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# Formulas Reference
Scientific references for all calculators used in the fitness-nutrition skill.
## BMI (Body Mass Index)
**Formula:** BMI = weight (kg) / height (m)²
| Category | BMI Range |
|-------------|------------|
| Underweight | < 18.5 |
| Normal | 18.5 24.9 |
| Overweight | 25.0 29.9 |
| Obese | 30.0+ |
**Limitation:** BMI does not distinguish muscle from fat. A muscular person
can have a high BMI while being lean. Use body fat % for a better picture.
Reference: Quetelet, A. (1832). Keys et al., Int J Obes (1972).
## TDEE (Total Daily Energy Expenditure)
Uses the **Mifflin-St Jeor equation** — the most accurate BMR predictor for
the general population according to the ADA (2005).
**BMR formulas:**
- Male: BMR = 10 × weight(kg) + 6.25 × height(cm) 5 × age + 5
- Female: BMR = 10 × weight(kg) + 6.25 × height(cm) 5 × age 161
**Activity multipliers:**
| Level | Description | Multiplier |
|-------|--------------------------------|------------|
| 1 | Sedentary (desk job) | 1.200 |
| 2 | Lightly active (1-3 days/wk) | 1.375 |
| 3 | Moderately active (3-5 days) | 1.550 |
| 4 | Very active (6-7 days) | 1.725 |
| 5 | Extremely active (2x/day) | 1.900 |
Reference: Mifflin et al., Am J Clin Nutr 51, 241-247 (1990).
## One-Rep Max (1RM)
Three validated formulas. Average of all three is most reliable.
- **Epley:** 1RM = w × (1 + r/30)
- **Brzycki:** 1RM = w × 36 / (37 r)
- **Lombardi:** 1RM = w × r^0.1
All formulas are most accurate for r ≤ 10. Above 10 reps, error increases.
Reference: LeSuer et al., J Strength Cond Res 11(4), 211-213 (1997).
## Macro Splits
Recommended splits based on goal:
| Goal | Protein | Fat | Carbs | Calorie Offset |
|-------------|---------|------|-------|----------------|
| Fat loss | 40% | 30% | 30% | 500 kcal |
| Maintenance | 30% | 30% | 40% | 0 |
| Lean bulk | 30% | 25% | 45% | +400 kcal |
Protein targets for muscle growth: 1.62.2 g/kg body weight per day.
Minimum fat intake: 0.5 g/kg to support hormone production.
Conversion: Protein = 4 kcal/g, Fat = 9 kcal/g, Carbs = 4 kcal/g.
Reference: Morton et al., Br J Sports Med 52, 376384 (2018).
## Body Fat % (US Navy Method)
**Male:**
BF% = 86.010 × log₁₀(waist neck) 70.041 × log₁₀(height) + 36.76
**Female:**
BF% = 163.205 × log₁₀(waist + hip neck) 97.684 × log₁₀(height) 78.387
All measurements in centimeters.
| Category | Male | Female |
|--------------|--------|--------|
| Essential | 2-5% | 10-13% |
| Athletic | 6-13% | 14-20% |
| Fitness | 14-17% | 21-24% |
| Average | 18-24% | 25-31% |
| Obese | 25%+ | 32%+ |
Accuracy: ±3-5% compared to DEXA. Measure at the navel (waist),
at the Adam's apple (neck), and widest point (hip, females only).
Reference: Hodgdon & Beckett, Naval Health Research Center (1984).
## APIs
- wger: https://wger.de/api/v2/ — AGPL-3.0, exercise data is CC-BY-SA 3.0
- USDA FoodData Central: https://api.nal.usda.gov/fdc/v1/ — public domain (CC0 1.0)