Good news fitness fans - you can finally leave your smartphone at home.

Garmin has been churning out fantastic sports watches for years, but it's taken until now for one to get music playback. The 645 Music takes the basic Forerunner formula and adds a splash of Bluetooth, so all you have to do is hook up a pair of headphones, and you're good to go - tunes and all.

It's smaller than most running watches too, but with enough clout to keep its enthusiast appeal - it has just about all the features of the Garmin Fenix 5 but in a much more compact package.

We have some reservations. It's pretty expensive, and battery life, a traditional Garmin selling point, is not close to its chunkier siblings. 

However, if you don’t mind the higher price tag and a bit of extra charging, this music-packing Garmin could be one of their best watches yet.

READ: The 10 best smartwatches 2018

Design & build: smaller and more refined

The 645 is significantly smaller than the rest of the Forerunner range, and borrows a lot of its design queues from the Vivoactive 3. That means it’s only about as large as the Apple Watch, and gets rid of the ultra-nerdy look of many runners' watches. 

What’s the difference between the Vivoactive and Forerunner 645 Music? On the outside it’s about buttons. The 645 is operated using buttons alone, while the Vivoactive 3 has a touchscreen.

Buttons are better for use during exercise as you’re less likely to accidentally interrupt a workout.

Both go for the same stainless steel bezel on top of a very tough-feeling plastic shell, though.

And while I haven’t worn the Foreunner 645 Music every night, I do find it comfy enough for 24/7 wear. The ultra-stretchy silicone strap as something to do with this. It makes the watch feel snug, not tight, even when you’ve tightened it up to keep the HR sensor reliable.

It's pretty lightweight too, with little of the heft you'd find on a high-end Forerunner or Fenix.

It isn’t as stylish as some Android Wear Watches or any of Nokia’s ones. However, it’s clearly a looker next to any GPS running watch.

Screen: great in sunlight

Like just about every high-end Garmin watch, the Forerunner 645 Music has a “MIP” screen. That stands for memory in pixel, a kind of LCD screen where pixels can retain their contents without using significant energy. Similar to an Amazon Kindle, then.

This kind of screen is not natively backlit, so needs a light like a digital watch in the dark. There’s a dedicated button for it, although any interaction turns it on as standard.

In very bright sunlight you’ll struggle to find any smartwatch that looks clearer than the Garmin Forerunner 645 Music. Normal LCDs and OLED have to fight against ambient light. This screen feeds off it.

I find this perfect for a runner’s watch. Just don’t expect ultra-vivid colour. The Garmin Foreunner 645 Music’s does do colour, and it’s brighter than some older Garmins. But try to get your eyes on one of these first if you’ve never seen a Forerunner in person.

Software & features: more functional than fancy

If you’re expecting all the gloss of an Apple Watch, you’re looking in the wrong place. The Garmin Forerunner 645 Music’s software is more functional than fancy, which fits the all-button style.

Press the “down” and “up” buttons on the left of the watch from the watch face and you see homescreens for your step count, recent notifications, the weather and your weekly exercise report.

Press the Start/Stop button on the right side and you’ll see the list of activities you can track. This is also where any extra apps you download appear, proving the Garmin Foreunner 645 Music really isn’t meant primarily as a smartwatch. It’s also slower than most smartwatches, and seemingly slower than some Garmins, with a beat of lag between your inputs and the on-screen reaction.

It handles the smartwatch basics fine, though. You’ll get notifications from your phone, if you want them, and the Run IQ store offers a smattering of extra apps, including a Pomodoro work timer and an app that tells you when your Uber is going to arrive. Garmin itself made that last one.

The vast majority of Garmin Foreunner 645 Music app are little sport wingdings, though, so keep your expectations in check.

Wireless payments are go here, thanks to NFC and a service called Garmin Pay. However, right now it’s not that useful in the UK as only a couple of banks support it. If yours doesn’t, it’s pretty much useless at the moment. Here's hoping for more support soon.

You pay an extra £50 for the Music version of the Forerunner 645, and it gets you 4GB extra storage and a little music interface accessible quickly by long-pressing the watch’s “down” button. You’ll need Bluetooth headphones to listen though, as there’s no jack input.

