ViewpointCommentaries on Viewpoint: Fragile bones of elite cyclists: to treat or not to treat?Published Online:28 Jun 2021https://doi.org/10.1152/japplphysiol.00335.2021MoreSectionsPDF (358 KB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInWeChat Whole body vibration with/without hypoxic stress as a potential therapy to prevent/treat fragile bones of elite cyclistsFranck Brocherie,1 Marta Camacho-Cardenosa,2 and Rafael Timon3.Author Affiliations1Laboratory Sport, Expertise and Performance (EA 7370), French Institute of Sport (INSEP), Paris, France.2Facultad Ciencias de la Vida y de la Naturaleza, Universidad Antonio de Nebrija, Madrid, Spain.3Faculty of Sport Sciences, University of Extremadura, Cáceres, Spain.to the editor: Hilkens et al. (1) suggest the integration of low-dose osteogenic stimulus through resistance- or impact-based training in elite road cyclists’ routine to treat their low bone mineral density (BMD) without interfering with their cycling performance. Although the feasibility, short- and long-term effectiveness, and potential side effects of such interventions, remain unsounded, we believe that treating this BMD issue is a health priority to avoid possible post-career osteoporosis and associated comorbidities in this particular population. Therefore, the long-term prophylactic or therapeutic application of whole body vibration (WBV) with/without additional hypoxic stress (2,3) prior to or following road cycling training or competition could be valuable. The addition of WBV (10 × 60 s at 30 Hz—30 s of rest, 3 times per week for 10 wk) in well-trained road cyclists’ training was effective in improving hip and preserving spine BMD (4). Furthermore, this could mitigate delayed-onset muscle soreness (3) and accelerate muscle recovery (5), thereby conferring an ergogenic aid to elite cyclists’ training or competition periods. With the hypoxia-inducible factor playing a critical role in osteogenic factors (i.e., bone-vascular coupling, inhibited bone resorption), adding hypoxic stress during WBV may have a synergic effect. Although not yet investigated in athletes, an increase in BMD has been reported after 18 wk of WBV training (4 × 30 s at 12.6 Hz—60 s of rest, 2 times a week) performed in moderate normobaric hypoxia (fraction of inspired oxygen FIO2 = 16.1%) in the elderly population (2). This avenue is worthy of attention to prevent/treat elite road cyclists’ fragile bones.REFERENCES1. Hilkens L, Knuiman P, Heijboer M, Kempers R, Jeukendrup AE, van Loon LJC, van Dijk J-W. Fragile bones of elite cyclists: to treat or not to treat? J Appl Physiol (1985). doi:10.1152/japplphysiol.01034.2020.Link | ISI | Google Scholar2. Camacho-Cardenosa M, Camacho-Cardenosa A, Burtscher M, Brazo-Sayavera J, Tomas-Carus P, Olcina G, Timon R. Effects of whole-body vibration training combined with cyclic hypoxia on bone mineral density in elderly people. Front Physiol 10: 1122, 2019. doi:10.3389/fphys.2019.01122.Crossref | PubMed | ISI | Google Scholar3. Timon R, Tejero J, Brazo-Sayavera J, Crespo C, Olcina G. Effects of whole-body vibration after eccentric exercise on muscle soreness and muscle strength recovery. J Phys Ther Sci 28: 1781–1785, 2016. doi:10.1589/jpts.28.1781. Crossref | PubMed | Google Scholar4. Prioreschi A, Oosthuyse T, Avidon I, McVeigh J. Whole body vibration increases hip bone mineral density in road cyclists. Int J Sports Med 33: 593–599, 2012. doi:10.1055/s-0032-1301886. Crossref | PubMed | ISI | Google Scholar5. Manimmanakorn N, Ross JJ, Manimmanakorn A, Lucas SJ, Hamlin MJ. Effect of whole-body vibration therapy on performance recovery. Int J Sports Physiol Perform 10: 388–395, 2015. doi:10.1123/ijspp.2014-0225. Crossref | PubMed | ISI | Google ScholarREFERENCES1. Hilkens L, Knuiman P, Heijboer M, Kempers R, Jeukendrup AE, van Loon LJC, van Dijk J-W. Fragile bones of elite cyclists: to treat or not to treat? J Appl Physiol (1985). doi:10.1152/japplphysiol.01034.2020.Link | ISI | Google Scholar2. Camacho-Cardenosa M, Camacho-Cardenosa A, Burtscher M, Brazo-Sayavera J, Tomas-Carus P, Olcina G, Timon R. Effects of whole-body vibration training combined with cyclic hypoxia on bone mineral density in elderly people. Front Physiol 10: 1122, 2019. doi:10.3389/fphys.2019.01122.Crossref | PubMed | ISI | Google Scholar3. Timon R, Tejero J, Brazo-Sayavera J, Crespo C, Olcina G. Effects of whole-body vibration after eccentric exercise on muscle soreness and muscle strength recovery. J Phys Ther Sci 28: 1781–1785, 2016. doi:10.1589/jpts.28.1781. Crossref | PubMed | Google Scholar4. Prioreschi A, Oosthuyse T, Avidon I, McVeigh J. Whole body vibration increases hip bone mineral density in road cyclists. Int J Sports Med 33: 593–599, 2012. doi:10.1055/s-0032-1301886. Crossref | PubMed | ISI | Google Scholar5. Manimmanakorn N, Ross JJ, Manimmanakorn A, Lucas SJ, Hamlin MJ. Effect of whole-body vibration therapy on performance recovery. Int J Sports Physiol Perform 10: 388–395, 2015. doi:10.1123/ijspp.2014-0225. Crossref | PubMed | ISI | Google ScholarCycling specificity and altitude training considerationsTadej Debevec12 and Jörn Rittweger34.Author Affiliations1Faculty of Sport, University of Ljubljana, Ljubljana, Slovenia.2Department of Automation, Biocybernetics, and Robotics, Jozef Stefan Institute, Ljubljana, Slovenia.3Institute of Aerospace Medicine, German Aerospace Center (DLR), Cologne, Germany.4Department of Pediatrics and Adolescent Medicine, University of Cologne, Cologne, Germany.to the editor: We would like to comment on two, potentially neglected but important, aspects pertinent to a recent insightful and timely Viewpoint regarding elite cyclists’ bone health approaches (1). First, despite limited experimental evidence, it seems that not all elite cyclists present with lower bone mineral density (BMD). Although studies hint at below-average BMD values in elite distance road cyclists, the same does not hold true for sprint and/or track cyclists—even at the master level (2). This might be related to faster speeds/loads-provoked higher muscle forces resulting in bone strains that are sufficient to enhance bone health in sprint/track cyclists. In addition to mechanical loads, one should also consider that the length of competitions, and thus energy expenditure, differs greatly between road and track cyclists. Second, most elite distance cyclists engage in prolonged altitude training camps. Although the independent effects of altitude-related hypoxia on bone metabolism remain unclear (3), evidence suggests that both positive and negative effects are possible (4), and the overall effects of such training camps should be considered. Combining training, competition, and altitude provokes profound increases in energy expenditure, on the one hand, and hypoxia-related appetite and energy intake reduction, on the other hand. This can, in turn, lead to limited energy availability, which is known to compromise bone metabolism (5). Collectively, we believe that even elite-level cycling is not necessarily bad for bone health. Nevertheless, particular attention should be dedicated to distance road cyclists subjected to long cumulative training and competition times, especially when combined with altitude and/or low energy availability.REFERENCES1. Hilkens L, Knuiman P, Heijboer M, Kempers R, Jeukendrup AE, van Loon LJC, van Dijk J-W. Fragile bones of elite cyclists: to treat or not to treat? J Appl Physiol (1985). doi:10.1152/japplphysiol.01034.2020.Link | ISI | Google Scholar2. Wilks DC, Gilliver SF, Rittweger J. Forearm and tibial bone measures of distance- and sprint-trained master cyclists. Med Sci Sports Exerc 41: 566–573, 2009. doi:10.1249/MSS.0b013e31818a0ec8. Crossref | PubMed | ISI | Google Scholar3. Rittweger J, Debevec T, Frings-Meuthen P, Lau P, Mittag U, Ganse B, Ferstl PG, Simpson EJ, Macdonald IA, Eiken O, Mekjavic IB. On the combined effects of normobaric hypoxia and bed rest upon bone and mineral metabolism: results from the PlanHab study. Bone 91: 130–138, 2016. doi:10.1016/j.bone.2016.07.013.Crossref | PubMed | ISI | Google Scholar4. Hannah SS, McFadden S, McNeilly A, McClean C. “Take my bone away?" Hypoxia and bone: a narrative review. J Cell Physiol 236: 721–740, 2021. doi:10.1002/jcp.29921.Crossref | ISI | Google Scholar5. Stellingwerff T, Peeling P, Garvican-Lewis LA, Hall R, Koivisto AE, Heikura IA, Burke LM. Nutrition and altitude: strategies to enhance adaptation, improve performance and maintain health: a narrative review. Sports Med 49: 169–184, 2019. doi:10.1007/s40279-019-01159-w. Crossref | PubMed | ISI | Google ScholarREFERENCES1. Hilkens L, Knuiman P, Heijboer M, Kempers R, Jeukendrup AE, van Loon LJC, van Dijk J-W. Fragile bones of elite cyclists: to treat or not to treat? J Appl Physiol (1985). doi:10.1152/japplphysiol.01034.2020.Link | ISI | Google Scholar2. Wilks DC, Gilliver SF, Rittweger J. Forearm and tibial bone measures of distance- and sprint-trained master cyclists. Med Sci Sports Exerc 41: 566–573, 2009. doi:10.1249/MSS.0b013e31818a0ec8. Crossref | PubMed | ISI | Google Scholar3. Rittweger J, Debevec T, Frings-Meuthen P, Lau P, Mittag U, Ganse B, Ferstl PG, Simpson EJ, Macdonald IA, Eiken O, Mekjavic IB. On the combined effects of normobaric hypoxia and bed rest upon bone and mineral metabolism: results from the PlanHab study. Bone 91: 130–138, 2016. doi:10.1016/j.bone.2016.07.013.Crossref | PubMed | ISI | Google Scholar4. Hannah SS, McFadden S, McNeilly A, McClean C. “Take my bone away?" Hypoxia and bone: a narrative review. J Cell Physiol 236: 721–740, 2021. doi:10.1002/jcp.29921.Crossref | ISI | Google Scholar5. Stellingwerff T, Peeling P, Garvican-Lewis LA, Hall R, Koivisto AE, Heikura IA, Burke LM. Nutrition and altitude: strategies to enhance adaptation, improve performance and maintain health: a narrative review. Sports Med 49: 169–184, 2019. doi:10.1007/s40279-019-01159-w. Crossref | PubMed | ISI | Google ScholarConsiderations regarding the use of impact training as treatment to prevent bone fragility in elite cyclistsMark J. Hutson, Emma O’Donnell, Katherine Brooke-Wavell, and Richard C. Blagrove.Author AffiliationsSchool of Sport, Exercise and Health Sciences, Loughborough University, Leicestershire, United Kingdom.to the editor: The Viewpoint offered by Hilkens et al. (1) is timely given the recent attention on relative energy deficiency in sport and long-term bone health in athletes (2). In addition to low bone mineral density (BMD) at multiple sites, endurance athletes with low energy availability (LEA) have exhibited thinner cortices, lower trabecular quality, and lower estimated bone strength at the tibia (3). Conversely, evidence suggests that frequently completing short bouts of high-impact exercise could increase BMD, cortical thickness, and estimated bone strength at similar sites in an energy-efficient manner (3). In a group of adolescent male cyclists, approximately 10 min of high-impact jumping daily increased total body and leg bone mineral content compared with a cycle-only training group (4). The suggestion that impact training exerts such osteogenic effects (alongside cycle training) while incurring