Final answer:
The increase in VO2 max after endurance training arises from increased mitochondria and capillaries in muscles, genetic predispositions related to muscle fiber type, and potential use of substances improving oxygen delivery and muscle recovery.
Step-by-step explanation:
The increase in VO2 max that occurs following 16 months of endurance exercise training results primarily from physiological adaptations within the body, such as an increase in the number of mitochondria and capillary density in skeletal muscle, enhanced cardiac function, and greater efficiency in oxygen utilization during aerobic respiration. This contrasts with resistance training, which mainly leads to hypertrophy and increased connective tissue development without significantly affecting mitochondrial or capillary increase.
Moreover, the presence of more slow-twitch fibers in individuals can contribute to better endurance outcomes since these fibers are more suited for aerobic activities due to their higher mitochondrial and capillary content, along with greater myoglobin levels.
Genetics also plays a role in how individuals respond to exercise, determining the proportion of slow-twitch versus fast-twitch muscle fibers, which influences the degree of endurance improvement observed. Other factors that contribute to endurance performance enhancements include the usage of substances like erythropoietin (EPO), which boosts red blood cell production and oxygen delivery, and human growth hormone (hGH), which assists in muscle recovery post-exercise.