It is well established that a sedentary lifestyle is negative for our health and many Americans attempt to improve their lifestyle with forms of active movement.

Several lifestyle based exercise programs abound from cross-fit to yoga to resistance training, some of which require heavy, high intensity exercise upwards of five times a week.

But is heavy exercise a good thing?

Or can it actually be detrimental to our health?

As a nutritionist, I see a range of clients, from those with sedentary lifestyles to athletes and body-builders and I’ve noticed certain correlations.

In many cases, my athletic clients have similar issues shedding body fat and have heightened stress responses that make sleep and recovery difficult.  They think they are doing themselves a favor with the extra exercise, that they are burning more calories and they enjoy the feeling of a “high” that they experience afterwards.

Some use this kind of frequent, intense exercise as a method of stress relief.

However, many of these clients develop issues related to stress, sleep, recovery, and weight maintenance that can sometimes be mitigated simply by cutting back on the amount and duration of activity.

Dangers of Too Much Cardio

We often look at marathon runners and endurance trainers with admiration.  People with very low resting heart rates seem to be the picture of health.  But this isn’t entirely accurate.  In fact, too much cardio pushes the body and heart beyond its natural limits.

Heavy exercise activates our adrenal axis, a set of glands that sit on top of our kidneys and produce the hormones cortisol and adrenaline.  These are responsible for that feeling of “high” after an exercise session, but they are also the reason you might have trouble sleeping if you work out in the late afternoon and evening. 

Both hormones are stress responses and activate the sympathetic nervous system, also known as our “fight or flight” response.  While we need this ability to respond with adrenaline and cortisol for times of real danger, our modern stressful lives actually activate this response far too often.

Issues at work, our relationships, even our cellphones and alarm clocks, all activate this response so that we are essentially living lives bathed in cortisol.  And too much cortisol is known to increase belly fat. 

So, while some cardiovascular activity is certainly beneficial and while the right type (i.e. walking) can certainly reduce cortisol, it is wise to approach heavier cardio like running and high intensity interval training with caution.

The key with cardiovascular exercise is balance.  Many people falsely assume they will lose more weight by “burning” extra calories on a cardio machine.  The reality is actually more murky.  

The body does not actually “burn” calories at a one to one ratio like these machines suggest.  In fact, they have been found to be highly inaccurate.  Not only that, but it is well established that no amount of cardio can account for poor dietary choices, even if the amount of calories burned should technically make up for it.

Because of the complicated biological processes of the breakdown of foods, including the insulin response and oxidative damage, many foods do more damage than a cardio session can account for. 

By contrast, muscle building actually increases something called the metabolic rate.  This means that the body of a person with more muscle naturally burns more calories just to stay alive, which gives them more liberty to indulge in extra calories without the consequences of weight gain.

Though these gains in metabolic rate may seem small (just a couple hundred calories over several months of muscle building) they make huge differences in the fat composition of a person- especially if they eat the same or less.

Why Recovery is Important

The danger with both muscle building and cardiovascular exercise is the tendency to over-do it.  But these tendencies actually set us back.

Our bodies need ample time to repair and rebuild muscle- this actually makes us stronger, more efficient fat burners.  Without enough recovery time, our bodies never have a chance to do that work, and thus, we don’t see positive results.

Muscle building activity is best done two to three days a week while heavy cardio is best once a week or less.  In fact, heavy cardio isn’t necessary for most people and is really an optional activity for those who enjoy it.  Instead, light cardio like walking should be done everyday and has been shown to be very beneficial for the body.

Activity which increases flexibility, like yoga, is also beneficial to regularly incorporate.  In fact, relaxation yoga is a great way to reduce stress and cortisol as well.

Don’t forget to rest as well and space out your muscle building activity for ample recovery!  There is nothing at all wrong with taking one day a week to just relax.