Final answer:
Starting an exercise program in midlife significantly improves bone density, especially through resistance training which plays a key role in preventing osteoporosis.
Step-by-step explanation:
An important outcome of starting an exercise program in midlife is that sedentary adults gain in bone density, which further promotes physical activity. Controlled studies have shown that regular exercise can lead to greater bone density in contrast to a sedentary lifestyle. While any form of exercise contributes to the deposition of bone tissue, resistance training is particularly effective. This type of training is crucial in slowing bone loss as we age, which is essential for preventing conditions like osteoporosis.