The cardiovascular system is significantly more malleable during teenage years, making it difficult to develop high cardiovascular fitness later in life if not trained intensely during adolescence.

“I suspect there's something to — being in that environment when you're young during the the formative years of your cardiovascular system — I I look at at like my daughter who's 13 and she loves volleyball and basketball but doesn't like cross country or track and I I'm trying not to be a psycho about it but I'm also sort of telling her like you have this really narrow window in which your cardiovascular system is quite malleable — and like I'm very fortunate that because I was involved in boxing I had to do so much cardio both aerobic and anerobic training during those formative years and even though I'm a fraction of that level of Fitness today I can still ride on you know what I had then but I feel like if you don't push that system hard in your teenage years it's very hard to develop it later I don't know if that's true but that has been my impression”