A report may show a rapid change in lean mass after a workout, a meal or a few days of different routines. It is tempting to call that new muscle. But an estimate of tissue composition is affected by the body's water distribution as well as longer-term change.
Why a consistent method matters
Bioelectrical impedance uses electrical properties to estimate body water and body composition through equations. Reviews highlight the importance of standardised procedures and appropriate models. Fat-free mass includes water and tissues other than skeletal muscle. A short-term increase therefore cannot automatically be interpreted as a direct measurement of muscle growth.
Newer devices may use different technologies or calculations, but each needs appropriate validation. You should not assume an old study validates a current product. Nor should results from different devices be combined into one seamless trend without considering their differences.
Compare like with like
For repeat assessments, follow the actual device instructions and aim for similar timing and conditions. Record relevant changes such as recent intense activity, illness or unusual hydration. Do not deliberately dehydrate or over-drink to improve a score. Certain conditions and implanted devices may affect suitability, so screening and device-specific advice matter.
- Use the same device when possible.
- Record conditions that could affect the reading.
- Look for a trend over a suitable interval.
- Check whether strength or function is changing too.
A review at Zhen can place estimates alongside your goals and other physical findings. We should not market a favourable one-day fluctuation as proof that a treatment built muscle or reversed ageing. A sensible interpretation makes the data useful without pretending it is more exact than it is.
Putting this into practice at Zhen
At Zhen Wellness in Onchan, Isle of Man, we help you turn health information into realistic next steps. The £97 Longevity MOT is a standalone 60-minute assessment of your history, priorities, posture, mobility and body composition estimates, with pain mapping where relevant. It is not a biological-age blood test, medical diagnosis or prediction of lifespan. Any further service is chosen separately around your needs, with costs discussed before you decide.
Research and safety
Sources checked on 14 October 2026. Studies describe their own participants and interventions, not Zhen treatment outcomes. Evidence can change; research is not free of bias. This article is general education, not individual medical advice. Adult fasting or exercise protocols are not suitable instructions for children. Seek appropriate clinical advice for new symptoms, medical conditions, pregnancy or treatment changes. Never stop prescribed medicines to follow a wellness plan.