[Research Rundown] Your Inconsistent Pacing is Wasting Energy and Ruining Races (& How to Fix It)
- Jul 6
- 6 min read
Let’s say you ran your last 10K at your exact goal pace. Great! But how did it feel? Were you locked into a steady groove… or were you swinging between surging and hanging on for dear life? Because according to new research, the way you get to your average pace matters, a lot.
It turns out that inconsistent pacing with fluctuating effort - the ol’ "go fast, slow down, go fast again" routine - costs more energy, leads to more fatigue, and might be one of the biggest hidden reasons you’re not reaching your potential.
In this Research Rundown, we’re looking at a 2025 study from the ASICS Institute of Sport Science that puts two pacing strategies head-to-head. And the findings are clear: your ability to maintain a consistent effort is more important than whether your average pace hits the target. Let’s break it down.
The Study: Steady vs. Fluctuating 10K Pace Showdown
Scientists at the ASICS Institute of Sport Science in Japan wondered just how much those pace swings cost us. They took 10 experienced male runners and had them run 10K trials on a treadmill under two different conditions
Constant Pace (CON): One 10K at a steady, unchanging speed set to about 80% of the runner’s VO₂max (think of this as a challenging but sustainable effort level). No speeding up or slowing down – just cruise control.
Fluctuating Pace (FLU): Another 10K where the speed yo-yoed between a bit slower (75% VO₂max) and a bit faster (85% VO₂max) in an alternating pattern, meaning the runners kept surging and easing off, averaging out to the same intensity & pace as the constant pace trial.
Crucially, both trials were designed so that the average pace was the same. In fact, the runners finished both 10Ks in virtually identical time – about 38.6 minutes in each case. So if you only looked at finish time or average speed, you’d think both pacing strategies were equal. But the researchers dug deeper, measuring the runners’ physiological responses (what was happening under the hood of the engine, so to speak). This is where things get interesting.
The Results: Fluctuating Effort = Higher Cost
Even though the fluctuating-pace runners hit the same 38.6-minute 10K time, their bodies paid a higher price. Here’s what the study found:
Lactate Levels Were Significantly Higher in the fluctuating trial (4.5 mmol/L vs. 2.9 mmol/L in the constant run)
Breathing and Oxygen Demand Increased with fluctuating effort (higher average VO₂ and ventilation)
Perceived Exertion Was Likely Higher: though not directly reported, the increased physiological strain strongly suggests it
Abbreviations: CON, constant running speed during a 10-km running trial; FLU, fluctuating running speed during a 10-km running trial. †Significant difference versus CON. https://pubmed.ncbi.nlm.nih.gov/40010368/
The yo-yo runners were burning through more energy and accumulating more fatigue just to run the same time.
Why? Because surging and backing off throws your body into an endless loop of revving the engine and slamming on the brakes. That costs way more than cruising; you’re working harder without getting there faster. The study’s conclusion put it succinctly: the fluctuating pace “elevated physiological strain” compared to a constant speed, even with the same finish time. That extra strain is wasted effort that doesn’t translate into a faster time.
Why Pacing Consistency is a Game-Changer
Here’s where runners get tripped up: not all pace variation is bad. Sometimes your pace needs to change, but your effort should stay consistent.
✅ Varied Pacing with Even Effort = Smart Running
Pace changes, but effort doesn’t.
Hills? Slow down a bit going up, pick it up going down...but effort level feels steady.
Windy? You push harder into a headwind and ease off with a tailwind so that your effort stays even.
This is: strategic, controlled, and efficient.
Think: Running with the course, not against it.
❌ Varied Pacing with Fluctuating Effort = Energy Waster
You surge when you feel good, then slow down when you overheat.
You’re chasing splits, panicking, pushing hard, then backing off when it hurts too much.
It might “average out” to your goal pace… but your body pays a high price for the rollercoaster.
Think: Every mile is a different story, and none of them end well.
This study is all about that second scenario: the one where effort is bouncing all over the place. And the data says it loud and clear: fluctuating effort is inefficient, tiring, and counterproductive to performance.
Why Inconsistent Pacing Matters for Training & Racing
Let’s say you’ve been stuck on a plateau. You’re hitting the workouts, your weekly mileage is solid, your race pace targets are reasonable. But you still fall apart in races - going out way too fast, struggling to stay "in the groove" - , or your splits are all over the place in workouts. This might be your missing piece.
