What do biomechanics scientists study?
Biomechanics scientists study the structure and function of biological organisms.
Biomechanics scientists are actually referred to as biomechanists.
If you major in kinesiology (the study of movement -particularly concerning humans), you'll have the pleasure of taking at least one course in sports biomechanics.
Sports biomechanists primarily focus on physics (specifically mechanics), how they influence (both positively and negatively) an athlete's performance, and how we can prevent injury (from forces the body encounters).
Sports biomechanics investigate the forces involved in a movement or the factors that played into an injury (we call these etiologic factors) and how they can be prevented in the future.
For example, sports biomechanists may ask: How much force does it take to cause a radial fracture in a femur with a mass of 310 grams when the foot is planted? To prevent from being too discursive, I won't get into the specifics on how they could go about coming up with a solution (they use computer simulations and life-like models). The reason this is an important question is because from this we can determine how fast and heavy someone or something needs to be to break the bone. Among other things the research from sports biomechanics can lead to rule changes in sports and new protection (padding, helmets, et cetera) for athletes.
I hope this helps!