What influences on skill-related fitness cannot be changed to improve fitness levels?

Heredity plays a significant role in determining an individual's skill-related fitness abilities, as it encompasses genetic factors that influence physical characteristics, such as body composition, muscle fiber type distribution, coordination, and overall athletic potential. These innate traits can set natural limits on an individual’s ability to improve in various fitness skills, such as agility, balance, and power. While dedicated practice and specific training can enhance one's abilities and skills to some extent, they cannot surpass the foundational limits established by genetics. Therefore, heredity remains a constant factor that cannot be altered, even though other elements like practice and specificity can indeed be manipulated to improve fitness levels.