Significant discrepancies and controversies exist in assessing and understanding the “flat feet” syndrome (FFS). Understanding the underlying aetiology of FFS is essential to understanding how FFS may cause symptoms and how to manage, treat, and prevent symptoms and progression of the deformity (1). However, understanding the underlying aetiology of the prevalent FFS remains limited—as a formal diagnosis is not established (2, 3, 4).

This limited understanding and, significantly, no diagnosis of the underlying cause of the prevalent FFS (including the related valgus-pronatory mechanical phenomenon of the rearfoot) is the most significant gap in the foot and ankle orthopaedics and musculoskeletal (MSK) podiatry clinics and their to-go scientific literature. Additionally, there is limited understanding, research, and controversy about the FFS-related foot orthoses (FOs) intervention, prescription/assessment, and design (5).

Challenging the editorial's premise and the general concept that “flat feet” are “healthy anatomical variants” mainly assessed on symptoms is essential. The assessment of the FFS, if problematic, based on whether it is symptomatic, represents a limited understanding of the physiological alignment of the arthroskeletal structures and related mechanisms of the foot and ankle. Throughout the editorial, the assumption is that the FFS is not a problem if there are no symptoms or only a problem if (when) there are symptoms. Do malalignment, exostosis-ankylosis-arthrosis deformities progress without symptoms? Owing to the indolent nature of the growth of exostoses or deformities, they are usually asymptomatic; furthermore, they may cause or be associated with various symptoms throughout the patient's life (6).

Additionally, aside from the “normal” or physiologically developing foot arches being more "flatter" until, on average, between 5-7 years of age—health-related quality of life (HRQOL) measurements of asymptomatic FFS and "normal" foot arches in children 5-10 years revealed that the asymptomatic FFS exhibited significantly lower overall HRQOL scores and lower scores in the physical, emotional, social, and school functioning domains (7). Similarly, as did other HRQOL research on symptomatic and asymptomatic FFS in children (>7 years) and adults (8, 9).

Moreover, what is driving the mechanics of the FFS? Does FFS arthroskeletal “deformity” malalignment mean anything in loading? Is there a correlation between arthroskeletal morphology and alignment and mechanics or moments?

Research exists, progressing and narrowing an understanding towards an underlying valgus morphology and alignment deformity of the talus bone as a potential cause and diagnosis of the FFS and the increased valgus-pronatory phenomenon of the ankle joint complex (2, 3). As Apostle et al. (2014) and Probasco et al. (2015) hypothesised, Sangeorzan and Sangeorzan (2018) (10) reported that a valgus (sub) talus axis leads to altered force vectors about the foot and ankle that place unusually high stresses on the medial soft tissues of the ankle, hypothesising that this altered axis is the primary cause of FFS.

Is the FFS with asymmetric alignment and eccentric loading moments, exostosis-ankylosis-arthrosis, mechanical dysfunction, potential activity limitation, and significantly lower overall HRQOL measures—a “benign” or "healthy” “anatomical variant" of the foot and ankle—despite being asymptomatic?

Furthermore, the reporting on "overdiagnosis" and "unnecessary interventions for asymptomatic flat feet (e.g., foot orthoses…)" further reflects this limited understanding of the relationship between arthroskeletal malalignment, its mechanical implications, and FOs. Additionally, these views may overlook the value or appreciation of preventive medicine. Such perspectives could inadvertently diminish the potential of foot and ankle clinics and the benefits that FOs can offer patients.

Intervention in asymptomatic FFS is required to prevent indolent-asymptomatic progressive deformities and potential symptoms. With an improved understanding and appreciation of the malalignment of arthroskeletal (rigid-body) structures and their mechanical or force implications, FOs should be the most significant form of conservative management-dampening of the mechanical FFS condition/moments—provided they are effectively designed. FOs may improve asymptomatic FFS HRQOL in children, and a more proactive approach to identifying and managing asymptomatic FFS is needed (7). Furthermore, intervention is also required, as FFS can potentially lead to foot and ankle lower limb symptoms (8).