4GB isn’t masses of room, but you do get pretty decent navigation and different sections for music, audiobooks and podcasts. You can simply drag and drop files onto the watch with either a Mac or PC when the watch is plugged in.

Don’t have a lot of MP3 files lying around any more? At some point in the future you’ll be able to sync Deezer playlists over wi-fi too, with Garmin promising it in an update. Right now you can sync iHeartRadio playslists, but this service is only available for US users at the moment.

It's not as versatile as an Apple Watch for music streaming, then. But it does let you listen to stuff on a run without a phone, and that’s the main thing.

Fitness tracking: approachable hardcore stats

So, how is it as a fitness tracker? When I go out for a run it seems just like a Fenix model, but is more comfortable because the watch is smaller. Plus you don’t feel a charlatan wearing it when you just run 5Ks, not marathons.

Press the start/stop button on the side and you’re taken to the list of activity tracker types. All the usual run, walk, cycle and swim options are there (it's 5ATM waterproof), and so are more unusual picks like snowboarding, rowing and yoga. 

In fact, the only things missing from the 645 are advanced navigation, and multisport / open water modes. Otherwise pretty much every Fenix feature is present and correct. That means you're getting one of the most comprehensive runner's watches around, in a much smaller package than before.

The Garmin Foreunner 645 Music also records more metrics than most. You get GPS, of course, for a map of all your routes. Your pace gets transformed into a series of graphs and tables, and you can zoom into your heart rate read-out for a closer look at your exertion level.

While no wrist-worn HR tracker is quite as good as a chest strap, the Garmin Foreunner 645 Music’s gets pretty close. During interval training, the ups and downs closely track the intensity spurts and your heart rate is monitored 24/7. Press down from the watch face and you’ll see a graph of your HR over the last four hours.

The Garmin Foreunner 645 Music also tracks your elevation, and even the temperature. As the sensor is within the watch, the temperature reading is affected by your body heat. But it offers an idea of changing temperatures during a hike or run, for example.

You get hardcore stats here. But as the front page of the Garmin Connect app is actually pretty colourful and fluffy, it’s way less intimidating than the high-end Garmin experience used to be.

Battery life: the chink in the armour

There’s only one other issue with the Garmin Foreunner 645 Music, as long as you’re not desperate for Spotify streaming. In chipping down the size of the watch, battery life has taken a hit.

The Fenix 5 lasts for up to 24 hours of HR and GPS tracking. Use the Garmin Foreunner 645 Music’s audio streaming as well as HR and GPS, and Garmin says you’ll only get five hours’ use.

That does increase to 14 hours when you don’t use music streaming, but there’s a clear trade-off for the smaller size and extra functionality.

I’ve used the Forerunner 645 for several weeks now, and it tends to last me around four days, including tracking a few 30-minute runs. Clearly, though, if you use music streaming quite a lot, or your workouts are more intense, you’ll have to keep an eye on the battery level much more.

To charge the Forerunner 645 Music, you use a little crocodile clip cable that clamps onto some contacts on the watch’s underside. It’s not as swish as a wireless charger, but also means you don’t need a flat surface to lay the 645 on when charging. It’s practical, like most other aspects of the watch.

Garmin Forerunner 645 Music verdict

The Garmin Forerunner 645 Music is a great GPS sports watch that has just about all the chops of the most expensive Garmin watches. Plus it comes with support for music, while looking much more accessible.

It doesn’t last as long as the Forerunner 935 or Fenix 5, though, which is worth considering if you run every day rather than one or twice a week.

That's no biggie for those who use exercise to keep the cheese and wine pounds off. But the price may be - £400 for a friendlier Garmin Forerunner is steep, especially when the similar Vivoactive 3 costs £250 online. 

READ: Top 10 best fitness trackers

Stuff says... 

Garmin Forerunner 645 Music review

A serious runner’s watch without the intimidating design, but the price will put many off
£399
Good Stuff 
Hardcore fitness skills in a smaller watch
Great screen for sunny days
Excellent fitness and HR tracking
Bad Stuff 
Interface lag
High price
Battery life doesn’t match Garmin’s best