When I was in Holland Frans Bosch introduced the concept of Positive Running to me. I thought it was thought provoking and should be put on the table for discussion. Frans was kind enough to translate some of his remarks on his idea into English. Much of the background for this is the Book and the DVD available at www.gambetta.com
Positive Running – Maintaining top speed in running – Basic ideas
By Frans Bosch
In top speed running there are limiting factors. One could be the amount of power muscles can generate. There is good reason to assume this not a very important factor. An important factor is the ability to maintain elastic energy in the system by converting it to kinetic energy and back to elastic energy again. This means a lot of elastic energy is transported from one leg to the other each step. In sprinting this occurs 4-5 times per second.
How is elastic energy transported from one leg to the other?
In top speed running hamstrings play a crucial role. In the swing phase, at the moment of the fast knee extension, the hamstring is stretched elastic by the pendulum motion of the lower leg. To load the hamstrings elastic pelvic rotation backward has to be avoided, since backward rotation unloads the hamstrings. Therefore it is necessary to have the pelvic not in a forward tilted position immediately before the hamstring-loading phase. This means that at the end of the stance phase forward pelvic rotation has to be avoided. Abdominal muscles play a crucial role in this.
When there is no or limited forward tilt at the moment of toe-off. m. iliopsoas activity of the behind leg can help with loading the hamstring together with the knee extension. (See BK book)
Around the moment of toe off (in the leg that was the stance leg) there is an important transition in muscle activity from one set of muscles (hamstring gluteus erector spinae) to an other set of muscles (abd. Iliopsoas rectus). This big change in muscle activity means transferring elastic energy from one group of muscles to the next is under pressure. It becomes even more difficult when there is forward tilt of the pelvis, because abdominals only have a narrow range in witch they can generate big forces.
Is avoiding of forward rotation of the pelvis difficult and is it a limiting factor in high speed running?
Avoiding too much forward tilt of the pelvis together with keeping the pelvis in a forward position (like M Johnson etc. >> making it possible to load the abd, iliops rectus -set with lots of elastic energy) facilitates the energy transfer from one leg to the other. Losing control of the hip position under fatigue can be observed in many runners (being unable to bring the swing leg forward fast enough).
How is this stabilizing of the pelvis done?
In positive running a large retroflecive motion of the stance leg is avoided, because that will always result in pelvis tilt forward. The knee of the stance leg does not travel far behind the hip. In Asafa Powell's technique this is done to an extreme, the knee hardly travels until behind the hip. Many sprinters that are excellent in the last stage of a 100m show this pattern and they show it even more in their best races (Carl Lewis in his world record race).
Why is it called positive Running?
Take the moment of toe off and draw lines trough the upper legs (yellow dotted line). Divide the angle in two equal parts (a) and draw a new line (blue). In sprinters with the mentioned speed maintaining technique this blue line points forward (positive) in runners with less suited technique the blue line points more downward (more in a negative direction). This positive resultant is seen in the whole running cycle, also for instance at the when the stance leg is vertical, the swing leg has passed it already a lot in positive running.
Maintaining elastic energy in the system by keeping the pelvis in the right position is difficult at high speed and could be the limiting factor in running. This can be improved with;
Conditioning the muscles in the front of the body to a much higher level than done before. (from my experience this easily can be achieved) Muscles in the front are often neglected.