Here’s how inconsistent effort hurts you:
Wasted Energy: Every surge uses more glycogen and spikes lactate, which builds fatigue faster.
Harder to Recover: The more up-and-down your effort, the more stress you accumulate. It adds up across the week.
No Rhythm: Erratic pacing kills mental flow. You’re either trying to hold back or catch up instead of just running.
Poor Finishes: That late-race fade? Often caused by going out too fast or yo-yo pacing early on.
And it’s not just anecdotal: data from world records to amateur PRs show that runners with more consistent pacing and effort profiles tend to race faster and feel better doing it.
When You Should Change Pace (But Not Effort)
Of course, there are smart reasons to vary your pace:
Hilly Courses: You’ll naturally slow on climbs and speed up on descents. That’s fine... as long as your effort stays steady.
Trail Running: Technical terrain demands pace changes. Again, focus on consistent effort, not pace.
Windy Conditions: A hard headwind or tailwind will require pace adjustments to keep effort even.
Tactical Racing: In shorter events or competitive situations, intentional surges can be strategic, but know they come at a cost and require training.
In all of these, effort management is the key. Don’t try to force perfect mile splits if you’re climbing a mountain or dodging rocks. Instead, learn how your effort feels at different paces so you can adapt smartly.
Takeaways for Runners: How to Train for Consistent Pacing
Here’s how to apply all this to your running starting now:
Train by Effort, Not Just Pace
Get comfortable using RPE (Rate of Perceived Effort) to guide your runs. Ask, “How does this feel?” instead of “What does my watch say?”
Use Tech as a Check, Not a Crutch
Heart rate monitors and pace alerts can help, but they’re only tools. Learn how to feel your pace so you’re not reliant on tech in every situation
Practice Consistent Effort in Workouts
In tempo runs, intervals, and long runs, focus on hitting even splits and even effort. Don’t blast the first interval. Don’t die in the last mile.
Adjust for Terrain, Intelligently
Use effort as your anchor when running hills, trails, or in bad weather. Your pace will change, but your energy management stays stable.
Start Slower Than You Think in Races
Ease into your goal pace. Blasting the first mile often triggers fluctuating effort that wrecks the rest of your race.
Analyze Your Splits Honestly
Look at your last few races or workouts. Are you wildly inconsistent in your splits? That’s your red flag. Time to smooth it out.
This study isn’t just about treadmill 10Ks - it’s about how you run every single run. If you’re chasing average pace but ignoring effort, you’re probably working harder than you need to and not seeing the payoff you want.
It’s not about “perfect splits.” It’s about steady effort. That’s what unlocks breakthroughs, builds durability, and helps you run smarter, faster, and stronger.
So next time you're tempted to surge mid-run, ask yourself: Am I being smart, or am I just reacting? Then take a breath… and run steady.
Bonus Tip: The Right Watch Helps (a LOT)
If you want to get better at managing your effort and dialing in your pacing, having the right tools makes a huge difference. That’s why I recommend COROS.
COROS watches are built for serious endurance athletes and recreational runners alike. They offer:
✅ Easy-to-read pace and effort data
✅ EvoLab performance metrics (including race predictor & fatigue tracking)
✅ Customizable workout screens so you’re not glued to one number
✅ Ridiculously long battery life (no dying mid-run!)
I use my COROS Pace 3 for both real-time pacing feedback and post-run analysis to help guide smart training decisions.
🎁 Want one? Use my code RUNEXP when purchasing from coros.com and you’ll get a FREE second watch band with your order (add 2nd band to cart -> enter promo code!)
Want to learn how to pace smarter using your COROS? Listen to or watch this episode of The Running Explained Podcast where I dig into how to use your watch to master pacing strategies that actually work!
Sources:
Sumi D, Takii Y, Abe S, Sakaguchi M. Fluctuating Running Speed During 10-km Running Elevates Physiological Strain [published correction appears in Int J Sports Physiol Perform. 2025 Apr 16;20(6):885. doi: 10.1123/ijspp.2025-0153.]. Int J Sports Physiol Perform. 2025;20(6):764-769. Published 2025 Apr 16. doi:10.1123/ijspp.2024-0445
Want a training plan that teaches you HOW to train like a pro? Check out the downloadable training plans and coaching options at Running Explained. Your breakthrough could be just one training cycle away!
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