One of the biggest causes of injuries on treadmills is jumping off a fast-moving treadmill. If you need to run to the bathroom, grab a towel, or get some water, slow the machine down to a very reduced pace and lower the incline. Better yet, try to make sure you have everything you need -- towel, water, headphones, etc. -- before you start your run, so you won't be tempted to hop off.
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