Warming up before you exercise intensely helps you to jump higher, run faster, lift heavier and throw further.
You do not warm up to increase muscle temperature because heating a muscle does not prevent injuries or make the muscle contract with more force. You warm up to bring in more muscle fibers to contract at the same time. It's called recruitment. Muscles are made of millions of individual fibers. When you contract a muscle for the first time, you use fewer than one percent of your muscle fibers. The second time you bring in more fibers, and you keep on increasing the number of muscle fibers used in each contraction for several minutes of using that muscle.
To warm up, jog in place, spin on a stationary bicycle or do any other activity to get yourself moving. Start slowly and then increase your pace gradually. Usually you are warmed up when you start to sweat. Then when you contract more muscle fibers, there is less force on each individual fiber to help protect them from injury.