Future investments in "research funds and time" are essential to address the gaps in the existing literature regarding the FFS and improve our understanding of FFS assessment, mechanics, aetiology, and diagnosis. Additionally, "research funds and time" are necessary to improve our knowledge of FFS-orthoses prescription, assessment, design, and manufacture. Moreover, a comprehensive understanding of the fundamental primary aetiology of FFS is essential for developing an effective treatment and cure for FFS.

References:

1. Kothari, A., Bhuva, S., Stebbins, J., Zavatsky, A.B. and Theologis, T., 2016. An investigation into the aetiology of flexible flat feet: the role of subtalar joint morphology. The Bone & Joint Journal, 98(4), pp.564-568.

2. Apostle, K.L., Coleman, N.W. and Sangeorzan, B.J., 2014. Subtalar joint axis in patients with symptomatic peritalar subluxation compared to normal controls. Foot & Ankle International, 35(11), pp.1153-1158.

3. Probasco, W., Haleem, A.M., Yu, J., Sangeorzan, B.J., Deland, J.T. and Ellis, S.J., 2015. Assessment of coronal plane subtalar joint alignment in peritalar subluxation via weight-bearing multiplanar imaging. Foot & Ankle International, 36(3), pp.302-309.

4. de Cesar Netto, C., Saito, G.H., Roney, A., Day, J., Greditzer, H., Sofka, C., Ellis, S.J., Society, W.B.C., Richter, M., Barg, A. and Lintz, F., 2021. Combined weightbearing CT and MRI assessment of flexible progressive collapsing foot deformity. Foot and Ankle Surgery, 27(8), pp.884-891.

5. MacKenzie, A.J., Rome, K. and Evans, A.M., 2012. The efficacy of nonsurgical interventions for pediatric flexible flat foot: a critical review. Journal of Pediatric Orthopaedics, 32(8), pp.830-834.

6. Rupprecht, M., Spiro, A.S., Rueger, J.M. and Stücker, R., 2011. Temporary screw epiphyseodesis of the distal tibia: a therapeutic option for ankle valgus in patients with hereditary multiple exostosis. Journal of Pediatric Orthopaedics, 31(1), pp.89-94.

7. Žukauskas, S., Barauskas, V., Degliūtė-Muller, R. and Čekanauskas, E., 2023. Really Asymptomatic? Health-Related Quality of Life and Objective Clinical Foot Characteristics among 5–10-Year-Old Children with a Flexible FlatFoot. Journal of Clinical Medicine, 12(9), p.3331.

8. Kothari, A., Stebbins, J., Zavatsky, A.B. and Theologis, T., 2014. Health-related quality of life in children with flexible flatfeet: a cross-sectional study. Journal of Children's Orthopaedics, 8(6), pp.489-496.

9. Damayanti, Y., Hadisoemarto, P.F. and Defi, I.R., 2018. Flatfoot decreases school functioning among children< 11 years of age. Universa Medicina, 37(1), pp.50-56.

10. Sangeorzan, A. and Sangeorzan, B., 2018. Subtalar joint biomechanics: from normal to pathologic. Foot and Ankle Clinics, 23(3), pp.341-352.

Dear Editor,

Hamilton et al (1) conducted a study to assess strength, power and aerobic capacity of transgender athletes. They conclude the results may be useful for sports governing bodies and inform sports policy. However, policy should be informed by accurate scientific information and, unfortunately, this study contains fundamental errors in design, methodology and interpretation. In this letter, we focus on the incorrect interpretation of respiratory testing, the inappropriate definition of ‘athlete’, and group matching.

The study compares respiratory function of transgender and non-transgender individuals using cardiopulmonary exercise testing, as well as conventional lung function testing (spirometry, lung volumes and gas transfer). The authors report that transgender women (TW - male individuals who identify as women) had greater forced expiratory volume in 1s (FEV1), forced vital capacity (FVC) and peak expiratory flow rate (PEFR) and a reduced FEV1/FVC ratio relative to cisgender women (CW - female individuals without a differing gender identity). From this data, the authors conclude that TW have decreased lung function, increasing their work of breathing relative to CW.

