Your inability to run for 15-20 minutes is simply cardio fitness. There is no reason you can’t bring yourself back up to a quite respectable level simple using a simple exercise program. I really like intervals. As to the whole weight thing. You get strong by challenging your body. If you build up your strength your bones build up as well. That is why a primary recommendation for people who have Osteoporosis is that they do weight training. Weight training properly done will challenge your body to adapt to increased loads and you get bigger muscles and increased the bone strength and density.
Nobody is suggesting that you go out and immediately leg press 800 lbs. But if you undertake a training progam to get stronger and increase the amount of weight you can lift, then over time you will find that your bones are strong and you are strong.
But don’t just listen to us, if it worries you ask your doctor and see what he recommends. My bet is that he suggests physical therapy aimed at exactly what I just told you.
