Sex Differences in Exercise Physiology

Biological sex is associated with systematic differences in body composition, cardiovascular and respiratory dimensions, skeletal muscle, substrate metabolism, and fatigability, all of which shape the integrative response to exercise. This entry describes how these sex-based differences influence exercise physiology and athletic performance.

Definition

Sex differences in exercise physiology are the average, biologically grounded differences between males and females — in body composition, cardiorespiratory dimensions, skeletal muscle, substrate metabolism, and fatigue — that modify the acute and chronic physiological responses to exercise and contribute to differences in performance.

Scope

The entry covers the principal physiological differences between males and females relevant to exercise — body size and composition, oxygen-transport capacity, muscle mass and fiber characteristics, substrate use during exercise, and neuromuscular fatigability — and the resulting differences in performance. It is a reference account of group-level physiology, not a basis for individual assessment, training prescription, or clinical advice, and it does not address differences arising from gender identity or specific clinical populations.

Core questions

• Which physiological characteristics differ on average between males and females and are relevant to exercise?
• How do differences in body composition and oxygen transport contribute to performance gaps?
• How does substrate metabolism during exercise differ by sex, and what is the role of sex hormones?
• Why do females tend to be more fatigue-resistant in some tasks, and what mechanisms underlie this?

Key concepts

• Body composition (fat-free mass, fat mass)
• Oxygen-transport capacity (haemoglobin, heart and lung dimensions)
• Skeletal muscle mass and fiber-type distribution
• Substrate utilization (greater relative fat oxidation in females)
• Role of sex hormones (e.g., 17β-estradiol)
• Neuromuscular fatigability
• Sex differences in athletic performance

Mechanisms

On average males have greater fat-free mass, larger hearts and lungs, and higher haemoglobin concentration, giving a higher absolute and body-mass-adjusted oxygen-transport capacity, while females carry a higher proportion of fat mass; these differences underlie much of the average sex gap in maximal aerobic and power output (Ansdell et al., 2020). During submaximal endurance exercise females tend to oxidize proportionally more fat and less carbohydrate than males at the same relative intensity, a difference associated with the effects of 17β-estradiol on substrate metabolism (Tarnopolsky, 2008). Females also show, on average, greater resistance to fatigue in some contraction types, attributable to differences in muscle mass, fiber-type proportions, and perfusion (Ansdell et al., 2020). At the elite level these physiological differences translate into consistent performance gaps that vary by discipline (Solli, Sandbakk & Sandbakk, 2024).

Clinical relevance

Recognizing sex-based physiological differences is important for interpreting exercise testing, normative values, and research that historically under-included female participants. This entry describes group-level physiology and the evidence base; it does not provide individualized assessment, training, or clinical recommendations, and individual variation within each sex is large.

Evidence & guidelines

The integrative physiology is summarized in a review of sex differences in the exercise response (Ansdell et al., 2020); substrate-metabolism differences and the role of estradiol are reviewed by Tarnopolsky (2008); and performance differences at the elite level are characterized in a narrative review of endurance sport (Solli, Sandbakk & Sandbakk, 2024). There is no single clinical guideline for this topic; it is a physiological reference.

History

For much of the twentieth century exercise-physiology research was conducted predominantly in male participants, and female-specific responses were under-studied. Growing recognition of this gap, together with the expansion of women's sport, drove systematic investigation of sex differences in oxygen transport, substrate metabolism, and fatigability and prompted calls to report sex as a biological variable.

Debates

Under-representation of female participants and the menstrual-cycle variable

A long-standing concern is that exercise research has disproportionately studied males, so female-specific physiology is less well characterized; how to account for hormonal variation across the menstrual cycle in study design and interpretation remains an active methodological debate.

Key figures

• Sandra K. Hunter
• Mark A. Tarnopolsky
• Øyvind Sandbakk
• Paul Ansdell

Seminal works

• ansdell-2020
• tarnopolsky-2008

Frequently asked questions

Why do males on average have a higher maximal aerobic capacity?

On average males have greater fat-free mass, larger hearts and lungs, and higher haemoglobin concentration, which together raise oxygen-transport and -delivery capacity, while females carry proportionally more fat mass. These group averages overlap substantially between individuals.

Do males and females burn fuel differently during exercise?

On average, at the same relative intensity females tend to oxidize proportionally more fat and less carbohydrate than males during endurance exercise, a difference linked to the influence of the sex hormone 17β-estradiol on substrate metabolism.