Brian Kim

Posted on Dec 23

Fitness is a complex numbers game

#tooling #webdev #discuss #showdev

If only there was an equation
https://fitnessequation.onrender.com/

Fitness Equation - Future Formula Ideas & Features Brainstorm

✅ What I ALREADY Have

I've implemented:

Weight Loss/Gain Timeline - Calorie-based weight change prediction
BMR (Basal Metabolic Rate) - Mifflin-St Jeor formula
TDEE - Total Daily Energy Expenditure with activity levels
1RM Predictions - Epley Formula
Relative Strength - 1RM normalized by body weight
BMI & Categories
Ideal Body Weight - Range-based formula
Lean Body Mass - Calculated from BMI
Protein Intake - Activity-based recommendations
Creatine Recommendations - Loading and maintenance phases
Daily Water Intake - ml per kg of body weight
Weight Tracking & Trends - Weekly loss calculation, weight trend direction, progress percentage
Estimated Goal Dates - Based on current weight loss velocity
Streak Tracking - Activity/consistency metrics

🎯 What You're MISSING (Real Gaps)

These are the features that would add the most value and differentiate your app:

TIER 1: HIGH-VALUE ADDITIONS (Strong demand, easy to implement)

1. Body Fat Percentage Estimation

Algorithms:
- U.S. Navy 3-Measurement Formula (chest, abdomen, neck for males)
- Jackson/Pollock 7-Fold Formula (most accurate)
- Katch-McArdle Formula (if LBM is known)
What users need: Know their body composition, not just weight
Visualization: Trend chart showing fat % changes over time
Integration: Compare to ideal ranges by age/gender

2. Calorie Macro Split Recommendations

Variables: Activity level, goal (bulk/cut/maintain), metabolism type
Common ratios:
- Balanced: 40% carbs, 30% protein, 30% fat
- High-protein cut: 50% carbs, 35% protein, 15% fat
- Bulk: 50% carbs, 25% protein, 25% fat
Additional: Micronutrient suggestions (vitamins, minerals)

3. Progressive Overload Tracker & Recommendations

Formula: Calculate 5-10% weight increase for next session
Volume tracking: Total reps × weight = volume
RPE Scale Integration: Rate of Perceived Exertion (1-10)
Auto-suggest: When user has completed 3+ sets of same weight, suggest increase
Historical comparison: Show progress from same exercise 1-6 months ago

4. Strength Standards by Lift

Strength Level Classifications:
- Novice, Intermediate, Advanced, Elite (by Wilks/IPF standards)
Input: Exercise name, weight, body weight
Output: How user compares to population percentiles
Lifts to support: Squat, Bench, Deadlift, Overhead Press, Rows
Formula: Wilks or OpenIPF coefficient for normalized strength

5. Caloric Expenditure by Activity (Exercise Specific)

METs (Metabolic Equivalent of Tasks):
- Running (different speeds): 6-12 METs
- Weightlifting: 3-6 METs (varies by intensity)
- Cycling, Swimming, HIIT: varies
Formula: (MET × weight_kg) / 60 = calories burned per minute
Integration: Log workouts → auto-calculate calorie burn
Benefit: More accurate TDEE for the day

6. Maintenance Calories Calculation (Multiple Methods)

Methods to offer:
- Mifflin-St Jeor (current, best general)
- Harris-Benedict (alternative)
- Katch-McArdle (if LBM known, most accurate)
User benefit: See range of possibilities, find personalized baseline
Long-term: Adjust based on actual weight change data

TIER 2: MEDIUM DIFFICULTY (More complex but high impact)

7. Daily Macro Calculator (Adaptive)

Inputs: Current weight, goal weight, timeline, activity level
Calculation:
- Target daily calories based on deficit/surplus
- Protein = LBM × 1.0g (minimum, up to 1.6g for training)
- Fat = 20-35% of calories (minimum 0.5g/lb LBM)
- Carbs = remaining calories
Dynamic adjustment: Recalculate weekly based on weight trends

8. Form Quality Score (Integration with wearables/video)

If integrating phone camera:
- Angle detection using pose estimation
- Compare to ideal form ranges
- Flag form breakdown
Alternative (manual): User rates their own form (1-10), system suggests deload if < 7

9. Periodization Recommendations

Training Phases:
- Hypertrophy (8-12 reps): High volume, moderate weight
- Strength (3-6 reps): Heavy weight, lower volume
- Endurance (12-20 reps): Light weight, high volume
- Deload (50-60% normal weight): Recovery week every 4-8 weeks
Auto-recommend: Based on current lifts, suggest next phase
Cycle duration: 4-12 week cycles depending on goal

10. Calorie Cycling & Carb Cycling

Algorithms:
- High days (workout days): +15-20% calories
- Low days (rest days): -10-15% calories
- Average to target goal
Carb cycling: Higher carbs on training days, lower on rest
Science: Often better for performance & sustainability

11. Heat Map - Exercise Performance by Time of Day

Track: Lifts logged at different times → analyze peak performance time
Insights: Am I stronger in morning? After work? Post-meal?
Recommendation: Schedule heavy lifts during peak performance window

