🏋️ FitEngine API — AI-Powered Fitness & Nutrition Intelligence

Stop building workout and nutrition logic from scratch. FitEngine API gives your app instant access to expert-level fitness coaching — personalized workout plans, macro calculations, 7-day meal plans, and weekly progress analysis — all via simple REST calls returning clean structured JSON.
One API replaces months of fitness algorithm development, nutritionist consultations, and training program design.

⚡ Why FitEngine API

Alternative	Problem
Build it yourself	⚠️ Months of development — exercise databases, macro formulas, periodization logic, nutrition science — before writing a single feature
Hire a nutritionist/trainer consultant	⚠️ Expensive, slow, not scalable — can't serve thousands of users with personalized plans simultaneously
Static workout databases	⚠️ Generic templates that ignore the user's age, injuries, equipment, and goals — users churn because plans don't fit
Other fitness APIs	⚠️ Exercise lists only — no plan generation, no nutrition, no macro calculation, no progress feedback
FitEngine API	✅ 4 endpoints cover the full fitness loop — plan, eat, track, adjust — personalized per user, structured JSON, one API call

🛒 The Problems FitEngine API Solves

Problem	Without FitEngine API	With FitEngine API
Fitness app onboarding	❌ Generic starter plans that don't match the user's body, goal, or equipment — low engagement, high churn	✅ One call generates a fully personalized weekly program from the user's profile data
Nutrition tracking	❌ Hardcoded TDEE calculators with fixed multipliers — wrong for most users, no diet-type support	✅ Precise BMR, TDEE, and macro targets from user stats, activity level, and dietary preference
Meal planning features	❌ Static meal plan templates — allergies ignored, calories not matched, grocery lists missing	✅ Full 7-day meal plan with per-meal macros, ingredient lists, and a categorized grocery list
User retention	❌ No feedback loop — users complete week one and don't know what to do next	✅ Weekly progress check-in returns a performance score, adjusted recommendations, and motivation
Personal trainer tools	❌ Trainers writing programs manually for each client — hours per client, not scalable	✅ Generate a starting program instantly, trainer reviews and adjusts — 10x faster client intake
Health & wellness platforms	❌ Separate vendors for workouts, nutrition, and coaching — integration overhead, inconsistent UX	✅ All four pillars from one API with a consistent JSON response structure
Gym management software	❌ No way to offer personalized plans at scale without hiring staff per member	✅ Serve personalized plans to every member automatically at signup or check-in

🛠️ Endpoints

✅ POST /workout-plan

Generate a complete personalized weekly workout program. Pass the user's age, goal, fitness level, available equipment, and days per week. Optional fields include gender, weight, injuries, and preferences. Returns a full weekly schedule with exercises, sets, reps, rest periods, technique tips, muscles worked, warm-up, cool-down, and progression notes.

POST /workout-plan

{
  "age": 28,
  "gender": "male",
  "weight_kg": 80,
  "goal": "muscle_gain",
  "fitness_level": "intermediate",
  "equipment": "dumbbells",
  "days_per_week": 4,
  "injuries": "bad knees",
  "preferences": "no running"
}

Response:
{
  "success": true,
  "data": {
    "plan_name": "4-Day Dumbbell Hypertrophy Program",
    "goal": "muscle_gain",
    "fitness_level": "intermediate",
    "duration_weeks": 8,
    "weekly_schedule": [
      {
        "day": "Monday",
        "focus": "Chest & Triceps",
        "exercises": [
          {
            "name": "Dumbbell Bench Press",
            "sets": 4,
            "reps": "8-10",
            "rest_seconds": 90,
            "technique_tip": "Keep elbows at 45° to protect shoulder joints",
            "muscles_worked": ["pectorals", "anterior deltoid", "triceps"]
          }
        ],
        "estimated_duration_minutes": 55
      }
    ],
    "warm_up": ["5 min light cardio", "arm circles", "shoulder rolls"],
    "cool_down": ["chest stretch", "tricep overhead stretch"],
    "weekly_tips": ["Progressive overload every 2 weeks", "Sleep 7-9 hours for recovery"],
    "progression_note": "Increase weight by 2.5kg when you hit the top of the rep range for 2 consecutive sessions"
  },
  "meta": { "model": "...", "generated_at": "2026-06-01T10:00:00Z", "api_version": "1.0" }
}