minimal energy cost is a crucial advantage, given that LEA is implicated in the pathogenesis of poor bone health in athletes (2). Furthermore, it seems feasible to integrate 10 min of impact training into an elite cyclist’s daily training schedule, and this is unlikely to interfere with the intensity of subsequent cycling sessions given the bone specificity of the stimulus. We have previously described the data that suggest impact exercise may benefit bone during periods of LEA (an important consideration in elite cyclists); however, regarding this hypothesis, controlled studies in athletic populations are not yet reported (3). Research should focus on impact training as a treatment to prevent bone fragility in elite cyclists who regularly experience LEA during a prospective period.REFERENCES1. Hilkens L, Knuiman P, Heijboer M, Kempers R, Jeukendrup AE, van Loon LJC, van Dijk J-W. Fragile bones of elite cyclists: to treat or not to treat? J Appl Physiol (1985). doi:10.1152/japplphysiol.01034.2020.Link | ISI | Google Scholar2. Mountjoy M, Sundgot-Borgen JK, Burke LM, Ackerman KE, Blauwet C, Constantini N, Lebrun C, Lundy B, Melin AK, Meyer NL, Sherman RT, Tenforde AS, Klungland Torstveit M, Budgett R. IOC consensus statement on relative energy deficiency in sport (RED-S): 2018 update. Br J Sports Med 52: 687–697, 2018. doi:10.1136/bjsports-2018-099193. Crossref | PubMed | ISI | Google Scholar3. Hutson MJ, O’Donnell E, Brooke-Wavell K, Sale C, Blagrove RC. Effects of low energy availability on bone health in endurance athletes and high-impact exercise as a potential countermeasure: a narrative review. Sport Med 51: 391–403, 2021. doi:10.1007/s40279-020-01396-4. Crossref | PubMed | ISI | Google Scholar4. Vlachopoulos D, Barker AR, Ubago-Guisado E, Williams CA, Gracia-Marco L. The effect of a high-impact jumping intervention on bone mass, bone stiffness and fitness parameters in adolescent athletes. Arch Osteoporos 13: 128, 2018. doi:10.1007/s11657-018-0543-4. Crossref | PubMed | ISI | Google ScholarREFERENCES1. Hilkens L, Knuiman P, Heijboer M, Kempers R, Jeukendrup AE, van Loon LJC, van Dijk J-W. Fragile bones of elite cyclists: to treat or not to treat? J Appl Physiol (1985). doi:10.1152/japplphysiol.01034.2020.Link | ISI | Google Scholar2. Mountjoy M, Sundgot-Borgen JK, Burke LM, Ackerman KE, Blauwet C, Constantini N, Lebrun C, Lundy B, Melin AK, Meyer NL, Sherman RT, Tenforde AS, Klungland Torstveit M, Budgett R. IOC consensus statement on relative energy deficiency in sport (RED-S): 2018 update. Br J Sports Med 52: 687–697, 2018. doi:10.1136/bjsports-2018-099193. Crossref | PubMed | ISI | Google Scholar3. Hutson MJ, O’Donnell E, Brooke-Wavell K, Sale C, Blagrove RC. Effects of low energy availability on bone health in endurance athletes and high-impact exercise as a potential countermeasure: a narrative review. Sport Med 51: 391–403, 2021. doi:10.1007/s40279-020-01396-4. Crossref | PubMed | ISI | Google Scholar4. Vlachopoulos D, Barker AR, Ubago-Guisado E, Williams CA, Gracia-Marco L. The effect of a high-impact jumping intervention on bone mass, bone stiffness and fitness parameters in adolescent athletes. Arch Osteoporos 13: 128, 2018. doi:10.1007/s11657-018-0543-4. Crossref | PubMed | ISI | Google ScholarWorld-class cyclists must risk it all—including their bone healthOwen N. Beck12 and Shalaya Kipp3.Author Affiliations1The George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, Georgia.2School of Biological Sciences, Georgia Institute of Technology, Atlanta, Georgia.3School of Kinesiology, University of British Columbia, Vancouver, British Columbia, Canada..to the editor: The inordinate endurance training of elite cyclists may cause several