Source: https://guthlabs.ai/docs/instruments/target-heart-rate-zones/implementation/

instrument implementation / implementation-contract

# Target Heart Rate Zones implementation

A source-bound implementation contract for Target Heart Rate Zones; deployment and executable qualification remain separate.

Status: **VERIFIED_CLEAN**Lifecycle: **implementation-contract**

## Binding contract

This record describes what an executable surface must bind and validate. It does not claim that a public calculator, package, or production route is deployed.

**Record owner**: Guth Instruments

**Lifecycle**: verified-clean

**Evidence ID**: t4-206

**Effect**: Computation or source lookup only

## Input and validation requirements

The specification has no stated validation for non-physiological ages, intensity bounds, or numeric overflow. Extreme inputs can produce -Infinity, and an intensity-unit ambiguity can produce 8460 bpm instead of 144 bpm.

## Required corrections

No binding erratum is attached to this unique-name record. Implementers must still preserve the declared units, domain, and failure behavior.

## Inspectable interface fixture

The sample below is evidence for interface and validation tests, not a production implementation.

````
{
  "inputs": {
    "age": 30,
    "resting_hr_bpm": 60,
    "formula_choice": "220-age",
    "intensity_ranges": [
      [
        0.5,
        0.6
      ],
      [
        0.6,
        0.7
      ],
      [
        0.7,
        0.8
      ],
      [
        0.8,
        0.9
      ],
      [
        0.9,
        1
      ]
    ]
  },
  "expected_outputs": {
    "hrmax_bpm": 190,
    "zone_table_bpm": [
      {
        "intensity": "50%-60%",
        "range": [
          125,
          138
        ]
      },
      {
        "intensity": "60%-70%",
        "range": [
          138,
          151
        ]
      },
      {
        "intensity": "70%-80%",
        "range": [
          151,
          164
        ]
      },
      {
        "intensity": "80%-90%",
        "range": [
          164,
          177
        ]
      },
      {
        "intensity": "90%-100%",
        "range": [
          177,
          190
        ]
      }
    ]
  },
  "working": "HRmax = 220−30 = 190 bpm. HR reserve = 190−60 = 130 bpm. Zone 1: 130×0.50+60 = 65+60 = 125; 130×0.60+60 = 78+60 = 138. Zone 2: 130×0.60+60 = 138; 130×0.70+60 = 91+60 = 151. Zone 3: 130×0.70+60 = 151; 130×0.80+60 = 104+60 = 164. Zone 4: 130×0.80+60 = 164; 130×0.90+60 = 117+60 = 177. Zone 5: 130×0.90+60 = 177; 130×1.00+60 = 130+60 = 190."
}
````

## Other records

[01**Overview**](<https://guthlabs.ai/docs/instruments/target-heart-rate-zones/>)[02**Mechanism**](<https://guthlabs.ai/docs/instruments/target-heart-rate-zones/mechanism/>)[04**Qualification**](<https://guthlabs.ai/docs/instruments/target-heart-rate-zones/qualification/>)

## Sources and evidence

These pointers bind the page to evidence. They do not grant authority or collapse verification into deployment.

- `VERIFIED_LEDGER.json`

- `evidence-tranche4/tranche4-results.json`