Indeed. And I'd wager that what works on them is not even constant, but varies with time, experience, body composition, etc. If you start from zero, doing anyt

Indeed. And I'd wager that what works on them is not even constant, but varies with time, experience, body composition, etc. If you start from zero, doing anything a little bit improves your body, but it's also very easy to overdo it and break your body. If you then switch the activity, your body is already much stronger and better prepared for a new activity and is not as likely to break. Maybe the lesson is that variation is the key? Do all sorts of physical activities and switch them occasionally?