A lot of talk has been going on about the Jamaicans and grass sprinting. One of the benefits talked about is increased tendon stiffness. After doing a bunch of searching I couldn’t find why sprinting on grass/softer surfaces increases tendon stiffness. I was wondering if somebody or multiple people could help me understand the reasoning behind this. Thanks.
When you run, there are signals that go from your muscles to the cerebellum. The cerebellum kind of acts to modulate/correct movement. When you run, there are a couple of things that happen to keep you moving. The first is the amount of force you generate before your foot contacts the ground. The second is when your foot hits the ground the amount of stiffness(lack of bend at any of the joints in the legs). The quicker this phase is, the more elastic energy that can be stored and reused to help propel yourself forward when running. There is also a slight pushoff phase. When you run on grass or some other compliant surface at first, the time that you spend on ground contact is increased. This means that not only will you run slower at first, but you also have to rely more on pushing off in order to keep running fast. This is very inefficient and much more metabolically costly. So what the cerebellum does to correct this is to further increase the stretch reflex at ground contract, much more than it would running on a stiffer surface. When you move back to a harder track that does not have as much compliance, that increased stiffness at ground contact is still maintained, resulting in shorter ground contact times, which helps you run faster. Hope this helps,
Its hard to say for sure. Obviously like any other skill, it probably takes repeated practice to make the change in stiffness carry over to the track and in general the more times you practice the more permanent that change will be. But as far as general time frames before you get a significant carryover from running on a compliant surface to the track, alot of that is probably individual and depends on how much running on grass you have done.
I would like to add to your excellent post.
I would like to add that running on a compliant surface causes muscles to become STIFFER (working almost isometrically) to save energy, and tendons to be more compliant (more elastic band in behaviour than say a steel rod). In fact the human body and mammals in particular can change the compliance and stiffness of tendons and muscles depending on the running surface hence the difficulty faced by robot designers trying to produce biped bots that can replicate the walking and running gait of humans on different surfaces. When running on a hard surface, muscles become more compliant to absorb the shock and tendons become stiffer. It is in fact the STIFFNESS of muscle that becomes greater when running on a soft surface and the greater compliance of tendons. When you switch to a hard surface the muscle will react with greater stiffness and the tendons will react with greater compliance. Compliance equates to elasticity. So… you want elastic tendons and stiff muscles. Training and running on a compliant improves this effect and transfers hopefully onto a harder surface…
"A fully activated muscle contracting isometrically uses metabolic energy at a predictable rate. It uses energy faster when doing positive work and less fast when doing negative work (12). Also, it exerts less force when shortening and more when lengthening. Together, the metabolic rate-velocity and force-velocity relationships (Eqs. 2 and 5 in Ref. 11) imply that a muscle that does negative followed by positive work uses more metabolic energy than one that contracts isometrically while exerting the same forces. From this follows the principle of energy saving by elastic mechanisms in running; by doing some of the required (negative and positive) work, tendon compliance enables the muscles to work more nearly isometrically, and so saves metabolic energy (3). Ferris and Farley (6) explain this point by treating the metabolic cost of hopping as the sum of a cost of force production and a cost of work performance, an approach that may seem conceptually helpful but does not reflect the underlying physiological processes.
It is not clear to what extent the reduction of leg compliance, when hopping on compliant surfaces, is a reduction of true elastic compliance, and to what extent it is reduction of pseudocompliance. It is only by reducing the pseudocompliance that metabolic energy can be saved."
Pseudocompliance refers to the elasticity of muscle components.
Well its to do with maintaining running mechanics, and the center of gravity. In other words if your overall leg stiffness/compliance did not change in relation to different surfaces then your mechanics would have to change. The added benefit is the development of greater muscle stiffness on a compliant surface.
No argument here about the potential benefits of grass sprinting. But consider–
Despite the country being a track-and-field powerhouse, Jamaica has only four all-weather tracks. There is one each at Stadium East, the National Stadium, G.C. Foster College and the Catherine Hall complex
Bolt, for example, does a lot of his training on grass at the University of the West Indies, Mona Bowl, while Asafa Powell and Shelly-Ann Fraser mainly utilise the grass surface at the University of Technology.
Based on this information, it seems to me that training on grass as much as possible is a good thing. My question: does this training transfer directly over to better performances on the track or does some level of track work need to be done either throughout the training cycle or before a big meet in order to groove the neuromuscular system to use the added stiffness developed by grass running? i.e How does one periodize grass training?