What Is Activity Deep Dive?
Activity Deep Dive lets you explore every detail of your workout by loading FIT, TCX, or GPX files directly in the browser. Instead of relying on the summary screens of Garmin Connect or Strava, you get access to the raw, second-by-second data: heart rate curves, pace fluctuations, cadence patterns, power output, elevation changes, and GPS tracks. This is especially valuable for coaches and data-driven athletes who want to analyze specific segments — like how your heart rate responded during a hill repeat, or whether your cadence dropped in the final kilometres of a marathon.
Interactive Charts and Data Visualization
The tool renders your activity data as interactive Chart.js graphs. You can overlay multiple metrics — for example, heart rate and elevation on the same time axis — to see how terrain affected your effort. Hover over any point to see the exact value at that moment. Zoom into specific intervals to study your pacing strategy during a race or the recovery pattern between intervals. For wheelchair athletes and handcyclists, the tool processes the same FIT data fields but presents them in context: push frequency instead of running cadence, and handcycle power metrics where available.
Common Mistakes in Post-Activity Analysis
Focusing only on averages hides important patterns. Your average heart rate might be 155 bpm, but Deep Dive reveals you spent 12 minutes above 175 bpm during hill sections — crucial information for understanding cardiac drift and recovery needs. Another common mistake is ignoring GPS artifacts: tunnels, dense tree cover, and tall buildings cause GPS spikes that distort pace and distance calculations. Look for sudden unrealistic speed jumps in the data. Finally, comparing absolute numbers between different conditions (hot vs. cold weather, flat vs. hilly terrain) without accounting for environmental factors leads to misleading conclusions about fitness progress.
Aerobic Decoupling and Heart-Rate Drift
One of the most revealing metrics you can extract from a single activity is aerobic decoupling — sometimes called cardiac drift or the Pw:HR ratio. The concept is straightforward: in a well-paced aerobic workout your heart rate and pace (or power) should move together. If your pace holds steady while your heart rate climbs over the course of the session, your cardiovascular system is working progressively harder to sustain the same output. That drift is decoupling.
Practitioners often compare the pace-to-HR ratio in the first half of a run against the second half. A common guideline from endurance coaching literature suggests that a difference of less than 5% indicates good aerobic efficiency for that session — meaning your aerobic system could sustain the effort without significant drift. A reading above 5–8% on what was intended as an easy run is a signal worth noting: either the pace was too high, the heat was a factor, or your aerobic base needs more work at lower intensities. These thresholds are guidelines, not hard rules, and vary by individual fitness level, temperature, and terrain.
To calculate it yourself from the data visible in this tool: divide average pace by average HR for the first half of your session, do the same for the second half, then express the change as a percentage. The elevation profile and HR zone charts here let you cross-reference where drift began against the course terrain.
Reading Your Time-in-Zone Distribution
The HR zone chart above shows how many data points fell into each zone during your activity. For an easy recovery run, you want the vast majority of your time in Zone 1 and Zone 2 — if you are regularly slipping into Zone 3 or Zone 4 on runs you call 'easy', your easy pace is probably too fast. For a tempo or threshold session, the goal is a sustained block of time in Zone 4 with a controlled build rather than spikes into Zone 5.
Time-in-zone data is also useful for judging interval sessions. A good VO₂max interval session typically shows repeated short bursts into Zone 5 separated by recoveries that bring you back down to Zone 2 or Zone 3. If your recovery periods never dip below Zone 4, you started the next rep too soon or the total session volume was too high. Use the zone builder on raacon to define your personal zones more precisely, or check the HR zone calculator to compare different max-HR estimation methods.
Worked Example: Interpreting a 10 km Easy Run
Imagine uploading a 10 km run with these numbers: average pace 5:45/km, average HR 152 bpm, max HR 171 bpm, Zone 2 time 38%, Zone 3 time 45%, Zone 4 time 14%. The zone spread immediately tells you this was not an easy run — nearly 60% of the session was in Zone 3 or above. The elevation profile shows two significant climbs totalling 180 m of gain, which explains part of the drift. Cross-checking the first-half versus second-half HR: the first half averaged 147 bpm at 5:42/km; the second half averaged 157 bpm at the same pace. That is roughly 6.8% decoupling — above the 5% guideline. The practical takeaway: slow the easy pace by 15–20 seconds per km on hilly routes, or move these sessions to flatter terrain until base fitness improves.
Grade-Adjusted Pace and Elevation Context
Pace alone is misleading on hilly routes. A 6:00/km split going uphill represents a far greater effort than 6:00/km on flat ground. Grade-adjusted pace (GAP) normalises your pace to the equivalent flat-ground effort, letting you compare the physiological cost of hilly and flat runs fairly. While this tool's elevation profile shows your ascent and descent, keep GAP in mind when comparing average paces between sessions — a run that looks slower than last week might actually represent equivalent or greater effort once gradient is accounted for.
Frequently Asked Questions
Why does my average HR seem high even on easy days?
Common causes include heat and humidity (the cardiovascular system works harder to dissipate heat), accumulated fatigue from the previous days, dehydration, caffeine, or a pace that is simply too fast for your current aerobic fitness. Cardiac drift from heat can add 10–15 bpm to your average even without any change in effort. Compare your HR data across multiple sessions at similar conditions before drawing conclusions.
Can I use this tool for cycling power data?
FIT files from cycling computers (Garmin, Wahoo, Hammerhead) carry power data if you ride with a power meter. The current tool surfaces HR zones, elevation, and duration for cycling sessions. For detailed power curve analysis and Training Stress Score calculations, Garmin Connect and TrainingPeaks have dedicated power analytics. The FIT analyzer on raacon covers broader file inspection.
Is a 5% decoupling threshold the same for everyone?
No. The ~5% figure is a widely cited guideline in aerobic training literature but it is not a clinical cutoff. Beginners often see higher decoupling simply because their aerobic base is still developing. What matters more than any single number is the trend over time: if your decoupling percentage on comparable easy sessions decreases over months of consistent aerobic training, your cardiovascular efficiency is improving.
What file format gives the most data?
FIT files carry the most complete data — second-by-second HR, cadence, power, GPS, elevation, temperature, and device-specific fields like Garmin running dynamics. TCX files include HR and basic GPS but lose many advanced fields. GPX is GPS-only with no HR or power. If your device supports FIT export, always prefer it for deep-dive analysis.
About This Tool
Activity Deep Dive replaces 7 separate converter and analyzer pages. Upload a FIT, TCX, or GPX file to get a complete picture of your workout — from elevation gain to HR zone distribution — and export to any supported format.
Supported formats
FIT (Garmin, Suunto, Wahoo), TCX (Garmin, Polar), GPX (universal GPS standard). Export to GPX, TCX, or CSV for analysis in other tools. All processing happens in your browser — your data never leaves your device.
For further analysis, explore the FIT file analyzer for raw field inspection, the HR zone calculator to fine-tune your zones, and the zone builder to create custom training zones you can import into Garmin Connect.