These days we hear everywhere about the benefits of high intensity training – ‘more work done in less time’, ‘more calories burnt during and after exercise’, ‘get fitter faster’, ‘work hard for 45 minutes and you’ve earned yourself that bottle of wine or bar of chocolate’ – these are some of the supposed benefits of high intensity training. And don’t get me wrong, I love high intensity training – that feeling of stress relief that comes with sweating hard and that lovely sense of relaxation afterwards – there is a place for high intensity training for achieving certain goals. However, you may be wrong in thinking that high intensity training is necessarily going to get you the results you desire – more weight loss or more fat burning, faster metabolism, run faster, more able to do that Park Run or half marathon quicker.
So what’s not to like about high intensity training? Firstly, the claims relating to greater weight loss are bogus because they rest on an energy balance theory where all calories are equal and if you simply count what goes in and burn more than you consume, either during or after exercise, you will create a calorie deficit that will produce weight loss, as sure as the sun rising tomorrow. This is the theory that has been pounded into us under the influence of government and the food giants to imply total individual responsibility and exonerate themselves from blame for the public health disaster they have created with sugar. But we know that sugar calories are metabolised totally differently from fat calories and that protein calories require a large chunk of energy to digest and absorb, so calories are different depending on where they come from. This is one reason why you’re not losing the weight you thought you would by punishing your body with gruelling workouts every day.
Secondly, you are not necessarily burning more fat, as it’s claimed. As soon as you exceed a certain intensity of exercise, you start to burn proportionately more carbohydrates for energy and less fat. Moreover you will crave more sugars for future energy needs. As your consumption of carbohydrates increases, so does insulin and the presence of insulin inhibits fat burning. So if you are constantly fuelling your body on carbohydrates, then you will never get to access your fat stores for energy. Fat is a much more abundant and efficient form of energy than carbohydrates – the body can only store up to around 2000 calories in carbohydrates, but can access potentially 60,000 or more calories in fat – enough to run up to around 600 miles! The best way to access these fat stores is by exercising at a much lower intensity, within your truly aerobic zone (up to around 65-70% of your maximum heart rate, depending on the individual), and combining this with a diet that is high in healthy fats and very low in processed carbohydrates. In this way, your body gets used to turning to fats for fuel and you truly will lose body fat if you give the body time to get used to this change.
With regard to running faster, I know from my own experience that very high intensity intervals of varying lengths will produce results over a range of distances, at least in the short term, if you’re lucky enough not to get injured or ill. But it was also known way back in the 1970’s that you can actually get faster by going slower, even if it seems counter-intuitive and many distance runners followed the LSD method (that’s long slow distance, not the illegal substance!). And it makes perfect sense because any race longer than 400 metres is going to rely on the aerobic (with oxygen) system for energy, not the anaerobic (without oxygen). Indeed a 10k race is more than 90% aerobic, whilst a marathon is 99% aerobic. They don’t depend hardly at all on the anaerobic system so why on earth would you spend time improving it? Rather we should be improving our aerobic system first by training at low intensity to be able to go faster at a lower heart rate. If we decide to train for that tiny amount of anaerobic system used it should be a very minor part of the training, perhaps as a sharpener for a race, although, even there, the benefits are highly debatable since it is well-established that you cannot train both systems simultaneously. Indeed, once you start to train one, the other becomes less effective!
Finally, the metabolic stresses created by high intensity training are often such that the body does not fully recover between sessions, thereby increasing the likelihood of injury or illness, especially if you add in the inflammatory and other effects of a typical high carb diet, which is what you will most likely crave. You will also develop a very poor aerobic system unless you take periods where you just focus on rebuilding this by going slow and a strong, healthy body relies heavily on this for everyday life and indeed most sports. Just one more thing; as intensity increases, there is a negative impact on our gait, form and posture which encourages muscular imbalance and leads to injury.
Like I say, I love high intensity workouts because they make you feel good. However, they need to be approached with caution and not overdone. More importantly perhaps, they should be preceded in most cases by establishing a solid aerobic base, good form and posture, otherwise they may do you more harm than good in the long run.