Is cardio killing you?

Is cardio killing you?

Prolonged, intense aerobic exercise may be doing your health more harm than good. Ramping up your heart rate too high and for too long on a regular basis is associated with raised cortisol levels, increased oxidative damage, systemic inflammation, depressed immune system function and decreased fat metabolism. So what is the alternative?

What if the exercise guidelines that we've been given over the last few decades were completely misguided? What if we're exercising too hard, for too long, and doing more harm than good in the process?

This is exactly what is being suggested by followers of the “primal” or “paleo” approach to health and fitness. Better known for its dietary regulations, this perspective on our well-being also has some thoughts to offer on fitness and exercise based on our evolutionary heritage.

Think about our caveman ancestors for a moment. What did they have to do to survive? They would have spent a lot of time foraging for food (nuts, berries and small insects, for example) and done some fishing and hunting. The latter is more likely to have involved long periods of tracking prey before going in for the kill, rather than relying on speed and stamina (fancy outrunning a cheetah to secure your lunch? Thought not.). In some parts of the world, a nomadic lifestyle would have been the norm, with all of the slow travel that brings with it. In other words, we're talking about gentle, sustained exercise. Yes, there would have been the occasional burst of more intense effort – closing in on prey during a hunt, perhaps, or escaping from predators. But these bursts would have been short and infrequent.

In other words, our evolutionary heritage suggests that we have evolved to engage in long periods of low-intensity exercise, with occasional brief bursts of all-out high intensity exercise. A far cry from, say, extended spinning classes or marathon training.

So what is the problem with high intensity aerobic exercise?

It seems that high intensity aerobic exercise brings with it a number of different problems. Adherents of a “primal” approach to health and fitness define four different processes inherent in sustained, high-intensity cardio workouts that are problematic for the body:

The creation of a need for carbohydrates

Prolonged, intense cardio workouts depend on high levels of carbohydrate consumption to sustain them, as the body depends on glucose to fuel muscle tissue at high levels of exertion. There is increasing evidence that we are not, as a species, well adapted to relying on a carbohydrate-fuelled energy system. The unprecedented level of carbohydrate consumption in the Western world is being blamed by more and more nutrition experts for a whole host of lifestyle-related diseases, particularly obesity, and less than optimum quality of life. It follows that engaging in a form of exercise that apparently increases the need for carbohydrate intake is not a good idea.

Hyperinsulinaemia (overproduction of insulin)

The carbohydrate consumption associated with high intensity cardio exercise in turn causes insulin levels to spike. High insulin levels are associated with all sorts of forms of ill health. An increased inflammatory response is a particular problem, and is often associated with a depressed immune system. The bottom line: A cardio workout that is too intense and too prolonged, undertaken on a regular basis, can actively damage your health.

Increased oxidative damage

Intense, prolonged aerobic exercise increases the production of free radicals by a factor of 10 or 20 times the normal level, according to some health experts.  This can cause oxidative damage to muscle tissue in particular, and is thought to be one of the processes underlying chronic sports injuries.

Cortisol generation

Our bodies respond to exercise as they would to any other environmental stressor, by activating the cortisol response. Cortisol is the hormone that helps us to respond to any perceived threats. At low levels of exercise intensity, this translates into a glowing feeling of mild euphoria. But when the cortisol response is activated for too long or at too high a level, it becomes damaging. Physiologically, it is as though the body were trying to deal with a life-threatening situation. The effects of being bathed in cortisol include a depressed immune system, difficulty concentrating, and disrupted sleep, and chronically elevated cortisol levels have been linked to all sorts of diseases.

An alternative approach to exercise

So does this case against cardio mean that we should all cancel our gym membership and relish our time on the sofa instead? Of course not. It's all about exercising in ways that are in harmony with our body's needs and capacities, and the gym is a great place for doing that if you use it wisely. What we need is plenty of low-level exercise with the occasional burst of high intensity effort. A brisk walk (outdoors or on the treadmill) or a gentle swim or cycle for less than an hour, a few times a week, interspersed with a few intense interval sessions of maximum exertion (think 20-40 seconds of going as fast as you can) should do the trick. Just don't spend hours and hours pounding away, red-faced and puffed out and bored – you won't be doing yourself any favours!



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