Firstly, the methodology employed to measure lung function does not appear to conform to accepted, published testing guidelines (ATS/ERS) (2). Lung function is typically measured repeatedly within 150mL, with the highest numeric value for each variable recorded, to ensure reproducible high-quality measures, and not until a ‘declining performance occurred’. Secondly, in the TW group, data was included from an individual with abnormal findings (FEV/FVC ratio of approximately 0.62), indicating an individual with probable obstructive airways disease (3,4), confounding interpretation of mean data. Thirdly, the authors fail to correct lung function data for factors known to influence these variables, in addition to sex, e.g. height, ethnicity and age (5,6). In this study, the TW group are older and taller, and male, and as such, would be expected to have a lower FEV1/FVC relative to CW. When the published mean values are considered relative to these factors and compared with internationally validated Global Lung Initiative (GLI) reference ranges, the FEV1/FVC values are within normal ranges for corresponding predicted values in all groups (including the TW). Within these normal ranges, these results do not reflect reduced lung function in the TW, as a group, and do not represent an increased challenge to the ‘work of breathing’ as presented and discussed in this paper (6,7). The reported difference of FEV1/FVC, 0.88 (CW) vs. 0.83 (TW), arises because CW have a disproportionately lower FVC, as is normal for female and shorter individuals. This difference is further exacerbated by the inclusion of one individual with probable pathological airflow obstruction in the TW group. The study also reports that TW have a higher FEV1, FVC and PEFR relative to CW and therefore, if hypothesising on exercise performance based on absolute respiratory test values, it would be appropriate to discuss that TW may have improved lung function for sports performance (8), precisely the opposite conclusion drawn by the authors.

Methodologically, there is also a significant grouping error. The stated primary aim was to ‘compare cardiorespiratory fitness, strength and body composition of transgender athletes to that of matched cisgender cohorts’. Yet groups in this study were not matched, with clear differences in height, body mass index, fat mass index, and relative V ̇O2 max, between TW and CW. The TW group have the highest BMI (26.2kg/m2), Fat Mass Index (8.2 kg/m2) and Fat Mass (31.5%) and lowest V ̇O2 Max (45.1ml/kg/min) of any group in the study. These values are not physiologically representative of an athlete cohort (9). The study defines participants as athletes based on self-reported participation in a sport (unspecified) or in any physical training (unspecified) at least 3-times per week. This is not aligned with study guidelines on the definition of an ‘athlete’ (10). The authors suggest their study should influence sporting governing bodies and athletic sports policy, providing ‘sports governing bodies with laboratory-based performance related data from transgender athletes’. Neither the questionnaire-based criteria nor the physiological parameters are consistent with this being an athlete cohort.

In conclusion, we recommend the paper by Hamilton at al undergoes significant revision. The interpretation of respiratory testing is inaccurate and should include discussion on FEV1/FVC in the context of age, sex and height and relative to normative data. If the discussion on respiratory testing values and their possible impact on exercise performance is then retained, the potential for improved exercise performance of an increased FVC, FEV1 and PEFR in the TW group, relative to the CW group, should be discussed. Erroneous conclusions regarding ‘decreased lung function and increased work of breathing’ in TW should be removed. The study did not effectively match groups and the TW group do not meet published recommendations or physiological criteria to support an ‘athlete’ designation. Accordingly, we advise the study title is changed, the discussion, conclusions and ‘summary box’ corrected, and references to this as an athlete group removed. This is a contentious area of sports policy (11,12) and the British Journal of Sports Medicine should ensure that published scientific work draws credible conclusions and accurately informs readers.

