Garmin’s Run Coach Can Help You Train for a Marathon

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As someone who’s completed six marathons over six years, I approached Garmin’s marathon training plans with cautious optimism. After all, Garmin dominates the running tech space, and their watches are virtually ubiquitous among serious runners. Surely their training plans would reflect the same attention to detail and runner-focused design? Plus, I’m already a huge fan of racing with my no-nonsense Garmin Forerunner 165. After months of following the program (and eventually customizing it), here’s what I learned about the reality of trusting your watch to get you to the finish line.

How Garmin’s run coach works

Garmin’s run coach offers personalized, adaptive marathon training programs that adjust based on your performance metrics and recovery data. Your watch data drives your training, with workouts that evolve based on how you’re actually responding rather than blindly following a static plan pulled from a book.

The system analyzes metrics like your VO2 max, training load, recovery time, and recent workout performance to tailor each session. When you crush a tempo run, the plan might push you a bit harder next time. If your recovery metrics suggest you’ve overtrained, it dials things back. It’s smart, responsive training that theoretically removes the guesswork. However, I wouldn’t recommend blindly trusting whatever shows up on your wrist. 

What Garmin gets right

The speedwork, tempo runs, and interval sessions were genuinely helpful. Having these structured workouts automatically adjusted to my current pace meant I wasn’t second-guessing whether I was running too hard or too easy. The watch would beep when I drifted out of my target zone, keeping me honest during those tough threshold efforts.

The adaptive nature of the program also shines during the day-to-day grind. Recovery runs automatically adjust based on how your body is responding. If you’re showing signs of fatigue, the plan gives you easier days. This attention to recovery is rare in cookie-cutter training plans, and I both appreciate and depend on it.

Where Garmin falls short

The most glaring issue with Garmin’s marathon training plans is its overly conservative approach to long runs. As any experienced marathoner knows, the long run is the cornerstone of marathon preparation—it’s where you build the aerobic base, practice race-day fueling, and develop the mental fortitude to push through mile 20 and beyond.

Some specific examples from my experience:

• A 34-minute recovery run recommended on a day when my own intermediate plan called for five miles.

• A 90-minute long run when I was planning an 18-miler (which actually takes me closer to three hours).

Credit: Meredith Dietz

Garmin clearly has safety and recovery in mind, which is admirable. But here’s the reality: if you’re crazy enough to be training for a marathon, you’ve already committed to pushing beyond normal comfort levels. The long runs that feel “inherently crazy” are simply necessary. If I’d relied solely on Garmin’s workouts, I wouldn’t have gotten those crucial 20-milers that prepare you for race day.

Yes, the three-hour run isn’t a rigid rule—it’s a guideline to cap training runs since injury risk increases beyond that point. Some coaches advocate for shorter long runs with a focus on quality over quantity. But for many runners, especially those new to the marathon distance, getting one or two 20-milers under your belt builds irreplaceable mental toughness. Personally, I always risk a little more time on my feet to ensure I’m truly prepared, and it’s never hurt me.

Perhaps equally frustrating is Garmin Connect’s “stay tuned for more” approach to future workouts. The platform often won’t show you upcoming long runs or key sessions until just days before, making it difficult to plan your training calendar effectively. As runners, we need to see the big picture. We need to know when that crucial 20-miler is scheduled so we can plan our weekend, arrange childcare, or adjust work commitments. While you can move workouts around once they appear, long runs are major time commitments that ideally should be mapped out from day one of training until race day.

Strong foundation, but customization is key

Garmin’s marathon training plans are solid and convenient, but they’re better used as a starting point rather than gospel. By most training standards, Garmin sits on the lower end for long run distance and overall weekly mileage. Following their plan strictly would be survivable, but not ideal or practical for many runners looking to truly prepare for 26.2 miles.

Setting up your Garmin training plan

Getting started is straightforward:

1. Open the Garmin Connect app or website.

2. Navigate to Training > Training Plans,

3. Select your goal race (marathon) and target date,

4. Answer questions about your current fitness level and running experience,

5. Choose your goal (finish, set a PR, or hit a specific time).

6. The plan syncs automatically to your watch, and workouts appear in your daily training calendar.

Once set up, your watch will prompt you to start the scheduled workout when it’s time to run. The workouts include detailed instructions, target paces or heart rate zones, and real-time feedback during your run.

How to customize your Garmin training for success

Use Garmin’s adaptive features for your daily runs and speedwork, but take control of your long runs and overall mileage progression.

1. Reference an established plan

Look at free, time-tested programs—like those from Hal Higdon—to understand what your training should look like at different phases. Between one and two months out from race day, you should have several runs in the 16- to 20-mile range. Use this as your benchmark to evaluate whether Garmin’s recommendations are on track.

2. Know what to prioritize

When customizing your plan, focus on:

• Long run progression: Your longest runs should gradually build to 18-20 miles (or around three hours, for slower runners).

• Peak weekly mileage: Know what total weekly mileage you should hit during your peak training weeks.

• Consistency over perfection: It’s better to complete 90% of a slightly ambitious plan than 100% of an overly conservative one.

3. Use Garmin’s “Create Workout” feature

This is where the magic happens. Garmin allows you to create custom workouts and load them into your training calendar:

1. In Garmin Connect, go to Training > Workouts > Create a Workout.

2. Build your custom long run: Set distance goals, add fueling reminders, or program pace ranges.

3. Schedule it to replace Garmin’s recommended workout.

4. The workout syncs to your watch, giving you the same guided experience with your custom parameters.

You can create workout templates for your key long runs, tempo sessions, or any other workout you want to follow. This way, you still get the benefit of your watch guiding you through the workout with real-time feedback, but you’re following a training progression that actually prepares you for marathon day.

4. Let Garmin handle the details

While you override the long runs, let Garmin’s adaptive system manage your recovery runs and easy days, and fine-tune your speedwork intensities. This gives you the best of both worlds: proven long-run progression from established marathon programs, plus data-driven daily adjustments from your Garmin.

The bottom line

I still consider myself a loyal Garmin user—but a strategic one. The interface is excellent, the adaptive features are genuinely helpful for day-to-day training, and having structured workouts pushed to your watch eliminates decision fatigue. However, blindly following the marathon plan would have left me underprepared for race day.

With a little customization and the willingness to push beyond Garmin’s conservative recommendations, you can create a training experience that combines the best of data-driven coaching with the proven principles that have gotten millions of runners to the finish line. Your watch is a powerful training tool—just don’t let it hold you back from the big miles that make marathoners.