Although scuba diving is accessible to people of all different abilities and can be modified to meet many people's needs, having good physical fitness can greatly contribute towards your safety and experience underwater.
Here's a schedule I follow to keep in good fitness to optimize my diving experiences.
Click Here to Download a Scuba Diver's Workout Guide
Disclaimer: This is a plan that works for me. Please consult your doctor and do your research on mixing working out and diving