Is Cycling Non-Weight Bearing?

Cycling - Tour de France Singapore Criterium - Singapore - Astana Qazaqstan Team’s Mark Cavendish crosses the line to win the race REUTERS/Edgar Su

Introduction

This question may seem simple to some, yet upon closer inspection, it appears there is more to it than meets the eye. The hypertrophic effects of cycling can be observed in many recreational and elite cyclists, as it tends to promote muscular development in the legs⁽¹⁾. However, we know that well-developed muscles are not a good indicator of bone health, as osteopenia is common amongst elite cyclists, with many elite Norwegian cyclists showing diminished bone health despite performing strength training^(2,3). These findings have led several authors to describe cycling as non-weight bearing (NWB), yet this may not be entirely true, as there is evidence that cycling exerts a gravitational load on the body^(4,5).

Clinicians may prescribe a period of NWB as part of the initial treatment for many lower limb injuries, such as anterior cruciate ligament (ACL) ruptures, ankle sprains, Achilles tendon ruptures, and fractures⁽⁶⁾. Major injuries such as ACL and Achilles ruptures often require surgery too, which introduces an additional risk in that one should take care not to dislodge the surgical site.

Cycling Posture Affects Weight Bearing

Weight is the product of a body’s mass and the perpendicular gravitational force acting on the body⁽⁷⁾. Thus, gravitational force is maximized through the limb when it is perpendicular to the ground, as with full weight-bearing activities such as running, hiking, walking, and traditional strength training⁽²⁾. Full weight-bearing activities are superior in stimulating bone growth, also known as osteogenesis, compared to weight-supported activities such as swimming and cycling⁽²⁾.

Diminished bone mineral density is evident in elite road cyclists. However, cyclocross, a different discipline of cycling, might exert similar gravitational forces on the body to running⁽⁵⁾. Cyclocross involves cycling off-road using a bicycle with similar architecture to a road bicycle⁽⁵⁾. The ground reaction force (GRF) during cyclocross can exceed two times bodyweight, unlike road cycling, which usually exerts gravitational forces less than two times bodyweight⁽⁵⁾. American researchers measured forces during seated, standing, uphill, and downhill cyclocross⁽⁵⁾. All positions on the bicycle during cyclocross exerted GRFs greater than body weight, suggesting that cyclocross at least involves a degree of weight-bearing. It must be noted, however, that they studied elite cyclocross cyclists, and the results may differ in recreational athletes⁽⁵⁾. Furthermore, although cyclocross demonstrates some weight-bearing, these gravitational forces might be considerably lower during stationary bicycling.

Cycling biomechanics can differ significantly depending on the force exerted on the pedals and the posture assumed by the cyclist on the bicycle⁽⁸⁾. For example, less weight is transmitted through the upper and lower limbs when seated on the bike than when standing on the pedals^(7-9). As the weight of the body is more perpendicular to the ground when standing on the pedals, greater gravitational force will act on the cyclist’s limbs, thus increasing weight-bearing on the legs and arms  However, when seated, the legs and arms are more parallel to the ground, meaning that less gravitational force is transmitted through the limbs of the cyclist^(10,11). 

"Cycling is often described as a non-weight-bearing activity, but the reality is more nuanced."

Weight Distribution During Cycling

The weight of the cyclist is mainly distributed along the bicycle’s frame and the two bicycle wheels, with only some of the cyclist’s body weight being distributed along the upper body, lower body, and spine⁽¹²⁾. The GRF is divided between the two bicycle wheels, which is further dissipated along the frame and further via the rotational motion of the bicycle wheels and chain (see figure 1)⁽¹²⁾.