here is scientific explanation for some of this:
http://www.pponline.co.uk/encyc/strength-and-endurance-train...
and
http://www.pponline.co.uk/encyc/strength-and-endurance-train...
http://www.pponline.co.uk/encyc/strength-and-endurance-train...
and
http://www.pponline.co.uk/encyc/strength-and-endurance-train...