I Asked an Elite Marathoner (and Exercise Physiologist) Every Question I Had About Running

Brady Holmer on building a smarter training week, Zone 2, VO₂ max, fuelling, strength training, shoes, and injury prevention

One of my favorite parts of having an online presence is getting to connect with interesting people from around the world and, somewhat selfishly, getting to ask them all the questions that have been rattling around in my head.

I’ve become more serious about running over the past few years, and also more curious about the physiology behind it: Zone 2, VO2 max, threshold training, fueling, shoes, injury prevention, and why some runners keep improving while others plateau.

So I asked Brady Holmer, exercise physiologist, 2:24 marathoner, and author of the popular Physiologically Speaking newsletter.

He’s one of the rare people who can explain the science and actually live it himself.

I came in with my full list of burning questions. He answered every one, and he did not disappoint.

Here’s Brady:

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A lot of runners hear that most of their training should be in Zone 2. In practice, how should recreational runners identify Zone 2, and how reliable are methods like chest straps vs. wrist-based heart rate sensors, perceived effort, and the “can you hold a conversation?” test?

• The best (and simplest) way identify zone 2 is using the talk test. If you were exercising with a friend or spouse and can hold a conversation, then you can be somewhat sure that’s an intensity that roughly corresponds to zone 2 intensity. For people who want to be a bit more accurate, heart rate is a good guide, but make sure you’re using a chest strap if you want the most accurate measurement. Wrist-based heart rate is ok for resting and light activity but accuracy tends to go down if you’re moving more vigorously. I’m also a HUGE fan of perceived effort, and there are plenty of studies showing that it reliably correlates with lactate/VO2 max intensities compared to methods like heart rate and lactate. For zone 2, target a 3–5/10 effort level.

My ranking:

• Lactate measures

• (Chest) heart rate

• Wrist or arm band heart rate

• Talk test

• Perceived effort

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Once someone has a reasonable sense of their Zone 2 intensity, what percentage of their training do you think should actually be in Zone 2? Does this change depending on how much someone runs each week or what their goals are?

• Despite what you might hear about the “80/20” rule, there really no single law on how someone should distribute their training across zones in a given week—it will be highly dependent on total volume, life demands, etc. That being said, the 80/20 rule isn’t necessarily wrong and it’s a good framework once people know what it actually means: it means making 80% of your total weekly sessions lower intensity and 20% of them higher intensity. It does NOT refer to time distribution. For example, if someone runs 5x per week, then 4 of those sessions should be easier and 1 should be harder. For 6–7 sessions per week, 2 sessions can be higher intensity. But if someone is not devoting a lot of time to running—maybe 1–3 hours per week, I think nudging up the intensity on each run allows for better adaptations. Zone 2 combined with low volume may not be enough stimulus to really improve much.

• Here’s generally my recommendation: below 5–6 hours per week, don’t be afraid to do an extra run at a slightly more uptempo pace. Above 6 hours, 80/20 rule becomes a bit more valid for injury prevention.

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For someone like me who runs consistently, around 15-25 miles per week across 4-5 runs, what would a realistic training week look like if the goal is to improve fitness and race performance without making running take over their life? How would you split that week between easy runs, a long run, tempo or threshold work, strides, hills, intervals, or anything else?

• 3 runs: easy “zone 2” base building runs (3–6 miles each). You can add strides or uphill repeats to the end of 1–2 of these runs (e.g., 6x20–30” strides or uphill strides with full walk recovery).

• Workout: tempo run, intervals, threshold work (3–5 miles total)

• Long run: 7–10 miles

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What would you tell someone whose VO₂ max has plateaued after months or years of consistent training? How should they think through whether the limiting factor is training volume, intensity, threshold work, recovery, or simply how VO₂ max is being estimated?

• The easy way to determine whether volume or intensity is the limiter would be to add both (independently). Take your current workload and add easy volume. If you see VO2 max moving or trending up, maybe volume was your limiter. More often than not, if someone has been training a long time and hit a plateau, intensity will be the limiter. But you want to increase gradually. Start adding a few extra intervals or 10–25% more time to your interval session each week, rather than add an entire session.

• Recovery could be an issue if someone is training very hard and seeing no progress (that’s one definition of “overtraining”). For many full-time professionals, lack of recovery could just mean life’s demands are high in addition to training. But for most people this likely isn’t the main cause of a plateau.

• A lack of an improvement could very likely be due to measurement, and if you’re relying on a smartwatch estimated number, please be careful. That value can be deflated by a run where heart rate is artificially elevated (due to heat, stress, humidity, etc.), which automatically penalizes you. I’d say if someone knows they’re training hard VO2 max isn’t budging (watch), it’s probably a measurement error versus true non-response. My advice here—do a field test (some watches have them built in) like a 12-minute run test. If that improves, it’ll track pretty well with fitness/VO2 max (you can even put your score into a calculator online).

