Scientific Research

 Circulating Testosterone as the Hormonal Basis of Sex Differences in Athletic Performance

• published by the Endocrine Society at Oxford Academy.
• supports lowering  testosterone limit to 5nmol/L in womens sports 
•  "Testosterone is responsible muscle mass and strength"

 Women and Men in Sport Performance: The Gender Gap has not Evolved since 1983

• Journal of Sports and Science Medicine
•  "Results suggest that women will not run, jump, swim or ride as fast as men "
• " Sex is a major factor influencing best performances and world records "

Comparing Athletic PerformancesThe Best Elite Women to Boys and Men

• published by Duke Law
• " This differential isn’t the result of boys and men having a male identity, more resources, better training, or superior discipline. It’s because they have an androgenized body."
• " There is no other physical, cultural, or socioeconomic trait as important as testes for sports purposes."

 Exploring the Biological Contributions to Human Health: Does Sex Matter?

•   National Center for Biotechnology Information 
• "The hallmark of human biology is variation, and much of the observed variation both within and between the sexes is encoded within the human genome."

 Different Endurance Characteristics of Female and Male German Soccer Players

• Biology of Sport - US National Library of Medicine
• " During incremental testing, the running performances of female and male players reflect different distributions of aerobic and anaerobic metabolic pathways. The revealed gender differences should be considered for soccer endurance training."  

 Myonuclei acquired by overload exercise precede hypertrophy and are not lost on detraining

• Proceedings of the National Academy of Sciences of the United States of America
• " .. and because anabolic steroids facilitate more myonuclei, nuclear permanency may also have implications for exclusion periods after a doping offense "

Anna Wiik 1 , Mats Holmberg 1 , Tommy Lundberg 1 , Mats Lilja 1 , Daniel Andersson 1 , Stefan Arver 1 , Thomas Gustafsson 1 1. Karolinska Institutet 

"Background Many biological differences seen in men and women are driven by relative differences in estrogen and testosterone levels. In transgender individuals, gender-affirming treatment includes inhibition of endogenous sex hormones and subsequent replacement with the cross-sex hormones. Yet, the effect of this treatment on functional muscle strength and mass remains poorly described. The aim of the current study was to assess the effects of an altered sex hormone pattern on muscle strength and cross-sectional area. 

Methods Twelve transgender individuals, 6 trans women and 6 trans men who had been accepted to start gender-affirming medical intervention, were recruited. Knee extensor and flexor muscle strength was assessed using isokinetic dynamometry at three different angular velocities (0, 60 and 90 °/s). The assessments were made at four time points: (T1) before treatment initiation, (T2) four weeks after initiated gonadal hormonal down regulation but before hormone replacement, (T3) three months after hormone replacement therapy and (T4) eleven months after hormone replacement therapy. The cross-sectional area and radiological density of the thigh muscles were assessed by CT scans performed bilaterally at the midpoint of femur of each subject at baseline and after 11 months of cross-sex hormone treatment. 

Results and Conclusions Muscle area increased 17% in trans men (p<0.001) with an 8% increase in radiology density after eleven month of cross-sex hormone treatment. No change was seen in trans women. There were significant (P<0.05) group x time interactions at each angular velocity. Thus, while the trans men increased their strength over the four time points, strength levels were generally maintained in the trans women. When averaging the three strength tests, knee extension (16%) and knee flexion (34%) strength increased from T1 to T4 in trans men. The corresponding changes in the trans women group were -6% and 0%, respectively. CONCLUSIONS: These results show that ~1 year of cross-sex hormone treatment results in increased muscle strength in trans men. Cross-sectional area and radiological density is also increased after testosterone treatment. However, trans women maintain their strength levels as well as cross-sectional area and radiological density throughout the treatment period. We conclude that the altered sex hormone pattern induced by gender-affirming treatment deferentially affect muscle strength in trans men vs. trans women."

*Trans Women are men who self identify as women*

Evaluation of Testosterone/Epitestosterone Ratio Influential Factors as Determined in Doping Analysis 

Skeletal muscle mass and distribution in 468 men and women aged 18–88 yr

A Comparative Study on Strength between American College Male and Female Students in Caucasian and Asian Populations   

Molecular basis of Gender Dysphoria: androgen and estrogen receptor interaction