Final answer:
Weight-bearing exercises are the most effective for clients with osteoporosis, as they stimulate bone building and increase bone mineral density. Swimming is less beneficial for preventing osteoporosis as it doesn't stress the bones as much.
Step-by-step explanation:
For clients with osteoporosis, the most effective exercises on the reformer would be weight-bearing exercises that stimulate bone building. Weight training, dancing, stair climbing, running, and hiking are all examples of weight-bearing exercises that can help maintain or increase bone mineral density. These exercises put stress on the bones, which stimulates bone remodeling and helps improve bone strength. On the other hand, swimming is less beneficial for preventing osteoporosis because it doesn't stress the bones as much.