Physiological Differences in Training Between Women and Men: Beyond Body Size, Also Concepts of Metabolism and Hormonal Cycles

Preface: Gender Differences Should Not Be an Excuse for Stereotypes

In discussions of endurance sports training, “physiological differences between men and women” are often reduced to a few stereotypes: women are weaker, women have better endurance, women are not suited for high-intensity training, and women’s training must be “aligned with the menstrual cycle.” Some of these claims contain a partial basis in real physiology, while others are oversimplifications or even misconceptions spread by word of mouth. More importantly, regardless of what average physiological differences exist between men and women, the magnitude of these differences is often far smaller than the differences between individuals—that is, a well-trained female athlete may be clearly superior to an untrained male in many physiological metrics, and vice versa.

What this article aims to do is to objectively break down the generally recognized concepts of differences between men and women in body composition, metabolism, and hormonal cycles as currently understood in the field of exercise physiology, while repeatedly emphasizing one core principle: these are group-average tendencies, not rules for predicting or limiting any individual. This article does not cite any specific research figures, precise percentages, or study sources; all content is merely an explanation of generally recognized mechanistic concepts in the field, and actual responses vary enormously between individuals.

Average Differences in Body Size and Composition

From an evolutionary and endocrine perspective, there are some commonly observed tendencies in average body size and composition between men and women. These differences are primarily related to the physiological effects of sex hormones (testosterone and estrogen):

This table presents tendencies at the group-average level, not individual rules. It is worth emphasizing that the differences in absolute heart and lung volume are largely related to overall body size (height, weight) rather than sex per se; when body size is taken into account (for example, comparing men and women of similar stature), the magnitude of differences in many cardiorespiratory metrics narrows considerably. This is also why, in the endurance sports field, well-trained female athletes can achieve excellent aerobic capacity relative to body weight (a concept often expressed in relative terms such as maximal oxygen uptake per kilogram of body weight), with a gap from male athletes far smaller than the difference in absolute values.

Concepts of Differences in Metabolic Characteristics

Beyond differences in body size, exercise physiology has long examined whether there are systematic tendencies in how men and women select energy metabolism pathways. Below are several conceptual directions commonly discussed, with the same emphasis that these are general tendencies, not absolute individual rules:

Relative Tendencies in Fat and Carbohydrate Metabolism

One view widely discussed in exercise physiology holds that women, relative to men, may tend to utilize a higher proportion of fat as an energy source during moderate-intensity aerobic exercise, while being more sparing in their use of glycogen stores. This difference is thought to be related to estrogen’s regulatory effects on metabolic enzyme activity and adipose tissue metabolism. If this tendency holds, its practical significance may lie in the fact that during prolonged, low-to-moderate-intensity endurance exercise (such as long road cycling events or ultramarathons), this metabolic tendency could theoretically help delay glycogen depletion and postpone the onset of “hitting the wall,” but the actual magnitude of such effects varies enormously between individuals and should not be overstated or treated as the sole basis for training and fueling strategies.

Discussion of Recovery and Fatigue Resistance

Another direction often discussed is whether women may exhibit different characteristics from men in certain types of fatigue resistance—for example, showing a relatively slower rate of fatigue accumulation during repeated submaximal efforts. The mechanistic explanations for such phenomena are quite complex and may involve interactions among multiple factors, including muscle fiber type distribution, neuromuscular recruitment patterns, and metabolic pathway selection. The field of exercise physiology is still actively investigating the complete mechanisms behind such phenomena. This article does not draw definitive conclusions on this matter but merely presents it as a research direction that is being observed and discussed.

The Relationship Between Hormonal Cycles and Training: A Conceptual Understanding

The female menstrual cycle involves regular fluctuations in estrogen and progesterone concentrations. These hormonal fluctuations could theoretically influence thermoregulation, fluid balance, energy metabolism, subjective fatigue perception, and even connective tissue laxity (some discussions suggest that progesterone fluctuations may be related to changes in ligament laxity). This is a topic that has received increasing attention in the field of female athlete training science in recent years, but it is also one of the areas most prone to oversimplification or misunderstanding.

