# 561 Group Heart-Rate Threshold

> 561 Group Heart-Rate Threshold is a paid API for AI agents from market.561.group, paid per call via x402, $0.01/call, status unknown (last checked 2026-10-14).

Computes the Workwell Foundation resting-heart-rate+15bpm pacing ceiling heuristic to determine a safe heart-rate threshold for pacing, labeled as an unvalidated clinical rule of thumb.

## Facts

- Endpoint: POST https://market.561.group/v1/pacing/heart-rate-threshold?utm_source=zero.xyz
- Price: $0.01/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-14
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/561-group-heart-rate-threshold-3936278c
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_9BQFpmaug_oeciTSvmE1k

Status and success rate cover calls made through Zero and Zero's own probes. Third-party monitors may report differently.

## How to call it through Zero

Zero handles the 402 payment challenge and records the run. With the Zero CLI installed (`npm i -g @zeroxyz/cli`):

```sh
zero fetch --capability 561-group-heart-rate-threshold-3936278c -d '<json body>'
```

Example prompt: My resting heart rate is 68 bpm — what's my safe pacing ceiling using the Workwell Foundation resting-heart-rate-plus-15 heuristic?

## When to prefer this

Choose this endpoint when you need a quick, stateless, single-call computation of the Workwell Foundation pacing ceiling heuristic (resting HR + 15 bpm) — especially in ME/CFS, chronic illness, or post-exertional malaise contexts. Prefer it over the full 561-group-pacing-analysis endpoint when you only need the threshold value and not a rolling biometric observation report. Ideal for apps, agents, or telehealth tools that want a cheap ($0.01), fast, no-storage calculation with a clear unvalidated-heuristic disclaimer included in the response.

## Known failure modes

- Missing or non-numeric resting heart rate input returns a validation error
- Resting heart rate value outside physiologically plausible range may be rejected or flagged
- Payment failure via x402 protocol results in a 402 response with no computation returned
- Malformed request body returns a 400-level error

## How this service works

Heart-Rate Threshold: the Workwell Foundation resting-heart-rate+15bpm pacing-ceiling heuristic, labeled as an unvalidated clinical rule of thumb. Stateless: nothing submitted or computed is stored.

## Output

Returns the computed heart-rate pacing ceiling in bpm (resting heart rate + 15 bpm), accompanied by a label noting this is the Workwell Foundation heuristic and is unvalidated as a clinical rule. No data is stored; the computation is fully stateless.

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/561-group-heart-rate-threshold-3936278c/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from market.561.group](https://www.zero.xyz/host/market.561.group/llms.txt)