Issue #11: Negative Split Pacing

✍️ Author’s Note

Welcome to this edition of the Threshold Lab newsletter! I’m Stephen Pelkofer, an aspiring HYROX Elite 15 athlete with a men’s pro personal best of 59:41 and men’s pro doubles best of 51:39.

The goal of this newsletter each week is to pick a training topic related to running or HYROX, do deep research into it, and provide actionable protocols that the reader can take away and apply to their training immediately. Let me read the research, listen to the experts, and then give you the tools to make it work for you.

Side note this week: check out the Next Level Physio podcast that Dylan Scott and I were on last week - we get into the details of HYROX training, racing, and coaching.

😁 Work with Me

I have helped many athletes either achieve a new PR or prepare for their first race. Fill out the 1:1 intake form below if you want a free consult – you can also signup for a free call with me through this booking link here.

👨‍💻 Introduction

Topic: Negative Splits: The Science of Finishing Stronger

A “negative split” is a pacing strategy where you complete the second half of a race faster than the first. This approach, often used by elite marathoners, gets attention for one simple reason: it usually leads to better performance. By holding a little in reserve early on, athletes can avoid the dreaded slow down and finish strong. In this issue, we dive into the physiology behind why starting conservative can pay off, how pacing strategies differ in a 5K vs. a half-marathon, and what this means for events like HYROX (which last about an hour, similar to a 10K-half marathon, but with added muscular fatigue from functional exercises).

For this research, I focused on the following sources:

1. The physiology and psychology of negative splits: insights into optimal marathon pacing strategies

2. Pacing profiles and tactical behaviors of elite runners

⚡ Fast Finds for the busy reader

• Fuel efficiency wins: Starting slower conserves glycogen and uses more fat for fuel, delaying fatigue and the infamous “wall”.
  

• Stay cool and steady: A controlled first half reduces heat buildup and cardiovascular strain, so you don’t overheat or redline before the finish.
  

• Short vs. long: In a 5K you might sprint and kick (U-shaped pacing), but for longer races, even or negative splits yield better overall times.

🔬 Deep Dive

Why do negative splits work? It comes down to managing your body’s resources. If you blast off the start line, you burn through muscle glycogen faster and accumulate lactate and acid byproducts early. This leads to premature fatigue and a likely late-race slowdown. A negative-split strategy avoids this by spreading out energy expenditure. Early on, a slower pace means a greater fraction of energy comes from fat oxidation instead of carbs, saving your limited glycogen for when you really need it. The payoff: runners who hold back then accelerate often achieve better overall times and suffer less of a performance decline in the final miles. There’s also a neuromuscular benefit – conserving fuel helps your muscles stay coordinated and your running form won’t be as sloppy late in a race because of it.

Negative splits also aid in thermoregulation. A hot start generates excess heat that your body struggles to dissipate, especially in warm or humid conditions. Opening at a steadier, lower intensity helps keep your core temperature cooler for longer and buys time before heat-induced fatigue hits. Similarly, your heart rate rises more gradually. A moderate start prevents the early spike that contributes to cardiovascular drift (that creep of heart rate upward even at steady effort). The result is a more stable cardiac output and better blood flow to your muscles in the later stages. You feel strong instead of spent at the end because you didn’t spend all your chips in the first half. Even perceived effort is lower for the first part of a negative-split race, which means mentally you stay calmer and more in control. Instead of hanging on for dear life, you can make strategic moves and actually race in those closing miles

Does this apply to all race distances? Pacing strategy differs by race length. In short races like a mile or 5K, the intensity is near your max aerobic capacity – athletes often go out fast and rely on a final kick. Many 5K/10K world records show a U-shaped curve: blistering first lap, a steadier middle, then a fast finish. That’s partly due to racing tactics and the shorter time frame; there’s less time to negative-split, and a quick start can be necessary. But as distance increases, the balance shifts strongly toward even or negative pacing. The longer the race, the more critical energy management becomes. Positive splits (fast start, slow finish) are common in inexperienced runners and in championship-style racing, but they usually result in suboptimal times. By contrast, negative splitting is the standard for many record performances. In fact, most world records from 1500m up through the marathon have been achieved with a negative or even splits. Even mid-distance elites have learned that holding a little something in reserve leads to a stronger finish. For half-marathons and beyond, a conservative start is almost always the smart move for the best overall result.

Does this apply to all athletes? It’s hard to say – most research is focused on elite athletes and not recreational runners. These athletes are often racing in good conditions on flat courses with pacers aiding them. For a recreational runner that is prepping for a hilly 10k or half-marathon, negative splitting might not be possible. Regardless, it’s likely a worthwhile investment for anyone to get more pacing awareness in training and racing.

HYROX Athletes: should we do a deep dive on elite 15 and top pro racers to see if negative or even splits work? We often hear about how athletes go out way too fast on the first run and the ski erg, but I’ve yet to see any good data analysis to support that going out conservative is better or worse for placement in races. Reply to this email if you want to see a deep dive! Maybe we will do a collaboration with our friends at RoxOpt to explore this.

Time for the lab notes ⬇️

🧪 Lab Notes

In every issue of this newsletter, the “Lab Notes” are going to be the protocols that you can apply to your training and routine right away. The goal of this section is to translate the science into actionable steps for the reader, whether you’re a recreational runner/HYROX competitor, or someone pushing the limits of their peak potential.

• Practice Progressive Long Runs: Train yourself to finish fast. For your next long run, start slower than usual and gradually speed up. Example: On a 10-mile run, run the first 5 miles at an easy, conversational pace, then crank the last 5 miles at your goal race pace or faster. Workouts like these teach your body and mind to transition from cruising to pushing when fatigued. They build confidence that you can accelerate late in a race (Check out more training tips in table 4 of this paper).
  

• Start Conservative on Race Day: Execute the negative split by design. Go into your next race with a pacing plan that has you holding back early. For instance, in a half-marathon, aim to run the first 10K slightly slower (~3-6 seconds per mile behind goal pace). It should feel almost “too easy” at the start, and that’s a good sign! Then you can crank up the pace in the second half if you’re feeling strong. This approach requires patience and trust in your training; as the Frontiers review noted, resisting the urge to bank time and instead finishing with a kick is key to negative-split success.
  

• HYROX Pacing: If you’re competing in events like HYROX, incorporate pacing practice into your training. For example, in a HYROX simulation workout, aim to complete your second half of runs/stations faster than the first. This could mean deliberately taking it easier on the first two runs and stations so that you are not overcooked by the halfway point. You can even structure interval workouts with negative splits. For example: 4 rounds of 1 km run + exercise + rest, each round a bit faster than the last. By training this way, you learn to manage your energy across modalities, keeping that heart rate in check early so you can smash the final phase with a strong finish.

That’s it for this edition of the Threshold Lab. If you enjoyed this and found it useful, please share it with a friend!