Anatomical Considerations in Bike Fit: Fitting the Machine to the Athlete – Part I

In a previous article, I went through a brief case study concerning some of the steps I go through in troubleshooting a painful or uncomfortable bike position. In this series I’m going to expand on that by taking you, the rider, through the process of measuring yourself up and selecting an appropriate ride for your dimensions and range of motion limitations. In my opinion, this process of fitting the machine to the man is far preferable to the standard process of fitting the man to the machine, that is, selecting a stock frame that looks cool or weighs in as the lightest on the market then attempting to contort your body to “make it work.”

In this first installment I am going to give a little background as to why a proper fit is integral to both power output and speed.

The first key, oft-ignored, principle is that a long muscle is a strong muscle. In other words, a muscle is strongest and most economical when placed in a position slightly greater than its resting length. This is displayed graphically in the diagram below .

A muscle that is too short is weak. Similarly, a muscle that is too long is weak. The key then is to get the muscles that count at or slightly beyond their resting length. So what muscles count?

Cycling is primarily a movement of hip extension, knee extension and, to a lesser extent, knee flexion and ankle plantar flexion. Unsurprisingly, Ryan, et al (1992), found greatest EMG activity in the gluteus maximus, vastus lateralis, semitendinosus and gastrocnemius.

A key element in bike fit should be to get these muscles to a position of optimal length as they enter their respective power phases of the stroke. We’ve all seen the results of cyclists put in positions where their muscles are taken a long way beyond their resting length — cyclists who are forced to push their knees out to the side to pedal because they lack the hip flexibility to get their knees up. I would argue that the opposite is just as bad — cyclists who pedal with their legs perpetually bent due to seats that are too low. If you’ve ever tried riding a bike that is ridiculously small for you, you’ll know what I mean. It is very tiring when muscles are kept in a shortened postion. While these are extremes, many cyclists are falling far from optimal because they are being set up according to “traditional” bike fits based on generic formulae (often based on elite cyclists).

The first obvious step then in setting up a cyclist so that he or she can hit his or her most powerful muscle length during each pedal stroke is to determine what the individual athlete’s personal resting muscle length limits are, that is, to assess the active range of motion in the key muscle groups. In Part 2, I’ll outline some key range of motion assessments that can help you determine the position that provides the highest levels of both comfort and power on the bike.

Until then….
Train smart