Reasons for Caution

Discussion in this area requires particular care, for the following reasons:

• Enormous individual variation: The regularity of menstrual cycles, the magnitude of hormonal fluctuations, and the degree of impact on subjective training perception vary greatly among different women. A single formula of “periodized training aligned with the menstrual cycle” may not apply to everyone.
• The cycle itself may be irregular: Factors such as high training volume, dietary status, stress, and body fat percentage can all affect the regularity of the menstrual cycle, and may even lead to cycle disturbances or absence (if irregular menstruation or amenorrhea persists over the long term, professional evaluation by gynecology and sports medicine should be sought, as this may be related to inadequate energy intake or other health issues and should not be taken lightly).
• Methodological challenges in research: Accurately tracking hormonal fluctuations and establishing causal relationships with training performance involves considerable methodological complexity. This is why the scientific evidence in this area is still accumulating and being refined, and no specific “cycle-adjusted training formula” should currently be regarded as an established conclusion.

Directions That Can Be Reasonably Discussed at the Conceptual Level

Nevertheless, some conceptual-level discussions are considered to have a reasonable basis and can serve as reference points for athletes’ self-awareness and training adjustments, rather than as rigid rules:

• Some female athletes subjectively report changes in perceived fatigue, motivation, or physical discomfort at certain phases of the menstrual cycle. Such subjective perceptions are themselves real information worth incorporating into training planning, even if the precise hormonal mechanisms behind them remain to be further clarified.
• Thermoregulation and fluid balance may show subtle changes across different phases of the cycle. This may be an aspect worth noting during prolonged training or competition in hot, humid environments (such as Taiwanese summers), and moderately adjusting hydration and electrolyte supplementation strategies is a reasonable conservative approach.
• If, through long-term tracking, one finds consistently similar patterns of performance or recovery changes at specific phases of the cycle, these personalized observations can be incorporated as reference points for fine-tuning one’s training plan. However, this should be based on individualized, long-term self-observation rather than applying a generic formula that has not been validated for oneself.

Extremes to Avoid

Both completely ignoring the potential effects of the hormonal cycle and excessively using the cycle to restrict or oversimplify female athletes’ training arrangements are insufficiently comprehensive approaches. A more robust attitude is to treat the hormonal cycle as one of many factors that may influence training response and recovery (other factors include sleep, stress, nutrition, and existing training base), and to gradually develop a personalized training adjustment strategy through individualized long-term observation and record-keeping, rather than relying on a single, simplified rule.

Individual Differences Far Outweigh Sex-Based Averages: This Is the Core Point

This article has devoted considerable space to describing some group-average tendencies between men and women, but it must be emphasized repeatedly here that a more important fact exists: differences between individuals are, in nearly all of these aspects, far greater than the average differences between the two groups of men and women.

What does this mean? For example:

• A female endurance athlete with long-term training and exceptional talent may clearly surpass most untrained men or men with weak training foundations in aerobic capacity, lactate threshold, and even absolute strength.
• Between two female athletes, the differences in metabolic characteristics, the regularity and impact of hormonal cycles, and recovery responses to training may be greater than the differences between the “female group average” and the “male group average.”
• Factors known in training science to significantly influence performance and adaptation—such as training history, cumulative training volume and intensity, nutritional status, sleep quality, existing muscle fiber type composition, and age—often have a far greater influence on individual performance than what the single variable of sex can explain.

This is also why, when designing a training plan, “whether this person is male or female” is far less important than individualized information such as “how this person has responded to training in the past, what their current fitness level is, and how they recover from different training stimuli.” Treating sex as the primary basis for training planning is, in essence, an oversimplification that easily overlooks the truly critical sources of difference between individuals.

Strength Training Responses: Another Frequently Misunderstood Aspect

Strength training is another area often shrouded in gender stereotypes. Many female sports enthusiasts harbor excessive concerns about “whether weight training will make me too bulky,” and to some extent, this concern also hinders them from fully utilizing strength training to enhance endurance performance and prevent injuries.

