spike in cortisol, the natural stress hormone, which can prevent deep, regenerative sleep, making it even harder to sleep. It's a vicious circle," he explains. "Exercise is the one factor that has been shown to redress that imbalance." Mile repeats might
decreases, so your heart has to pump less blood faster to keep you cool, making you heat up more and making your heart beat even faster."The hours of training you put in make your body better at transporting oxygen to your muslces, so you stay below your
