Female Athlete Formula Suite
Female-specific training math accounts for energy availability (EA — IOC 2018 RED-S framework) and menstrual cycle phase. EA = intake minus exercise calories per kg fat-free mass. Below 30 kcal/kg FFM is clinically low and disrupts menstrual function and bone health. Cycle phase modulates training response. Standard Mifflin underrates lean female athletes.
Formula
Copy the exact expression or work through it step by step below.
energy_availability = (energy_intake_kcal − exercise_energy_kcal) / fat_free_mass_kg
EA < 30 kcal/kg FFM: clinically low, RED-S risk
EA 30-45 kcal/kg FFM: suboptimal
EA ≥ 45 kcal/kg FFM: adequate
cycle_phase_modifier:
Follicular (Day 1-14): training capacity baseline
Ovulatory (Day 13-15): peak strength + power
Luteal (Day 15-28): −5-8% high-intensity capacity, +slight aerobic capacity
Late luteal (Day 25-28): GI symptoms, fluid retention — schedule deload Variables
energy_intake_kcal
Daily energy intake
Total kcal eaten. Track for 7-14 days for accuracy (food labels + USDA + cooked-weight measurements).
exercise_energy_kcal
Exercise energy expenditure
Calories burned in structured training (above NEAT baseline). Use the food-to-exercise formula or a calibrated HR-based tracker. Don't double-count BMR.
fat_free_mass_kg
Fat-free mass
Total mass minus fat mass. Requires accurate body-fat % (DXA, BIA, skinfolds). Critical input — EA is reported per unit lean mass, not total mass.
cycle_phase
Menstrual cycle phase
Phase relative to first day of menstruation. Track 3+ cycles to identify personal pattern; cycle lengths vary 21-35 days normal. Hormonal contraceptive users have suppressed natural cycle; flat hormone profile across the month.
Step By Step
- 1
Measure fat-free mass. DXA is gold standard; calibrated BIA scale is acceptable (±5% error).
DXA shows 18% body fat at 60 kg → FFM = 60 × (1 − 0.18) = 49.2 kg.
- 2
Track 7-day average daily energy intake.
Week average: 2,100 kcal/day.
- 3
Compute exercise energy. Use MET × time × mass for sessions, or HR-based tracker (de-bias by 15-20% if a wrist wearable).
5 sessions/week × 350 kcal = 1,750 kcal/week → 250 kcal/day average.
- 4
Compute energy availability: EA = (intake − exercise) / FFM.
EA = (2,100 − 250) / 49.2 = 1,850 / 49.2 = 37.6 kcal/kg FFM/day.
- 5
Classify. If <30 + amenorrhea or stress fractures, address before any performance work. If 30-45 + sub-optimal performance, increase intake 200-400 kcal/day for 2-4 weeks and re-assess.
EA 37.6: suboptimal. Add 300 kcal/day (carbs + healthy fats), re-evaluate after 3 weeks. Expect: training quality up, menstrual regularity if disrupted.
Worked Example
Recreational runner (60 kg, 18% BF) training 5x/week, suspects under-fueling
Body mass
60 kg
Body fat %
18%
Fat-free mass
49.2 kg
Daily intake
2,100 kcal
Exercise energy
250 kcal/day avg
EA = (2,100 − 250) / 49.2 = 37.6 kcal/kg FFM/day Classification: 30-45 = SUBOPTIMAL
EA 37.6 indicates suboptimal energy availability. Symptoms to watch: irregular cycle, declining HRV, frequent illness, fatigue not relieved by rest, plateaued or declining performance. Intervention: increase daily intake 300 kcal (~75g carbs) for 4 weeks. Re-evaluate cycle regularity + training response. If symptoms persist or cycle disrupted (oligo/amenorrhea), refer to sports dietitian + GP — RED-S requires medical oversight.
Common Variations
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Macro Calculator
Convert calorie targets into protein, carbs, and fat grams for your goal.
Sources & References
- Mountjoy et al. (2018). IOC consensus statement on relative energy deficiency in sport (RED-S): 2018 update. — British Journal of Sports Medicine — IOC 2018 RED-S framework
- Mountjoy et al. (2014). The IOC consensus statement: beyond the Female Athlete Triad — Relative Energy Deficiency in Sport (RED-S). — British Journal of Sports Medicine — original RED-S framework
- Nattiv et al. (2007). American College of Sports Medicine position stand. The female athlete triad. — Medicine & Science in Sports & Exercise — original ACSM Triad position
- Sims & Yeager (2016). Reframing female fueling and recovery: the next gen sports nutrition for women. — Current Sports Medicine Reports — practical female-athlete fueling
- Boyle, Holmes, Vasconcelos, Loucks (2024). Low energy availability and Relative Energy Deficiency in Sport (REDs) in female endurance athletes. — Sports Medicine — 2024 prevalence + screening review