Background Paragraph: Sometimes muscles and tendons get injured when a person starts doing an activity before they have warmed up properly. A warm up is a slow increase in the intensity of a physical activity that prepares muscles for an activity. Warming up increases the blood flow to the muscles and increases the heart rate. Warmed-up muscles and tendons are less likely to get injured. For example, before running or playing soccer, a person might jog slowly to warm muscles and increase their heart rate. Even elite athletes need to warm up ( Figure below ). 
Story: Greg and Carl and about to do a marathon. Greg sees Carl doing some warm ups and laughs to himself and thinks it is silly. They both want to get a good time, and are both avid runners.
Does Carl have a higher or lower chance of injury than Greg? Does Carl's warm up cause an increase or decrease in the likely hood of an injury? Does Greg have a higher or lower chance of injury than Carl? Does Greg's lack of a warm up cause an increase or decrease in the likely hood of an injury? Who is less likely to get an injury during the race? Who is more likely to get an injury during the race?