Flexibility is defined as the range of motion available at a joint, and it is a component of physical health and performance. It can be categorized as static flexibility (passive range of movement) or dynamic flexibility (active range of movement). Adequate flexibility helps reduce the risk of injury, improves posture, and enhances movement efficiency.
Documenting the Gender Difference in Range of Motion
Scientific findings consistently show that gender influences flexibility, with biological females generally demonstrating a greater overall range of motion across most joints compared to biological males. This difference is seen across the hips, shoulders, and trunk.
The sit-and-reach test, a widely used assessment for the hamstrings and lower back, is one common example where this gender difference is documented. Studies using this test routinely show that females achieve a significantly better score than males of the same age. Similarly, assessments of the upper body, such as shoulder joint rotation, often reveal a larger range of movement in females.
The Role of Hormones and Soft Tissue Composition
A primary explanation for the difference in flexibility lies in the internal physiological environment, particularly the influence of sex hormones on connective tissues. Estrogen, present in higher concentrations in females, plays a significant part in the structure and extensibility of collagen, the main protein component of ligaments, tendons, and skin. Estrogen stimulates fibroblasts, the cells responsible for producing collagen and elastin, resulting in more pliable connective tissues.
Furthermore, the hormone relaxin affects ligament laxity. Relaxin is present in both sexes but fluctuates more significantly in females, particularly during the menstrual cycle and pregnancy. It reduces the integrity of ligaments like the anterior cruciate ligament (ACL) by activating enzymes that break down collagen, leading to increased joint looseness.
Anatomical Differences in Skeletal Structure
Beyond soft tissue, the underlying skeletal structure also places biomechanical limits on joint movement, and these bony structures differ between the sexes. The most pronounced skeletal difference affecting flexibility is found in the pelvic girdle. The female pelvis is typically wider and shallower than the male pelvis, which is an adaptation for childbirth.
This wider structure results in a larger subpubic angle and greater distance between the hip sockets, allowing for a greater range of motion, particularly in hip joint abduction and flexion. In the upper body, the carrying angle of the elbow (cubitus valgus) is another structural difference. This angle is typically greater in females and may influence the mechanics of upper extremity movements.
These variations in bone size, shape, and joint surface orientation dictate the maximum possible range of movement before bone-on-bone contact restricts further motion.
Training, Activity, and Environmental Factors
While biological factors establish a baseline, external and behavioral factors significantly influence the final expression of flexibility. Individuals who regularly engage in activities that emphasize stretching and full range of motion, such as gymnastics, dance, or certain forms of martial arts, will develop and maintain greater flexibility regardless of their gender.
Conversely, participation in sports that prioritize strength and bulk, such as powerlifting or American football, may lead to muscle development that passively restricts joint movement. Cultural expectations and activity preferences often steer males and females toward different types of exercise from a young age, leading to a disparity in flexibility training.
Flexibility universally declines with age due to tissue stiffening, but the absolute difference between the sexes tends to persist.