Force at take off

[Quinn]

I am trying to determine the force at take off that I am generating but have been unable to locate and equation to help me out. I suffer from Medial Tibial Stress Syndrome (form of shin splints) and after a recent stint with Physcial therapy after countless other attempts and doctors at resolving the problem I feel like I have made progress to reducing the pain this causes me. Most the therapy centered around ASYTM (not to be congused with Estim or Grastym) and lots of stretching and strengthening.

According to the PT I need to find my trigger point of the pain (how much force I am generating) to strengthen my legs to and beyond that point. I have no idea what that point is but it happens most when I am in a full sprint and preparing to jump/Take off. I have used the trigger point approach with this PT for a couple other injuries and have found good success. The trigger point in my legs though has gone beyond the weight available on the weight machine I use

I need some help to determine how much force I am putting on my legs at take off in order to find that trigger point.

[EIUvltr]

Well "trigger points" as it relates to force is a strange theory but probably has some merit. There is no equation for the take-off since no two people take off the same. It depends on angle of take-off, your body weight, your speed, and how hard you take off. I was slow but I took off well so I was able to jump higher than some people who were easily faster than me. To be honest, the "jumps" in track and field are probably the absolute worst sport for you (with the exception of ski jumping) considering your problem. The amount of force you put into the ground at take off is incredibly high. Much much higher than your squat max, even though its only one leg. The Russians used to use altitude jumps to train their ski jumpers and figured out that the maximum amount of force the human legs could withstand was upwards of 1500-3500 kgf (over 7000 lbs!!!). This was attained by jumping off of a platform roughly 3.2 metres high (Don't try this at home). Any higher than this and the athletes couldn't land properly. Anyway what I'm saying is that during a dynamic movement where muscles are loaded eccentrically, such as the take off in the pole vault, very large forces are at work. You will never come close to simulating these forces in a traditional weighted exercise, not safely anyway, nor should you ever try...ever. If your problem won't go away with rest, then it is unlikely to ever get better.

[superpipe]

Here's comments I posted in another forum on this site:

Guys,

Shin splints are caused by 3 things and are fixable and preventable:
1. You have pronation issues with your feet ( lots of people have this problem including myself )
2. Your doing too much hard training too quickly
3. Over training

The first thing to do is see a podiatrist ( specialized foot doctor ). They can tell you if you have foot problems and how to fix them. Usually they can custom mold an orthodic for you. Ask for the hard plastic ones with NO cushioning. The cushioning wears out and causes your foot to not sit properly on the hard orthodic which ends up defeating the purpose. I wish someone told me about a podiatrist when I was in high school or college. I personally think every track athlete except maybe throwers, should see a podiatrist just to make sure your feet are correct or not.

After a podiatrist's diagnosis, the rest is easy, adjust your training based on the diagnosis. Except finding the right running shoe for your orthodic is very difficult.

Note -> The only negative about most podiatrists, in my experience, is they don't know footwear very well and can't tell you what kind of running shoe ( neutral, stability, motion control ) to use with an orthodic they have created. Very annoying. You'd think you could use a neutral running shoe since the orthodic, in theory, keeps your foot positioned correctly. Not so, as I eventually found out by experience and seeing a very educated Physical Therapist who specialized in running ( Very hard to find good PT's ). My PT confirmed my findings, but explained very well why you can't just use a neutral shoe after having orthodics made. He said your orthodic works perfectly when you heel strike and roll your foot to flat when running, but it does not work very well when you transition to the balls of your feet when running. Sprinting and jumping, where you're really ripping off the balls of your feet intensify this problem more of course. Made perfect sense. Just wish I found the info earlier. I was amazed I couldn't find this info anywhere on the web during my research about it. The point is, the orthodic does help a bit on that transition to the balls of your feet, but not alot. So depending on how bad your foot problems are, you need to figure out what type of running shoe you need with your orthodics.

Also, don't ever use any orthodic not made specifically for you by a podiatrist. They are specifically trained in this. PT's are not. Any off-the-shelf orthodic is useless because it's not 100% correct if it's even close. It's expensive, but worth every penny.

Some advice for figuring out what type of running shoe to get after getting orthodics is to go see a PT or running store that specialize in running, but most importantly, they have a treadmill setup with video to analyze your foot contact while running. My PT did this for me to confirm I finally bought the right running shoes for my orthodics. They can slow motion the video so you can see your foot position during heel strike, transition to flat, and transition to the balls of your feet.

Sorry for the long post, but this was one of my biggest issues that started in high school and I didn't get it figured out perfectly until this year. About 14 years, though I stopped vaulting for 7 or so years.

Shins splints have been around forever, yet the podiatrist part never seems to be apart of the solutions in all of the research I did on it for years.

IMPORTANT -> I actually went to a second podiatrist 2 years ago because this guy was nationally known and understands athletes and high-level running. He worked with an Olympic silver medalist in the marathon and made orthodics for her. Forget the athlete's name. Sorry. Dr. Rinaldi, the new podiatrist did a much more details foot analysis and knew exactly what type of running shoe I needed. My original podiatrist's orthodics weren't bad, but Rinaldi's were perfect. It's like anything, finding the "true" experts is hard. Either way, seeing a podiatrist for anything foot related in sports is a MUST.

