getfitcraft.com

{
  "type": "object",
  "additionalProperties": false,
  "properties": {
    "age": {
      "type": "number",
      "description": "Age in years.",
      "minimum": 13,
      "maximum": 100
    },
    "formula": {
      "type": "string",
      "enum": [
        "tanaka",
        "gulati",
        "nes",
        "legacy"
      ],
      "description": "Max HR formula used for the zones: tanaka (default, recommended), gulati (women), nes (active adults), legacy (Fox 1971, 220 minus age, unvalidated). Every formula is returned in max_heart_rate.byFormula regardless of this choice."
    },
    "resting_heart_rate": {
      "type": "number",
      "description": "Optional resting heart rate in bpm. Unlocks Karvonen heart rate reserve zones.",
      "minimum": 30,
      "maximum": 120
    },
    "measured_max_hr": {
      "type": "number",
      "description": "Optional measured or watch-learned max HR in bpm. Overrides the age formula and feeds the zones directly.",
      "minimum": 120,
      "maximum": 230
    }
  },
  "required": [
    "age"
  ]
}