Cyclists: Make No Bones About It

Competitive cyclists are potentially at risk of suboptimal bone health. Although cycling is excellent for cardiovascular fitness, this type of non skeletal loading exercise does not mechanically stimulate osteogenesis (bone formation). This situation of low mechanical osteogenic stimulus to build bone can be compounded by restrictive eating patterns and associated hormone dysfunction of relative energy deficiency in sports (RED-S).

In a recent pilot study 7/10 competitive cyclists (Cat 2 and above) had low age-matched bone mineral density (BMD) in the lumbar spine. This is comparable to another study where 15/28 male cyclists training over eight hours a week were found to have low BMD for their age and were therefore at risk of low trauma fracture. However, cyclists with a lower training volume (Cat 4) did not fair so badly in terms of BMD, due to higher body mass index (BMI) and fat mass. Although greater body mass mechanically loads the skeleton, the downside is that you need to generate more power to get up a hill.

Why is cycling unique compared to other sports where an important adaptation to training is to improve, not impair, bone health? What are the practical solutions to prevent this potential negative effect of cycle training?

fullsizeoutput_2b8
Site Specific Effects on Bone Mineral Density

The illustration shows how different sports exert site specific effects on the bone mineral density of the skeleton. In general terms, hip femoral neck BMD is more dependent on mechanical loading osteogenic stimuli, whereas lumbar spine BMD is more dependent on nutritional and Endocrine status.

What are the most effective mechanical osteogenic stimuli? Evidence from animal models demonstrates that bone responds to exercise that is dynamic, non-repetitive and unpredictable. Load and repetitions are not such important factors. This is shown in a study of track and field athletes, where sprinters were found to have higher BMD at load bearing sites of the skeleton than long distance runners due to a local loading effect rather than a systemic effect associated with repetitive loading nature of longer distance running. The other important consideration is that sprinters and rugby players tend to weigh more with higher lean mass than distance runners, providing higher skeletal loading forces. These differences in anthropometric and body composition metrics are also associated with different nutritional and Endocrine status.

In contrast to sports involving running, rowing creates a mechanical osteogenic stimulus that is directed through the lumbar spine, resulting in an associated increase in BMD at this site. This site specific effect of rowing can prevent bone loss at the lumbar that would be anticipated with rowers experiencing RED-S.

Swimming and cycling are similar in that both these types of exercise do not provide mechanical skeletal loading osteogenic stimulus. However the consequences on BMD, particularly at the lumbar spine, can be compounded in cycling by the performance advantage of low body mass and therefore potential of restrictive nutrition and consequent effect on Endocrine status: factors which impact bone health.

In the recent pilot study of competitive cyclists, although 7/10 had below average for age lumbar spine BMD, those with stronger bones had a previous history of other sports that improve BMD at this site: namely rugby and rowing, together with the cyclist doing concurrent and consistent weight training throughout the season. These findings were consistent with a study where male riders who had undertaken pre-season weight training had better BMD than riders who had not. Cumulative skeletal loading over a lifetime determines BMD. However, the skeletal system is dynamic and as with any training adaptation, any beneficial effects of skeletal loading exercise are reversible if not maintained throughout the lifespan.

Typically, the objective of off-bike strength and conditioning (S&C) is aimed at producing higher watts on the bike. Some strengthening exercises may, as by product, produce an osteogenic stimulus indirectly by muscle pulling on bone. Should off-bike work include specific mechanical axial skeletal loading exercises that are continued throughout the season? Skeletal loading exercises for cyclists would have to be effective and practical, not requiring access to gym and possible to fit into training schedule throughout the season. This will be investigated in an forthcoming study of competitive male cyclists.

In meantime there will be more discussion on “Health, Hormones and Human Performance” at the BASEM conference 22 March. All welcome, including athletes and coaches, alongside healthcare professional working with athletes.

