Professional athletes train hard to stay in peak physical condition because it helps prevent injuries. Unfortunately, they can still happen no matter how much you train. The following are five of the worst injuries that professional athletes can experience:

1. Vertebrae Fracture - Vertebrae fractures occur most often in football due to tackling. It's a potentially career-ending injury that can also cause paralysis depending on the severity.

2. ACL Tear - The ACL (Anterior Cruciate Ligament) is responsible for 90% of the leg's stability, which means that tearing it basically leaves you immobile. The injury occurs more often in football players as a result of quick changes in direction while on the run. It generally takes eight to 12 months to recover.

3. UCL Tear - The UCL (Ulnar Collateral Ligament) is a part of the body more prone to injury for baseball pitchers. At one point, experiencing a UCL tear signified the end of your career. Now, players can receive surgery, but won't return to the field for at least 12 to 18 months.

4. Severe Concussion - Concussions in general are considered much more serious than they once were. Severe concussions can cause a loss of vision, memory problems, motor function problems plus long-term effects, such as CTE. Severe concussions have been known to force players into early retirement.

5. Broken Leg - Broken legs happen in almost all sports, from soccer to basketball. Wherever the leg breaks, it usually takes at least a year to recover.

These are five of the worst injuries that pro athletes can experience. Although they can be career-ending, many athletes do return following an intensive recovery period.