calculated using Training Load and/or Relative Effort to measure your daily training, and an impulse-response model to quantify its effect over time. This will intuitively capture the development of fitness from training, as well as the loss of fitness during a break.

and you won’t find Relative Effort or Training Load in the glossary.

So training volume goes into a black box where it is fiddled with in mysterious ways and out comes the answer in unspecified units.

Fitness is indeed a complicated concept. The word fitness has a great deal of work to do. At it’s broadest it means capacity to do something. It’s gets a lot easier to get a handle on it when you define the something. Let’s make that endurance exercise. Now we can consider the factors that contribute to capacity. They may be physical characteristics that the athlete in question is stuck with such as leg length or characteristics that are amenable to manipulation such as weight and body composition.

Endurance sports are various ways of turning food into distance covered with the prize going to the fastest person to the finishing line. Oxygen is required to burn the food. A good measure of fitness therefore is the maximum rate at which oxygen can be utilised or VO₂max. It comes in two flavours – absolute and relative.

To measure VO₂max accurately is a laboratory task. Inspired air is compared with expired air to find the amount of oxygen removed by an athlete as they perform a steadily harder task until the athlete cannot continue or the oxygen consumption reaches a plateau. The difference in humidity and temperature of inspired and expired air has to be addressed. A mask is worn throughout.

The Absolute VO₂max is simply the number of litres of oxygen taken up per minute going full gas. For relative VO₂max you divide by weight and express the result in millilitres per minute per kilogram. In a series of tests for a single athlete it’s handy to have both in order to distinguish between the contributions of adaptation and weight loss. If comparing one athlete with another relative VO₂max is more useful.

As the saying goes “Test is better than guessed” but it requires attendance at a lab and a fee in the vicinity of $200 a time. It’s not a one off – if it’s worth doing then it’s worth doing regularly to ensure that training is having the desired effect.

There are ways to estimate VO₂max rather than measure it. These don’t involve wearing a mask and analyzing expired air. Some don’t even involve exercise!

If you are interested in an estimate at the level of a general health interest try the online calculator at worldfitness.org. In my case I think the answer was a little flattering. Four different ways are on offer at MDApp including one based solely on resting heart rate and age. For the other three you will need to do some exercise. The Rockport Walking Test involves a one mile walk. The formula includes a refinement that reduces the error involved in being the wrong gender.

For the price of five or six visits to the laboratory you can buy a smart watch that will estimate your VO₂max and tell the time. Passler et al 2019 (International Journal of Environmental Research and Public Health) tested a bunch of wearable devices and concluded that they don’t do a particularly good job of measuring energy expenditure or calculating VO₂max.I believe they are reasonably good at keeping time and some play music.

If you are male and have a power meter you can estimate VO₂max by investing six minutes of your life in all out effort on the bike and plugging the result into a calculator provided by Michael Konczer. I haven’t been able to find a formula for females. So sorry girls – you’re walking. The formula used is …

It is an informative site with a table that you can consult to see how your result stacks up.

Regular testing is the ideal way to keep track of progress. A six minute test over the same course is directly comparable especially when measured by power rather than distance because that reduces the problem of variable winds. Estimating VO₂max from it may not be as exact as a lab measurement but the error will be much the same each time and it gives a value that will serve well enough for rough comparisons with other athletes. Friends will be delighted to hear of your improvement.

VO₂max is a very handy metric but by itself it will not tell you who will win the next race. Economy is the ratio of work done to energy expended and this varies from athlete to athlete as does the ability to tolerate workloads close to maximum. According to Allen, Coggan and McGregor VO₂max is to be found somewhere between 106 and 120% of functional threshold power (FTP).  If you know all those numbers for every entrant your crystal ball has a better chance. And the higher your VO₂max the better the chance that it will be you.