References

Male Cyclists: bones, body composition, nutrition, performance

Cycling and bone health: a systematic review BMC Medicine 2012

Male Athletes: the Bare Bones of Cyclists

Comparisons of Bone Mineral Density Between Recreational and Trained Male Road Cyclists Clinical Journal of Sport Medicine 2016

Longitudinal Assessment of Bone Mineral Density and Body Composition in Competitive Cyclists Journal of Strength and Conditioning Research 2017

Kings and Queens of the Mountains Science4Perforamnce

Inhibition of osteopenia by low magnitude, high-frequency mechanical stimuli Drug Discovery Today 2001

Bone density and neuromuscular function in older competitive athletes depend on running distance Osteoporosis International 2012

Menstrual state and exercise as determinants of spinal trabecular bone density in female athletes BMJ 1990

Male Athletes: the Bare Bones of Cyclists

Resistance Training Is Associated With Higher Lumbar Spine and Hip Bone Mineral Density in Competitive Male Cyclists Journal of Strength and Conditioning Research 2018

A meta-analysis of brief high-impact exercises for enhancing bone health in premenopausal women  Osteoporosis International 2012

Jumping Improves Hip and Lumbar Spine Bone Mass in Prepubescent Children: A Randomized Controlled Trial JBMR 2001

Longitudinal Changes in Bone Mineral Density in Male Master Cyclists and Nonathletes The Journal of Strength & Conditioning Research 2011

 

 

Cumulative Endocrine Dysfunction in Relative Energy Deficiency in Sport (RED-S)

Screen Shot 2017-12-24 at 22.35.18

Unfortunately I continue to see athletes, both male and female, whose health and athletic performance is hampered due to Relative Energy Deficiency in Sports (RED-S). There have been some high profile athletes who have been very open about how RED-S has affected them, alerting younger athletes to potential pitfalls.

Does this issue warrant highlighting? Yes! The athletes I see and those that speak out are only just the tip of the iceberg. In a study of exercising females, half were found to have subtle menstrual hormone disruption such as luteal phase deficit or anovulation. A third were amenorrhoeic, with no periods at all. All women of reproductive age, whether an athlete or not, should have regular periods, otherwise there are potential serious health and performance sequaelae. However studies in both the USA and Australia have revealed that the majority of young exercising women are not aware of the link between menstrual disruption and deleterious, potentially irreversible effects on bone health.

The impact of non-integrated periodisation of training, nutrition and recovery has evolved since the early description of the female athlete triad. The constellation of amenorrhoea, disordered eating and osteoporosis is now considered to be a clinical spectrum. In turn the female athlete triad is part of a much broader picture of RED-S, which includes adverse multi-system effects beyond bone health and is also seen in male athletes.

Although an athlete may appear healthy, what are the underlying Endocrine disruptions occurring in RED-S that ultimately will impede both optimal health and performance to full potential? In general, female exercisers are more susceptible to internal and external perturbations as the female Endocrine system is more finely balanced than in males. Nevertheless, in a study of male athletes, in the short time period after completing a training session, bone turnover was adversely affected, with an increase in markers of resorption relative to formation, if an athlete did not refuel rapidly with protein and carbohydrate. In the now classic research by Loucks, 5 days of manipulated energy restricted availability, via dietary intake and exercise output, caused disruption in LH pulsatility in previously eumenorrhoeic women. From this research and subsequent studies, not only is the reproductive axis disrupted with reduced energy availability, in addition hypothalamus-pituitary-thyroid (decreased T3) and adrenal axes (increased cortisol) and decreased IGF1 due to relative GH resistance are all disrupted. These interactive hormonal dysfunctions occur even before reduction in sex steroids. A recent study demonstrated that beyond the average energy availability over a 24 hour time window, within day energy deficits in terms of duration and magnitude are associated with a greater degree of disruption of Endocrine and metabolic markers, in particular decreased oestradiol and increased cortisol. So consistency of nutrition, not only during a training season but from day to day is vital.

