Exercise is Destroying You.
Earlier today I was at the gym .. well my mini home gym that doubles up as a shed, complete with some dumbbells, kettlebells, bands and some pull-up equipment. I did about a 45 minute session, tough enough. As I exercised my energy expenditure went up as I burned calories to fuel my activity. Afterwards, I was a little tired and somewhat sore.
Interestingly, after exercise, it takes quite a while for your body to return to it's resting metabolism - you still expend energy for quite a time after your exercise session. This state of heightened energy consumption after exercise is scientifically called post-exercise oxygen consumption (EPOC), but is informally known as afterburn.
What is going on? Well, my exercise session not only used calories but it was also quite physiologically stressful. As I exercised, my body released a whole load of stress hormones - including cortisol and epinephrine which helped in speeding up my heart rate and releasing energy reserves. As my muscles consumed calories they pumped out waste products and my cells produced a whole range of harmful free radicals that damage DNA and other molecules throughout the body. In addition, my muscles also developed a whole load of microtears. I also put great stress on my skeletal system that may have caused some microcracks. No wonder I was sore!
So, if exercise is so destructive, then why is it healthy? Once I stopped exercising my body started to repair itself but interestingly my body goes into overdrive and also repairs some of the damage to my body that occurred outside of exercising - the day-to-day wear and tear of just being. In this afterburn state, my body starts to lower its heart rate, lower cortisol levels and puts the unused energy back into my muscle and fat cells. My body produced an inflammatory response to deal with muscle and skeleton damage and huge amounts of anti-oxidants are produced to mop up the free radicals. These repair activities require energy, less than my exercise, but result in EPOC for a few hours after my workout as my body repairs and replenishes. As mentioned though, the body just doesn't repair in afterburn, it makes things even better than before and increases the strength of bones and muscles resulting in a net benefit to the body.
Build. Destroy. Rebuild.
