How PaceForm Plans Are Built

The majority of free half marathon training plans share the same flaw: they hand you a table of distances and paces with no explanation of why. Tuesday is a tempo run. Saturday is long. What is a tempo run doing physiologically? Why is Saturday the long run? How does this week relate to next week? The plan doesn't say.

This gap is not trivial. Runners who understand why they're doing a session run it better — they hold the right effort, they don't skip it because they don't understand its purpose, and they can make sensible adjustments when life intervenes. Understanding the reason is part of the training.

Every session in a PaceForm plan includes a plain-English rationale: what this session is training, why it sits at this point in the plan, and what it's setting up for next week. This is what makes a plan a coaching document rather than a spreadsheet.

PaceForm uses a VDOT-adjacent methodology — developed from the work of exercise physiologist Jack Daniels, who spent decades studying the relationship between running performance and physiological variables. VDOT is a single number derived from your race performance that encodes your current aerobic capacity and predicts performance across distances.

What this means in practice: a runner targeting 2:10 and a runner targeting 1:45 don't receive the same plan with different colours. The paces, the session structure, the mileage ramp, the long run distances, and the quality session formats are all calibrated to what is appropriate for a runner at your fitness level targeting your specific goal.

This is the opposite of the 'Beginner / Intermediate / Advanced' system used by most free plans. Those labels are ambiguous and often inaccurate. A runner who has been running for six years but has never followed a structured plan is not 'intermediate' in any useful sense. A runner targeting 2:00 who has run eight half marathons is not 'advanced'. VDOT-based calibration bypasses these labels entirely.

Every PaceForm plan moves through four phases, each with a distinct physiological target. The phases don't overlap — each one builds the capacity the next one requires.

• →Base phase (weeks 1–3): Aerobic foundation. High proportion of easy running at conversational pace. Builds mitochondrial density, improves fat oxidation, conditions connective tissue. No hard speed work — the body is not yet ready to absorb it.
• →Strength phase (weeks 4–6): Lactate threshold development. Weekly tempo runs at a comfortably hard pace raise the speed at which lactic acid accumulates faster than you can clear it. This is the rate limiter for runners targeting times between 1:45 and 2:30.
• →Speed phase (weeks 7–9): VO2max and race-pace specificity. Interval sessions and race-pace long run segments teach your body to sustain goal pace under fatigue. This phase is the hardest in the plan and sits here deliberately — on top of the base and threshold fitness built in phases 1 and 2.
• →Taper phase (weeks 10–12): Absorption and freshness. Volume drops 30–40% while intensity is maintained. The fitness is already built — the taper converts accumulated adaptation into race-day performance. Runners who don't taper arrive at the start line with fitness and fatigue. Runners who taper correctly arrive with fitness and fresh legs.

PaceForm plans include five run types. Each appears in the plan for a specific reason and at a specific stage. Understanding what each type does makes it easier to run at the right effort and not skip the ones that feel too easy.

• →Easy runs: conversational pace, 60–70% of max heart rate. Trains aerobic base, speeds recovery between hard sessions. Should feel almost too easy. This is intentional — 80% of your mileage should be here.
• →Tempo runs: comfortably hard, 80–85% of max heart rate. Raises lactate threshold — the pace you can sustain for about an hour. The cornerstone session for runners targeting 1:45–2:15.
• →Interval/speed sessions: significantly faster than race pace, high effort. Trains VO2max — the upper limit of your aerobic system. Appears in the speed phase only, after the aerobic base and threshold are established.
• →Long runs: easy pace, progressive distance. The primary predictor of race day fitness. Trains fat oxidation, builds mental resilience, and develops the musculoskeletal durability needed for 21 km.
• →Race pace: goal pace or slightly faster. Appears in the speed phase as segments within long runs. Teaches your body what controlled discomfort at goal pace feels like — the neurological rehearsal for race day.

Sports scientist Stephen Seiler's analysis of elite endurance athletes consistently found that 80% of training is at easy intensity and 20% at hard intensity — with very little time in the moderate zone. This pattern holds across running, cycling, rowing, and cross-country skiing at the elite level, and research increasingly shows the same results apply to amateur runners.

Most amateur runners accidentally do most of their running at moderate intensity: too fast to be genuinely easy, too slow to be genuinely hard. This produces some fitness but is suboptimal for both aerobic base development and anaerobic threshold adaptation.

PaceForm plans are structured to reflect this distribution. Three to four of your runs per week are genuinely easy. One run per week (in the strength and speed phases) is genuinely hard. The easy runs aren't filler — they're doing real physiological work, and they make the hard sessions productive rather than survival exercises.

Missing sessions is normal — every plan assumes some will be skipped. The rules for handling a missed easy run, a missed tempo, or a missed week are printed in your PDF so you never need to figure out the arithmetic yourself.

The core principle: never try to make up missed sessions by doubling up the following week. For easy runs, skip and move on. For quality sessions (tempo, intervals), reschedule within 48 hours or drop entirely. For a missed week due to illness, drop back one week in the plan and continue.