Get The Most From Your Warm-up

I would define a warm-up simply as light exercise in preparation for more strenuous exercise. Warm-ups can and should vary a great deal, but you should always progress from general lighter exercise to more specific and strenuous exercise.  

The goals for your warm-up include:

• increasing your heart rate and blood flow throughout the body;
• increasing body temperature;
• increasing blood flow and temperature in the muscles you're about to use;
• increasing elasticity of muscles you're about to use;
• increasing mobility in joints you're about to use; 
• and finally practicing the motor patterns you'll need for the upcoming exercise.

If your warm-up accomplishes these things, then you'll be ready to perform at your very best and less likely to hurt yourself doing it.

Stretching is an important part of any fitness plan and is vital to keeping the body balanced and building flexibility and mobility.  Despite that, stretching alone is not a warm-up.  Warm-ups don't necessarily need to include stretching at all.  In fact, stretching can be detrimental to certain athletic activities.  

Static stretching (traditional stretch where a position is held for a period of usually 10-30 seconds) impairs muscle contraction speed and force for up to two hours.  The reason being, static stretching reduces the elastic properties of your muscle.  Muscles are like waist bands, if they are stretched out (elongated) too much, then they will lose the elasticity.  To increase the elasticity of a muscle you must warm it up, literally increasing the temperature.  Think of a rubber band that's been in the freezer.  If you stretch it out, it'll probably break.  

If you are preparing for an explosive activity and you feel like you must stretch, then do dynamic stretching instead.  Dynamic stretching (using active movements to gradually increase the range of motion) doesn't seem to have the same detrimental effect that static stretching does.

If you're not worried about being powerful, and you don't feel loose after your warm-up, then do some dynamic or static stretching to help increase your range of motion and loosen up particularly tight muscles.

Here are some examples of proper warm-ups.  These are just examples that certainly should be adjusted for individual needs.

Light Exercise:

• If the exercise is truly light then you don't need a warm-up.  For walking, light jogging, or very easy activity of any kind you should be fine to simply start moving. 
• If you feel the need to stretch, then stretch.

Running a race or a fast workout:

• Begin with light jogging or easy running that might be as short as 2 minutes for a beginner or more than 20 minutes for a more advanced runner.
• Many advanced runners will follow that up with form drills, and dynamic stretching.
• Finally a few strides at around race pace will have you ready to run fast.
• Warming up too early and then standing around getting cold and stiff is a common mistake.  Ideally you want to be warm and sweaty with an elevated heart rate on the starting line (this doesn't mean tired).

Weight Training:

• Start with full body calisthenics (body weight exercises) or a few minutes on the elliptical trainer starting slow and building to a moderate or even vigorous pace.  Running or jogging could also be used here as a general warm-up.
• Follow the general warm-up with a more specific warm-up, as in light warm-up sets for the first exercise and any other exercise that is using a different muscle group.
• Continue to use warm-up sets if the weight being used feels heavy.

Explosive or Maximal Strength Exercise:

There are so many exercises that could fit in this category that I'll have to be very general in my description.  

• Start with a general warm-up that could be jogging, running, calisthenics or any other means that increases blood flow and body temperature.  
• Progress to more specific activities.  If you're throwing then throw, jumping then jump, lifting, then lift.  At this point you should still not be taxed.  
• Now that you're starting to feel ready, ramp up the intensity bit by bit until you're fully simulating the activity.  The slow, methodical increase in intensity helps activate the muscle fibers you’ll need for peak performance.
• The only difficult part to this process is finding the right balance.  Doing too little will not activate and warm-up all the muscle fibers necessary for a good performance.  Doing too much will quickly fatigue you.  Trial and error will help you find the sweet spot.