The question of whether years of intense endurance training might, just possibly, be harmful to the heart is hardly new.
When people train for marathons, a lot of extra endurance training is involved.
This study adopted RT-PCR technique to observe the change of express of gene of rats' ANP and BNP during 11 week's moderate intensity endurance training;
Their meeting will occur on a random basis, where the school's hungriest students will start with "stretching and a warm-up lap", followed by "speed training" and "endurance training".
Take the exercise theory. If play evolved to build muscle or as a kind of endurance training, then you would expect to see permanent benefits.