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This weekend I ran my 7th marathon in Frankfurt, Germany, and, while worrying about the pouring rain and strong gusts of wind, I made things even more interesting by putting the Apple Watch Ultra 4 and Garmin Fenix 9 Pro head-to-head.

The Apple Watch Ultra 4 is Apple's newest rugged sports watch, with a new heart rate monitor and a readiness score, helping you work out when to push yourself and when to recover. The Fenix 9 Pro, on the other hand, is Garmin's most advanced sports watch yet. Both came out this year, and both offer all the sports modes and stats you need to track workouts, plus comprehensive daily activity and sleep tracking.

We've put all the features head-to-head in our Apple Watch Ultra 4 vs Garmin Fenix 9 Pro face-off here, but read on to see which came out on top on race day.

The Apple Watch Ultra 4 is Apple's latest rugged adventure watch, with a new heart rate sensor and a daily Readiness score.

I wore the Apple Watch Ultra 4 and the Garmin Fenix 9 Pro for a marathon: Here's what happened

Like most European marathons, the Frankfurt Marathon had a marker every kilometer, so for this test, I switched both watches from miles to kilometers. I manually lapped each watch every 5km, so I could be sure I was on pace, and when I finished running, I downloaded the data to see which watch was more accurate.

The GPS is notoriously unreliable in Frankfurt itself, especially around the business district, as, like most built-up cities, you've got buildings and skyscrapers to navigate. Chuck in crowds of people and 18,000 other runners, and things are never going to be 100% accurate, but I found immediately that the Garmin Fenix 9 Pro was far better at not letting these GPS dead zones give me inaccurate pace data.

You'll never run 26.2 miles, or 42.19 kilometers on race day unless you're perfectly sticking to the blue line, which it's near impossible to do as you weave around other runners. My Garmin Fenix 9 Pro recorded the run as 42.76km, or 26.5 miles. The Apple Watch Ultra 4, on the other hand, recorded the run as 43.33km, or 26.9 miles. I found the Apple Watch Ultra 4 was about half a kilometer ahead of my Garmin throughout the race.

When it comes to my pacing, my bib, which recorded my pace at every kilometer marker, recorded my average pace as 4:52 min/km. The Garmin Fenix 9 Pro recorded an average pace of 4:48 km, and the Apple Watch Ultra 4 recorded 4:44 km. Of course, this accounts for the fact that the Apple Watch Ultra 4 recorded the longest run.

The main difference between the Apple Watch Ultra 3 and Apple Watch Ultra 4 is that the newer watch has Apple's latest continuous heart rate monitor, which Apple says is the most accurate of any wearable device. During the run, the Apple Watch Ultra 4 recorded my average heart rate as 172 beats per minute, which is exactly the same as the Garmin Fenix 9 Pro. While I didn't wear a chest strap, as there's only so much tech a girl can wear on race day, I did have my Oura Ring 5 on my finger, which recorded my average heart rate as 179 beats per minute.

While both watches are more than capable of recording all of your training runs, as well as your recovery, on race day itself, the Garmin Fenix 9 Pro came out on top in terms of GPS accuracy. I also found it easier to use in the pouring rain, thanks to the extra buttons. Of course, this isn't to say that the Apple Watch Ultra 4 is inaccurate, but on this particular wet Sunday morning, Garmin was the winner.