References
1. Hamilton B, Brown A, Montagner-Moraes S, Comeras-Chueca C, Bush PG, Guppy FM, Pitsiladis YP. Strength, power and aerobic capacity of transgender athletes: a cross-sectional study. Br J Sports Med. 2024 Apr 10;bjsports-2023-108029.
2. Graham BL, Steenbruggen I, Miller MR, Barjaktarevic IZ, Cooper BG, Hall GL, et al. Standardization of Spirometry 2019 Update. An Official American Thoracic Society and European Respiratory Society Technical Statement. Am J Respir Crit Care Med. 2019 Oct 15;200(8):e70–88.
3. Singh D, Agusti A, Anzueto A, Barnes PJ, Bourbeau J, Celli BR, et al. Global Strategy for the Diagnosis, Management, and Prevention of Chronic Obstructive Lung Disease: the GOLD science committee report 2019. Eur Respir J [Internet]. 2019 May 1 [cited 2024 May 31];53(5). Available from: https://erj.ersjournals.com/content/53/5/1900164
4. Recommendations | Asthma: diagnosis, monitoring and chronic asthma management | Guidance | NICE [Internet]. NICE; 2017 [cited 2024 May 31]. Available from: https://www.nice.org.uk/guidance/ng80/chapter/Recommendations#objective-...
5. Hankinson JL, Odencrantz JR, Fedan KB. Spirometric reference values from a sample of the general U.S. population. Am J Respir Crit Care Med. 1999 Jan;159(1):179–87.
6. Cooper BG, Stocks J, Hall GL, Culver B, Steenbruggen I, Carter KW, et al. The Global Lung Function Initiative (GLI) Network: bringing the world’s respiratory reference values together. Breathe. 2017 Sep;13(3):e56–64.
7. Haynes JM, Stumbo RW. The Impact of Using Non-Birth Sex on the Interpretation of Spirometry Data in Subjects With Air-Flow Obstruction. Respir Care. 2018 Feb;63(2):215–8.
8. McNeill J, Chernofsky A, Nayor M, Rahaghi FN, San Jose Estepar R, Washko G, et al. The association of lung function and pulmonary vasculature volume with cardiorespiratory fitness in the community. Eur Respir J. 2022 Aug;60(2):2101821.
9. Degens H, Stasiulis A, Skurvydas A, Statkeviciene B, Venckunas T. Physiological comparison between non-athletes, endurance, power and team athletes. Eur J Appl Physiol. 2019 Jun 1;119(6):1377–86.
10. McKinney J, Velghe J, Fee J, Isserow S, Drezner JA. Defining Athletes and Exercisers. Am J Cardiol. 2019 Feb 1;123(3):532–5.
11. IOC. IOC Framework on Fairness, Inclusion and Non-Discrimination on the basis of Gender Identity and Sex Variations [Internet]. IOC; 2021. Available from: https://stillmed.olympics.com/media/Documents/News/2021/11/IOC-Framework...
12. Lundberg TR, Tucker R, McGawley K, Williams AG, Millet GP, Sandbakk Ø, et al. The International Olympic Committee framework on fairness, inclusion and nondiscrimination on the basis of gender identity and sex variations does not protect fairness for female athletes. Scand J Med Sci Sports. 2024 Mar;34(3):e14581.

We thank Brown and O'Connor (1) for their interest in our research (2) and we welcome their constructive criticism, especially regarding our study design, analysis and interpretation. We consider such exchanges equally important as the dissemination of the original research and hence, we wish to address all concerns. Concerns were raised about the need for more specific inclusion criteria to ensure comparability among research participants. Specifically, Brown and O’Connor (1) raised valid concerns about the lack of detailed information on the frequency, intensity, duration, and mode of exercise among our research participants. While we appreciate and totally agree with these comments, the task of recruiting suitable research participants, mainly from small demographic groups such as transgender athletes, is challenging. Many transgender athletes, especially those with high profile, feel too intimidated to come forward in the current polarised climate. Given this, we had to balance the need for stringent inclusion criteria with the necessity of obtaining a representative sample of transgender athletes to better understand their physiological and performance characteristics. We aimed to strike a balance between providing an informative overview of the participants' sporting backgrounds and protecting the anonymity of the transgender athletes involved in the study. We fully acknowledge that a more granular breakdown would have been beneficial for assessing comparability among groups, and we recognise the value of more specific data and will continue to prioritise this in all our future research endeavours. Without a doubt, this balancing act, while essential for the advancement of knowledge in this field, will have contributed to some of the variability in training backgrounds among participants and may have influenced the findings of this research. For example, some of the differences between cisgender men, cisgender women and transgender women in terms of body composition, muscle strength, and aerobic fitness may be the result of variations in training backgrounds and the specifics of their chosen athletic pursuits. We attempted to reduce the impact of this important limitation by imposing the inclusion criteria of training three times per week and participating in competitive sport. Therefore, it can be inferred that all volunteers participating in our study were actively engaged in competitive sports, which would involve a variety of different training modalities. Given the status quo of almost no published data from transgender athletes, we opted to do the best we could in recruitment and design, appropriately analyse the data and present the findings while stressing the limitations of the research. As a result, our paper includes a detailed limitations section which addresses most of the concerns raised by Brown and O’Connor and others. For instance, in our limitations, we declared that the composition of the study cohort may not fully represent the diversity of athletes in elite sports from worldwide populations, and the study may suffer from selection bias (2, 3). While we acknowledge that this research we present is meant to encourage larger subject numbers and better methods in participant selection to improve the generalizability of research findings, there is a notable absence of studies that can establish an optimal sample size to determine whether transgender athletes possess unfair advantages. We acknowledged the limitations of our research but at the same time celebrate the uniqueness of our study and its strengths, which also include appropriate methods to assess the subjects’ strength, power and aerobic capacity, not to mention that all transgender participants have undergone years of hormonal treatment and have consistently maintained hormone levels within acceptable ranges; strengths that have received almost no attention. We believe that our research, despite its limitations, is a significant step towards better understanding the physiological and performance characteristics of transgender athletes, and we are committed to furthering this understanding through more collaborative research.

