Common Issues

Preferential fatigue

Have you ever dismounted after a long, hard ride and felt that your quadriceps or calves were completely “dead” and struggled to walk up stairs? Do you cramp at the end of a big effort, but the cramping is always in the same muscle group on one leg or both? If you answer YES to either of these questions, you may be suffering from what I call Preferential Fatigue.

During a cycling stroke there are a multitude of different muscle systems contributing to generating power to push on the pedal. To simplify the pattern drastically, the quads act to extend your knee and push downwards, the hamstrings act to pull the knee into flexion and provide extra power through the bottom of the stroke whilst preventing excessive anterior pelvic tilt, the calves stabilise the foot on the pedal and provide extra power during hard sprints and the glutes act to drive downwards and assist the quads whilst stabilising the pelvis and back. The activation patterns and firing sequences of these muscles are infinitely complex and poorly understood, but it is logical and necessary for endurance riding that the correct timing and pattern of activation should occur to allow the greatest spread of metabolic load. Metabolic Load is what occurs on a cellular level within our muscle bellies. The act of delivering energy to fuel the muscle contractions and removing the waste substances once the fuel has been spent.

Here we can see a rider with good knee control through the whole stroke riding at a moderate intensity. He is able to use both his hamstrings and quadriceps to control the knee movement and spread the metabolic load derived from power generation.

Road cycling (sprints, crits and velodrome aside) is all about delivering the highest AVERAGE power over a given time. With an ideal position, the pelvis is stable, the back isn’t having to contribute stabilisation effort, and the quads, hamstrings and glutes are firing in perfect sequence without wasted energy to provide maximum average power. This can only come through careful positioning on the bike. A common fault, for example, is too high a seat – the knee unlocks into extension too violently at the bottom of the stroke, and for a brief period of time the hamstrings are disengaged due to the speed of the extension moment at the knee. For perhaps 15% of the stroke, your hamstrings don’t contribute to power generation. Similarly, seat setback plays a role in this movement pattern – generally speaking a more forward position of pelvis relative to crank centre will result in higher recruitment of your quads and lower recruitment of your hamstrings. The end result after long distance or hard effort, is an UNEVEN spread of metabolic load. One of the muscle bellies contributes more to the movement than the other, and so fatigues more quickly. As the fatigue sets in, power generation goes downhill quickly and you get off the bike with “jelly legs” or dead quads for example.

This is an example of a positional problem – if this sounds like you, then your bike fit is not optimal. Through careful positioning and placement of your pelvis relative to the crank, we can spread the metabolic load as evenly throughout your quads, hamstrings and glutes which results in even bloodflow distribution, and hence oxygen and energy delivery to the various muscle bellies. The fatigue is spread over the largest possible area of muscle belly. You can ride harder, for longer, without excessive fatigue in a focal muscle system. A detailed post regarding this topic is listed below – click on “Seat height and setback” for more detailed information on this topic.