Target heart-rate zones (Karvonen) API

Compute the 5 training heart-rate zones via the Karvonen heart-rate-reserve method (target = HRrest + (HRmax − HRrest)·intensity), falling back to %-of-max when resting HR is omitted; HRmax from Tanaka. Answers 'what are my heart rate zones', 'fat-burn zone', 'Karvonen target heart rate', 'zone 2 for age 30'.

Price$0.01per request

MethodPOST

Route/v1/health/heart-rate-zones

StatusLive

MIME typeapplication/json

Rate limit120/minute

CacheNo cache

healthheart-rate-zoneskarvonencardiotraininghr-reservefitnesscalculator

API URLhttps://x402.hexl.dev/v1/health/heart-rate-zones

Integration docs

Example request

{
  "ageYears": 30,
  "restingHr": 60
}

Example response

{
  "maxHeartRateBpm": 187,
  "method": "Karvonen (heart-rate reserve)",
  "restingHr": 60,
  "heartRateReserve": 127,
  "zones": [
    {
      "zone": "Zone 1 — very light / recovery",
      "lowBpm": 124,
      "highBpm": 136,
      "intensity": "50-60%"
    },
    {
      "zone": "Zone 2 — light / fat burn",
      "lowBpm": 136,
      "highBpm": 149,
      "intensity": "60-70%"
    },
    {
      "zone": "Zone 5 — maximum",
      "lowBpm": 174,
      "highBpm": 187,
      "intensity": "90-100%"
    }
  ]
}

Input schema

{
  "type": "object",
  "required": [],
  "properties": {
    "ageYears": {
      "type": "number",
      "description": "Used to derive HRmax via Tanaka",
      "examples": [
        30
      ]
    },
    "restingHr": {
      "type": "number",
      "description": "Enables Karvonen reserve method",
      "examples": [
        60
      ]
    },
    "maxHr": {
      "type": "number",
      "description": "Override HRmax directly",
      "examples": [
        185
      ]
    }
  }
}

Output schema

{
  "type": "object",
  "additionalProperties": true
}