[aseinc]

a lot of use have had pains and strains. Some you have to be worked through, and some you have to rest and use Ice on. When it comes to work outs that help with shine splints (after the pain goes away) I found that using the leg press machine at a weight a little over twice my body weight helped, this weight is heavy enough to give your leg and calf a workout, yet light enough to allow you to push through your calf's to a slight toe raise. this I have been told by my PT help to keep the nerves in the lower leg from becoming inflamed and painful during our type of sport. the weight is subject to each individual ability so remember go slow the object is to get better not to re injure .

[Lax PV]

While EIU is right that no single equation is going to work for all vaulters, if given some physical stats (i.e. runway velocities, take off angle, height of vaulter/length of limbs) a reasonable estimation is possible for how much total force is going on. However, I think it would be very difficult to pinpoint the stress on the shin/lower leg alone without quantifying the ground reaction force at take off as well (which even then, would still be an estimation as some force is developed in your foot etc...)

[vault3rb0y]

Superpipe, I would add a huge factor of causes of shin splints to that equation:

"Incorrect running technique"

If you run correctly you are tall, and the majority of your energy goes into keeping your body tall and pushing the ground behind you. There should be very little upward force into the shin at full speed more than there would be if you were jogging- IF you can sprint correctly. This requires that you not pound into the ground and instead sweep your toes underneath you when you run.

Now, preparing to JUMP at take off is another case, but can still be corrected or at least partially alleviated with proper training. If you stay on the balls of your feet, you are able to create quite a powerful force production at take off without that force pulling the muscles away from the bone of your tibia. This pulling away (shin splints) generally happens when the normal force you apply into the ground overcomes the force your muscles and tendons are able to absorb for a "rebound" force. Essentially your shins and legs are strong enough to control the force you are applying into the ground, so that force has to go somewhere. It goes into the sheath between your shin and your bones, pulling on it.

As for an equation for force at take off, You are going to get a ton of variation from jump to jump. But, we know that F=MA, and we can estimate your acceleration by how long you are in the air. However, the impulse is your force/time, so for how long is that force being applied to your take off foot? This is a better estimate of the force that is being applied to your foot. Then you should look at how that force is distributed into your foot (this is where orthotics come into play). Do you stay on the balls of your feet or do you have more of a heel-toe strike at take off? All this should be taken into account if your doctor is wanting a really accurate measurement of the forces applied to your foot at take off.

Or... he can take the fact that while running we generally apply i believe between 4-6 times our body weight into our feet. So if you weigh 150 Ibs then you are applying about 700 Ibs/area of force to your take off leg. But this only happens for a fraction of a second.

This is all rough estimation so don't quote me. Punchline is.... you are applying a TON of force into your shin when you jump. If you were to reach the "trigger point" weight with a leg press, you would probably severely damage your shin within a matter of seconds, because when you jump off the ground you only apply that force for about .10-.20 seconds. So for a whole second would be 5-10 times as painful.

[Pogo Stick]

Superpipe, I would add a huge factor of causes of shin splints to that equation:

"Incorrect running technique"

If you run correctly you are tall, and the majority of your energy goes into keeping your body tall and pushing the ground behind you. There should be very little upward force into the shin at full speed more than there would be if you were jogging- IF you can sprint correctly. This requires that you not pound into the ground and instead sweep your toes underneath you when you run.

As support of vault3rbOy explanation, here is an excerpt from article about shin splints on Wikipedia. It describe overstriding as a reason for pain:
It might not be immediately obvious why a muscle which raises the toe can be stressed (injured) by running, because propulsion is not its function. Overstride is the reason: the stress derives from the runner landing heavily on the heel with each footstrike; thus, shin splints are a common ailment in military recruit training centers,[1] where recruit soldiers march extensively, by extending the leg forward and forcefully striking the boot heel on the ground. When this happens, the forefoot rapidly slaps down to the ground. Effectively, the foot, which is dorsiflexed before striking the ground, is forcefully plantarflexed, slapping the ground with the full sole of the foot.
http://en.wikipedia.org/wiki/Shin_splints

My first hand experience: I've been in the army and went trough all basic infantry drills including marching and had problems with shin splints for few months.
I have slightly flat foot, but I don't recall problems with shin splints caused by this. Usually I got problems with shin splints in the beginning of preparation period when more running was involved or after longer pause. Running on hard surface made things worst and switching to soft surfaces like grass helped a lot. One of my teammates had theory that changing surface can trigger shin splints pain.

[superpipe]

If your feet are perfect (or you got perfect orthodics and the right running shoe), and you've trained correctly and you are getting shin splints because of running mechanics, you couldn't be pole vaulting, sprinting or jumping. Walking is about the only thing you could do.

My first hand experience: I've been in the army and went trough all basic infantry drills including marching and had problems with shin splints for few months.
I have slightly flat foot, but I don't recall problems with shin splints caused by this. Usually I got problems with shin splints in the beginning of preparation period when more running was involved or after longer pause. Running on hard surface made things worst and switching to soft surfaces like grass helped a lot. One of my teammates had theory that changing surface can trigger shin splints pain.

If you have never been to a podiatrist to have your feet analyzed and fixed per the podiatrist's diagnosis, you can't even begin to make a statement on what caused your shin splints. A good podiatrist will watch you run and tell you if your running mechanics are causing your issues as well. If your feet are proven to be correct by nature or by a proper custom orthodic combined with the right running shoes, then you can make statements on whether your training is the issue.