I m 76 years of age. I feel good when I get up in the morning-usually about 3:00. Every other day, I work out at Planet Fitness for about an hour and 10 minutes. I do the treadmill for 25 minutes at 4mph and 4% rise. The rest of the time I exercise the arms, legs, and shoulders. Whether I exercise or not, by noon, I get real tired and my back begins to hurt. I have to sit down and rest a lot. This has been this way for the past six months. I hope there s an exercise that can help me. I don t take any prescription medicine. I do take some vitamins.