Half Marathon Series, Week 4: Where Should You Be Today?

Four Weeks In

If you started this series on October 22, today you're standing at a specific point on the road: week 4 of 16. It's not a magic week. But it is the first one where the body starts giving clear signals about whether the plan is working — or whether something is quietly piling up wrong: fatigue that won't clear, sleep that isn't enough, a knee that gives a warning before it actually hurts.

This post is short on purpose. I want you to be able to read it in the time it takes to cool down after a run, and walk away with one question answered: am I where I should be?

What You Should Be Running Right Now

The structure of this series follows the most well-validated principle in half marathon preparation: weekly volume and long run distance predict performance — but only up to a point, beyond which injury risk starts to outweigh the benefit [PMID:32421886]. The study by Fokkema and colleagues, which followed thousands of Dutch recreational runners, found that more kilometers per week and longer long runs were associated with better finish times — but also with more injuries when the increase was abrupt. The plan in this series is designed precisely in that middle zone: enough stimulus, without crossing the line.

Here's how the progression looks for the first four weeks:

Week	Weekly Volume	Long Run	Easy Pace
1	15–18 mi	5 mi	Conversational, zone 2
2	17–20 mi	6 mi	Conversational, zone 2
3	18–21 mi	7 mi	Conversational, zone 2
4	16–19 mi (cutback week)	5.5 mi	Conversational, zone 2

Notice that week 4 drops down? That's not a typo. It's intentional. After three weeks of progressive loading, the body needs a week to absorb the stimulus before building further. If your week 4 looks like this table — give or take a mile or two — you're on track.

The easy pace, in every one of these weeks, should feel easy. That's not a soft suggestion — it's the point where aerobic base gets built without paying the price of accumulated fatigue that later steals quality from your harder weeks.

The Three-Question Self-Check

Before moving on to week 5, answer these three questions honestly. You don't need to justify the answer — just answer yes or no.

1. Did you complete at least 80% of your planned mileage over the last three weeks? I'm not talking about perfection. I'm talking about reasonable consistency. If you missed a day because of rain or work, that's fine. If you missed half your runs for multiple weeks, that's important information.

2. Did this week's long run feel controlled in the final third, not desperate? This one matters. The long run shouldn't turn into a survival test. If the last 2–3 miles felt like a fight against an out-of-control heart rate, your volume or your pace is above what your current fitness can handle.

3. Are you sleeping and recovering roughly the same way you did before starting the plan? If you're noticing persistent fatigue, irritability, or needing more coffee than usual just to get moving, your body is talking to you. It's worth listening now, in week 4, when it's cheap to correct — not in week 10, when it's expensive.

If you answered yes to all three, you're exactly where you should be. Keep going.

If You've Fallen Behind, Here's What NOT to Do

If you answered no to one or more of these questions, I want to be direct with you: don't try to make up for it by stacking extra miles next week. It's the most common — and most costly — mistake I see in runners who fall behind on a plan.

The temptation makes sense: "I missed two runs, so I'll add them in this week to not fall behind." But the body doesn't operate on linear accounting. Training stress accumulates nonlinearly, and cramming two weeks of load into one tends to produce exactly the kind of injury that Fokkema's study documented when volume increases came too fast [PMID:32421886].

What you should do instead: repeat the week you fell behind on. If you were in week 3 and missed it, go back and run week 3 exactly as written — not a compressed version of weeks 3 and 4 combined. The 16-week plan has room for this. Losing one week of real progression doesn't take you out of contention for half marathon day, as long as you don't try to "make up lost time" with doubled volume.

This applies whether you got sick, traveled for work, or just had a rough week of life in general. Repeating a week isn't failing. It's training with intelligence.

A Thought on Why This Matters So Much

I understand the anxiety of feeling like the calendar is moving faster than your preparation. I compete in the masters category on the track — the 3000m — and I know that feeling well: looking at the race calendar and sensing that your body isn't quite in sync with the plan. The difference between a runner who reaches the start line healthy and one who doesn't often has nothing to do with who trained harder. It has to do with who respected the recovery signals in time.

There's also a benefit we rarely mention in these series: consistent aerobic training, even during these building phases, has measurable effects on brain function. The meta-analytic review by Szuhany and Bugatti showed that regular exercise consistently increases brain-derived neurotrophic factor (BDNF), a protein linked to better memory, mood, and neural plasticity [PMID:25455510]. In other words: these weeks of easy runs and controlled long runs aren't just building your endurance for November — they're building something longer-lasting too.

And on the general safety of this effort: accumulated evidence on marathons and half marathons continues to show that, for healthy runners training progressively, serious cardiac events are extremely rare [PMID:31321073]. Recent research on the cardiac effects of prolonged endurance exercise in both younger and older athletes reinforces that the heart adapts well to repeated aerobic stress when the load is built gradually — not imposed all at once [PMID:40667749]. That, again, is the underlying reason behind the cutback week you just completed.

What I'm Taking From This Week

If you're within the range of the table, follow the plan as written. If you fell behind, repeat the week — don't double it up with the next one. And if the three questions left you unsure, reach out or adjust before moving forward. There are twelve weeks left. There's plenty of time to arrive in good shape, as long as you don't try to shortcut the process.

See you in week 5.

References

• Fokkema T, van Damme AADN, et al. 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]
• Szuhany KL, Bugatti M, et al. A meta-analytic review of the effects of exercise on brain-derived neurotrophic factor. J Psychiatr Res. 2015. [PMID:25455510]
• Dayer MJ, Green I. Mortality during marathons: a narrative review of the literature. BMJ Open Sport Exerc Med. 2019. [PMID:31321073]
• Frandsen J, Aaroe M, et al. Cardiac Effects of Prolonged Endurance Exercise in Young and Older Athletes. Scand J Med Sci Sports. 2025. [PMID:40667749]
• Couvert A, Goumy L, et al. Effects of a Cycling versus Running HIIT Program on Fat Mass Loss and Gut Microbiota Composition in Men with Overweight/Obesity. Med Sci Sports Exerc. 2024. [PMID:38233990]