✅ POST /macros

Calculate BMR, TDEE, goal-adjusted calories, and precise macronutrient targets from the user's body stats and goals. Supports all major diet types and activity levels. Returns protein, carb, and fat targets in grams and percentages, daily hydration, meal timing tips, foods to prioritize, foods to limit, supplement suggestions, and expected weekly body weight change.

POST /macros

{
  "weight_kg": 75,
  "height_cm": 175,
  "age": 30,
  "gender": "female",
  "goal": "weight_loss",
  "activity_level": "moderate",
  "diet_type": "vegetarian"
}

Response:
{
  "success": true,
  "data": {
    "bmr_calories": 1542,
    "tdee_calories": 2388,
    "goal_calories": 1888,
    "macros": {
      "protein_g": 142,
      "carbs_g": 189,
      "fat_g": 63,
      "protein_pct": 30,
      "carbs_pct": 40,
      "fat_pct": 30
    },
    "hydration_ml": 2500,
    "meal_timing": ["Eat protein within 30 min of training", "Avoid large meals 2hr before bed"],
    "foods_to_prioritize": ["lentils", "Greek yogurt", "quinoa", "eggs", "cottage cheese"],
    "foods_to_limit": ["refined sugar", "white bread", "fried foods"],
    "supplement_suggestions": ["Vitamin B12", "Iron"],
    "weekly_calorie_target": 13216,
    "expected_weekly_change_kg": -0.5,
    "notes": "Vegetarian protein sources prioritized to hit targets without meat"
  }
}

✅ POST /meal-plan

Generate a complete 7-day meal plan matched to a calorie target. Supports diet types (balanced, keto, vegan, vegetarian, paleo), allergy exclusions, and meals-per-day preference. Returns every meal for every day with full macro breakdown per meal, prep time, ingredient lists, and a complete categorized grocery list ready to hand to the user.

POST /meal-plan

{
  "daily_calories": 2000,
  "diet_type": "balanced",
  "allergies": "nuts",
  "goal": "weight_loss",
  "meals_per_day": 3
}

Response:
{
  "success": true,
  "data": {
    "plan_name": "7-Day Balanced Weight Loss Plan",
    "daily_calories": 2000,
    "days": [
      {
        "day": "Monday",
        "meals": [
          {
            "meal_type": "Breakfast",
            "name": "Oats with Banana and Honey",
            "ingredients": ["80g rolled oats", "1 medium banana", "1 tbsp honey", "250ml skimmed milk"],
            "calories": 420,
            "protein_g": 14,
            "carbs_g": 78,
            "fat_g": 5,
            "prep_minutes": 5
          }
        ],
        "total_calories": 1998
      }
    ],
    "grocery_list": {
      "proteins": ["chicken breast", "eggs", "Greek yogurt"],
      "vegetables": ["spinach", "broccoli", "bell peppers"],
      "grains": ["rolled oats", "brown rice", "whole wheat bread"],
      "dairy_alternatives": ["skimmed milk"],
      "fats": ["olive oil", "avocado"],
      "other": ["honey", "soy sauce"]
    },
    "meal_prep_tips": ["Batch cook rice on Sunday", "Pre-chop vegetables to save time on weeknights"]
  }
}

✅ POST /progress-check

Submit a user's weekly workout data and receive an AI-generated performance analysis. Returns a 0–100 performance score, written progress summary, strengths, areas to improve, adjusted recommendations for the next week, a motivational message, and whether the user should increase training intensity with a suggested weight increase percentage.

