The conversation begins by defining hypertrophy as an increase in muscle fiber size, rather than an increase in the number of fibers, which is known as hyperplasia. The speaker explains that hypertrophy is primarily due to an increase in protein content, such as actin and myosin, within the muscle cells. This process is typically measured using tools like MRI to observe changes over time. The discussion then shifts to strength, which is initially attributed to neurological changes, such as improved neural signaling and reduced inhibition, rather than muscle size. Over time, muscle hypertrophy also contributes to strength gains, although the exact relationship between muscle size and strength is debated. The speaker suggests that both neural and local muscle changes might explain strength improvements, though evidence is still being explored.