Some of the scientific stuff

The fundamental difference between men and women is that women have two X chromosomes whereas the men have one X and one Y chromosome. Although the rest of the chromosomal make up is the same, the genetic differences caused by the differences in the sex chromosomes are responsible for the differences between the sexes.

The Y chromosome contains the genes for development of the testes. These produce the male sex hormone testosterone. Although this hormone is also present in women, the larger amounts in males accounts for the male primary and secondary sexual characteristics including body fat distribution and muscle bulk. Without testosterone men would be women.

It is these fundamental differences in hormones which lead to the differences observed between the sexes. These can be summarised as…

biomechanical differences
physical size
body fat distribution and percentage
dietary requirements
effects of training
psychology and behaviour

Biomechanical differences.

The sex of skeletons can be determined from the shape of the forehead and the width of the pelvis and lower vertebrae. Whilst the first does not affect athletic performance the latter certainly does. A girl’s gait and ability to run fast alters dramatically following puberty due to the widening of the pelvis and the change in orientation of the hip muscles. In cycling terms this means women may require different saddles and a different angle of saddle tilt. Furthermore the obvious anatomical differences in this area need appropriate consideration in terms of position and clothing.

Women tend to have relatively longer legs in comparison with their height than men, with the thigh often accounting for a greater percentage of leg length. These factors need to be taken into account when setting up a female cyclist’s position or when buying a bike. Long thigh bones mean the saddle will need to be further back and the seat angle shallow. However, women with short legs, relative to their total height, will need a steeper frame angle and the seat further forward.

Women also tend to have a shorter reach and weaker upper body than men of a similar height. This means that they need a relatively smaller frame size to allow for a reasonable stem length to be fitted (8/10cms minimum). As women are naturally more flexible, a greater seat to bar height difference can usually be accommodated. Too many women are wrongly advised when purchasing a bike and purchase too large a frame and compensate by pushing their saddle forward and use a short stem. Thus the handling of the bike and the potential power output are impaired. 

Women also tend to have smaller feet than men. As the foot forms part of the functional lever system when cycling the "109% of inside leg length rule" for saddle height cannot be applied. Indeed in one of the rare studies on female cyclists the optimum saddle height was 107% of pubic symphysis height. This may not seem much but computes to around 1.5cm for the "average" female. This study only looked at 10 women and foot size was not recorded. A women with a 28" inside leg and small feet would need the saddle considerably lower than a male with a similar leg length and size 12 feet.

Very little work has been published on the role of foot size in cycling but it certainly has an effect on rider position. Similarly, crank length may need to be adjusted with smaller women , with petite feet, possibly benefiting from 165cm, as opposed to the standard 170cm cranks.

The key muscles involved in the flexion and extension of the ankle, and thus in transmitting force along the foot lever to the pedal interface, are the calf (gastrocnemius) and shin (tibialis anterior) muscles. The shorter the distance from the ankle to the pedal interface (the ball of the foot) the greater the force required in this muscles. Thus the rider with larger feet has a greater mechanical advantage over the small footed rider.

Due to this mechanical disadvantage the fore and aft positioning of the saddle is even more critical. The saddle should be positioned so that maximum efficiency is attained in the transfer of muscle power from the knee extensor muscles (the quadricep group) to the pedal. Positioning the saddle so that a point just behind the patella (knee-cap) is vertically above the pedal spindle has been shown to be the most effective. Similarly, a smooth pedalling action with minimum resistance applied to the up-pedal stroke is required.

Physical size.

Women tend to be physically smaller than men. Larger cyclists have a lower oxygen requirement relative to body weight than small cyclists at a given speed meaning that women are disadvantaged even in flat time trials. In the hills, percentage body fat and absolute body weight are more important, so most women are again handicapped. Like their male counterparts small, lightly built women are more suited to hilly courses than taller, heavier riders who tend to excel at events on level ground.

Body fat distribution and percentage.

The key physiological differences between men and women relates to the fact that the male hormone testosterone is a much more potent anabolic agent than female oestrogen, thus men tend to have larger, stronger muscles and less subcutaneous fat than women. On average women are 7-10% fatter than men. Top female runners tend to have 12-20% body fat compared to 5-10% for their male counterparts. This contrasts with 18-25% for elite female cyclists and 10-15% for elite males. This additional body fat is a consequence of being female and a difference that needs to be accepted by women athletes in general.

The additional body fat does not seem to offer any benefits to women in endurance events even though up to 50% of the energy requirements may be met through fat metabolism. This is because a woman’s additional body fat is stored in localised deposits, or sub-cutaneously, rather than intra-muscle.

The differences between male and female world records in endurance running events is greater than in the speed events although there have been instances where females have out-performed males. For example, in cross channel swimming several of the records are held by women and the late Beryl Burton OBE held the 12hr cycling record outright. In both these events weight bearing is less than in running and, in swimming, the higher body fat of women improves insulation and buoyancy and reduces drag. However, in general, there is no scientific evidence to suggest body fat offers women any advantages in endurance events such as cycling. Fatty tissue provides a site for steroid hormone inter-conversion thus maintaining sufficient circulating levels of oestrogen.

In summary, whilst women cyclists should endeavour to keep their body fat down to a reasonable level, they must ensure that their diet contains enough calories and carbohydrate to support the rigours of training and competition.

next