3. Bicycle accident
Bicycles are a fun and healthy way to exercise until you wreck. Scenic trails and time alone with nature are beneficial to your mental health; however, spiral fractures due to bike accidents are not. Competitive cyclists, mountain bikers and the novice bicyclist can all suffer broken bones when their feet get tangled in the pedals or they flip over the handlebars and twist their upper body.
The heavy force here is momentum. You are traveling at a certain rate of speed, something impedes that forward progress and the cyclist falls, probably twisting something on the way to the impact with the ground.
This scenario can be dangerous for the cyclist because oftentimes they are riding on a trail alone. If you fall and suffer a spiral fracture, you could go into shock and die without first aid. Ride with a buddy or let someone know where you will be in case there is an accident in the woods or on the trail.