POST /progress-check

{
  "workouts_completed": 3,
  "workouts_planned": 4,
  "avg_effort_1_to_10": 7,
  "notes": "Felt tired on leg day but pushed through"
}

Response:
{
  "success": true,
  "data": {
    "performance_score": 78,
    "progress_summary": "Strong week overall — 75% completion with solid effort. Missing one session is minor and recoverable.",
    "strengths": ["Maintained high effort at 7/10", "Pushed through fatigue on leg day — shows mental resilience"],
    "areas_to_improve": ["Consistency — aim for all 4 sessions next week", "Sleep and recovery may need attention given the fatigue"],
    "adjusted_recommendations": ["Add a 10-min walk on rest days to improve recovery", "Front-load your hardest session to Monday when energy is highest"],
    "next_week_focus": "Hit all 4 sessions — even a shorter workout counts as completion",
    "motivation_message": "78% of success is just showing up. You showed up tired and trained anyway — that's the difference-maker.",
    "should_increase_intensity": false,
    "suggested_weight_increase_pct": 0
  }
}

✅ GET /health

Service health check. Returns API status, version, and available endpoints. No authentication required. Use this to verify connectivity before your first integration call.

💡 Common Use Cases

📱 Fitness & Workout Apps

At user signup, collect age, goal, fitness level, and equipment. One call to /workout-plan generates a full personalized program. Weekly, call /progress-check with their logged workouts to generate the next week's feedback. Full fitness coaching loop without building any algorithm logic.

🥗 Nutrition & Diet Apps

Use /macros to calculate each user's exact calorie and macro targets from their profile. Then call /meal-plan to generate a week of meals that hit those targets — respecting their diet type and allergies. Hand the grocery list directly to the user. Complete nutrition feature in two API calls.

🏢 Personal Trainer Platforms

Trainers spend hours writing programs for each new client. Use /workout-plan at client intake to generate a starting program in seconds. The trainer reviews and tweaks — cutting intake time from hours to minutes. Scale to hundreds of clients without scaling headcount.

🏥 Corporate Wellness Platforms

Offer personalized fitness and nutrition plans as an employee benefit. Every employee gets a plan matched to their goals and schedule — not a generic PDF. Weekly progress check-ins keep engagement high. No fitness staff required.

⌚ Wearables & Health Trackers

Pull activity data from the wearable, pass it to /progress-check, and surface personalized coaching feedback in your app. Combine with /macros to adjust calorie targets as activity levels change week to week.

🎮 Gamified Fitness Products

Use performance scores from /progress-check to power leaderboards, badges, and streaks. Generate new workout plans as users level up their fitness level from beginner to intermediate to advanced. Dynamic progression built on real AI analysis.

🛒 Supplement & Sports Nutrition Stores

Add a free macro calculator and meal planner to your store. Users enter their stats, get a macro target and meal plan, and see which of your products fit their supplement suggestions — direct integration between nutrition recommendations and your product catalog.

📥 Input Fields Reference

/workout-plan

Field	Type	Required	Notes
age	integer	✅ Yes	10–100
goal	string	✅ Yes	weight_loss, muscle_gain, endurance, flexibility
fitness_level	string	✅ Yes	beginner, intermediate, advanced
equipment	string	✅ Yes	none, dumbbells, full_gym, resistance_bands, etc.
days_per_week	integer	✅ Yes	1–7
gender	string	❌ Optional	male, female
weight_kg	number	❌ Optional	Improves exercise load recommendations
injuries	string	❌ Optional	Free text — e.g. "bad knees", "lower back pain"
preferences	string	❌ Optional	Free text — e.g. "no running", "prefer compound lifts"

