From the RDA floor to the trained-athlete range
The 0.8 grams per kilogram of bodyweight figure is the established Recommended Dietary Allowance, set to prevent deficiency in generally sedentary adults rather than to optimize muscle or performance. People who train regularly have higher needs, and the commonly cited range for building or maintaining muscle is roughly 1.6 to 2.2 grams per kilogram per day.
Plotting intake against bodyweight produces sloped target bands rather than a single number, because the requirement scales with body size.
What the bands assume and where they shift
The trained-athlete band is most supported during resistance training and during a calorie deficit, when slightly higher protein helps preserve lean mass. For very high body-fat individuals, some practitioners base the target on lean mass or an adjusted weight rather than total weight, which lowers the absolute grams.
These are population ranges, not personalized prescriptions, and people with kidney disease or other medical conditions can need different targets. Treat this as general educational information and consult a qualified professional for individual goals.