Adding speedwork to your training has lots of benefits, including improved performance, form, efficiency, confidence, and even more calories burned. But to prevent running injuries, it's important that runners take some precautions before jumping into speed training. Follow these steps before you add speedwork to your training.
If you're a beginner runner or you've taken an extended break from running, you should be running consistently (3-4 times a week) for at least three months before starting speedwork.
During speed sessions, you're less likely to pay attention to potential hazards because you may be a little more uncomfortable than you are during an easy run, and you're really focused on your workout. So try to pick a course that's relatively traffic-free and look for a smooth, obstacle-free route. For example, you may be running so fast that you don't see sidewalk cracks, potholes on the road, or tree roots on a dirt path. If you have access to a rubberized track (check your local high school), that's a great option.
Always begin with 5-10 minutes of easy running before picking up the pace. A pre-run warm-up gets your blood flowing, slowly elevates your heartrate and temperature, and gets your muscles warmed up and ready to go. Jumping into speedwork without a warm-up increases your chances of injury. Even if you don't get injured, the quality of your workout will suffer because you'll feel uncomfortable when you start.
Runners who are new to speedwork sometimes make the mistake of running way too hard and fast for every interval. You should put in a good effort, but don't run so fast that your breathing and heart rate are totally out of control. Try to run your intervals consistently so that your last one is the same effort as your first. If you feel like you have nothing left for your last interval or the last few minutes of a tempo run, you did it too fast.
Speed training helps to improve your biomechanics and running form, so don't let your form fall apart when you're running fast. Follow tips for proper running form during your speed workouts.
Also see: Video – How to Run Properly
Don't be tempted to run hard two days in a row. You may feel fine the next time, but your body is still recovering -- and some people feel more muscle soreness two days later. Give yourself some down time by either taking a complete rest day or doing easy cross training the day after doing speedwork.
Don't get too enthusiastic and do two sessions of speedwork a week. A little speed training goes a long way -- even just adding one session of speedwork can make a big difference in your running. Once you improve your fitness and confidence, you can add another session (but, again, never two days in a row).
A 5-10 minute cooldown at the end of your workout is just as important as your warm-up. Easy running or walking after you finish your speedwork will prevent blood from pooling in your legs and help flush out the lactic acid and other waste products from your muscles.
http://running.about.com/od/speedworkouts/tp/8-Rules-For-Speed-Training.htm