Running From A to F: Everything You Need to Know to Race from 5K to Marathon

Every season I get some version of the same message: "Henri, I don't know where to start." Doesn't matter if it's a first-time 5K runner or someone chasing a marathon PR — the questions overlap more than people think. So I built this A-to-F framework. It's not a gimmick. It's the six pillars I actually use in TrainingPeaks when I build a plan, whether the race is 5K or 26.2 miles.

Let's go letter by letter. Evidence included, no fluff.

A — Aerobic Base

Everything you build sits on top of your aerobic engine. Mitochondrial density, capillarization, fat oxidation efficiency — none of that develops from hammering intervals three times a week. It develops from volume run at low intensity, repeated over months.

This is where I see the most self-sabotage. Runners think base building is boring, so they skip it or shorten it. Then they wonder why their 10K workouts fall apart in week 6.

The evidence on volume matters here. A study of half-marathon runners found that both training volume and longest training run were significantly associated with race performance — but injury risk climbed when weekly volume increases were too aggressive or when the longest run exceeded a certain threshold relative to total mileage [PMID:32421886]. The takeaway isn't "more is always better." It's that base building has to be progressive and structured, not a random pile of miles.

Coach's take: I build 8-12 weeks of aerobic base before any athlete touches serious threshold work, regardless of race distance. For a 5K runner, this feels counterintuitive — "why am I running easy for two months before a short race?" Because your ceiling for VO2max and lactate threshold work is determined by how big your aerobic tank is first.

Practical takeaway: 80% of your weekly mileage should be conversational pace. If you can't hold a conversation, you're not building base — you're accumulating fatigue.

B — Biomechanics & Body Awareness

Running economy — how efficiently you convert oxygen into forward motion — is shaped heavily by biomechanics: cadence, ground contact time, vertical oscillation, and strength asymmetries. This is squarely physiological territory, and it's measurable.

As a CFSC-certified coach, I don't treat strength training as optional extra credit. Weak glutes and poor hip stability show up as compensations at the knee and ankle, which shows up as injury. This isn't opinion — it's biomechanics 101, and it's why I program 2x/week strength work for every athlete I coach, from 5K to marathon.

Coach's take: Cadence obsession is overrated. I don't chase a magic 180 spm number for every athlete — that's an average, not a prescription. What I do chase is consistency of form under fatigue. Watch your last mile of a long run. If your form falls apart there, that's your biomechanical weak link, and it's a strength-training problem, not a shoe problem.

Practical takeaway: Twice-weekly strength sessions focused on single-leg stability (step-ups, split squats, lateral band work) reduce the compensations that lead to overuse injury.

C — Cardiac Adaptation & Cardiovascular Health

Your heart is an organ that adapts to training stress just like your muscles — but it also has limits worth respecting, especially as we age.

Recent research on cardiac effects of prolonged endurance exercise compared young and older athletes and found that while both groups show beneficial adaptations from sustained aerobic training, older endurance athletes show distinct patterns in cardiac remodeling and recovery kinetics after prolonged efforts compared to younger athletes [PMID:40667749]. This matters enormously for masters runners — a population I coach and compete within myself (USATF Masters, 3000m).

This doesn't mean older runners should be scared of marathon training. It means recovery protocols, effort distribution, and volume progression need to be individualized by age and training history — not copy-pasted from a 25-year-old's plan.

Coach's take: I've had 45+ athletes tell me they