Although energy availability is the crucial factor in the pathophysiology of RED-S, measuring this is not practical for all athletes in terms of accuracy and cost. Clinical menstrual status in female athletes and basic Endocrine markers are proposed as being more reliable and accessible. The Endocrine system is very sensitive to internal and external perturbations, as described above, and presages performance consequences of RED-S, such as injury. An important starting point is for all female athletes is to ask themselves: are my periods regular? This is also a vital question that coaches and parents need to consider for athletes in their care. If the answer is no, then this needs to be assessed, ideally by those with experience in Sports Endocrinology.

Why are these clinical and biochemical markers of Endocrine dysfunction important for athletes? Essentially there are significant health and performance implications for athletes. As outlined in the stories of female athletes, by the time career limiting stress fractures become obvious, typically in early twenties, the Endocrine system has been in disarray for a significant time. Long term, irreversible poor bone health and adverse body composition have been established.

In my opinion, emphasis should be placed on the positive outcome of integrating periodised training, nutrition and recovery to support a functional Endocrine system and therefore optimal health and ability to reach full athletic potential. For example for female athletes, competing in sports where low body mass confers a performance advantage, such as ballet, gymnastics and road cycling, finely tuned neuromuscular skills are essential to reach maximal potential and minimise injury risk. Yet these are the athletes most at risk of developing RED-S, with consequential adverse effects on menstrual cycles, endogenous oestrogen secretion and neuromuscular function.

Rather than reading headlines about the concerning health issues amongst athletes, more guidance for athletes and those working with them, on the warning signs and how to combat RED-S are needed so that athletes can reach their full potential and the headlines become about athlete achievements.

For more discussion on the Endocrine and Metabolic aspects of Sport and Exercise Medicine, all members of multi-disciplinary team working with athletes, including athletes and coaches are welcome to the BASEM Spring Conference

BAsem2018_SpringConf_BJSM

References

Relative Energy Deficiency in Sports (RED-S) Practical considerations for endurance athletes

British middle-distance runner Bobby Clay is struggling with osteoporosis but wants her experience to act as a lesson for fellow young athletes Athletics Weekly 2017

In a special AW report, former English Schools champion Jen Walsh reveals the devastation that the female athlete triad can wreak Athletics Weekly 2017

Optimal Health: Especially Young Athletes! Part 3 – Consequences of Relative Energy Deficiency in Sports BASEM 2017

Prevalence High prevalence of subtle and severe menstrual disturbances in exercising women: confirmation using daily hormone measures. Human Repro 2010

Energy deficiency, menstrual disturbances, and low bone mass: what do exercising Australian women know about the female athlete triad? Int J Sport Nutr Exerc Metab. 2012

Female adolescent athletes’ awareness of the connection between menstrual status and bone health J Pediatr Adolesc Gynecol. 2011

Optimal health: including female athletes! Part 1 Bones BJSM 2017

Optimal Health: For All Athletes! Part 4 – Mechanisms BASEM 2017

Optimal health: including male athletes! Part 2 Relative Energy Deficiency in sports BJSM 2017

Sports Endocrinology – what does it have to do with performance? BJSM 2017

The Effect of Postexercise Carbohydrate and Protein Ingestion on Bone Metabolism Translational Journal of the American College of Sports Medicine 2017

Luteinizing hormone pulsatility is disrupted at a threshold of energy availability in regularly menstruating women JCEM 2003

Within-day energy deficiency and reproductive function in female endurance athletes Scandinavian Journal of Science and medicine in Sports 2017

Low Energy Availability is Difficult to Assess But Outcomes Have Large Impact on Bone Injury Rates in Elite Distance Athletes Sports Nutrition and Exercise Metabolism 2017

Body Composition for Health and Sports Performance

Reduced Neuromuscular Performance in Amenorrheic Elite Endurance Athletes Medicine & Science in Sports & Exercise 2017