Health effects of the London bicycle sharing system: health impact modelling studyBMJ 2014; 348 doi: https://doi.org/10.1136/bmj.g425 (Published 13 February 2014) Cite this as: BMJ 2014;348:g425
All rapid responses
Dr Saripanidis is correct that we did not model the potential effects that he lists. However, we did discuss the most established risk, erectile dysfunction, “Among potential adverse effects we did not model an effect of cycling on erectile dysfunction, as there is little evidence that rates of this condition are increased for cyclists doing low to moderate amounts of cycling on non-sports bicycles (indeed, modest rates of cycling might be protective owing to the benefits from physical activity).”
Cycling has been shown to be a risk factor for erectile dysfunction amongst occupational cyclists (e.g. cycling police officers) who are riding for a large part of the day. In a population study cycling was an independent risk factor amongst those who cycled more than 3 hours per week but was not associated with erectile dysfunction amongst those cycling fewer than 3 hours (the point estimate suggested a protective effect). Exercise is a protective factor against erectile dysfunction so plausibly the effect may be curvilinear. Very few cyclists are using the hire bikes for more than 3 hours per week. We do not know how many users are cycling in total for more than 3 hours per week but our model suggests this is a small minority. However, it is not just time spent cycling that matters but also riding posture and saddle design. The hire bikes encourage an upright riding style (lower risk than a racing posture) and are well-padded (lower risk than a hard saddle), although they are not the optimal ‘nose-less’ design.
For the other risks that Dr Saripanidis mentions we would also argue that these are also largely relevant risks to professional or sports cyclists rather than our population.
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Competing interests: No competing interests
I was pleased to read the positive outcome of the bicycle hire scheme in London.
I was interested to read the rapid response of 10 March 2014 which pointed out the author had failed to take into account the potential health risks relating to cycling including genitourinary tract injuries, pudendal nerve entrapment, erectile dysfunction, infertility in both men and women, priapism, penile thrombosis, haematuria, torsion of spermatic cord, prostatitis, perineal nodular indurations and elevated serum PSA levels. However the bulk of evidence for these risks are in cycling at least 320km, "overuse" or cycling over 3 hours per week. The mean number of journeys taken by those in the cycle sharing scheme over the year in this study was fewer than 13, although some may use the scheme more than others only the most frequent of those users would manage more than 3 hours a week, and very few would achieve 320km in one use. The risks are related to the perineum-saddle interface, and worse in saddles with nose extension. The bicycles in the cycle sharing scheme do not have the exaggerated nose extensions of a racing bicycle, nor the aggressive stance that would increase perineal pressure, for that reason I believe it was correct to leave these potential health risks out of the article.
The benefits to health from regular exercise cannot be over-emphasised, especially as the National Obesity Observatory identified in 2007 that by 2050 the prevalence of obesity is predicted to affect 60% of adult men, 50% of adult women and 25% of children . The article explored the relationship between physical exercise and mortality [5,6] but due to the design of the study, and the length of the sharing scheme could not comment on long term benefits. I would argue that encouraging activity in the UK population is unmeasurably beneficial in any domain. Encouraging exercise in patients can be in itself a form of exertion. Cultural changes are required to prevent the worsening epidemic of obesity and obesity related health problems. Any scheme, which can both demonstrate population benefits, and encourage physical activity must be praised highly. And if these schemes can help to make cycling and other physical activity more mainstream, then the overall benefits to the UK population will be great.
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The vicious cycling: bicycling related urogenital disorders. Leibovitch I, Mor Y. Department of Urology, Meir Medical Center, Affiliated to Sackler School of Medicine, Tel Aviv University, 59 Tchernichovski st., Kfar Saba, Israel. http://www.ncbi.nlm.nih.gov/pubmed/15716187
3. J Sex Med. 2005 Sep;2(5):596-604. Bicycle riding and erectile dysfunction: an increase in interest (and concern). Huang V, Munarriz R, Goldstein I. Institute for Sexual Medicine, Department of Urology, Boston University School of Medicine, 720 Harrison Avenue, Boston, MA 02118, USA.
4. NHS Information Centre. Healthy lifestyles: knowledge, attitudes and behaviours. Findings for the Health Survey for England 2007. The Health and Social Care Information Centre, London; 2008.
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Competing interests: No competing interests
This study did not take into account important morbidity associated with cycling.
As potential health risks, only road traffic incidents and exposure to air pollution were included.
Genitourinary tract injuries, pudendal nerve entrapment, erectile dysfunction, infertility in both men and women(!), priapism, penile thrombosis, hematuria, torsion of spermatic cord, prostatitis, perineal nodular indurations, elevated serum PSA levels, were not even mentioned.
          
Studies have demonstrated that a high percentage of cyclists are affected by all these pelvic symptoms.
Failing to include all this cycling-associated morbidity has compromised Authors' final conclusions, regarding the amount of health risks associated to cycling, in my opinion.
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Department of Urology, Institute of Men's Health, University Medical Centre Hamburg-Eppendorf, Hamburg, Germany.
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Department of Radiology, Dartmouth-Hitchcock Medical Center, Lebanon, NH 03756, USA.
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Only the nose knows: penile hemodynamic study of the perineum-saddle interface in men with erectile dysfunction utilizingbicycle saddles and seats with and without nose extensions.
Munarriz R, Huang V, Uberoi J, Maitland S, Payton T, Goldstein I.
Institute for Sexual Medicine, Department of Urology, Boston University School of Medicine, 720 Harrison Avenue, Suite 600, Boston, MA 02118, USA.
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Bicycle riding and erectile dysfunction: an increase in interest (and concern).
Huang V, Munarriz R, Goldstein I.
Institute for Sexual Medicine, Department of Urology, Boston University School of Medicine, 720 Harrison Avenue, Boston, MA 02118, USA.
 J Urol. 2004 Aug;172(2):637-41.
Erectile dysfunction after a long-distance cycling event: associations with bicycle characteristics.
Dettori JR, Koepsell TD, Cummings P, Corman JM.
Department of Epidemiology, School of Public Health and Community Medicine, University of Washington and Department of Urology, Virginia Mason Medical Center, Seattle, USA.
 Eur Urol. 2005 Mar;47(3):277-86; discussion 286-7. Epub 2004 Dec 30.
The vicious cycling: bicycling related urogenital disorders.
Leibovitch I, Mor Y.
Department of Urology, Meir Medical Center, Affiliated to Sackler School of Medicine, Tel Aviv University, 59 Tchernichovski st., Kfar Saba, Israel.
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Competing interests: No competing interests