It's important to remember to include a warm-up and cool-down period in your exercise program. These give your body a chance to adjust from rest to exercise, and from exercise back to rest. The warm-up helps prepare your body for the work you are going to do. It can improve your workout performance, but, more importantly, can decrease the risk of cardiac problems. The cool-down will keep your blood pressure from dropping too quickly after your workout, and helps your body clear the metabolic waste that develops in the muscles during exercise.
Warm-up and cool-down should be about 5-10 minutes. Warm-up should consist of any movement that gradually gets your muscles warmed up and increases your respiration. Your level of effort should only be about half of the effort you plan for your workout. Cool-down is the same, just taking you in the opposite direction - slowing you down.
Older individuals, as well as people at risk for cardiac events benefit from longer warm-up and cool-down periods.
These are the general principals. At Life-Cise and Stay Fit Stay Strong, some of our clients struggle to get 10 minutes of exercise into their workout. The general principal of warming up and cooling down still holds. No matter what the length of your workout is, warm up and cool down. Start your exercise session slowly, moving in any manner to get your muscles warmed up. Gradually increase the intensity. When you're done, make sure to slow down to allow your body to adjust. Your blood pressure can drop rapidly if you stop exercising suddenly.
Exercise, just do it safely.