12. Recovery Score & Sleep Impact

Integration inputs:
- Sleep hours (manual or from wearables)
- Training volume (from logging)
- Stress level (manual)
Output: Recovery readiness score (0-100)
Formula: Suggests lighter workout if recovery score is low
Science: HRV (Heart Rate Variability) based if device integrated

TIER 3: ADVANCED / SPECIALIZED (High value for serious lifters)

13. Maxes Calculator (Alternative Formulas)

Implement multiple formulas & compare:
- Epley (current): 1RM = w × (1 + reps/30)
- Brzycki: 1RM = w × (36 / (37 - reps))
- Lander: 1RM = (100 × w) / (101.3 - 2.67123 × reps)
- O'Conner, Simmons, Lombardi formulas
- Mayhew formula (good for endurance-style athletes)
Benefit: Show range of estimates, most conservative/aggressive
User choice: Let them select preferred formula

14. Periodized Strength Cycle (Auto-Generated Programs)

5/3/1 Wendler Formula Implementation:
- Training max = 90% of actual 1RM
- Week 1: 65% × 5, 75% × 5, 85% × 5+
- Week 2: 70% × 3, 80% × 3, 90% × 3+
- Week 3: 75% × 5, 85% × 3, 95% × 1+
- Deload: 40-60% for 5, 3, 1
Auto-calculate: Based on current maxes, generate next 4-week cycle
Integration: Push notifications for each week's targets

15. Estimated Daily Energy Expenditure (TDEE) Auto-Adjust

Algorithm:
- Track actual weight change weekly
- If expected ≠ actual: adjust calorie target
- Learn individual metabolic rate
Formula: If lost 1 lb in 1 week vs expected 1.5 lb → metabolism might be faster
Benefit: Account for individual variance (thyroid, genetics, etc.)

16. Body Recomposition Tracking

Challenge: Simultaneous fat loss + muscle gain (rare but possible)
Metrics: Mirror same weight, but different body composition
Formula: Track body fat % changes while weight stays stable
Visual: Side-by-side photos with % changes
Timeline: Show "invisible" progress when scale doesn't move

17. Max Strength Potential Predictor

Inputs: Age, training age, genetics (self-reported)
Formulas:
- Wilks score ceiling (elite = 600+)
- Natural vs enhanced estimates
- Age-adjusted standards
Output: "Based on your progress, elite status would be X lbs"
Motivational: Set realistic long-term goals

18. Deficit/Surplus Sustainability Analyzer

Problem: 1000 cal deficit is unsustainable for many
Analysis:
- 500 cal/day deficit = ~1 lb/week, highly sustainable
- 1000 cal/day deficit = ~2 lb/week, sustainable for obese only
- 250 cal/day deficit = ~0.5 lb/week, very sustainable
Recommendation Engine: Given timeline goal, suggest sustainable pace
Adjust: "To hit your goal in 6 months, eat 400 cal below TDEE (sustainable)"

TIER 4: GAMIFICATION & SOCIAL (Engagement boosters)

19. Achievement Unlocks & Milestones

Lift body weight (squat)
2x body weight deadlift
1.5x body weight bench
Reach "elite" on Wilks chart
52-week consistent logging streak
Hit specific body fat %
Perfect form 10 reps in a row

20. Competitor Leaderboards (Optional Privacy)

Strength rankings by lift (normalized by weight class)
Consistent logging streaks
Biggest transformations (by %)
Goals nearest to completion

21. AI Workout Suggestions

Based on last workout, suggest next:
- Different muscle group (avoid overuse)
- Opposing movement (antagonist pairing)
- "Your bench is weak relative to your squat - more upper body push"
- Auto-deload detection: "Heavy 3 weeks straight, suggest deload week"

TIER 5: INTEGRATION & WEARABLE DATA

22. Heart Rate Variability (HRV) Integration

From smartwatch/Apple Watch:
- HRV → recovery readiness
- Suggest workout intensity based on HRV
- Track trends: does training improve HRV?

23. Resting Heart Rate (RHR) Trending

Metric: Fitness indicator (lower = more fit)
Formula: Compare RHR to fitness level benchmarks
Trend: Should decrease with consistent training

24. Sleep Quality Scoring Integration

From wearables: Sleep duration, deep sleep %, REM %
Impact on: Recovery score, workout recommendations
Insight: "Your lifts are down 10%, check your sleep"

25. Real-time Calorie Tracking Integration

Connect: MyFitnessPal, Cronometer APIs
Auto-log: Daily calories vs TDEE
Insights: Deficit adherence, macro hit rate

TIER 6: SPECIALIZED ANALYSIS

26. Movement Pattern Analysis Over Time

From lift logs:
- Squat improving faster than bench?
- Weak point in lifts (stalls at certain position)
- Suggests accessory work to fix weak points
Example: "Your bench stalls at chest - add board press & pin press"

27. Injury Risk Prediction

Inputs:
- Volume spikes week-to-week (>10% increase = risk)
- Imbalances (one-sided lifts)
- Frequency (overtraining certain muscles)
Output: Warning when risk increases
Formula: (Current week volume - avg 4 weeks) / avg × 100

28. Personalized Supplement Recommendations

Evidence-based only:
- Creatine (already implemented)
- Beta-Alanine (endurance athletes)
- Caffeine (pre-workout)
- Citrulline Malate (pump/performance)
- BCAAs (if fasted training)
- Electrolytes (high sweat activity)
Note: Show science, not hype

29. Hypertrophy Optimizer

For muscle gain:
- Reps per set: 6-12 optimal
- Volume per muscle per week: 10-20 sets
- RPE: 6-9 (moderate intensity)
- Rest days: 48 hours between muscle groups
Analysis: Are you doing enough volume for hypertrophy?

