Which fitness API does your app need?
Short answer: it depends on the moment you are building, because fitness APIs do six different jobs. One reads the phone’s health data, one pipes wearables into your backend, one scores readiness, one watches the rep, one builds workouts from templates, and one writes the coaching. Name the moment first, then pick the API that does that job. The map, with public prices and sources, is below.
Six jobs, six kinds of fitness API.
| Job | Kind of API | Examples | Public price | Pick it if |
|---|---|---|---|---|
| Read the phone’s health data | Platform health store | Apple HealthKit, Android Health Connect | No API fee; part of the iOS and Android SDKs. | your app runs on the phone and the data it needs is already in the user’s health store. Records stay on the device until your app uploads them. |
| Bring many wearables into your backend | Wearable data pipe | Terra | Terra: From $399/mo on the annual plan ($499 monthly), 100,000 credits included, roughly 200 credits per active user per month, overage from $0.005 per credit. | you need raw wearable and app data flowing into your backend from hundreds of sources. That is their whole job and they are good at it. |
| Turn signals into a readiness number | Scoring API | Sahha | Sahha: Self-serve tiers with a free start; usage-based beyond. | you want a readiness or wellbeing number with contributing factors, including phone-only (no wearable required), and your app writes its own coaching copy around it. |
| See the rep while it happens | Camera motion SDK | Sency, Kemtai | Sency: Per unique active user per month, pay as you go past 100 users; the published curve slides to roughly $0.10 per user at volume (August 2026 reading). Kemtai: Sales-led; no public price list. | your product moment is DURING the rep: live counting, live form cues, a camera pointed at the athlete. A language model cannot do that job. |
| Build workouts from templates | Generator and exercise library | WorkoutX, Hyperhuman | WorkoutX: $0 to $24.99/mo, keys in minutes. Hyperhuman: From $191/mo. | parameterized templates and an exercise database are all your product needs. It is the honest price floor for generation without interpretation. |
| Write the coaching itself | Coaching layer | CoachLayer, Zing Coach (B2B), or your own build on a frontier model | CoachLayer: free Sandbox (300 credits, no card), paid tiers on the pricing table. Zing Coach (B2B): Sales-gated; no public pricing, no self-serve keys. | your users need the numbers interpreted: why today is a deload, what to change next week, an answer to their own question. That is the job the other five leave to you. |
Vendor prices are their public lists, checked August to September 2026; the platform row was checked against Apple’s and Google’s developer documentation in October 2026. If a vendor page disagrees with this table, trust the vendor page.
How the six jobs fit together.
The jobs line up in the order data flows. The phone or a wearable produces the signal. A health store read or a data pipe gets it to your backend. A scoring API can compress it into a number. A coaching layer turns the signal and the training log into words a user acts on. A camera SDK sits apart, inside the workout itself.
CoachLayer sits at the end of that chain and never connects to a wearable: your backend sends the training and recovery data it already holds in the request body, and gets back a readiness brief, a coach reply, a program change or a session analysis, across 8 endpoints behind one key. That keeps the choice of pipe independent of the choice of coach: swap one without touching the other. The wiring, auth and failure handling are in how to integrate a coaching API.
What developers ask before they pick one.
What is the best fitness API for developers?
There is no single best one, because fitness APIs do six different jobs. Platform health stores (Apple HealthKit, Android Health Connect) read data on the phone. Wearable data pipes such as Terra bring many devices into your backend. Scoring APIs such as Sahha turn signals into a readiness number. Camera SDKs such as Sency count reps and check form live. Generators such as WorkoutX build workouts from templates and an exercise library. A coaching layer such as CoachLayer writes the personal coaching itself. Name the moment you are building, then pick the API that does that job.
Is there a free fitness API?
Several, with limits. Apple HealthKit and Android Health Connect have no API fee, but they run on the phone, not on your server. WorkoutX lists $0 to $24.99/mo, keys in minutes. CoachLayer has a free Sandbox tier with 300 credits a month and no card, enough to test every endpoint before a pricing conversation.
Can my server read Apple Health or Health Connect data directly?
No. Apple stores HealthKit data on the device and encrypts it when the device is locked, and Health Connect also keeps its data on the device. Your app reads the records it was granted with the user’s permission and uploads them to your backend. The old Android cloud route is closing too: Google stopped new sign-ups to the Google Fit APIs on May 1, 2024 and is deprecating them in 2026. Plan for a read on the phone either way.
Do I need both a wearable data API and a coaching API?
Only if you need both jobs done. CoachLayer never connects to a wearable: training and recovery data arrives in the request body, sent by your backend. If your app already logs workouts and reads Apple Health on the phone, you can call a coaching API with no pipe. If you need sleep, HRV and activity from many devices and vendor clouds, a pipe saves one integration per source, and its output becomes the coaching layer’s input.
Which fitness APIs let me start without a sales call?
Self-serve, with public pricing or a free start: Terra, Sahha, Sency, WorkoutX, Hyperhuman, and CoachLayer (a free Sandbox key at signup, no card). Sales-led, with no public price list: Kemtai, Zing Coach (B2B). Vendor terms change, so check each vendor’s own page before you commit.
Test the coaching job on your own data.
The Sandbox tier is free, needs no card and covers all 8 endpoints.
Get a sandbox key