Which of the following is a biological factor affecting physical fitness?

Factors affecting physical fitness can be broadly classified into biological (internal, inherited) factors and environmental/social (external) factors.

Genetics is a biological factor because it is determined by the DNA inherited from one's parents. Genetic makeup influences many aspects of physical fitness, including:

• Muscle fibre type distribution - the ratio of slow-twitch (Type I) to fast-twitch (Type II) fibres, which affects endurance versus power capabilities
• Body type (somatotype) - inherited tendencies toward endomorphic, mesomorphic, or ectomorphic builds
• Maximum oxygen uptake (VO₂ max) - a significant portion of aerobic capacity is genetically determined
• Height, limb proportions, and joint flexibility

The remaining options are not biological factors. Social media and peer influence are social factors that may affect motivation and behaviour related to fitness but are not inherited or biologically determined. Climate is an environmental factor that affects the conditions under which physical activity occurs but is external to the individual's biology.