The Concept of Differences in Muscle Hypertrophy Response

Testosterone is one of the important hormones that drives muscle protein synthesis and thereby leads to pronounced muscle hypertrophy responses, and the average testosterone concentration in women is far lower than in men. This makes it considerably less likely for women, under the same strength training stimulus, to exhibit the pronounced hypertrophic response of “muscles becoming extremely large” compared to men. This physiological background can, to some extent, alleviate the common concern that “weight training will make women overly muscular”—such a pronounced hypertrophic response, even in men, requires long-term, systematic training and dietary strategies specifically designed for hypertrophy, and does not naturally occur simply from engaging in general strength training.

Neural Adaptation and Pathways to Strength Gains

Even if the muscle hypertrophy response is relatively limited, strength training can still bring substantial gains in strength and power output for female athletes through neural system adaptations (such as improved motor unit recruitment efficiency, movement coordination, and skill refinement). This neural adaptation pathway can produce effects without relying on significant increases in muscle size. This is also why many female athletes, after beginning systematic strength training, experience noticeable improvements in strength and power performance even if their external muscle definition changes are not dramatic.

The Value of Strength Training for Endurance Performance and Injury Prevention

Regardless of sex, strength training offers endurance athletes multiple values beyond simply “getting bigger”: improving movement efficiency, strengthening connective tissue tolerance to repetitive loading, correcting muscle imbalances, and preventing overuse injuries. For female athletes, these benefits apply equally, and they should not abandon strength training—a tool with positive implications for overall athletic performance and long-term health—due to excessive concerns about appearance changes.

Training Considerations Across Different Life Stages

Across different life stages (adolescence, reproductive years, pregnancy and postpartum, and the perimenopausal transition), women experience relatively substantial changes in their hormonal environment. These changes may introduce additional considerations for training planning. This section only provides a conceptual overview; actual planning requires individualized professional assessment:

Training planning during pregnancy and lactation involves special considerations for maternal and infant safety that go far beyond the scope of this article. Any athlete who is pregnant or postpartum should have their training assessed and planned jointly by an obstetrician/gynecologist and sports professionals with relevant expertise, and should not simply apply general training principles on their own. Around the perimenopausal transition, as estrogen levels decline, bone density loss and cardiovascular disease risk may change. Incorporating moderate strength training and weight-bearing exercise at this stage is considered beneficial for maintaining bone and cardiovascular health, but actual training planning should still account for individual health status, with consultation of medical professionals when necessary.

Practical Implications for Training Planning

Synthesizing the above discussion, several principles with practical value for training planning can be summarized:

1. The Starting Point of a Training Plan Should Be Individualized Assessment, Not Sex Classification

Whether in cycling, road running, or triathlon, training plan design should prioritize individual fitness test results, training history, and current recovery status, rather than applying oversimplified sex-based rules such as “because you are female, you should train this way.”

2. Relative Performance Metrics Are More Meaningful Than Absolute Values

When comparing or evaluating performance, relative metrics (such as power output per kilogram of body weight, or VO₂max per kilogram of body weight) generally reflect true athletic performance levels better than absolute values. This is especially important when comparing men and women, where group-average differences in body size exist, and it also reminds athletes not to sell themselves short because of gaps in absolute numbers.

3. Female Athletes’ Hormonal Cycles Are Worth Incorporating into Self-Awareness, but Should Not Be Over-Regulated

Female athletes are encouraged to keep long-term records of their menstrual cycles, subjective feelings, training performance, and recovery status, accumulating their own individualized data as a reference for future training adjustments. However, there is no need to force themselves to apply formulas from certain commercially circulated periodized training protocols that may not suit them, especially since the scientific evidence in this area is still accumulating.

4. Watch for Health Warning Signs of Menstrual Irregularity or Amenorrhea

If a female athlete experiences long-term irregular menstrual cycles, abnormally reduced menstrual flow, or amenorrhea, this may be related to insufficient energy intake relative to training expenditure (relative energy deficiency, which is not uncommon among endurance athletes with high training loads), excessively low body fat percentage, or other endocrine-related issues. This should not be dismissed as a “normal sign of serious training.” Long-term relative energy deficiency can negatively affect bone density, reproductive health, immune function, and other areas. Professional evaluation and assistance from gynecology, sports medicine, or sports nutrition should be sought.

