By Miles SinclairThe Garmin Fenix 5 is a multisport GPS watch that many runners consider for fartlek training, the Swedish method of mixing fast efforts with easy recovery jogs at irregular intervals. This review is aimed at runners who want to know whether the Fenix 5 can handle unstructured speed play, structured interval sessions and everyday mileage without becoming a hassle. It suits runners who like outdoor features, long battery life and a watch that doubles as a training tool for trail or road. It is less suited to runners who want a light, minimal device for short workouts, or anyone who finds menu-heavy watches frustrating. Because the Fenix 5 is an older generation, buyers should weigh its strengths against newer models before committing.
Product Overview
The Fenix 5 belongs to Garmin’s Fenix line of rugged multisport watches. It is built around a round, sport-style case with physical buttons, a color display and built-in GPS and GLONASS satellite support. For fartlek, the main appeal is that the watch can track pace, heart rate and distance in real time while letting you switch quickly between sport profiles, so you can log a run, a bike ride or a cross-training session without changing devices. Garmin positions the watch for outdoor athletes, which means it leans toward trail and endurance use rather than gym-focused tracking.
For interval and fartlek runners, the practical value is in the data. You can set up pace and heart rate alerts so you hear or feel a cue when you drop below an easy pace or push above a target effort. Because fartlek is unstructured, many runners rely on the watch mainly for after-run analysis: pace per lap, elevation, heart rate zones and total time spent above a threshold. Those summaries help you see whether your “easy” jogs were actually easy and whether your surges were long enough to count as a real stimulus.
Key Features & Specifications
The table below lists specifications that Garmin publishes for the Fenix 5 family. Exact figures can vary by model variant, so check the manufacturer’s current spec sheet before buying.
| Feature | What It Means for Fartlek Runners |
|---|---|
| GPS and GLONASS satellite support | Improves pace and distance accuracy on surges, which matters when you change speed quickly |
| Wrist-based heart rate monitoring | Tracks effort during fast and easy segments; chest straps are more accurate for hard intervals |
| Multisport profiles | Lets you log running, cycling, swimming and other activities from one device |
| Pace and heart rate alerts | Cue you when to ease off or push, useful for keeping recovery jogs truly easy |
| Lap and auto-lap functions | Splits can be set to time or distance, helpful for reviewing surges afterward |
| Barometric altimeter and compass | Records elevation gain, relevant for hilly fartlek routes |
| Color display with physical buttons | Usable with sweaty or gloved hands, though the interface has a learning curve |
| Water resistance rating | Suitable for rain and swimming; manufacturers specify a depth rating in the product documentation |
| Battery life in GPS mode | Long enough for multi-hour outings; manufacturers list different figures for GPS-only and smartwatch modes |
Pros & Cons
Pros
- Strong GPS performance for tracking varied pace, which suits unstructured fartlek.
- Pace and heart rate alerts can keep recovery jogs from drifting into moderate effort.
- Long battery life for long runs and multi-stage sessions.
- Multisport functions let you cross-train from the same watch.
- Elevation and barometric data are useful for hilly or trail fartlek.
- Rugged build and water resistance suit weather and outdoor conditions.
Cons
- Menu navigation takes time to learn, especially for configuring custom alerts.
- Wrist heart rate can lag during rapid pace changes, so a chest strap is more reliable for hard surges.
- The case is large and heavier than slim running watches, which some runners dislike.
- As an older model, it may lack newer training-load and recovery metrics found on later Garmin watches.
- Battery life drops noticeably when GPS and continuous heart rate are both active on long sessions.
Performance Analysis
Because fartlek depends on quick, unplanned changes in speed, the most important question is how well the watch tracks those changes. Owners commonly report that GPS pace is reasonably responsive on open roads and tracks are consistent, though readings can smooth out during sharp accelerations under tree cover or between tall buildings. This is a general pattern rather than a lab result, and it affects any GPS watch. Many runners pair the Fenix 5 with a chest strap for surges, since heart rate sensors on the wrist tend to lag when effort rises and falls fast.
Battery performance is another area owners often praise. For a typical 60 to 90 minute fartlek session with GPS and wrist heart rate active, the watch will comfortably last through the workout with ample reserve. Multi-hour trail runs also tend to be manageable, though runners who record everything continuously should plan to charge after long outings. Alert functions work as intended once configured, but the setup process is detailed. Expect to spend some time in the settings before your first session.
