i'm failing to see how bodypart splits would be inferior to compound exercises for a natural? there's no real logic behind such a claim. being natural means you have lower nitrogen retention, lower protein turnover, etc... it just means your ability to add muscle is severely diminished compared to a steroid user. steroids are completely independent to what type of stimuli are required to cause muscle growth, the only way that argument can hold any water is if someone is making the claim that by isolating certain body parts and doing high reps you will be overtraining, which i have found to be the exact opposite. infact, i needed to train significantly harder while natural to cause any noticeable amount of muscle growth and i never overtrained when natural even when working out twice a day 6 days a week.
your muscle building ability when natural is capped at a very low level, it doesn't matter what type of training you do it will be the same either way provided you caused enough micro-fiber trauma when diet and recovery are sufficient. going heavy will increase the numbers on your lifts, yes, sure, because you are also increasing your motor-neural efficiency and training your cns to fire muscle motor neurons more effectively, but as i have already stated, you aren't actually adding more muscle this way just because your lift numbers are going up.