5. Hydration and Thermoregulation Strategies in Hot, Humid Environments Require Individualized Adjustment for Both Men and Women

Taiwan’s hot, humid summer training and racing environments challenge thermoregulation and fluid balance for all athletes. Regardless of sex, everyone should adjust their hydration and electrolyte replacement strategies based on their own sweat rate and individual physiological responses, rather than applying a single universal formula.

Medical Consultation and Health Warning Signs Checklist

The following situations warrant professional evaluation by gynecology, endocrinology, or sports medicine. The content of this article is a conceptual overview of physiology and cannot replace individualized medical diagnosis:

• Long-term irregular menstrual cycles, or absence of menstruation for three or more consecutive months (with pregnancy ruled out).
• Concerns associated with bone density loss (such as recurrent stress fractures).
• A combination of signs consistent with relative energy deficiency (for example, high training volume accompanied by continued weight loss, persistent fatigue, decreased immunity, and menstrual abnormalities occurring simultaneously).
• Cycle-related discomfort during training that clearly exceeds what can be self-managed (such as severe pain or abnormally heavy bleeding); gynecological evaluation should take priority to rule out other underlying gynecological conditions.

Clarifying Common Misconceptions

Misconception 1: Women are inherently unsuited to high-intensity training. There is currently no reliable physiological basis for this claim. Female athletes can and should undertake training programs that cover the full intensity spectrum, including high-intensity intervals and strength training.

Misconception 2: All women must adjust training intensity according to their menstrual cycle. The scientific evidence for this type of periodized training adjustment is still developing, and individual variation is extremely large. It should not be treated as a one-size-fits-all rule, nor should it become an excuse to limit training intensity for women.

Misconception 3: The physiological differences between men and women are so large that training methods must be completely different. The core principles of training science—progressive overload, specificity, and the balance between recovery and adaptation—apply equally to male and female athletes. What truly requires individual adjustment is based on each person’s fitness level, training response, and health status, not simply on sex.

Conclusion: Return to the Individual, Not the Group Average

Understanding the average physiological differences between men and women as groups helps avoid making unreasonable over-demands or over-protections toward either sex. However, this group-level knowledge ultimately cannot replace understanding and observing the individual. Whether for male or female athletes, the core basis of training planning should always be that person’s own fitness level, training history, recovery status, and health condition—not sex itself. Rather than asking “how should women train,” a more worthwhile question is: “Given this athlete’s own bodily signals and performance data, what kind of training arrangement suits her (or him)?”

Key Action Points

• Understand that men and women show some group-level average tendencies in body composition and metabolic characteristics, but the mechanisms and magnitude of these differences should be viewed cautiously and not over-simplified.
• Recognize that normalized performance metrics (such as power or VO₂ per kilogram of body weight) reflect true athletic ability better than absolute values, and are especially meaningful in cross-sex comparisons.
• Understand that menstrual cycle hormonal fluctuations may theoretically affect thermoregulation, metabolism, and perceived exertion, but the relevant scientific evidence is still developing, and unvalidated universal periodized training formulas should not be applied.
• Encourage long-term individualized record-keeping to observe one’s own response patterns to training and (where applicable) the menstrual cycle, as a reference for fine-tuning training.
• Keep in mind that individual variation far exceeds sex-based group average differences; training planning should be centered on individual fitness testing, training history, and current status.
• Watch for health warning signs such as long-term menstrual irregularities or amenorrhea, which may be related to relative energy deficiency or other health issues. Professional medical evaluation should be sought, and these signs should not be dismissed or treated as a normal consequence of serious training.
• Hydration and thermoregulation strategies in hot, humid environments should be adjusted according to individual physiological responses, for both men and women.

Related Reading

• Sex Differences in Athletic Performance: Physiological Basis, Sources of Performance Gaps, and Training Implications
• Different for Men and Women: Sex Differences in Endurance Sports Training and Scientific Approaches
• Menstrual Cycle and Training Planning: Physiological Characteristics of Each Phase and Workout Adjustment Approaches (Highly Individual, Not a Fixed Rule)
• Benefits of Strength Training for Women: Comparisons with Men and Research on Mechanistic Differences