Let me offer a concept I have been thinking over for some time and I’d love to hear some of your comments and opinions.
I could be very wrong, and maybe setting myself up for a big fall, but here it goes …
:o
In its most basic form movement in sport is a series of muscular contractions. Ignoring stride length momentarily, the speed at which these contractions can take place, and strength of these contractions are probably the two single biggest contributors to sports speed. To develop strength, weight training or basic muscular contraction is often the preferred option, which can induce muscular tension and tightness. The movement of a joint occurs between agonist and antagonist muscles.
I am of the opinion that the ability to relax the muscles, whether mentally or subconciously, opposing the contracting muscle(s) is of equal importance to the ability to contract fast and strongly.
Is there tension of some form in the non-contracting muscle? I believe there is tension of some sort, whether a residual tension or a muscular tightness. Tension in the muscle, and this is pure speculation on my part, must contribute to slowing the speed of contraction.
Massage is used to reduce tension pre-competition, but what happens in contact sports after the first 5, 10 or 15 mins (maybe seconds)?
In contact sports, I believe muscular tension is more present (bad English I know), more frequently of course, repeated and over a longer period of time. Tension may occur through lactic acid build-up, nerves even, mostly muscular movement, but more importantly preceding and following contact in the game situations, whether this is a receiver, running back, rugby back, etc.
If in a game situation a player is running with a ball and is tackled they will tense muscles in preparation for the contact to both protect themselves and the ball. The ability to relax the muscles post this induced tension is, in my opinion vital. When cutting and changing direction this ability to mentally relax and then contract the muscles, especially in the core abdominal area, is of great importance.
Can muscles be taught to subconciously release induced tension just as the opposing muscles are firing? This where I personally find AIS of most benefit. I think it helps teach muscles to automatically relax while the opposing muscles are contracting. Using the concept of using one muscle group to induce the stretch on another, forces the stretched group to relax and release tension. To underline my point, imagine a time when you have been playing touch a fun football/rugby game with younger people, the standard is lower, pressure is less and muscular tension is minimal. Your movement is often faster, smoother and sharper.
AIS is probably one method, there may be others but I believe that AIS is very important in helping teach muscles to relax and work in conjunction with other muscles. In terms of injury prevention during the eccentric action this muscle control could also be of benefit. Now I don’t suggest that AIS should be the only or primary stretching method, but I firmly believe that a method to teach muscular relaxation is important. Is this of benefit for longer sprints? 200’s and 400’s where a stage in the race muscular tension must be minimised and max speed must be maintained?
Not being a competitive sprinter I’ll leave that to someone else. 
Ss