In response to the comment by Brown and O'Connor (1) that transgender women in our study exhibited a higher body fat percentage compared to comparably aged men (4) and previously researched non-athletic transgender women (5, 6), it is essential to consider the influence of hormonal factors, specifically in the case of Alvares, Santos (5), who did not report any oestradiol findings, and Scharff, Wiepjes (6), who reported oestradiol (Range 225-257 pmol·L-1). Transgender women in our present study had oestradiol concentrations sixfold higher (742 pmol·L-1) than those of cisgender men (104 pmol·L-1), double that of cisgender women (336. pmol·L-1) and threefold higher than was reported in Scharff, Wiepjes (6). Given that oestradiol is known to be positively associated with fat mass accumulation (7), it is unsurprising that transgender women athletes presented with higher fat mass levels. However, as our research is cross-sectional, we cannot establish that causation. The result of higher oestradiol concentrations may be caused by athletes self-medicating with gender-affirmation hormone treatment, as we did not recruit from a clinic, which means that the gender-affirming treatment of transgender athletes in our study (2) was not controlled. Longitudinal studies tracking transgender athletes over time are crucial to better understanding the relationship between hormone levels, body composition changes, and athletic performance. An important limitation of cross-sectional studies, as we declare in our study (2), is the inability to determine causality, making it impossible to determine whether the lower performances (e.g., relative maximal aerobic capacity) we report in transgender women athletes compared to cisgender women are due to gender-affirmation hormone treatment or simply due to a lower training status. Likewise, the higher absolute fat mass observed in transgender women athletes may be influenced by oestrogen therapy, which can lead to increases in both visceral and subcutaneous fat. Therefore, longitudinal studies are crucial to provide a more comprehensive understanding.

Our study, which focuses on physical performance aspects such as strength, power, and aerobic capacity, should serve as a primer to the broader discussion of gender inclusion, highlighting the importance of recognizing the differences between groups, especially between cisgender men and transgender women. There is also a call for a more comprehensive approach to research on sports performance across diverse sports, utilizing specific metrics to gain deeper insights into the priorities of each sport. Additionally, studies focusing on physiological aspects such as metabolic, hormonal, and biomarkers are essential to address questions like the residual effects of testosterone in relation to the "muscle memory mechanism" (8); the current focus of our research on this topic.

Unfortunately, the issue of integration of transgender athletes into elite sport has generated so much negative and polarised discussion that no matter what design is employed, subjects recruited, and intervention applied, no amount of research would change the entrenched position of those who are vehemently either pro- or anti-inclusion. In short, this issue is now political and only scientific data, with its acknowledged limitations, can best inform the debate, not that scientists themselves are immune from contributing to the politics of this debate. Below are some examples of the social media critiques our paper has received that were addressed in the limitations of our paper (2).

