BMI

BMI - The fast (and limited) indicator

Definition

The BMI (Body Mass Index) is calculated by the formula: weight (kg) / height² (m²). It's a quick health screening tool used by doctors and public health authorities.

💡 BMI doesn't differentiate fat from muscle. A 90 kg lifter and a 90 kg sedentary at the same height have the same BMI — but very different bodies.

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WHO classification

BMI	Category
< 18.5	Underweight
18.5 - 24.9	Normal
25 - 29.9	Overweight
30 - 34.9	Obesity class I
35 - 39.9	Obesity class II
40+	Obesity class III

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Calculation example

• Height: 1.80 m
• Weight: 80 kg
• BMI = 80 / (1.80 × 1.80) = 80 / 3.24 = 24.7
• Classification: end of "normal"

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BMI's limits

• ❌ Doesn't differentiate fat from muscle
• ❌ Doesn't account for fat distribution (visceral vs subcutaneous)
• ❌ Less reliable for athletes (often classified "overweight" because of muscle)
• ❌ Less reliable for older adults (sarcopenia masks fat loss)
• ❌ Doesn't fit children or pregnant women
• ❌ Limited by ethnicity (Asian populations have a different threshold)

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Better alternatives to BMI

Indicator	What it measures
Body fat %	Real share of fat
Waist-to-height ratio	Abdominal/visceral fat
Waist circumference	Cardiovascular risk
Lean mass / fat mass ratio	True body composition

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How to use BMI properly

• ✅ As quick screening for the sedentary general population
• ✅ As a starting point, not the final answer
• ✅ Combined with other measures (waist, body fat %)
• ❌ Don't use it as a sole reference if you train
• ❌ Don't use it to classify a muscular athlete

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Common mistakes

• ❌ Believing a "high" BMI = automatically unhealthy
• ❌ Targeting a precise BMI as a goal
• ❌ Comparing BMI between very different individuals
• ❌ Ignoring more relevant measures (body fat %, waist circumference)

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Key takeaways

BMI is useful as quick screening but limited. For lifters, body fat % and waist circumference are far more relevant. Don't fixate on a number — track real body composition.