In the past, I did weighted crunches and ‘Dragon-flags’ (a classic Bruce Lee exercise) on a decline bench. They did not improove my sprinting speed.
However, when hopping and sprint volumes are consistent, I get great abdominal definition, and more speed in my running. And yes, even a 15 minute jog (once in awhile) makes me feel much better the next day (recovery factors ) than any amount of classic floor exercises such as sit ups etc…
In gluteal hip hyper extension tests, sprinters were the athletes that faired better (relative to their bodyweight) than all other athletes, including powerlifters. This was despite the fact that powerlifters could squat a lot more weight (including relative to their bodyweight.)
But the sprinters find hip-hyper-extension exercises very easy.
If you were to lay on your back, and push your hips up with a single bent leg, and the other leg elevated, you would find it very easy, and could bust out 20 reps without a problem. This is because you have done lots of sprinting, which from a ‘neural’ stand-point, is the best hip-hyper-extension exercise in the world. (Where as the squat is just hip extension.)
A lot of strength gain is mainly neural. A number of field athetes such as hammer throwers, can power clean ridiculous weights, comparable to Olympic lifters, despite no where near the rehearsal level of that spacific lift.
You also have to consider, that you can do more reps of running contacts in less time, than sit up contractions.
Throwing a basket-ball ( a med ball would have been a little better ) helped me to increase my speed. The one slight advantage of a basketball, is that it bounces back to you from the wall quicker than a med ball, so your reflexes are even more alert, and you can get more reps done in ess time. A med-ball will develope a little more power.
However, in sprinting, a lot of the power is expressed through the rythm and neural co-ordination. The rythm (neural) magnifies the power in sprinting, not just the ‘strength per se’ contribution. The strength needs to be reasonably relevent in my opinion, or the exercise is not worth doing. Even though niether are classed as spacific, I would contend that med ball throws are more relevent to running than sit ups. Even push ups are probably better than sit ups.
But lots of forwards hopping would be better than both the above exercises combined.