30. One-Handed/Unilateral Balance Tracker

Compare:
- Right arm bench vs left arm
- Single-leg squat vs bilateral
- Dumbbell rows: left vs right
Alert: If imbalance > 10%, suggest corrective training

QUICK WIN FORMULAS (Easy to add now)

31. Wilks Score Calculator

wilks_coefficient = 500 / (a + b*body_weight_kg + c*body_weight_kg^2)
wilks_score = total_weight_lifted * coefficient

Benefit: Normalized strength across weight classes

32. IPF Points (International Powerlifting Federation)

Calculates: Competition-style score
Useful for: Lifters serious about competition

33. TDEE Estimation Variance

Show: Low vs high estimate range (±200 cal)
Recommendation: "Your TDEE is likely 1900-2100, aim for 1700 to cut"

34. Gym Capacity Planner

If tracking body weight weekly:
- "Your average weekly loss is 1.2 lbs"
- "In 12 weeks, you should weigh 155 lbs"
- "That's 11 lbs from now"
Visual timeline: Interactive calendar showing projected dates

35. Calorie Burn Comparison

Show user:
- "Walking 30 min = 150 cal"
- "Running 30 min = 450 cal"
- "Your squat session = 200 cal"
Helps: Understand cost of activities for diet planning

IMPLEMENTATION PRIORITY MATRIX

🚀 HIGH IMPACT, LOW EFFORT (Do First)

Body Fat % estimation
Calorie macro split recommendations
Progressive overload tracker
Strength standards/Wilks score
Exercise calorie burn (METs)

⚡ HIGH IMPACT, MEDIUM EFFORT (Do Second)

Adaptive macro calculator
Periodization recommendations
Alternative max formulas (Brzycki, etc.)
TDEE auto-adjust based on results
Exercise analysis & weak point detection

💪 MEDIUM IMPACT, MEDIUM EFFORT (Do Third)

HRV/sleep integration
Recovery score
Injury risk prediction
Hypertrophy optimizer
Gamification/achievements

🎯 SPECIALIZED/ADVANCED (Future)

AI workout suggestions
Competition-style scoring (IPF, USPA)
Form analysis with pose detection
Leaderboards/social features
Third-party API integrations

RECOMMENDED NEXT SPRINT

Phase 1 (Sprint 1-2):

[ ] Body Fat % Calculator (Navy 3-measurement)
[ ] Macro Split Calculator
[ ] Progressive Overload Tracker
[ ] Strength Standards (Wilks Score)

Phase 2 (Sprint 3-4):

[ ] Alternative 1RM Formulas (drop-down selector)
[ ] Periodization Phase Recommender
[ ] Exercise Calorie Burn (METs database)
[ ] Performance trending by exercise

Phase 3 (Sprint 5-6):

[ ] Recovery Score (sleep + volume + stress)
[ ] TDEE Auto-adjust (learning algorithm)
[ ] Weak Point Analyzer
[ ] Injury Risk Flags

VALIDATION & SCIENCE NOTES

✅ All formulas recommended are evidence-based:

Used by certified strength coaches, nutritionists, athletic trainers
Published in peer-reviewed journals
Validated across diverse populations
Not pseudoscience or fitness myths

⚠️ Caveats to display:

Body fat estimates are ±3-5% accurate (for user education)
Individual variance is high (genetics, age, gender, training experience)
Formulas work best for general population (not extremes)
Medical conditions may invalidate assumptions

User Research Questions to Answer

Are users more interested in strength metrics or aesthetic metrics?
Do users want macro recommendations or simple calorie targets?
Should the app suggest specific workouts or just targets & metrics?
Interest level in competition-style metrics (Wilks, IPF)?
Would users integrate wearable data (Apple Watch, Garmin, Whoop)?
Priority: Individual progress or social/community features?

Database Schema Additions (For Future)

# New columns/tables to support:
- snapshots: body_fat_percent (decimal)
- snapshots: lbm_display (for tracking LBM changes)
- one_rep_maxes: formula_used (Epley, Brzycki, etc.) 
- one_rep_maxes: wilks_score (decimal)
- workouts: mets_activity_type (enum)
- workouts: calories_burned (decimal)
- user_preferences: preferred_1rm_formula
- user_preferences: macro_split_preference
- achievement_badges: (for gamification)
- recovery_logs: sleep_hours, stress_level, hrv_score