Final answer:
Ectomorphs typically have a harder time gaining muscle due to their lean build and fast metabolism, and the proportion of muscle fiber types varies among individuals which influences their muscle-building potential. Muscle hypertrophy in resistance training is mainly due to increased sarcomeres and myofibrils.
Step-by-step explanation:
The statement that ectomorphs have the hardest time building muscle is generally considered true. Ectomorphs are characterized by a lean build and fast metabolism, which can make it challenging for them to gain muscle mass. While everyone has a unique physiological makeup that can affect muscle growth, ectomorphs may need to put in extra effort with both nutrition and a tailored strength training program to see significant muscle hypertrophy.
Additionally, the assertion that all people have the same proportion of slow-twitch to fast-twitch muscle fibers is false. Different individuals can have varying ratios of these fibers, which can affect their potential for building muscle and their performance in various activities. Figure 10.19 suggests that bodybuilders tend to have a higher number of fast glycolytic (FG fibers) as opposed to slow oxidative (SO fibers) and fast oxidative (FO fibers), which supports their capacity for muscle hypertrophy.
When training, particularly resistance training, there is an increase in the number of sarcomeres and myofibrils which leads to hypertrophy. However, resistance training generally does not significantly increase the number of mitochondria or capillary density within muscles, as endurance training might.