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If someone has a very busy week and cannot train normally, what is the minimum amount of running they should do to maintain their fitness? For example, what would your “weekend warrior” or “bare minimum maintenance” protocol look like, and which types of runs should they prioritize?

• 3 runs MINIMUM — but that means frequency without respect to time. Just get out/get moving for as long as you’re able on those runs. Ideal protocol for 3 runs: 1 slow and easy, 1 hard run (tempo, intervals) and 1 run that’s ~2x distance if your long and slow run. Keep this easy.

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Running shoes have become increasingly complicated: daily trainers, plated shoes, shoe rotation, and mileage limits. What does the evidence actually suggest runners should care about, and what is mostly marketing?

• Comfort is #1. I truly mean that. Every brand nowadays has a good daily trainer, and most of the special features from brand to brand are marketing. Test a couple different brands and models of a non-plated trainer and pick the one that’s most fun to run in for you. And most comfortable.

• Rotation is important but you don’t need 10 pairs. I’d suggest 2 trainers you can rotate throughout the week (“resting” a shoe can help its lifespan). I also think everyone should have 1 “super shoe” or plated shoe for long runs and workouts, but you shouldn’t be wearing these daily! 1–2 times per week, or maybe 25% if your runs.

• The evidence on “motion control” stuff is not really there. Unless you’ve got a severe orthopedic issue, a “neutral” shoe with moderate cushion is the best choice.

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What is the simplest strength-training plan you would recommend for recreational runners who want to get faster, stay healthy, and prevent injury?

• 2–3 times per week “full body circuit” that hits 2–3 upper body/core exercises and 1–2 leg exercises. For injury prevention, you can stick to lighter dumbbells or body weight, but for performance enhancement experimenting with squats/deadlift/more advanced lifts could be helpful.

• For getting faster, plyometrics are underutilized. Jump, drop jump, skip, high knees… explosive (unweighted) movement WILL make you faster even without strength training. Primarily by enhancing neuromuscular efficiency/power output.

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What are the biggest mistakes recreational runners make that lead to injury? Are there any early warning signs that someone should reduce load before they get sidelined?

• Increasing single-run mileage too fast. Studies show that this correlates strongly to running related injuries, rather than the “total weekly mileage.” Try to refrain from increasing the distance of your longest run by more than 10–15% of the distance of your previous longest run. Don’t add speed to rapidly either. Strides are a good bridge from easy running to formal speed workouts.

• If you have something bothering you that doesn’t go away after 2–3 days of complete rest, that’s a good sign of an “injury” versus just a “pain.”

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What do runners most often get wrong about fueling, especially for long runs, half marathons, and marathons? How should people think about carbs before, during, and after running? What about hydration?

• That you NEED to fuel every training run. Don’t need to, but you can. My recommendation is usually 90 minutes or longer unless you’re running hard.

• Biggest mistake is doing something foreign or new on race day before testing in training. That means no gels, which many people end up doing because they use what the race provides to them. Bring your own or research what your goal race has available and use it in training.

• Next is trying to fuel more than you’re ready for. The gut can be trained to tolerate higher carbs, but jumping from 50 in training to 70–90 on race day is a recipe for disaster.

• Same with hydration—I’d bet many runners underfuel and over hydrate during races. Especially those who are spending more time on the course.

• Fueling after: don’t delay carbs! Protein can wait (doesn’t have to), but having a carb-containing meal or snack within 30 minutes of a training run speeds up glycogen replenishment and helps you adapt better.

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Warm-ups are another area where advice seems all over the place. For most recreational runners, is starting with a slow easy run enough, or should they be doing drills, dynamic movements, or other warm up routines before certain sessions?

• Easy running and some light dynamic drills is enough. But if it’s an easy run, the first few miles can just be the “warmup.” If you’re going to run hard, easy miles followed by strides and even a “practice repetition” slower than goal pace will help you reduce inertia and perform better on the first interval.

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How should runners think about mobility and stretching? What is actually useful, how much should people do each week, and what routines are most beneficial?

• The evidence here is SPARSE. My answer is do what you think you need. Extra tightness or notable lack of mobility could require attention. But nobody needs a daily 30-minute “stretching routine” just because.

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For readers who want to learn more about running science, endurance training, and performance, where should they follow your work? Could you also tell us a bit about your newsletter and what you cover there?

• Substack is the best place—I write a weekly newsletter on a study I found interesting and worth sharing, and I publish my own training quite often as well (I shared my entire training log leading up to last year’s Boston marathon). I also share a lot of science and personal advice on X (@brady_h).

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This newsletter is for educational purposes only. It is not personal medical advice. Opinions are my own. Always consult your own health-care provider for medical guidance.