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Abstract
We thank Kirk and Stebbings for their interest in our paper (1). Kirk and Stebbings
raise the point of absolute vs relative measures (2). Elite physical or sporting performance
should be judged on absolute performance (ie, race times), which is the most important
factor when assessing the impact of gender-affirming hormone therapy. However, given
a lack of data (only 3 studies), our review also discusses contributing factors to
physical performance (such as muscle mass and VO2 peak, which are dependent on weight)
(1).
When comparing muscle mass among groups, such as women from different ethnicities,
it is accepted that age, weight, and body mass index are covariates (3, 4), and body
mass index is influenced by height. There is great diversity in heights and weights
across cisgender populations, especially among elite athletes. Kirk and Stebbings
raise the hypothetical situation of a 95 and 65 kg woman; if they are both cisgender
women, outside of sports with defined weight categories, weight and height are not
considered to be an unfair “competitive advantage.”
Kirk and Stebbings claim “performance advantages [are] provided by greater stature”;
however, we note that their referenced studies by Norton and Olds and Monson et al
do not support this definitive assertion (5, 6). Male advantage in physical performance
is driven by much more than just stature. The review by Norton and Olds found great
diversity in morphology for athletes of different sports, some requiring larger players
whereas others demanded smaller morphological characteristics (5). Similarly, Monson
et al concluded that “athletic success are [sic] impacted by a myriad of factors,
and some of the most successful professional athletes do not have particularly long
arms relative to their height” (6).
Kirk and Stebbings’ letter implies an equivalence between transgender women and cisgender
men, assuming incorrectly that the taller height in transgender women leads to an
advantage that is equivalent to the advantage that cisgender men have over cisgender
women (2). This assumption overlooks the significant body composition changes (muscle
mass reduces 3-5% but fat mass increases 20-30%) with feminizing hormone therapy,
leading to distinct differences in muscle mass, strength, cardiorespiratory fitness,
and physical performance (1). We do not advocate for sex categories to be removed,
and relative measures are not equal between sexes. While the relative measures of
muscle mass and strength in transgender women are no different from cisgender women,
they are clearly lower than that of cisgender men (7).
Kirk and Stebbings draw attention to the only published small cross-sectional study
examining cardiorespiratory fitness (7). Several absolute parameters show that transgender
women have an intermediate value between cisgender women and cisgender men, expected
due to height differences, with relative percentage fat mass and muscle mass comparable
to cisgender women (7). It is imperative that VO2 peak is corrected or adjusted for
weight when making comparisons between groups of women (whether they be transgender
or cisgender) (1). Kirk and Stebbings reference De Pauw et al to support their assertion
that absolute VO2 peak is most important; however, De Pauw et al's systematic review
of cycling parameters in males in fact concludes that relative VO2 max (and absolute
peak power output) are the most important performance parameters for cycling (8).
Ideally, prospective controlled studies before and after gender-affirming hormone
therapy with physical performance outcomes relevant for individual sports should be
performed. Until further research is conducted, our conclusions are based on existing
performance data that suggest no significant difference in transgender women relative
to cisgender women in terms of long-distance running, 1.5-mile running times, or sit-ups
after feminizing hormone therapy (1).
The aim of this systematic literature review was to outline the various preexperimental maximal cycle-test protocols, terminology, and performance indicators currently used to classify subject groups in sport-science research and to construct a classification system for cycling-related research.
For transgender women (TW) on oestrogen therapy, the effects of prior exposure to testosterone during puberty on their performance, mainly cardiopulmonary capacity (CPC), while exerting physical effort are unknown. Our objective was to evaluate CPC and muscle strength in TW undergoing long-term gender-affirming hormone therapy. A cross-sectional study was carried out with 15 TW (34.2±5.2 years old), 13 cisgender men (CM) and 14 cisgender women (CW). The TW received hormone therapy for 14.4±3.5 years. Bioimpedance, the hand grip test and cardiopulmonary exercise testing on a treadmill with an incremental effort were performed. The mean VO2peak (L/min) was 2606±416.9 in TW, 2167±408.8 in CW and 3358±436.3 in CM (TW vs CW, p<0.05; TW vs CM, p<0.0001; CW vs CM, p<0.0001). The O2 pulse in TW was between that in CW and CM (TW vs CW, p<0.05, TW vs CM, p<0.0001). There was a high correlation between VO2peak and fat-free mass/height 2 among TW (r=0.7388; p<0.01), which was not observed in the other groups. The mean strength (kg) was 35.3±5.4 in TW, 29.7±3.6 in CW and 48.4±6.7 in CM (TW vs CW, p<0.05; TW vs CM, p<0.0001). CPC in non-athlete TW showed an intermediate pattern between that in CW and CM. The mean strength and VO2 peak in non-athlete TW while performing physical exertion were higher than those in non-athlete CW and lower than those in CM.
Over the course of the past century it has become increasingly difficult to find athletes of the size and shape required to compete successfully at the highest level. Sport is Darwinian in that only the 'fittest' reach the highest level of participation. Not every physical characteristic could be expected to play a role in this selection process, but two that are important and for which substantial data assemblies exist, are height and mass. Measurements of elite athlete sizes were obtained from a variety of sources as far back as records allowed. We charted the shift in these anthropometric characteristics of elite sportspeople over time, against a backdrop of secular changes in the general population. Athletes in many sports have been getting taller and more massive over time; the rates of rise outstripping those of the secular trend. In open-ended sports, more massive players have an advantage. Larger players average longer careers and obtain greater financial rewards. In some sports it is equally difficult to find athletes small enough to compete. In contrast, there are sports that demand a narrow range of morphological characteristics. In these sports the size of the most successful athletes over the century has remained constant, despite the drift in the population characteristics from which they are drawn. A number of social factors both drive and are driven by the search for athletes of increasingly rare morphology. These include globalisation and international recruitment, greater financial and social incentives, and the use of special training methods and artificial growth stimuli. In many sports the demand for a specific range in body size reinforces the need to adopt questionable and illegal behaviours to reach the required size and shape to compete at the top level. Future scenarios also include 'gene-farming' through assortative mating and athlete gamete banks.
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History
Date
received
: 15
December
2023
Date: 29
February
2024
Date: 20
March
2024
Related
Page count
Pages: 2
Funding
Funded by:
Australian Government National Health and Medical Research Council;
Award ID: #2008956
Funded by:
NHMRC Postgraduate Research Scholarship;
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