If you've ever met with me for a personal training session, you'd know that we are very careful about this topic. Many people show outstanding athletic skill and an unique ability to handle quite a bit of impact and repetitive movements without injury (IE Basketball players grabbing a rebound or baseball players swinging a bat 300 reps a day).
On the other hand, most people not only lack the bone, joint, or muscle strength to handle these movements in the beginning of a personal training program but with advanced training as well.
In the recent NY Times article Why High-Impact Exercise Is Good for Your Bones, the author gives a convincing argument to incorporate this type of exercise with your personal trainer: It generates forces great enough to help build bone. True, but special consideration should be considered for your body while reading this. Is your body equipped to handle such force? While it may help build your bones, will it breakdown your joints?
This is just one of the many questions you most ponder as you challenge your boundaries with a personal trainer.