Final answer:
For natural bodybuilding, a training intensity range of 70-80% of 1RM is most effective for muscle hypertrophy, with 80-90% being beneficial for advanced strength gains, and 90-100% leading to increased injury risk.
Step-by-step explanation:
To address the question of which training intensity range is most effective for natural bodybuilding, it is generally accepted that a range of 70-80% of one's one-repetition maximum (1RM) is effective for hypertrophy and increasing muscle mass, which is a primary goal in natural bodybuilding. Working in the range of 80-90% of 1RM can also be effective, especially for more advanced lifters focusing on strength gains. However, training at too high an intensity, such as 90-100% of 1RM, often leads to increased risk of injury and is not necessary for most people. It is also imperative to include proper rest, nutrition, and a well-rounded exercise program to maximize results.