1) “19 transgender women, 20 cisgender women, 19 cisgender men and 11 transgender men. Such low numbers, even for an experimental or preliminary study, is laughable and can hardly be taken seriously.” (9)
2) “When I first read it, it made me think that the IOC and their researchers simply could not find enough transgender athletes to study over time, and so instead, they’ve just taken whatever they could find, and then compared to them a group of whatever females they could find, and tried to portray it as a valid comparison.” (10)
3) “This study has numerous problems, including self-selection of participants, wide variation in ages of the participants, and no control over hormone treatment of its transgender participants.” (10)
4) “If you read the baseline characteristics of the study groups you see that the trans athletes have a BMI in the overweight range while the women are lower BMI. Basically the research is comparing fat blokes with athletic women. This is not a serious piece of research and seems designed to confirm the IOC bias that men can compete in women’s events.” (9)
5) “These demographic characteristics should already make us pause – these groups may not be comparable for reasons that really matter. We have a group of females who are on the higher end of cardiovascular capacity along the female spectrum, and there is a group of transgender women in the middle of that range, even the lower side of it. One group is overweight, the other is not.” (10)

We encourage all who read our paper to pay particular attention to our declared limitations and engage with generating original data rather than dismissing the work of others. So heated is the debate on transgender inclusion that we have received threats and emails that are too vulgar to be presented and constitute abuse and, in some countries, a criminal offence. We hope that publication of original studies such as our imperfect study, will encourage better funded collaborative research in this area to keep the emphasis on science and not politics.
 
References
1. Gregory A Brown, Mary I O'Connor. Concerns with Strength, power and aerobic capacity of transgender athletes: a cross-sectional study. Published on: 3 May 2024 https://bjsm.bmj.com/content/early/2024/04/10/bjsports-2023-108029.respo...
2. Hamilton B, Brown A, Montagner-Moraes S, Comeras-Chueca C, Bush PG, Guppy FM, et al. Strength, power and aerobic capacity of transgender athletes: a cross-sectional study. British Journal of Sports Medicine. 2024.
3. Tripepi G, Jager KJ, Dekker FW, Zoccali C. Selection bias and information bias in clinical research. Nephron Clinical Practice. 2010;115(2):c94-c9.
4. Imboden MT, Welch WA, Swartz AM, Montoye AH, Finch HW, Harber MP, et al. Reference standards for body fat measures using GE dual-energy x-ray absorptiometry in Caucasian adults. PloS one. 2017;12(4):e0175110.
5. Alvares LAM, Santos MR, Souza FR, Santos LM, de Mendonça BB, Costa EMF, et al. Cardiopulmonary capacity and muscle strength in transgender women on long-term gender-affirming hormone therapy: a cross-sectional study. British journal of sports medicine. 2022;56(22):1292-9.
6. Scharff M, Wiepjes CM, Klaver M, Schreiner T, t’Sjoen G, Den Heijer M. Change in grip strength in trans people and its association with lean body mass and bone density. Endocrine connections. 2019;8(7):1020-8.
7. Al-Ghadban S, Teeler ML, Bunnell BA. Estrogen as a Contributing Factor to the Development of Lipedema. Hot Topics in Endocrinology and Metabolism: IntechOpen; 2021.
8. Pitsiladis Yannis, Harper JMS, Betancurt JO, Martinez-Patino MJ, Parisi A, Wang G, Pigozzi F. Beyond Fairness: The Biology of Inclusion for Transgender and Intersex Athletes. Current Sports Medicine Reports 15(6):p 386-388, 11/12 2016.
9. Dineen, Robert. "Transgender sportswomen 'at a disadvantage' study claims." The Telegraph, 11 April 2024, https://www.telegraph.co.uk/sport/2024/04/11/transgender-sportswomen-at-...
10. Ben Rumsby. “IOC accused of new low by funding study that claims trans women are at a disadvantage” The Telegraph, 12 April 2024, https://www.telegraph.co.uk/olympics/2024/04/12/ioc-accused-new-low-fund...