For analysis after the run, the lap and split data is where the Fenix 5 earns its keep. You can review how each surge compared with your easy jogs, see total time in each heart rate zone and check elevation changes. That information helps you judge whether your fartlek was too easy, too hard or well balanced, which is what most runners want from interval training data.
Who Should Buy This Product?
The Fenix 5 makes sense for runners who train outdoors, mix road and trail, and want one watch for running, cycling and other endurance sports. It is a good choice if you value long battery life and want pace and heart rate alerts to guide unstructured sessions. Runners who already use a chest strap for accuracy will get the most from it.
You should skip the Fenix 5 if you want a slim, lightweight watch for short runs only, or if you mainly track structured track workouts with a simple stopwatch. Runners who prefer minimal menus, or who want the newest recovery and training-readiness features, may find a newer Garmin model or a simpler running watch a better fit.
Buying Guide
When choosing a watch for fartlek, start with what you actually need to track. If you mostly run by feel and only want a record afterward, basic GPS and pace data may be enough. If you rely on alerts to keep easy days easy, look for a watch with customizable pace and heart rate cues and a clear way to set them up. Check battery life for your longest typical session, not just the maximum figure printed on the box.
Next, consider the sensors. Wrist heart rate has improved over the years, but it still lags during rapid changes. If you run many hard surges, plan to add a chest strap or choose a watch that supports one. Size and weight matter too. A larger watch may feel secure on trail runs but can be uncomfortable on fast road days. Try to read specifications for case size and weight, and if possible, wear a similar watch before buying.
Finally, think about ecosystem and software. Garmin’s app and data tools are strong, but if you use another platform for coaching or analysis, confirm that the watch syncs with it. Here are three well-known alternatives worth comparing:
- Garmin Forerunner 265 for a lighter, running-focused watch with a bright display: View on Amazon
- Coros Pace 3 for a light, minimal design with strong battery life for running: View on Amazon
- Polar Vantage V2 for runners who prioritize training guidance and built-in heart rate analysis: View on Amazon
FAQ
Is the Garmin Fenix 5 good for fartlek training?
Yes, for most runners it works well. Its GPS tracking, pace and heart rate alerts and lap data give you useful feedback on unstructured speed work. Pairing it with a chest strap improves heart rate accuracy during fast surges.
How do I set up pace alerts for fartlek?
Open the activity settings for running, find the alerts section and set a pace or heart rate range. Many runners set a lower limit to keep recovery jogs easy and an upper limit to signal when a surge is too hard. Test the alerts on a short run before relying on them.
Does wrist heart rate work well during intervals?
Wrist heart rate is useful for general effort tracking, but it can lag behind rapid changes in intensity. For short, hard surges, a chest strap usually gives a more immediate reading.
Can I use the Fenix 5 for other sports besides running?
Yes. The watch supports multiple sport profiles, including cycling and swimming, so you can log cross-training from the same device.
Is the Fenix 5 waterproof enough for swimming?
The watch carries a water resistance rating suitable for swimming. Check the manufacturer’s documentation for the exact depth rating of your model and avoid using it in diving or high-pressure water activities.
How long does the battery last during a run?
Battery life depends on which features are active. GPS with continuous heart rate will use more power than GPS alone. Manufacturers publish estimates for each mode, and most runners find it sufficient for typical workouts, though very long sessions may need a charge.
Should I buy the Fenix 5 or a newer model?
If you want the latest recovery and training-readiness features, a newer model may be a better choice. If you mainly need reliable GPS, alerts and battery life for outdoor running, the Fenix 5 remains a capable option.
Final Verdict
The Fenix 5 is a capable watch for fartlek and interval runners who train outdoors and value long battery life, solid GPS and customizable alerts. Its main drawbacks are a learning curve in the menus, a larger case and wrist heart rate limitations during hard surges. Runners who pair it with a chest strap and take time to configure alerts will likely find it a strong tool for unstructured speed work. Anyone wanting a lighter, simpler or newer device should compare it with the alternatives above. Before buying, check current specifications and consider speaking with a qualified coach if you are building a structured training plan around heart rate or pace zones. View on Amazon
About Miles Sinclair
Miles Sinclair is part of our editorial team and reviews and edits our speed & interval running guides, checking product details against manufacturer specifications and owner feedback.
