|The Launching Pad|
This is what works for me: Short, Steep, and Intense.
Short: 15 ish seconds. I think. I actually don't time it. When I do sprint longer, the intensity has to come down. That's just the nature of the beast. I started out doing 8 of these sprints a couple of years ago and now I'm down to 5. My goal is to get it to 4 (counter-intuitive I know, but I explain below).
Steep: I sprint uphill. Makes it a bit easier to 'work harder' and is less jarring on your body. I actually prefer an incline of about 4 to 6 %. This still allows for a lot of speed. If the gradient gets much above this, you almost feel like you're sprinting in slow motion. I do like to get some very steep sets in once in awhile, just not as the backbone of my routine.
Intense: All out baby. I'm slowly getting my sprints closer to 100% max effort (I'd consider 100% running for your life, or maybe a gold medal). With increasing intensity, I can now get the same effect out of 5 sprints that I needed 8 to accomplish when I started. Within each sprint itself, I build for the first couple of seconds and then go full throttle. These sprints are so intense, that after each one, my hands are on my knees and I'm sucking wind. If I tried to walk I would fall down. I stay hunched over until I can remember what planet I live on and then I walk back down the Launching Pad to repeat the insanity.
Secret Weapon: Grid Roller. This is a firm roller that I use every morning on my legs. Every morning. That's the secret. I'll make no bones about it, this tool saves me time and reduces the likelihood of injury. It essentially 'warms up' the legs with direct pressure. This, combined with two mini warm up sprints, is all I need (even in sub-zero degree temperatures). It might not be all you need, especially at first, but at this point my warm up is ridiculously short. And I don't ever feel like I'm going to 'pull a hammy' or tweak something. Maybe some of that also has to do with my sprinting twice a week, every week, for over two years now. Either way, the roller is awesome.
Notes: I'm completely focused on my body during sprints. I talked about this focus and it's importance in Master the Moment.
I also fine tune and adjust my technique on occasion: What does a more powerful arm swing feel like? What if I swing my arms higher? Or lower? What if I push off more with my hamstrings? Or 'paw' at the ground with my toes? What if I tilt my head and look down? And on and on. It's kind of fun to play with form and feel what happens. And since I don't time myself, I'm not concerned whether or not something makes me faster or slower, just with how it feels.
In the summer I sprint in my Vibrams. For the other 11 months, I use a 'flat' running shoe.
Summary: Sprinting is King. It offers an incredible bang for your buck. It is, however, not for everyone. If you decide to try them, you must pay attention to your body and ease into a routine. As you become more comfortable with how you're handling things, you can up the intensity and truly reap the benefits.