/macros

Field	Type	Required	Notes
weight_kg	number	✅ Yes	30–300
height_cm	number	✅ Yes	100–250
age	integer	✅ Yes	10–100
gender	string	✅ Yes	male, female
goal	string	✅ Yes	weight_loss, muscle_gain, maintenance
activity_level	string	✅ Yes	sedentary, light, moderate, active, very_active
diet_type	string	❌ Optional	balanced, keto, vegan, vegetarian, paleo

/meal-plan

Field	Type	Required	Notes
daily_calories	integer	✅ Yes	800–6000
diet_type	string	❌ Optional	balanced, keto, vegan, vegetarian, paleo
allergies	string	❌ Optional	Free text — e.g. "nuts, dairy"
goal	string	❌ Optional	weight_loss, muscle_gain, maintenance
meals_per_day	integer	❌ Optional	Default 3

/progress-check

Field	Type	Required	Notes
workouts_completed	integer	✅ Yes	Number of sessions done this week
workouts_planned	integer	✅ Yes	Number of sessions that were scheduled
avg_effort_1_to_10	integer	❌ Optional	Self-reported effort rating 1–10
notes	string	❌ Optional	Free text — client notes, feelings, observations

⚡ Performance

Built on Cloudflare Workers edge infrastructure — deployed globally across 300+ locations. Requests are routed to the nearest edge node to your user automatically.

Endpoint	Typical Response Time	Notes
/workout-plan	2–4 seconds	Full personalized weekly program with exercises, sets, reps, and tips
/macros	1–3 seconds	Complete TDEE, macro targets, food lists, and supplement suggestions
/meal-plan	3–6 seconds	7-day meal plan with per-meal macros and full grocery list
/progress-check	1–3 seconds	Performance score, analysis, and adjusted recommendations
/health	<10ms	No AI call — pure edge response

Response times reflect AI generation — the API is doing expert-level coaching work in each call, not a database lookup. Results are fully personalized per request.

📊 Plan Comparison

Feature	BASIC $3 🆕	PRO $29	ULTRA $79 ⭐	MEGA $149
Requests / month	50	1,200	3,500	10,000
Best for	Try the API	Small apps	Growing apps	Production scale
/workout-plan	✅	✅	✅	✅
/macros	✅	✅	✅	✅
/meal-plan	✅	✅	✅	✅
/progress-check	✅	✅	✅	✅
/health	✅	✅	✅	✅
Overage (per call)	—	$0.008	$0.008	$0.008
Priority support	❌	❌	✅	✅

💡 New to FitEngine API? Start with the BASIC plan at just $3/month — 50 requests to test all 4 endpoints and see real results before committing to a larger plan. Upgrade anytime with one click.

Note: Each request to an AI endpoint (/workout-plan, /macros, /meal-plan, /progress-check) counts as 1 request. The /health endpoint does not count toward your limit. Overage is charged at $0.008 per call beyond your monthly limit (PRO and above).

🔐 Authentication

All endpoints require your RapidAPI key, passed automatically by the RapidAPI proxy:

X-RapidAPI-Key: YOUR_RAPIDAPI_KEY

No separate signup, no API key management, no OAuth flow. Subscribe on RapidAPI and start making calls immediately.

❌ Error Handling

All errors return a consistent JSON structure with a human-readable message:

{
  "success": false,
  "error": "age must be between 10 and 100"
}

HTTP Status	Meaning
400	Invalid input — missing required field or value out of range
405	Wrong HTTP method — check GET vs POST for the endpoint
429	Rate limit exceeded — 200 requests/hour per IP
500	Internal server error — contact support via RapidAPI messaging

⚠️ Disclaimer

FitEngine API generates fitness and nutrition recommendations for general wellness purposes only. Responses are not a substitute for professional medical advice, diagnosis, or treatment. Users with medical conditions, injuries, or specific health concerns should consult a qualified healthcare provider before starting any exercise or nutrition program.

🆘 Support

Questions or issues? Contact us through the RapidAPI messaging system. We respond within 24 hours on all plans.