unhealthy physiological adaptations, including adverse cardiac remodeling such as myocardial fibrosis and coronary artery calcification (1), in addition to low bone mineral density (BMD) (2,3). The unfortunate reality is, to be a world-class athlete, elite cyclists must prioritize performance over health.Although associated with health consequences (4), having low BMD by itself should improve cycling performance. To explain, elite cyclists have been reported to have 9.1% less dense skeletons than healthy people (3). Assuming that a 74-kg person’s skeleton comprises 15% of their body mass, decreasing BMD by 9.1% reduces their body mass by 1 kg. Reducing body mass decreases cycling rolling resistance and the mechanical work required to overcome gravity during uphill cycling (5). Such mechanical changes improve cycling speed at a given intensity on flat and uphill courses (5). For instance, if a cyclist maintained 259 W of mechanical power output at a body mass of 73 kg, compared with at a body mass of 74 kg, they would theoretically complete the Giro d’Italia’s (in)famous Passo dello Stelvio ascent ∼68 s faster, an improvement that is four times the margin of victory in the respective 2020 Giro stage. To recap, a low BMD decreases overall body mass, improving cycling mechanics, which likely improves cycling performance.Therefore, if elite cyclists want to reach the top of the podium, they should not increase their BMD. Alternatively, if elite cyclists wish to prioritize their health, they should adopt a less extreme lifestyle.REFERENCES1. Eijsvogels TMH, Fernandez AB, Thompson PD. Are there deleterious cardiac effects of acute and chronic endurance exercise? Physiol Rev 96: 99–125, 2016. doi:10.1152/physrev.00029.2014. Link | ISI | Google Scholar2. Hilkens L, Knuiman P, Heijboer M, Kempers R, Jeukendrup AE, van Loon LJC, van Dijk J-W. Fragile bones of elite cyclists: to treat or not to treat? J Appl Physiol (1985). doi:10.1152/japplphysiol.01034.2020.Link | ISI | Google Scholar3. Campion F, Nevill AM, Karlsson M, Lounana J, Shabani M, Fardellone P, Medelli J. Bone status in professional cyclists. Int J Sports Med 31: 511–515, 2010. doi:10.1055/s-0029-1243616. Crossref | PubMed | ISI | Google Scholar4. Johansson C, Black D, Johnell O, Oden A, Mellström D. Bone mineral density is a predictor of survival. Calcif Tissue Int 63: 190–196, 1998. doi:10.1007/s002239900513. Crossref | PubMed | ISI | Google Scholar5. Jeukendrup AE, Martin J. Improving cycling performance. Sports Med 31: 559–569, 2001. doi:10.2165/00007256-200131070-00009. Crossref | PubMed | ISI | Google ScholarREFERENCES1. Eijsvogels TMH, Fernandez AB, Thompson PD. Are there deleterious cardiac effects of acute and chronic endurance exercise? Physiol Rev 96: 99–125, 2016. doi:10.1152/physrev.00029.2014. Link | ISI | Google Scholar2. Hilkens L, Knuiman P, Heijboer M, Kempers R, Jeukendrup AE, van Loon LJC, van Dijk J-W. Fragile bones of elite cyclists: to treat or not to treat? J Appl Physiol (1985). doi:10.1152/japplphysiol.01034.2020.Link | ISI | Google Scholar3. Campion F, Nevill AM, Karlsson M, Lounana J, Shabani M, Fardellone P, Medelli J. Bone status in professional cyclists. Int J Sports Med 31: 511–515, 2010. doi:10.1055/s-0029-1243616. Crossref | PubMed | ISI | Google Scholar4. Johansson C, Black D, Johnell O, Oden A, Mellström D. Bone mineral density is a predictor of survival. Calcif Tissue Int 63: 190–196, 1998. doi:10.1007/s002239900513. Crossref | PubMed | ISI | Google Scholar5. Jeukendrup AE, Martin J. Improving cycling performance. Sports Med 31: 559–569, 2001. doi:10.2165/00007256-200131070-00009. Crossref | PubMed | ISI | Google ScholarCommentary on Viewpoint: Fragile bones of elite cyclists: to treat or to prevent?Ricardo J. Fernandes,12 Filipe Conceição,12 and J. Arturo Abraldes3.Author Affiliations1Centre of Research, Education, Innovation and Intervention in Sport, Faculty of Sport, University of Porto, Porto, Portugal.2Porto Biomechanics Laboratory, University of Porto, Porto, Portugal.3Research Group Movement Science and Sport, Faculty of Sports Sciences, University of Murcia, Murcia, Spain.to the editor: The Viewpoint about the decision of treating fragile bones of elite cyclists (1) has a solid background, but the debate might be better detailed. Lower bone mineral density (BMD) of professional cyclists compared with the nonelite and sedentary younger males is due to not only their extreme voluminous training but also the many resting hours spent in a lie-down position while their recreational and lower-level counterparts move to schools, universities, or working places. By drastically decreasing bone exposure to ground reaction forces during daily life activities, elite cyclists are significantly prone to osteoporosis and bone risk fractures in later life (like astronauts at spaceflight conditions; 2). Complementing traditional endurance conditioning with short-duration high-intensity stimulus and advanced recovery strategies (like compression and electrostimulation (3) might help in avoiding chronic inflammation and overcoming negative influences on bone health. Concurrently, promoting strength development (focusing on intra- and intermuscular coordination and on advanced postures) (4) that will not increase cyclists’ body mass would prevent musculoskeletal injuries and, indirectly, prevent low BMD. Agreeing to the fact that pharmacological treatment should be the last line of defense, vitamin C supplementation might also be helpful in dealing with this situation since it is an important nutrient to produce collagen in bone matrix and scavenges free radicals detrimental to bone health (5). More than treatment of this bone disorder, we suggest focusing on prevention so that cyclists would have a lower traumatic bone fracture probability (and consequent impaired exercise performance) and a lower stress fracture risk in later life.REFERENCES1. Hilkens L, Knuiman P, Heijboer M, Kempers R, Jeukendrup AE, van Loon LJC, van Dijk J-W. Fragile bones of elite cyclists: to treat or not to treat? J Appl Physiol (1985). doi:10.1152/japplphysiol.01034.2020.Link | ISI | Google Scholar2. Sibonga JD. Spaceflight-induced bone loss: is there an osteoporosis risk? Curr Osteoporos Rep 11: 92–98, 2013. doi:10.1007/s11914-013-0136-5.Crossref | PubMed | ISI | Google Scholar3. Broatch JR, Bishop DJ, Halson S. Lower limb sports compression garments improve muscle blood flow and exercise performance during repeated-sprint cycling. Int J Sports Physiol Perform 13: 882–890, 2018. doi:10.1123/ijspp.2017-0638.Crossref | PubMed | ISI | Google Scholar4. Serra N, Carvalho DD, Fernandes RJ. The importance of agonistic, antagonistic and synergistic muscles coordination on swimming dry land training. Trends in Sports Sci 3: 101–104, 2017. doi:10.23829/TSS.2017.24.3-1.Crossref | Google Scholar5. Chin KY, Ima-Nirwana S. Vitamin C and bone health: evidence from cell, animal and human studies. Curr Drug Targets 19: 439–450, 2018. doi:10.2174/1389450116666150907100838. Crossref | PubMed | ISI | Google ScholarREFERENCES1. Hilkens L, Knuiman P, Heijboer M, Kempers R, Jeukendrup AE, van Loon LJC, van Dijk J-W. Fragile bones of elite cyclists: to treat or not to treat? J Appl Physiol (1985). doi:10.1152/japplphysiol.01034.2020.Link | ISI | Google Scholar2. Sibonga JD. Spaceflight-induced bone loss: is there an osteoporosis risk? Curr Osteoporos Rep 11: 92–98, 2013. doi:10.1007/s11914-013-0136-5.Crossref | PubMed | ISI | Google Scholar3. Broatch JR, Bishop DJ, Halson S. Lower limb sports compression garments improve muscle blood flow and exercise performance during repeated-sprint cycling. Int J Sports Physiol Perform 13: 882–890, 2018. doi:10.1123/ijspp.2017-0638.Crossref | PubMed | ISI | Google Scholar4. Serra N, Carvalho DD, Fernandes RJ. The importance of agonistic, antagonistic and synergistic muscles coordination on swimming dry land training. Trends in Sports Sci 3: 101–104, 2017. doi:10.23829/TSS.2017.24.3-1.Crossref | Google Scholar5. Chin KY, Ima-Nirwana S. Vitamin C and bone health: evidence from cell, animal and human studies. Curr Drug Targets 19: 439–450, 2018. doi:10.2174/1389450116666150907100838. Crossref | PubMed | ISI | Google ScholarCommentary on Viewpoint: Fragile bones of elite cyclists: to treat or not to treat?Julie P. Greeves123 and Thomas J. O’Leary12.Author Affiliations1Army Health and Performance Research, Army Headquarters, Andover, United Kingdom.2Division of Surgery and Interventional Science, University College London, London, United Kingdom.3Norwich Medical School, University of East Anglia, Norwich, United Kingdom.to the editor: Bone loss occurs at the hip and spine in cyclists, determined by DXA. Hilkens et al. (1) highlight the prevalence of low bone mineral density (BMD) at these trabecular sites in cyclists, which may be a risk factor for osteoporosis, but the importance of BMD in fracture risk is unclear. DXA generates an areal (two-dimensional) projection of BMD from a three-dimensional bone but cannot measure other properties that contribute to strength. Bone strength is determined by density, structure, and material properties—at the macrostructure, microstructure, and nanostructure levels—in the trabecular and cortical compartments (2). Therefore, DXA is an insensitive tool for measuring responses of appendicular bone to loading (3), where compartment-specific changes in bone density, size, and microarchitecture increase strength (4). Better understanding the effects of cycling on other compartments of bone may provide greater insight into the link between cycling, “bone health,” and fracture risk.Hilkens et al. (1) discuss the role of dermal calcium loss in bone loss. The contribution of dermal calcium loss to exercise-induced disturbances in calcium homeostasis is not clear, but serum-ionized calcium decreases, and parathyroid hormone and bone resorption increase, during exercise (5). The long-term effects of the disturbance in calcium homeostasis is unknown, but maintenance of serum-ionized calcium during exercise can prevent the increase in parathyroid hormone and bone resorption (5). Calcium feeding in exercise training may be an interesting avenue to explore for protecting the skeletal health of those engaged in high volumes of exercise.REFERENCES1. Hilkens L, Knuiman P, Heijboer M, Kempers R, Jeukendrup AE, van Loon LJC, van Dijk J-W. Fragile bones of elite cyclists: to treat or not to treat? J Appl Physiol (1985). doi:10.1152/japplphysiol.01034.2020.Link | ISI | Google Scholar2. O'Leary TJ, Rice HM, Greeves JP. Biomechanical basis of predicting and preventing lower limb stress fractures during arduous training. Curr Osteoporos Rep. (First published February 26, 2021). doi:10.1007/s11914-021-00671-1.Crossref | PubMed | ISI | Google Scholar3. Turner CH, Robling AG. Designing exercise regimens to increase bone strength. Exerc Sport Sci Rev 31: 45–50, 2003. doi:10.1097/00003677-200301000-00009. Crossref | PubMed | ISI | Google Scholar4. O'Leary TJ, Wardle SL, Gifford RM, Double RL, Reynolds RM, Woods DR, Greeves JP. Tibial macrostructure and microarchitecture adaptations in women during 44 weeks