Methodology

Body-Fat Threshold Rules for Building Muscle

Francesco Zen, founder of ZTraining · Last updated June 19, 2026

Why body fat affects muscle building at all

Building muscle depends on the body's ability to efficiently synthesise protein and absorb glucose. Higher body fat levels work against both of those processes. Insulin sensitivity improves as body fat drops, which means the body is better able to absorb the glucose it actually uses during a workout, rather than storing it.

Level	Men	Women
Beginner threshold	Below 14%	Below 18%
Advanced, targeted results	Lower still	Lower still

What this means for performance

Muscle gain comes down to performance enhancement for the target muscle group, and higher carbohydrate availability translates directly into higher performance. The body-fat threshold matters because it determines how well that fuel actually gets used once it's eaten.

Francesco Zen is the founder of ZTraining and ZLIFE, with 18 years of coaching experience working with executives across the UK, US, and UAE. He built Mr Z, an AI coach trained on his methodology to bring the same approach to a wider audience.

Body-Fat Threshold Rules for Building Muscle

Why body fat affects muscle building at all

What this means for performance

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