Is this a good little exercise to train speed?

A light jog won't help increase your speed much, what you want to do is ultra-short interval training.

3 sets of 5 repetitions of running 20 meters at 100% intensity, with a 25 second break inbetween each rep (so no lactic acid builds up), and after every set, walk for 2 minutes.

Then 4 sets of 5 reps of running 10 meters at 100% intensity, with a 20 second break inbetween each rep, and jog 2 minutes between sets.

Finally, 2 sets of 10 reps of running 10 meters at 100% intensity with a 15 second break inbetween each rep, and jog 2 minutes between each set.

If your performance begins to deteriorate, the set should cease and the two-minute break should begin.

Now since you're jogging/running, that's fine for a warm up. Stretching reduces speed, power, force production, and doesn't decrease (actually increases) the chance of injury.

Now if you're going to play sports or work out, do a dynamic warm up.

Either biking or jogging, running, for 7-10 minutes (more or less depending on the person), or if you're doing sports:

High knees

Butt kickers

Side shuffles (feet nearly touch in between each rep)

Backwards running

Lunges (get low)

Karaokes

Arm Swing, circles

Running, sprints

Push ups

Or even a hot shower for 10 minutes. The goal is to raise the body temperature 1-1 1/2º C.

Now, why is that?

"When muscles are stretched beyond natural voluntary ranges of motion, the muscles and tendons are stretched unnaturally. Excessive stretching damages tissues and promotes inflammation" (Yang, Im, & Wang, 2005). Continual stretching can lead to "lengthened" muscles. That condition leads to two performance altering states.

1) The range of movement of the joint about which the lengthened muscles gird is increased. That results in the range of effective contraction of the muscles being altered. Maximum muscle performance will have to occur in a different range of motion to the original natural range. IF a lengthened muscle is required still to perform in the orginal natural range, then performance in that range will be reduced because of the extra stretch. Maximally lenghtened muscles about a joint are associated often with a loosening of the joint. Increased leaxity can expose the joint to increased injury through collisions or simply through maximum efforts. Intra-joint movements can also stimulate aggravations to other structural tissues as well as bony structures.

2) If continued for a long time, muscles, tendons, etc... will start to loose some of their elastic properties, which would further decrease power and speed [and will increase the chances of injury]."

From The Science and Art of Baseball Pitching (which in this section, discusses why one wouldn't want to stretch, and the literature out there that supports it), 44.4: "Running economy is actually improved when muscles are stiff. Craib, Mitchell, Fields, Cooper, Hopewell, & Morgan (1996) concluded running economy needs natural tightness in lower leg muscles and connective tissues to maximize the storage and return of elastic energy, and reduce the need for stabilizing activity. Continuing with the theme that the elasticity of muscles needs to be preserved for high performances, Jones (2002) attributed running performance to metabolism in the muscles and stiffer musculotendinous structures that facilitate a greater elastic energy return during the shortening phase of the stretch-shortening cycle. A certain level of muscle stiffness preservs the storage and return properties of elastic energy that can be used to generate energy in an activity. The contribution of elastic energy to overall muscle performance is as much as 25-40% (Cavagna & Margaria, 1966; Cavagna, Saibene, & Margaria, 1964).

Nelson, Driscoll, Landin, Young, and Schexnayder, (2005) found that stretching before sprinting, slowed 20-meter sprint times. A review of data-based investigations led to the conclusion that stretching did not improve performance capability (Ingraham, 2003)."

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I do highschool cross country and track and most of my workouts where I gain speed are atleast longer than 10 secs of intense speed.

(Warm-up and stretch before running at high speed)

Especially on the track. Most of the time in any event we would do 400 meters on the track full speed and timed, get a few minutes of rest(about 3mins) and than repeat the process ending each 400 under or at the same time every time at your pace. So if you got a 55secs on your first 400, you rest (must be moving, stretching etc.) you must get a 55 or below the next 400s. We usually do like multiple 400m in combination with 200m or even 100m.

(flexibility and form is the key to running fast)

I'm sure this is way different than what you'd expect to train your speed but I think its a good exercise. Remember, the harder your workouts are the better you trained yourself.

Have fun!

Yes! This is a very good training exercise to gain speed as well as stamina. It is called interval training. This is a very popular type of training amongst many types of athletes. This works best when you set a speed goal. Once you have your goal, you run at that speed for a period of time and then slow down to a fast walk or a slow jog for a period of time. I normally use my speed goal for twice the amount i "rest", but you are not fully at rest you are just moving slower.

Running is a muscular activity to increase your speed you need to increase the function of your muscles. Do total body work in lifting weights, do plyometric exercises, work on your flexibility. Run speed intervals to improve your running form. You can not improve by 50% unless you are starting at a very low point. The faster you get the less you can improve, most people improve by small percentages.

Yes, but sprinting for 30 seconds and then jogging for 10 seconds is better. Another great way to gain speed and agility is jump-roping. Jump rope on one foot, then the other, then both, then alternating. Doing this every day increases your speed and agility, and it doesn't take too long to do.

good exercise train speed

What we used to do in track was similar. Jog slow about 200 meters. Then sprint 200m all out. Repeat. Do about 8 laps or so. You need to sprint all out. (I've never heard of a "light sprint", that would be called "running")

It sounds like a good exercise.

You could try to add on a few more seconds if you wanted to.