Endurance by Endulytics – fitness app with wearables &…

Fitness

The Challenge

Accuracy, device diversity, and athlete expectations

Endurance athletes expect reliable real-time metrics and trustworthy history: heart rate, power (watts), cadence, and distance must stay stable outdoors, indoors, and when connectivity fluctuates. Sensor vendors implement different BLE GATT profiles and firmware behaviours; pairing, background reconnects, and multi-sensor setups do not behave identically across devices.

The app must also work when the network drops: recorded sessions cannot be lost if the user is briefly offline. When WiFi or mobile data returns, data should merge with the backend without duplicates or manual fixes.

Battery use, background work, and privacy

Continuous BLE scanning and connections, combined with screen-on use and occasional GPS scenarios, stress CPU and battery. iOS and Android apply different background limits—a flow that works on one test device may drop connections on older phones or under load. Health and performance data must be processed in line with GDPR, from on-device storage to synced history in the cloud.

Our Solution

App screenshots

Native clients, BLE layer, and robust sensor integration

We implemented the Endurance app natively for iOS (Swift) and Android (Kotlin), wiring the BLE stack per platform: scan intervals, reconnect strategies, and cached device metadata are tuned so typical combinations of chest straps, power meters, and bike computers remain stable. Where vendors use proprietary extensions, we isolate logic in modular adapters so SDK or firmware updates stay manageable.

Training planning combines structured intervals, target zones, and clear day/week views. Users see at a glance whether they trained in the planned range—with practical guidance without turning the app into a medical device.

WiFi sync, API design, and offline-first behaviour

Backend sync uses encrypted REST APIs; after a session, batches upload when connectivity is stable. A local queue with idempotency keys prevents duplicate entries if uploads fail mid-way, keeping history consistent whether the athlete syncs at home on WiFi or on mobile data.

Results

Field stability and maintainable architecture

Throughout the project we prioritised reproducible testing with real sensor sets and an architecture ready for follow-on features: more sports, deeper analytics, or third-party integrations. Collaboration with Endulytics was iterative—feedback from athletes and coaches fed into sprint planning and UX refinements.

User experience and performance

The UI targets fast pre-workout capture and clear post-workout review: minimal taps, readable metrics, and sensible defaults for zones and units. Profiling on mid-range devices keeps charts and animations smooth so the app stays responsive after long sessions.

Training in the field

Sensor adapters and offline sync

Vendor-specific BLE profiles sit in modular adapters so new sensors can follow without reopening the whole app. Offline queues with idempotency prevent duplicate entries after unstable uploads.

“Endurance athletes forgive no gaps in training history—sync must be invisible and reliable.”

Target zones and intervals are quick to capture in the UI; charts stay smooth even on mid-range devices.

Health data handled responsibly

“Performance and heart-rate data is personal—storage and transfer follow clear purposes.”

Endulytics and Groenewold IT Solutions iterated features from real training feedback—Made in Germany from East Frisia.

Features

Feature overview

BLE pairing for heart-rate, power, and cadence sensors
Structured training plans with target zones and session overview
Real-time display of key metrics during activity
Offline recording with later sync over WiFi or mobile data
Encrypted REST API to the backend with consistent history
Native iOS and Android implementation (Swift/Kotlin)
Queued uploads with retry logic
Modular device adapters for different sensor vendors
Trend views for training control and motivation
GDPR-oriented handling of personal health data
Configurable display and zone settings
Support for typical endurance scenarios (e.g. cycling, running)

Frequently asked questions about Endurance by Endulytics

What defines Endurance as a fitness and wearables app?

The app combines training planning with wearable data and practical mobile UX. Products like this need more than pretty charts, namely solid app development with clean data logic.

Why is wearable integration more than a minor API task?

Activity data, training plans, and user feedback all need to sync and make sense together. That is where API integration and product logic meet.

Which UX question is especially important in training apps?

Whether progress and next steps are instantly clear. Strong fitness apps guide users through plans instead of overwhelming them with numbers. That requires clean software architecture.

What other products is this reference relevant for?

For health, fitness, and coaching apps with data integration or sensor connectivity. Related topics include our mobile app references and app development cost.

Endurance by Endulytics – fitness app with wearables & training plans