Wednesday, September 16, 2009

What holds your engine together? Pedaling Interpretation!

Keeping it together! Today with all the marketing, someone is going to sell you their fit ideas, mostly old school subtleties of pedaling with a new marketing look!

I saw some where, if you have a credit card someone will provide you with a fit? What is behind the art?

The sport is evolving just like other sports! It's more than just finding the peak torque that is roughly when the crank/pedal is level. Is your stroke effective or not?

Are you just hitting the stroke or you swinging trough it to obtaining the effective (peak torque)? How are you developing crank torque? What is your net torque? There could be a asymmetry, leading to the upstroke imbalance vs. the downstroke.

The days are getting a little cooler, so you might want to get those legs warmed up a bit before you attack the hills!

Have you ever noted that your best ski turns or best golf shots can't be felt? How do you describe feel?

So if you can't feel it, how do we teach the brain? Work on the areas of small forces or the large forces? Interpretation at this point may seem trivial, but it is the area that makes a difference. Think about the 5,000 strokes per hour and that any improvement even the smallest will make a difference. Quantification of net torque really opens the doors for assessments. The hard part is keeping the human brain on the task or better defending the debates that your rivals say you can't use CAD to do this stuff.

Information and equipment is changing the game fast. In the past it has been mostly art or listening to a serious cyclists as they describe (blood, guts, spirit). Nothing new here! New insights will optimize the dynamics between machine & human, as long as the mind is open!

Biomechanics is a very broad scientific area and it has many issues. It includes anatomy, biology, physiology and physical sciences of engineering. No question, bike fitting shops, a laboratory setting to review your function has come a long way in only a few years. Look at all the bike fitting practices and you might note they appear to be more art than science. Why?

Devices are available to perform quick assessments of pedaling and then your own your own! "They will not know the difference." It's like the retail owner saying I don't want to hear that this bike that in on my floor is the wrong size! Sit on this and we can tell you what saddle you need? Effective integration of cyclist and cycle cannot be reached without explicit characterization of the rider.

You can measure (SRM), review strains, and review forces in almost any axis that permit some evaluation towards your needs. Creative mechanical and electrical engineers are always be challenged!

It's like attempting to understand what Tiger Woods is doing with his golf swing!

We started when the art major's said that computer and instrumentation technologies will not make a difference? After all, they have been performing their arts for years. I guess if you can read & write, hook up with a cycling network, you can better sell your ideas. Science comes slow as government! Now we have many not trusting that!

We continue to advance our ability to provide useful information for those who are a student of the sport i.e. coaches wanting to learn, leading to the recreational cyclists who then pays the learning coach. Too often, the coach doesn't know, he/she is only attempting to make a living in the sport.

The real issue is the accurate interpretation and effective communication of the data. It was just the other day, that the highest level coaches said that Hunter Allen, using power and learning how to review the data was crazy. We have observations for over 10 years of testing and the results are not just luck.

A demand of continued research in the subtleties of the pedaling stroke will never end. If you know it all, you will not stay tuned and you will go away! Understand, that you don't have to present a dissertation for a master's thesis to a University to learn what we have. In fact, we don't care to publish what is more a doctoral dissertation on the subject.

There is little question that the legs propel the bike. The upper body also plays a large role. The legs have to work under the upper body, so its not just about hip, knee, and ankle as seems to be the focus?

We knew that the old school of hanging a plum-line and sending you out the door was not a precise method to measure the muscles that drive the system. So we used sEMG electromyography in monitoring the electrical activity of the muscles that make a difference.

It is not just a single-joint action, but more a two-joint (biarticular) act. More than that, its a whole body action. We then started to gain better interpretation about the activation time and the actual force that came from the [to the primary muscles in question. In other words there is a delay of the initiation and the muscles doing the work.

We found that there are biarticular muscles transfer energy to the joints at critical times in the stroke. So they are the guides to the the system. That lead us towards a deeper understanding of the muscle coordination very much like a golfer learning more about joint movements or torques.

That being said, it could be said, it is more important to focus on the take-away in the golf swing vs. the down stroke. What makes this hard to understand is the "resultant forces. Think of a triangle and then understand that there is a relationship of the three sides.

During the down stroke the hip, knee, and ankle extensor muscles act to extend all these joints. Towards the end of the down stroke the extensor movement terminates and goes to a flexor moment. This is where things aren't clear. The knee joint keeps moving, gaining more distance from the hip before the leg is fully extended. It redirects the loads from a downward to a rearward direction.

