Disclaimer: I'm no expert on this
In Tony Robbins' book
Awaken The Giant Within, under the
Physical Destiny chapter, he writes about human growth hormone (HGH), which 'stimulates tissue growth, increases muscle tone and lean mass, enhances flexibility, thickens muscle, stimulates the growth of bones and organs, and helps maintain healthy tissue.'
HGH is released after heavy exercise, and he says that tests have shown that 'people in their sixties who've gone at least ten to fifteen years without any muscle tone are learning to lift weights and create muscle mass equivalent to that of twenty-one-year-olds, with energy levels to match.'
I'd be interested to hear what more informed opinions have to say
