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Posted: December 3, 2004

Cycling: Female cyclists health and nutrition - A guide to the proper care and feeding of female cyclists

The sex of skeletons can be determined from the shape of the forehead and the width of the pelvis and lower vertebrae. While the first does not affect athletic performance, the second certainly does. A girl's gait and ability to run fast alters dramatically after puberty because of 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 compared to 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 ordering a frame. 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 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 similar height. This means that they need a relatively smaller frame size to allow for a reasonable stem length to be fitted (8-10cm minimum). As women are naturally more flexible, a greater seat-to-bar height difference can usually be accommodated. Too many women cyclists are wrongly advised, buy too large a frame and are forced to compensate by pushing their saddle forward and using a short stem. Thus the handling of the bike and the potential power output are impaired.

Foot size is important
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 (Gregor and Rugg, 1986). Indeed, in one of the rare studies on female cyclists, the optimum saddle height was found to be 107% of pubic symphysis. This may not seem much, but computes to around 1.5cm for the 'average ' female. This study (Nordeen-Synder, 1977) only looked at ten women and foot size was not recorded. A woman with a 28in inside leg and small feet would need the saddle considerably lower than a male with a similar leg length and size 10 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 for smaller women with little feet - they may benefit from 165mm cranks instead of the standard 170mm.

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 (ball of the foot), the greater the force required in these muscles. Thus the rider with larger feet has a mechanical advantage over the small-footed rider.

Because of this mechanical disadvantage, the fore and aft positioning of the saddle for female cyclists 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 (kneecap) 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.

Small riders score in the hills
Women tend to be physically smaller than men. Larger cyclists have a lower oxygen requirement relative to body height than smaller cyclists at a given speed, meaning that women are disadvantaged even in flat time trials (Swain et al, 1988). In the hills, percentage body fat and absolute body weight are more important, so most women are handicapped once again. 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.

The key physiological differences between men and women relate 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, while the figure for elite female cyclists is 18-25% and 10-15% for elite males. This additional body fat is simply a consequence of being female, a fact which needs to be accepted by female athletes in general. In cycling body weight is supported, so fat doesn't represent such a drawback as it does in running, but it does account for the greater differences between men and women in hilly events as compared to flatter ones.

Is the fat any use?
The extra 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. The reason for this is that a woman's additional body fat is stored in localized deposits or subcutaneously rather than intra-muscle. The difference 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 outperformed males. For example, in cross-channel swimming several of the records are held by women, while the late, great 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 that body fat offers women any advantages in endurance events such as cycle racing.

Fatty tissue provides a site for steroid hormone inter-conversion, thus maintaining sufficient circulating levels of oestrogen. Early research suggested that low levels of body fat (below 17-18%) were responsible for disruption of menstruation. Presently, there are no well-defined limits for body fat, and inter-personal differences are great. It is likely that there are many factors that may influence disruption of menses, including weight loss, low weight, nutritional inadequacy, physical or emotional stress, and levels of certain hormones such as endogenous opiates and cortisol.

Menstrual dysfunction does not only involve total absence or irregular menstruation but also luteal-phase deficiency and anovulation, both of which influence fertility. Lack of oestrogen and menstrual dysfunction may lead to a number of other problems, including:
1. loss of bone density, possibly provoking stress fractures in the short term and increasing the risk of osteoporosis in later life
2. possible increased risk of breast and endometrial cancer.
Furthermore, being underweight and restriction of calories can lead to:
3. reduced immunity from bacterial and viral infections
4. increased recovery time after training
5. reduced effectiveness of training.

To summarize, while 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 (Shangold and Mirkin, 1993).

Menstruation and performance
Girls tend to reach puberty earlier than boys. This means that the advantages of early maturity seen in junior boy athletes are less prevalent in girls' events. It also means that while 13-year-old girls will often be able to beat boys of the same age in races, by 14 or 15 when the boys have started to go through puberty, the advantage has been lost. Excessive exercise tends to delay puberty by about five months for every year of training, with the associated medical, physical and psychological problems. At the other end of the scale, there is no evidence that exercise has any effect on the date of the menopause. However, exercise will protect against some of the side effects of the menopause such as fatigue and bone loss, although overtraining may exacerbate them.

