If You Can Only Do One Quality Workout a Week, Make It This One

The question I get more than you'd think

"Henri, I could only fit in one quality workout this week. Which one do I pick?"

It's not a strange question. It's the most honest one I get. Most of the runners I coach don't live in a lab of perfect periodization. They live with 50-hour work weeks, kids who get sick, delayed flights, and nights of four hours of sleep. When life hands you a single quality window in the week, the question isn't "what would be ideal?" — it's "what gets me the most marathon per minute invested?"

And the answer, almost always, is the long run with marathon-pace segments.

Why this session takes the throne

The marathon is one of the strangest events in the sport: it isn't run anywhere near VO2max. It's run at a sustained submaximal intensity that depends almost entirely on how efficiently your body uses fat and glycogen over hours, not minutes. Jones and Kirby's work on the physiological demands of running at 2-hour marathon race pace showed something that applies across performance levels: running economy, the ability to sustain a high %VO2max without accumulating metabolic fatigue, and fuel management are the three pillars that determine the outcome — not top-end speed [PMID:33151776]. That's a workout that trains all three of those pillars at once, under the same conditions (duration, cardiac drift, partial glycogen depletion) you'll be facing on race day.

No other session — not track intervals, not fartlek, not a short 20-minute tempo — reproduces that combination of muscular, metabolic, and mental stress. You can improve your VO2max with short reps. But the marathon isn't won or lost at VO2max. It's won or lost at kilometer 30, when glycogen runs thin and form starts to fall apart. That kilometer only gets trained by simulating it.

The evidence on volume and the long run

There's one data point I use constantly with my PMPRunning athletes, especially those coming up from the half marathon: Fokkema and van Damme's study on recreational runners found that both training volume and the distance of the longest run were related to performance — but also to injury risk when combined with sharp increases [PMID:32421886]. That's not an argument against the long run. It's an argument for doing it well: gradual progression, a clear purpose within the session, and not stacking it on top of an already overloaded week.

If you only have one quality session, the risk of "stacking" mostly disappears by definition — the rest of your week is already easy. That's, paradoxically, an advantage. You can afford to make this session demanding because it isn't competing with another hard stimulus.

What the session looks like in practice

I'm not talking about running a full 20 miles at marathon pace. For most recreational runners, that's a recipe for acute overtraining and a forced recovery week. The structure I use with intermediate and advanced athletes is progressive:

Typical structure (for a runner with a reference marathon between 3:30 and 4:15):

• 15–20 minutes of easy activation jogging
• 2–3 miles at easy pace, letting the body genuinely warm up
• The core block: 5 to 10 miles at marathon pace (volume depends on the phase of the block and the athlete's history)
• 2–3 miles of cooldown jogging

For more advanced runners, with a sub-3:15 marathon, that marathon-pace block can sit in the second half of an 18–20 mile long run, simulating exactly the accumulated fatigue they'll face on race day. For less experienced runners or those with an injury history, I prefer to break it up: two or three marathon-pace blocks of 15–20 minutes separated by 5 minutes of jogging, within the same long run. You get the metabolic stimulus without the mechanical risk of holding form under extreme fatigue for too long at a stretch.

What's happening in your heart during this session (and why it matters)

Something I talk about a lot with masters athletes, since I compete in that category myself: prolonged effort isn't free for the heart, even in healthy, well-trained runners. A recent analysis on the cardiac effects of prolonged endurance exercise in young and older athletes showed that long efforts produce measurable cardiac responses — acute changes in ventricular function that, in most cases, resolve with proper recovery, but that become more pronounced with age and with a lack of gradual progression [PMID:40667749]. A long-term follow-up in recreational marathon runners also documented changes in ventricular function associated with repeated exposure to efforts of this duration [PMID:41370052].

This isn't an alarm bell. It's a concrete reason not to wing the marathon-pace long run as if it were "run fast for a long time and see what happens." Gradual volume progression, real recovery between demanding sessions, and attention to early signs of overload (elevated resting heart rate, disrupted sleep, disproportionate perceived effort) are non-negotiable parts of how I structure this session, especially for masters athletes.

How to know if your body is absorbing the stimulus

You don't need a lab to monitor this, but it's worth mentioning where the science is heading: the field of exercise biomarkers is getting increasingly precise at identifying markers of accumulated fatigue and incomplete recovery, beyond what an athlete reports subjectively [PMID:41922043]. In day-to-day practice, without access to those markers, I use simple, reliable proxies: resting heart rate on waking, perceived sleep quality, and whether marathon pace "feels" like the same effort week to week or starts costing more for the same pace. That last one — perceived effort drift at a constant pace — is, to me, the most honest signal I have without lab technology.

What to do with the rest of the week

If this is your only quality session, the rest of the week needs to protect it, not compete with it. That means:

• Genuinely easy jogs on the remaining days, without the temptation to "sneak in a little pace" midweek
• A full rest day or light cross-training before the key session, so you arrive with fresh legs
• Don't chase mileage — if time is limited, prioritize the quality of this session over piling on more easy volume
• Sleep before everything else — given what the evidence shows about the cardiac load of prolonged effort, recovery isn't optional, it's part of the training

My take as a coach

Over more than one season I've watched athletes on five-quality-sessions-a-week plans arrive at the start line more broken down than the ones who did a single well-executed session, week after week, for 12 to 16 weeks. Consistency with one specific, well-dosed session beats, in most of the real cases I see, the ambition of a plan nobody can actually sustain alongside their real life.

If your week only gives you one quality window, don't waste it on speed you won't use in the marathon. Use it to train exactly what race day will demand of you: holding a specific pace, under accumulated fatigue, for a long time. That's the skill. Train it.

Key takeaways

• The marathon-pace long run trains the three real determinants of performance in the event: running economy, metabolic efficiency, and fuel management [PMID:33151776]
• Volume and the distance of the longest run are associated with better performance, as long as progression is gradual and not stacked onto an already loaded week [PMID:32421886]
• Prolonged effort produces a real, measurable cardiac load, more relevant for masters athletes; progression and recovery are not optional [PMID:40667749][PMID:41370052]
• If you only have one quality session a week, protect it by keeping the rest of the week genuinely easy
• Monitor simple signals: resting heart rate, sleep quality, and perceived effort drift at a constant pace

References

1. Jones AM, Kirby BS. Physiological demands of running at 2-hour marathon race pace. J Appl Physiol (1985). 2021. [PMID:33151776]
2. Fokkema T, van Damme AADN. Training for a (half-)marathon: Training volume and longest endurance run related to performance and running injuries. Scand J Med Sci Sports. 2020. [PMID:32421886]
3. Frandsen J, Aaroe M. Cardiac Effects of Prolonged Endurance Exercise in Young and Older Athletes. Scand J Med Sci Sports. 2025. [PMID:40667749]
4. Schindler MJ, Schoenfeld J. Long-Term Changes in Ventricular Function in Recreational Marathon Runners. JAMA Cardiol. 2026. [PMID:41370052]
5. Siebers M, Bizjak DA. Exercise biomarkers. Adv Clin Chem. 2026. [PMID:41922043]