of arduous military training. J Bone Miner Res. (First published April 15, 2021). doi:10.1002/jbmr.4290.Crossref | PubMed | ISI | Google Scholar5. Kohrt WM, Wherry SJ, Wolfe P, Sherk VD, Wellington T, Swanson CM, Weaver CM, Boxer RS. Maintenance of serum ionized calcium during exercise attenuates parathyroid hormone and bone resorption responses. J Bone Miner Res 33: 1326–1334, 2018. doi:10.1002/jbmr.3428. Crossref | PubMed | ISI | Google ScholarREFERENCES1. Hilkens L, Knuiman P, Heijboer M, Kempers R, Jeukendrup AE, van Loon LJC, van Dijk J-W. Fragile bones of elite cyclists: to treat or not to treat? J Appl Physiol (1985). doi:10.1152/japplphysiol.01034.2020.Link | ISI | Google Scholar2. O'Leary TJ, Rice HM, Greeves JP. Biomechanical basis of predicting and preventing lower limb stress fractures during arduous training. Curr Osteoporos Rep. (First published February 26, 2021). doi:10.1007/s11914-021-00671-1.Crossref | PubMed | ISI | Google Scholar3. Turner CH, Robling AG. Designing exercise regimens to increase bone strength. Exerc Sport Sci Rev 31: 45–50, 2003. doi:10.1097/00003677-200301000-00009. Crossref | PubMed | ISI | Google Scholar4. O'Leary TJ, Wardle SL, Gifford RM, Double RL, Reynolds RM, Woods DR, Greeves JP. Tibial macrostructure and microarchitecture adaptations in women during 44 weeks of arduous military training. J Bone Miner Res. (First published April 15, 2021). doi:10.1002/jbmr.4290.Crossref | PubMed | ISI | Google Scholar5. Kohrt WM, Wherry SJ, Wolfe P, Sherk VD, Wellington T, Swanson CM, Weaver CM, Boxer RS. Maintenance of serum ionized calcium during exercise attenuates parathyroid hormone and bone resorption responses. J Bone Miner Res 33: 1326–1334, 2018. doi:10.1002/jbmr.3428. Crossref | PubMed | ISI | Google ScholarOsteoporosis in elite cyclists and treatment optionsMary Vagula.Author AffiliationsGannon University, Erie, Pennsylvania.TO THE EDITOR: Although genetics account for up to 50% of our bone health, it is the lifestyle factors (nutritional, physical activity, and hormonal status) that determine the difference between a healthy skeleton and frail fracture-prone bones (1). Osteoporosis, a systemic skeletal disorder associated with reduced bone mineral density and increased risk for fracture, is a serious public health problem globally (2), costing about $75 billion for treatment in the United States alone. Mortality rates due to osteoporotic fracture range from 10% to 45% in the first year and are noted following spine and hip fractures (3). There are several types of osteoporosis: postmenopausal osteoporosis and senile osteoporosis (both of which are categorized as primary osteoporosis) and secondary osteoporosis. The causes of secondary osteoporosis are many, ranging from low calcium intake to Klinefelter’s syndromes to inflammatory digestive diseases and low-impact activities such as cycling. Cycling does not bestow any osteogenic benefit but can increase bone resorption. About two-thirds of professional road cyclists are believed to have osteopenia (4). Just as prediabetes is a warning signal for diabetes, so is osteopenia for osteoporosis, thus calling for preventive measures. Many intervention methods mentioned by the authors (5)—such as involving weight-bearing exercises as part of intensive training; proper dietary regimen including vitamin D, vitamin K, and bisphosphonates; and hormonal therapy—could help prevent osteopenia and osteoporosis in elite cyclists in their middle and old age. Hormone leptin is found to stimulate osteoblast proliferation and decrease osteoclast production, and it could play a future role in the treatment of osteoporosis.REFERENCES1. Maimoun L, Mariano-Goulart D, Couret I, Manetta J, Peruc