There is no evidence that exercise of any type during menstruation is harmful or that menstruation causes a drop in performance. Indeed, some women feel that they perform better at this time. Heavy bleeding may lead to anaemia, which will cause lethargy and tiredness, and the hormonal changes prior to menstruation may lead to bloating and fatigue. The symptoms of PMS have been largely attributed to a drop in the brain levels of serotonin or 5HT (Shangold and Mirkin, 1993). Exercise itself increases brain levels of 5HT, as does carbohydrate ingestion. A craving for chocolate is related to this but, sadly, its high-fat content has the wrong effect, so reach instead for fruit or a jam sandwich!

The contraceptive pill offers women some protection against hormonal fluctuations caused by increased levels of training. It also alleviates PMS symptoms and can, in special circumstances, be used to manipulate periods - but this should only be carried out with the consent of a doctor. The reduced blood loss during periods will also benefit athletes who often suffer from anaemia. Although a few women may experience mild side effects (most of which can be alleviated by changing formulations), both the contraceptive pill and hormone replacement therapy offer female athletes numerous benefits. There is no evidence to suggest that these hormonal therapies have a deleterious effect on athletic performance.

What about diet?
Despite the observed fact that women tend to perspire less than men, there is no evidence that they need less fluid or that they can tolerate heat better. Women also need as much protein and fat as men relative to their body weight. The dietary requirements for men and women are broadly similar with a few exceptions:
1. fewer total calories
2. extra iron and calcium to prevent anaemia and maintain or promote bone density
3. athletes on the contraceptive pill should take a multivitamin/mineral supplement as these drugs may affect absorption and metabolism of certain vitamins.

The absolute amount of carbohydrate needed will depend on the individual and the duration and intensity of training/competition. Total carbohydrate requirements of 2000 calories per day are not uncommon, even for women endurance cyclists. However, experience has shown that most female cyclists (in common with many other female athletes) are over-preoccupied with their weight and underestimate their nutritional needs. Like most endurance athletes, women cyclists are often guilty of eating far too little carbohydrate and would benefit from additional intake without the risk of gaining weight. This is caused by an increase in the training potential of the body and a resultant increase in metabolic rate (Anderson, 1997).

Training and recovery
The differences between the performances of men and women athletes are greatest in the lower ranks. This can be explained by the differences in lean body mass and muscle fibre size. Interestingly, the differences between the VO2max of elite men and women athletes can almost all be accounted for by the differences in lean body mass, red blood cell number and physique. Absolute maximal oxygen consumption (L.min-1) is typically 40% or more greater in men than in women of similar athletic standing. When body weight is taken into consideration (ml.min.kg-1) this difference is reduced to 20%. It decreases to less than 10% if expressed relative to LEAN body weight. Thus body fat accounts for almost all of the differences in VO2max between elite men and women. The remaining differences are accounted for by physical (eg, gait) and haematological factors (Shangold and Mirkin, 1993).

Women use the same number of calories per hour of exercise as men (relative to lean body weight) and have similar ratios of Type I and Type II muscle fibres. The production and clearance of lactic acid is also the same. Women, however, tend to have smaller hearts than men and higher heart rates at the same level of exertion, even when expressed as a percentage of maximum attainable. This needs to be taken into consideration when prescribing training levels purely on heart rate (vis-a-vis BCF guidelines, which were based on a male). Using perceived rate of intensity as an additional tool is advisable. A number of texts recommend the equation 226 minus age for predicting maximal heart rates in women, although, as with 220 minus age, this rule only applies in about 55% of cases. The variation in maximum heart rate and the relationship between VO2max and heart rate varies considerably between individuals even of the same sex. For this reason athletes must learn to listen to their own bodies and train accordingly.

Auriel Forrester and Pirkko Korkia

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