In very limited circumstances. For example, some states have upheld waivers at gyms. The waiver will protect the gym, if written properly, from injury caused in the ordinary use of equipment. (Pulled a muscle, tire a bicep, had a heart attack). But it will not protect the gym from lawsuit for an injury slipping on a wet floor, or from a defective piece of equipment or a pothole in the parking lot, say. The general rule is you can’t sign away your right to sue for negligence, but there are several exceptions. With enough injury a lawyer will always try and find a way to invalidate any waiver.