Final answer:
Performing 8-12 reps during resistance training is ideal for promoting hypertrophy, as this rep range stimulates muscle growth and size increase through the development of the Fast Glycolytic fibers and connective tissues.
Step-by-step explanation:
The question 'Why are 8-12 reps ideal for maintaining fitness?' revolves around the concept of resistance training and muscle adaptation. Repetitions in the range of 8-12 are widely considered optimal for promoting hypertrophy, which is the enlargement of muscle fibers through the addition of structural proteins. This range of repetitions strikes a balance between sufficiently challenging the muscles to grow and allowing for moderate weight to be lifted, which encourages the development of muscular size and strength.
During resistance exercise, these muscle fibers undergo adaptation through resistance training, resulting in increased muscular size and improved performance. Performing 8-12 reps stimulates a large number of Fast Glycolytic (FG) fibers, leading to powerful muscle contractions that are essential for hypertrophy. It's important to note that while resistance exercise does not generally increase mitochondria or capillary density significantly, it does enhance connective tissue development which is also crucial for muscle growth and preventing injury.