The Surprising Impact of Physical Fitness on Life Expectancy and Health

Working as a doctor, you are forced to confront the inevitability of the decline of the human body with age. One interesting thing you also quickly notice is that different people decline at very different rates. One patient in their nineties could have been living at home independently, going out to see friends when they want, whereas another patient in their early seventies could be too breathless and weak to get out of bed without assistance, even before they came to hospital. People who have significantly declined in their physical function like this  are far more likely to die in the coming year, and it also obviously hugely impacts their quality of life in the remaining time they do have. Some of this variability in the speed of decline  is due to genetics or luck, but I have recently come to consider how we may have far more control over the chances that this will be our fate in the future than I’d previously thought. 

We are all aware of the hugely detrimental impact smoking can have on our life expectancy and our quality of life, which is why many of us choose not to take up this habit. Similarly, we are aware that being physically fit has health benefits. What I have been surprised by are the claims that the benefits of being fit may be enormous. In some studies it seems as if the impact of being physically fit has a far bigger impact on a person’s future life expectancy and health than the impact of whether or not they smoke cigarettes. A 2016 scientific statement by the American Heart Association looked at the impact of physical fitness, specifically cardiorespiratory fitness, in detail. They reviewed a wide range of studies and advised that

‘CRF [cardiorespiratory fitness] is a potentially stronger predictor of mortality than established risk factors such as smoking, hypertension, high cholesterol, and type 2 diabetes mellitus’

Studies they cited found that the biggest benefits were in moving from a level of low fitness and improving to reach average fitness. This is important, suggesting that you have the most to gain if you are the most unfit. What was just as interesting was that you continue to gain benefit the fitter you get. The benefits don’t seem to peak at a certain level of fitness. This suggests that even if you are already of above average fitness, you can still gain significant benefits by increasing your level of fitness further. 

There are various forms of exercise of course, and different measures of fitness. The one I’ve begun to particularly focus on is VO2 Max. It is something that I had previously been very dimly aware of, but not really understood. VO2 Max is the maximum rate of oxygen that your body is able to use during physical exertion. The V is for volume, O2 for oxygen and max for, well, maximum. It is measured in ml/kg. Various smart watches, including my Garmin, will estimate your VO2 Max, but to get the true value you need specialised equipment. You need to be hooked up to a special mask, which is connected to its own air supply and tightly fitting, so that it won’t allow outside air in, whilst you are on a treadmill or stationary bike. You then have to run or cycle at gradually increasing intensity. As the exercise intensity increases your body uses more and more oxygen from the air you breathe in, which the machine can monitor. However, at a certain point, despite the intensity of the exercise increasing your body is unable to use a greater amount of oxygen. It reaches a plateau, a maximum volume of oxygen use, where even if greater demands are placed on it, your body just doesn’t have the ability to utilise oxygen at a faster rate. This is your VO2 Max. VO2 Max, when measured properly, is considered the ‘gold standard’ of cardiorespiratory fitness measurements. For now, although I can see the benefit of knowing my VO2 Max, I’ve not undertaken the test. That’s  because of the need to use a service with this specialised equipment, the cost involved and frankly the very unpleasant nature of the test (running at the intensity at which your body is desperately trying to get more oxygen but can’t physically meet that need sounds unpleasant). For now I’m just using the estimate provided by my Garmin watch, as that’s probably good enough for me at the moment in my goal to improve my cardiorespiratory fitness.

There are many different ways to improve your VO2 max. The Norwegian University of Science and Technology has done a  lot of research in this area, and has a really useful webpage. They recommend what they call 4×4 interval training. This involves a warm run jog, followed by running as hard as you can for four minutes (note this doesn’t mean sprinting – your aim is to keep up the same pace over the entire four minutes), then recover by gently jogging for 3 minutes, then run hard again for four minutes, and repeat this cycle until you have completed 4 rounds of the 4 minutes of hard running. This appeals to me because it’s simple, they have evidence to back up their claims about the effectiveness of the method, it doesn’t take a lot of time and I find this sort of interval running psychologically less challenging than running at a constant pace or sprints. I started using it three weeks ago. 

In conclusion, decline is inevitable, rate of decline may not be. Fitness, particularly cardiorespiratory fitness, likely has a huge impact on our rate of decline. This is supported by the AHA scientific statement in 2016, and specifically by the various papers they cite. The most important measure of cardiorespiratory fitness is VO2 Max. VO2 Max is the gold standard measure of cardiorespiratory fitness. One evidence based way to improve your VO2 Max in a time efficient manner is 4×4 interval training. I’m using this method now, and I’ll write an article soon on how I’ve got on.