I agree about duration of training, especially when you get older. My limit now is 2 hours uphill bike, but only once a week, mostly 1 to 1.5 hours. I've always preferred shorter harder workouts, it gives you more in return for your time and develops more muscle mass. The old fallacy, I never bought into, was "long slow distance" it always seemed absurd to me, now in the last 5 years even the research shows you burn more calories at the anaerobic threshold.
I follow the Burdenko Methods. You can build strong muscles without heavy weights, build the exercises by doing sets with slow, medium and fast speeds. It's safe, great for flexibility and joints, plus keeps developing speed, which is one of the first things we lose.
http://www.burdenko.comTabata training: long aerobic
Group 1 had a significant increase in the aerobic system (cardiovascular system). However, the anaerobic system (muscles) gained little or no results at all.
Group 2 anerobic short workouts:
Showed much improvement in all their athletes. Their aerobic systems increased much more than group ones, and their anaerobic systems increased by 28%.
Conclusion? Not only did high intensity interval training have more of an impact on the aerobic systems; it had an impact on the anaerobic systems as well.
BTW: This is not new, although Tabata is about 1995, also HIIT, (high intensity interval Training) we were doing these types of intervals back in the 60ies. and 70ies.