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Device & Product Engineering
PulseFit Dynamics
A Workout That Keeps the Heart Rate Honest
Live heart-rate telemetry, a plan that changes with the session, and a community board that does not invent a result.
React NativeHealthKitFastlaneNode.js
Sessions kept
Sample delay
The Challenge
What was already failing
The plan ignored the sensor. People closed the app when the number on the wrist and the number on the phone disagreed, and the leaderboard rewarded the glitch.
The Solution
Read the sensor, refuse a bad sample, and show a session the athlete can trust.
01 // edge
Sensor at the edge
Heart rate lands on the phone without a round trip. The session does not buffer the effort.
- HR·Live
- Round trip·None
- Buffer·Off
02 // guard
Sample guard
A dropped beat is marked, not averaged into a record. The board only accepts a finished session.
- Drop·Marked
- Board·Finished only
- Glitch·Rejected
03 // checkout
The session
The plan adapts on screen. The athlete is not sent to a web dashboard to see the work.
- Plan·Adaptive
- Dashboard·In-app
- Interval·Follows HR
Edge
Sensor at the edge
HRLiveWrist → phone
Round tripNoneOn device path
BufferOffEffort immediate
Guard
Sample guard
OKSealed
Drop
Marked
Not averaged
Board
Finished only
Gate kept
Glitch
Rejected
Honest score
Checkout
The session
Plan
Adaptive
Dashboard
In-app
Interval: Follows HR · Next beat
The Solution
Read the sensor, refuse a bad sample, and show a session the athlete can trust.
01 // edge
Sensor at the edge
Heart rate lands on the phone without a round trip. The session does not buffer the effort.
- HR·Live
- Round trip·None
- Buffer·Off
Edge
Sensor at the edge
HRLiveWrist → phone
Round tripNoneOn device path
BufferOffEffort immediate
02 // guard
Sample guard
A dropped beat is marked, not averaged into a record. The board only accepts a finished session.
- Drop·Marked
- Board·Finished only
- Glitch·Rejected
Guard
Sample guard
OKSealed
Drop
Marked
Not averaged
Board
Finished only
Gate kept
Glitch
Rejected
Honest score
03 // checkout
The session
The plan adapts on screen. The athlete is not sent to a web dashboard to see the work.
- Plan·Adaptive
- Dashboard·In-app
- Interval·Follows HR
Checkout
The session
Plan
Adaptive
Dashboard
In-app
Interval: Follows HR · Next beat
Key Capabilities
What the system is trusted to do
01
The wrist and the phone agree
Telemetry renders as it arrives. The plan changes inside the session, not after it.
02
No invented records
Incomplete samples are marked. The leaderboard waits for a session that actually finished.
03
A plan that listens
Effort on screen is the effort on the sensor. The next interval follows the heart rate.
Architecture
How the pieces connect
Engineered With
- React Native
- HealthKit
- Fastlane
- Node.js
Results and Impact
Active installs passed 850K. Sessions stay open because the number on the phone matches the number on the wrist.
- 850K+ active installs
- 92% of sessions kept open
- Wrist and phone heart-rate stay in agreement
850K+
Active installs
92%
Sessions kept
<80ms
Sample delay
App · PulseFit Dynamics
Live heart-rate telemetry, a plan that changes with the session, and a community board that does not invent a result.
“Athletes stopped screenshotting a different app to prove the workout.”
Start
A system with a number you can defend.
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