Now the question is: change the knee size and you change the forces! This is why you can't just hang a line and call it good. Then you have the upstroke and most of its forces act towards the knee motion, flexing early and then extending late. Its important to note the knee starts extending the lower leg before the top of the pedal cycle. The thigh is relatively stationary! If you miss with the fore/aft saddle placement "game over."

We also understand that a passive bike fit will not serve you well when you turn up the work loads! I think we all agree, most anyone can ride on the flats. That might be by so many can get the wrong fit and not know the difference.

We are not just a basic "how does that feel to you fit." Take a video of you and off you go! If you knew what the feel was, then you would not need someone to ask you that question?

Just using a video to review you moves is not taken into account the forces of a given joint! Things shift during climbing. The shift redistributes the effort among the limb motions and the many muscle groups! The many parts peak a lot sooner within the downstroke. The muscles turn on quicker and the cadence seems to lower, which necessitates the higher pedal forces. Then you stand, and you will see more ankle movement that peaks much later in the stroke, but before bottom dead center. More ankle plantar flexion suggest rapid fatigue, but that is also weight dependent. Standing also taxes the extensors and away from the use of the hamstrings.

One of our top guns, Georgia Gould (Luna) learned that her peak extensor moments are while seated when climbing both in magnitude and timing. So she gets her mind on that part of her stroke!

On the other hand, should one hit the stroke too quick will contribute to the force into the ligaments! They get sore knees.

In summary, just because the folks you are riding with stand to hammer out a short section, climbing out of the saddle plays a heavy role, as they have to support the body weight in addition to propelling the bike. You might be better off to remain seated!

What has not been reviewed by most fitting systems is the lateral body motions and what effects the upper body extremities have on the lower extremity. WE HAVE!

And we are working with Kurt to bring forth the motions that will make a difference!

Come see us at the Kurt "Rock & Road" booth at Interbike!


Biomechanics Truths:


Ligaments work as passive tensile restraints, controlling the separation of their attachment sites. Mechanical properties of ligaments are expressed graphically as load-elongation curves. Two distinct regions can be identified: At low loads, the 'Toe Region' has minimal stiffness associated with the 'crimp' pattern exhibited by collagen fibrils. As the load is increased, fibrils begin to straighten and these 'crimps' begin to decrease. Once the crimping has been removed, the load-elongation curve becomes a straight line signifying a constant stiffness and this region is referred to as the 'Linear Region”. The stiffness of this region are the values most often reported in the literature. The ‘ ultimate load’ is the load at which the ligament is defined to have failed. This is typically the peak load. The area under this load-elongation curve is the energy absorbed by the ligament.

Material properties of ligaments are described in terms of stress-strain curves. These can be obtained from the load-elongation curves of the whole ligament normalized with the geometry of the ligament by the ligament length and cross-sectional area. These curves have a similar shape to the load-elongationcurves. The stress-strain curve is geometry independent and modulus, ultimate stress, and ultimate strain values are obtained.

At low loading rates ligaments are viscoelastic structures: they display time- and history-dependent behavior. This is displayed in 2 ways: stress relaxation and creep. Timing is key or and you will pay in the long run!

With time, the stress required to hold a ligament at a constant length will decrease to a steady value (stress relaxation), and with time, the length of a ligament will increase to a steady length as a constant stress is applied to the ligament (creep). This may lead to creep rupture. Essentially, the viscoelastic nature of ligaments is due to fluid flow. At high rates there is not sufficient time for the fluid to flow. At rates, such as those associated with traumatic events (SHARP QUICK MOVEMENTS!) ligaments behave elastically.

Ligament properties change with age. Linear stiffness, ultimate load and energy absorbed to failure all decrease with increasing age.

1 comment:

Healthcare Advocate said...

Now this is educational!
I hope many read and truly understand the message you’ve posted here. Really summarizes the whole art and science aspect.
As an engineer this also characterizes the true obligation to teach others about the differences in art and science – especially in the bike fitting world! I’m amazed at how defensive others get concerning the validity and usefulness of computer aided design. I work with folks at Joe Gibbs Racing here in NC and know there’s nothing STOCK about a Stock car. The key element in Stock cars – the car - is derived using CAD! If you need to really appreciate the effectiveness of CAD I believe JGR gives tours if you’re ever in town. Of course the proof is in the pudding and with 75 cup wins and Denny Hamlin’s 4th place in this year’s points chase(20points behind the leader) I’d call that a positive TREND.
Let’s face it. If you’re not using technology to its highest effectiveness then you’re not being effective. You’re art!
Good Stuff!
Ronnie Dean
2 Wheel Coach / Wobble-naught
913 Countrymans Court
Kernersville, NC 27284