For natural lifters, the 6-8 rep range can be better for muscle growth than 10-25 reps for several reasons:

1. Higher Mechanical Tension

• Muscle growth is primarily driven by mechanical tension, which is best achieved through moderate to heavy loads (75-85% of 1RM).
• The 6-8 rep range allows lifters to use heavier weights while still getting enough time under tension for hypertrophy.

2. Better Strength Progression = More Growth Over Time

• Strength improvements in the 6-8 rep range allow for progressive overload at a faster rate than higher rep ranges.
• Over time, getting stronger in this range means you can use heavier weights for all rep ranges, including higher reps, leading to more muscle growth.

3. Less Fatigue = Higher Training Volume Over Time

• High-rep (10-25) training leads to more metabolic fatigue and central nervous system (CNS) burnout.
• The 6-8 range allows for more quality sets because you don’t accumulate as much metabolic waste (like lactate), keeping performance higher across the workout.

4. More Effective Stimulus Without Junk Volume

• The stimulus-to-fatigue ratio is better in the 6-8 rep range, meaning you get more muscle growth per set without excessive recovery demands.
• Sets in the 10-25 range can lead to junk volume—where fatigue builds up faster than the actual hypertrophy stimulus.

5. Better Muscle Fiber Recruitment

• Heavier loads in the 6-8 rep range recruit fast-twitch (Type II) muscle fibers, which have the greatest growth potential.
• Higher reps (10-25) rely more on slow-twitch fibers, which don’t grow as much in response to training.

6. Hormonal and Recovery Benefits for Natural Lifters

• Natural lifters don’t have enhanced recovery from steroids, so training needs to be efficient rather than just high-volume.
• 6-8 reps optimize hypertrophy while avoiding excessive cortisol spikes and systemic fatigue from high-rep sets.

7. Joint Health & Longevity

• Constantly doing high-rep sets (10-25) can cause joint inflammation due to excessive wear and tear.
• 6-8 reps provide enough volume for growth while keeping joint stress lower compared to endless high-rep pump work.

When Might 10-25 Reps Be Useful?

• Isolation exercises where joint stress is an issue (e.g., lateral raises, curls, triceps extensions).
• Metabolic stress training (finishing sets for extra pump).
• Endurance or muscle glycogen depletion phases (not optimal for pure hypertrophy).

Final Verdict

For natural lifters, 6-8 reps provide the best balance of strength progression, hypertrophy stimulus, recovery, and muscle fiber recruitment. Higher reps (10-25) have their place but are less efficient for overall muscle growth compared to progressing heavier loads in the 6-8 range.