Heart Rate Zones

{
  "age": 40,
  "asOf": "2026-10-11T08:36:50.345Z",
  "degraded": false,
  "disclaimer": "Screening signal computed from the named public source. Not financial, legal or investment advice; provided as is. Verify at the source before acting.",
  "maxHrFox": 180,
  "maxHrMeasured": null,
  "maxHrTanaka": 180,
  "maxHrUsed": 180,
  "method": "Karvonen heart-rate reserve",
  "notChecked": [
    "individual variation (the age formulas have a spread of about +/-10 beats per minute)",
    "medications such as beta blockers that lower heart rate",
    "…1 more"
  ],
  "reasons": [
    "Tanaka (2001): 208 - 0.7 x age, better for adults over 40 than Fox 220 - age.",
    "Karvonen: resting + percent x (max - resting).",
    "…1 more"
  ],
  "reserve": 120,
  "restingHr": 60,
  "source": "computed locally",
  "summary": "Max heart rate 180 bpm (Tanaka; Fox gives 180); Karvonen reserve zones: 120-132, 132-144, 144-156, 156-168, 168-180 bpm.",
  "verdict": "COMPUTED",
  "zones": [
    {
      "bpm": {
        "max": 132,
        "min": 120
      },
      "percentOfReserve": "50-60%",
      "zone": "Zone 1 recovery"
    },
    {
      "bpm": {
        "max": 144,
        "min": 132
      },
      "percentOfReserve": "60-70%",
      "zone": "Zone 2 endurance base"
    }
  ]
}

# bash or zsh: see the payment challenge. Nothing is charged.
curl -sS -g -i 'https://fitness-calc.x402tookit.com/heart-rate-zones?age=40&restingHr=60'

# x402 v2 sends the challenge base64-encoded in the PAYMENT-REQUIRED header (v1 sends it in the body).
# To read the header:
curl -sS -g -o /dev/null -D - 'https://fitness-calc.x402tookit.com/heart-rate-zones?age=40&restingHr=60' \
  | grep -i '^payment-required:' | cut -d' ' -f2 | tr -d '\r' | base64 --decode

// npm i @x402/fetch @x402/evm viem
import { wrapFetchWithPayment, x402Client } from "@x402/fetch";
import { registerExactEvmScheme } from "@x402/evm/exact/client";
import { privateKeyToAccount } from "viem/accounts";

// Pays at most $0.02 per call.
const client = new x402Client().setSpendControls({ maxAmountPerPayment: "$0.02" });
registerExactEvmScheme(client, { signer: privateKeyToAccount(process.env.EVM_PRIVATE_KEY) });
const pay = wrapFetchWithPayment(fetch, client);

// Not sure it's safe to pay? ToolVet checks it first for $0.005. Pay for that from a separate
// client: this one is capped at $0.02 per payment. GET https://toolvet.app/api/v1/check?url=https%3A%2F%2Ffitness-calc.x402tookit.com%2Fheart-rate-zones
const res = await pay("https://fitness-calc.x402tookit.com/heart-rate-zones?age=40&restingHr=60");
console.log(res.status, await res.text());

# pip install "x402[requests,evm]"
import os
from eth_account import Account
from x402 import x402ClientSync
from x402.http.clients import x402_requests
from x402.mechanisms.evm import EthAccountSigner
from x402.mechanisms.evm.exact.register import register_exact_evm_client

# Pays at most $0.02 per call.
client = x402ClientSync().set_spend_controls({"max_amount_per_payment": "$0.02"})
register_exact_evm_client(client, EthAccountSigner(Account.from_key(os.environ["EVM_PRIVATE_KEY"])))

with x402_requests(client) as session:
    res = session.get("https://fitness-calc.x402tookit.com/heart-rate-zones?age=40&restingHr=60")
    print(res.status_code, res.text)