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I’ve recently had a shocking change of heart as a runner: I no longer dread the treadmill. What changed? For one, poor air quality has left me no other choice. And secondly, I stopped using the treadmill solely for speed workouts, and started using it for hills.
I have to admit, this change of heart comes from the trendy 12-3-30 “hot girl walk” workout. In fact, now some of my favorite training sessions happen at a walking pace on my Merach 450 walking pad right at home. The key is incline.
Whether you choose greater incline or speed drills really depends on your goals. I’m coming at this decision from the perspective of marathon training, but I know the motivator for so many gym-goers: Which one will help me lose weight?
The truth is that no individual workout is going to be responsible for weight loss. As my colleague Beth Skwarecki put it, “You lose weight by eating slightly less than you burn, measured as an average over time. Exercise can help you burn more calories, but your body often compensates by burning fewer calories when you’re at rest, so you can’t just trust a treadmill walk to burn a certain number of calories each time.”
Still, if you’re staring at your treadmill display, wondering whether you want to focus on speed or incline for a more effective workout, here’s what you need to understand to make that decision.
When to embrace the incline
When you increase treadmill incline, you’re essentially simulating uphill running or walking. (And no, you do not need to set the incline to 1% to mimic outdoor air resistance every time). Your instinct may be to hit “quick start” on the treadmill and run as fast as you can for 30 minutes, but here are reasons you might want to consider a focus on incline instead.
Building your aerobic base
For marathon training, incline walking or easy running at 3-6% grade is invaluable for base building phases. The increased workload strengthens your cardiovascular system while keeping impact relatively low. I’d recommend 30-ish minute sessions at conversational pace on 4-5% incline for runners building their aerobic foundation.
Strength training without weights
Incline training is essentially resistance training for your legs. The steep grades target your glutes, hamstrings, and calves more intensely than flat running. For marathon runners who struggle to fit gym sessions into their training schedule, 15-20 minutes of steep incline walking (8-15%) can serve as supplementary strength work.
Active recovery sessions
On easy days between hard workouts, gentle incline walking allows you to maintain training stimulus while promoting blood flow and recovery. Variations of the 12-3-30 method work well here—something challenging enough to feel productive, but gentle enough not to interfere with your next quality session.
Injury prevention
When dealing with minor injuries or returning from time off, incline walking provides cardio benefits with reduced impact stress. The controlled environment of a treadmill also allows you to gradually increase intensity as you heal.
When to keep to keep it flat
It can’t all be walking up hills. I am a runner, after all. As someone who’s logged thousands of miles preparing for 26.2-mile races, I’ve learned that knowing when to keep it flat is just as important as knowing when to crank up that incline.
Speed work and intervals
Sometimes, adding incline to speed work can compromise running form and make it difficult to hit target paces. Runners doing true track-style speed workouts should generally stick to 0-1% incline. Unless you’re training for a notoriously hilly marathon (like Boston), practicing your goal race pace should happen on minimal incline.
Form focus sessions
When working on running mechanics, cadence, or efficiency, flat treadmill running provides the most stable platform. Inclines can mask form issues or even create compensatory movement patterns that don’t translate well to outdoor running.
High-volume days
Incline may be trendy, but there’s still a time and place for focusing on your VO2 max. Long runs and high-mileage weeks should prioritize time on feet over intensity. Excessive incline can turn what should be aerobic base-building sessions into more strength-focused workouts, potentially leading to overtraining and poor recovery.
My personal incline strategy
As a recent treadmill convert, my relationship with incline is finally looking strategic rather than arbitrary. Here’s how I plan to integrate incline work into training cycles:
Base phase: 2-3 weekly sessions of moderate incline (4-6%) at conversational effort, focusing on aerobic development and strength building.
Build phase: One weekly hill-specific session using steeper grades (6-12%) for shorter intervals, preparing legs for race-day climbs.
Peak phase: Minimal incline work except for race-specific preparation. If your goal marathon has significant hills, practice those specific grades and gradients.
Recovery phase: Gentle incline walking for active recovery, using methods like 12-3-30 to maintain fitness.
The bottom line
Luckily, incline and speed don’t need to be mutually exclusive. You can do hills one day, and speed work another. The key insight for runners—that going slower but steeper can be more beneficial than going faster—applies broadly to whatever training you’re doing.
Remember: the best workout isn’t necessarily the “hardest” one. Sometimes, the most productive thing you can do is slow down, turn up the incline, and let time and consistency work their magic. Other times, you’ll want to leave the incline button alone and focus on true heart-pumping cardio.
