Do you perform a warm up before exercising? If not, you are not properly preparing your body for what it is about to endure.  Warm ups perform several different duties:

They gradually increase muscle and overall body temperature.  Warm muscles contract and relax quicker than cold, tight muscles; therefore, warm muscles are at less risk for injury.  

• Warm ups enable a slow, gradual increase in heart rate.  A sudden spike in heart rate can cause the heart to work harder than it wants to and reach exhaustion quicker.
• During a warm up, blood vessels dilate.  A decrease in resistance to blood flow occurs during vasodilation; therefore, the heart does not have to work as hard to supply blood to the rest of the body.  If the heart works too hard, exhaustion occurs. 
• In addition to an increase in body temperature and heart rate, cooling mechanisms are kick started during a warm up.  Starting the cooling process at the beginning of a work out prevents overheating from occurring too quickly.
• Finally, different hormones are released that make carbohydrates and fatty acids readily available for energy production.  Without a warmup, it will delay the process. 

Warm ups can be as simple as walking a few laps around an outdoor track or lightly jogging before a long run.  Athletes prefer to slowly increase the intensity of drills that prepare them for their particular sport.  Regardless of the activity, warm ups are crucial for a good work out!