When people determine their riding position, they almost always focus on how much knee extension they have, sometimes assess their reach but very rarely pay any attention to their range of hip flexion while riding.
The 'hip angle' is a term used frequently in bike fitting articles and refers to the angle between the torso and the thigh at the top of the pedal stroke: as the foot travels towards the bottom of the stroke the hip extends and as the foot returns to the top the hip flexes. The maximum point of hip flexion occurs as the pedal passes over the top of the pedal stroke and it’s at this point where the angle of hip flexion can adversely affect comfort, power and biomechanical efficiency.
The range of hip joint mobility varies considerably between different people. It’s important to assess this mobility during a bike fit as a riding position which provides an excessive amount of hip flexion can cause the following compensations:
Rocking hips:
Because the restriction in the hips prevents the necessary degree of hip flexion at the top of the pedal stroke the body can achieve the angle it requires by lifting the hip to allow the foot to pass over the top. This can clearly be observed from behind as the hips visibly rock from side to side. This is inefficient and a spin scan will often show a drop-in power at the top of the stroke as the restriction causes a dead spot in every pedal stroke.
Abducted knees:
If the leg can’t go over the pedal stroke it will go around instead. Knees that visibly stick out at the top of the stroke are often compensating for a restricted hip angle as the hips open up to allow the legs to pass around the point of restriction.
This is a less direct application of power and also causes faulty tracking of the patella, often with the cyclist reporting knee pain when riding.
So what can be done if someone has a limited range of hip flexion? There are three main factors to consider:
Saddle height:
Saddle height is largely determined by hamstring and lower back flexibility but the higher the saddle the less flexed the hip will be at the top of the pedal stroke.
Handlebar height:
Once saddle height has been established the issue is to then fit the handlebars at a height which provides the necessary of range of movement in the hips. More often than not this means handlebars need to be raised, sometimes by several centimetres.
Saddle position:
The relaxed geometry of a road bike results in a tighter hip angle which can be especially problematic if tribars are fitted. For anyone using a time trial bike this problem is largely resolved as the steeper seat tube positions the saddle further forward over the bottom bracket. This position therefore ‘opens’ up the hip and the rider can usually race without restriction with greater speed and comfort.
Conclusion:
Hip flexibility is an important consideration when determining the most effective riding position during a bike fit. Limited range of hip flexion can be accommodated, and the cyclist can ride efficiently without discomfort if the bike is fitted correctly.
Sisu Racing Triathlon Endurance Coach