Reproductive hormones do more than regulate reproduction. In sport and exercise, changes in progesterone, estrogen, and testosterone can alter temperature control, energy use, recovery, tissue health, and training responses.

Why reproductive hormones matter

Reproductive hormones influence more than reproduction. They affect metabolism, temperature regulation, tissue remodeling, and recovery, so they can change both health and athletic performance. Their effects are important in training, competition, and long-term adaptation.

In female athletes, hormone levels change across the menstrual cycle, so the size and type of response may vary over time.

Reference curves for estradiol (the main oestrogen) and progesterone across a typical menstrual cycle, aligned to cycle timing. The figure highlights the mid‑cycle rise in estradiol and the luteal-phase elevation in progesterone, which underpins time-varying effects on temperature regulation, sleep, and substrate use in exercise physiology. Source

In male athletes, testosterone is usually more stable, but natural differences between individuals still affect adaptation and performance. A key principle is that hormones do not act in isolation; they interact with training load, nutrition, sleep, and environment.

Progesterone

Effects on thermoregulation

Progesterone tends to increase resting body temperature slightly. When progesterone levels are higher, an athlete may begin exercise with a higher core temperature and may feel heat strain sooner, especially in warm conditions or during prolonged exercise.

This matters because a smaller margin before overheating can make it harder to maintain pace, skill, and decision-making. For some athletes, higher progesterone may therefore reduce comfort and performance in the heat, even if the actual exercise intensity is unchanged.

Effects on sleep quality

Progesterone is also linked to sleep quality. Changes in progesterone across the cycle can alter how well an athlete sleeps, and poorer sleep can reduce recovery, concentration, motivation, and readiness to train.

The effect is not identical in every athlete. Some may notice little change, while others report worse sleep near phases when progesterone is elevated, partly because increased body temperature and related symptoms can disturb normal sleep patterns.

Effects on fuel availability

Progesterone also affects fuel availability, meaning the body’s access to usable energy during exercise. Higher progesterone can change how carbohydrate and fat are used, and it may reduce the availability of carbohydrate for high-intensity efforts if nutrition is not well matched to the session.

This is important because high-intensity exercise depends heavily on rapid carbohydrate supply. If progesterone is relatively high, athletes may need to pay closer attention to pre-exercise fueling and recovery nutrition to support training quality.

Estrogen

Glycogen sparing

Estrogen can promote glycogen sparing, which means less muscle glycogen is used at a given exercise intensity. In practice, this may increase reliance on fat as a fuel source and help preserve carbohydrate stores during submaximal endurance exercise.

For endurance performance, glycogen sparing can be beneficial because it may delay fatigue when exercise lasts a long time. However, the advantage depends on the activity because sprinting and very high-intensity efforts still require substantial carbohydrate use.

Joint stiffness

Estrogen also affects joint stiffness. Changes in estrogen can alter the mechanical behavior of connective tissues such as ligaments and tendons. Lower stiffness may improve mobility, but it can also change joint stability and force transmission.

For performance, altered joint stiffness can influence movement efficiency, technique, and injury risk. The effect is highly individual, so it is better to think of estrogen as changing the conditions under which movement occurs rather than guaranteeing better or worse performance.

Testosterone

Bone formation

Testosterone supports bone formation and bone maintenance. This matters for athlete health because strong bones tolerate repeated training loads better and are less vulnerable to stress-related injury.

Adequate testosterone is therefore important not only for performance but also for long-term skeletal health. Low testosterone levels can reduce bone density over time and may impair an athlete’s ability to tolerate consistent training.

Protein synthesis

Testosterone also increases protein synthesis, the process of building new proteins in the body. In sport, this supports muscle repair after exercise and contributes to gains in muscle size and strength when training is appropriate.

Because protein synthesis underpins adaptation, testosterone can influence how effectively an athlete responds to resistance training and recovers between sessions. This does not mean performance is determined by testosterone alone, but it is a major factor in muscular development.

Erythropoietin

Testosterone affects erythropoietin, a hormone involved in red blood cell production.

Diagram of the erythropoietin (EPO) pathway: kidneys release EPO, which stimulates the bone marrow to increase red blood cell production. This visual links hormonal signaling to oxygen-carrying capacity—one mechanism by which testosterone can support endurance performance via improved oxygen delivery to working muscles. Source

Higher erythropoietin activity can increase the oxygen-carrying capacity of the blood, which is especially relevant for endurance performance.

Through this pathway, testosterone may support aerobic performance by improving oxygen delivery to working muscles. It can therefore contribute to both training capacity and recovery from repeated endurance sessions.

Implications for athletes

The performance effects of reproductive hormones are usually context-dependent. The same hormonal profile may help one type of activity but challenge another. For example, glycogen sparing may help prolonged endurance work, while reduced carbohydrate availability can matter more in repeated high-intensity efforts.

Hormonal effects also vary between athletes. Some experience clear changes in heat tolerance, sleep, or movement quality, while others notice minimal effects. For this reason, monitoring symptoms, cycle patterns, training quality, and recovery can be more useful than assuming all athletes respond the same way.

In practice, coaches and athletes should use hormonal knowledge to support individualized training, recovery, and health monitoring rather than to make simplistic predictions about performance.