Eccentrics....bad!

In the last post, I defined the types of muscular contractions and stated that the pedal stroke is comprised of concentric contractions.

Here are some areas where eccentric contractions show up. These are caused as a result of rider being out of position or because the rider has a poor motor plan and therefore "doesn't know how to pedal".

The first situation occurs as the foot crosses top dead center and moves toward the forward position. If the heel is dropped below horizontal at the forward position, it indicates that the heel has moved faster than the pedal. To do this, the gastrocnemius has lengthened while contracting and dampened force. It has absorbed force that should have been delivered to the pedal.

The second situation occurs as the pedal is moving from the forward position to dead bottom center. For the rider that tends to mash to produce power will continue to utilized the quadriceps for too long during the down stroke. As the pedal begins to move through the down stroke, the rectus femoris remains "on" while the knee is flexing and the hip is extending. This lengthens the rectus femoris across two joints and adversely affects the center of gravity and the stability of the pelvis.

The third situation occurs when the pedal is leaving dead bottom center. If the axis of rotation is behind the bottom bracket at the point, the ankle is forced to go into eccentric plantar flexion so that the knee can be positioned for flexion as the upstroke begins. This situation is driven by position in many cases. It can also be technique driven if the rider pedals through the bottom of the stroke with the rather flat. This can cause the knee to extend too far and which places the axis of rotation behind the bottom bracket at dead bottom center.

Each of these problems causes a breakdown in the pedal stroke. Each causes the rider to dampen force or prevents their ability to ride a straight line.

Situations like these indicate why bike fitting and technique training must go hand in hand. If someone fits you to your bike, yet, they don't have an ability to assess how you are operating in that position, they are only offering a portion of service. The two must go hand in hand.

Time for the tweak

It's that time of year again. Time to get tweaked(bike fit that is.)

Things have slowed down a good bit. The holidays are in full swing. Some of you may have even been lucky enough to recieve bike related gifts. It's time to get things tuned.

If it's been over a year since your last bike fit, it's time to get re-checked for fit. Most riders have purchased something new for their bike within the last 12 months. New pedals, shoes, handlebars, shifters or saddles can all have an impact on fit. If you have changed any of these products, you need to get checked out before things start ramping up again.

Changes in body composition also have their impact on fit. If you have gained or lost more than 15 lbs. You need to have your fit checked as well. (Pardon my direct approach to this). Extra weight in the thighs and abdomen changes the way the cockpit is set up. If your thigh and abdomen are touching when you are in the drops, your handlebars need to come up, or you need to loose weight. Continuing to ride in this situation causes you to loose power because you are dampening force by moving your abdomen each time it the thigh comes over the top. Also, changes in weight impact how you sit on the saddle. The size and shape of your bottom drives where you sit. If you are sitting in a different place on the saddle, your power production has changed. This requires a new look at fit as well.

Other items mentioned at the top are important as well. If you purchased new shoes, the cleat position needs to be verified. New pedals present with the same issues. If you purchased a new bar or if you are using a different component group, handlebar placement and hood placement has to be reset based on the new design.

It's great to purchase new bike stuff, however, don't discount the fact that these items need to be set properly so that you get the most from your new gear and you avoid aggravation of new injuries.