A question that commonly comes up whenever discussing this subject is the probability of injury, both in training and a live event. Dynamic techniques that rely on strength and momentum will be subjecting the delicate carpal bones of your hands and wrists to considerable forces. The fingers in particular are vulnerable to damage. It stands to reason that injury is far from out of the question. Even in the case of soft or subtle techniques relying upon picking or tool usage you might need to struggle mightily in order to position yourself for success. The answer to the question of whether or not your hands or wrists will be injured, either injuries to tissue, ligaments and tendons or something worse like a fracture or dislocation, is complex as there are many factors involved in the calculus. Perhaps the most obvious is the innate fitness and sturdiness of your own biology. People who are young, fit and athletic are less likely to be injured. Stronger tissues and bones are more resistant to injury, especially over multiple sharp movements or impacts. Folks who are already dealing with infirmity, old injuries or a general lack of athleticism will probably suffer more. The type of the restraint, too, makes a big difference. Ropes and duct tape, while more than capable of being strong enough to lead to pull the muscles, sprained tendons and serious chafing generally are yielding and flexible enough to afford you a margin of error for multiple or botched attempts without serious injury. Handcuffs, by comparison, are invariably made from steel or other alloys and generally will not give way from force alone before your bones and tissues will. They are notorious for biting into the wrists of those wearing them under load and can dislocate your thumb if you try to pull them free. Zip ties are somewhere in the middle. They are flexible but pretty hard, and though they can be broken as described above a botched attempt will see them cut into your flesh readily and they may prove strong enough to withstand attempts to break them, potentially leading to soft tissue injuries. Keep in mind that meaningful practice at escaping restraints, particularly when using dynamic techniques, is definitely going to involve some pain and may involve injury. Don't sell yourself short by softballing restraints used in training and practice, and always take proper precaution when practicing these techniques.