You feel good. Your last few runs have been strong. You’re thinking about adding a few extra miles this week — maybe bumping your long run from 8 to 10, or throwing in an extra midweek run. You’ve got the energy. Why not?
This is the moment where most training apps say nothing. Your plan was set weeks ago, and if you want to manually add more, that’s on you. No guardrails. No feedback. Just a blank calendar that doesn’t care whether you’re making a smart decision or a dangerous one.
Pacewright won’t let you do that unchecked. Not because it doesn’t trust you, but because the research is clear: how fast you increase volume matters more than how much you run in absolute terms. And the right rate of increase depends on how much you’re already running.
Why the 10% Rule Falls Apart
You’ve probably heard it: don’t increase your weekly mileage by more than 10%. It’s one of the most commonly cited rules in running, and it’s a reasonable starting point. But it treats every runner the same, and that’s where it breaks down.
Ten percent of 10 miles is 1 mile. That’s a trivially small increase — barely a warm-up. A beginner running 10 miles per week could safely add more than that without blinking.
Ten percent of 60 miles is 6 miles. That’s a substantial jump for a high-mileage runner — an entire extra session’s worth of stress on top of an already demanding week. Nielsen and colleagues found in their 2014 study that the injury risk from weekly distance progression wasn’t uniform: it varied by injury type and was most pronounced at higher absolute volumes.
A flat percentage doesn’t account for this difference. What matters isn’t the percentage in isolation — it’s the percentage applied to a specific volume, combined with how long you’ve been running at that volume, combined with how your body is responding.
Mileage-Dependent Caps
Pacewright uses a tiered system where the maximum weekly increase scales inversely with your current mileage:
| Your Weekly Mileage | Maximum Weekly Increase |
|---|---|
| Under 15 miles | 20% |
| 15–30 miles | 15% |
| 30–50 miles | 10% |
| Over 50 miles | 5% |
Here’s why the tiers work this way.
Under 15 miles per week: You’re early in your running journey. Your cardiovascular system adapts quickly at this stage, and the absolute load on your musculoskeletal system is modest. A 20% increase from 12 miles is about 2.4 miles — an extra easy run or a slightly longer existing one. Your body can handle that progression.
15–30 miles per week: You’re past the beginner phase and building a real base. Adaptation is still happening, but the absolute loads are getting meaningful. A 15% increase from 25 miles adds about 3.75 miles. Still manageable, but the tissue stress is real.
30–50 miles per week: You’re running enough that your body is under significant cumulative load. A 10% increase from 40 miles adds 4 miles — and those 4 miles are landing on a body that’s already absorbing a lot of impact every week. The research from Damsted and colleagues showed that even moderate weekly distance increases in half-marathon trainees were associated with elevated injury risk when base mileage was already substantial.
Over 50 miles per week: Extreme caution. The margins at high mileage are thin. A 5% increase from 60 miles adds just 3 miles, but at this volume, that additional stress accumulates on top of an already heavy weekly load. Runners at this level are more susceptible to overuse injuries because their tissues are already operating closer to their capacity.
The Stability Bonus
There’s a reward for consistency built into the system.
If you’ve been running at a stable weekly volume for 3 or more consecutive weeks, you earn a 25% bonus on your volume cap. This means your maximum allowed increase gets multiplied by 1.25.
Example: you’re running 25 miles per week with a base cap of 15%.
- Weeks 1-2 at 25 miles: Your cap is 15%, so the maximum next week is 25 + 3.75 = 28.75 miles.
- Week 3+ at 25 miles: The stability bonus kicks in. Your effective cap is 15% × 1.25 = 18.75%, so the maximum becomes 25 + 4.69 = 29.69 miles.
Why does this make sense? Because a runner who has held steady at 25 miles for three weeks has demonstrated that their body can handle 25 miles. The tissues have adapted to that load. The tendons, ligaments, and bones have had time to remodel under the current stress. That established base earns a little extra room.
A runner who just jumped from 18 to 25 miles last week hasn’t earned that same confidence. Same volume, but the history is different — and the history matters.
The Single-Session Spike Guard
Volume caps aren’t just about total weekly mileage. How that mileage is distributed across individual runs matters just as much.
Pacewright enforces a single-session spike guard: no individual run can exceed 110% of your longest run in the past 30 days.
This catches a specific and common mistake. You’re planning a long run and thinking “I’ll just go a little farther this week.” Your long run has been 8 miles for the past month. You go out and run 12. That’s a 50% jump in a single session — even if your weekly total stayed reasonable.
The spike guard caps it. If your longest run in the last 30 days was 8 miles, your maximum for any single run is 8.8 miles. You can push your long run up, but it has to grow gradually — just like your weekly volume.
This matters because single-session load spikes concentrate all the additional stress into one bout. Your body doesn’t distribute the impact evenly across the week. A 12-mile run after weeks of 8-mile long runs creates a dramatically different tissue demand than the same extra 4 miles spread across several easy runs.
The Long Run Limit
There’s a related constraint on long runs specifically: your weekly long run should not exceed 30% of your total weekly volume.
If you’re running 30 miles this week, your long run caps at 9 miles. If you’re running 20 miles, it caps at 6.
This prevents a pattern that’s especially common among time-pressed runners: running just a few days per week with one massive long run. Three 3-mile easy runs plus a 15-mile long run adds up to 24 miles — a reasonable-sounding total. But that long run represents 63% of your weekly volume, concentrated into one session. The fatigue from that single effort disproportionately affects the rest of your week’s recovery.
Keeping the long run at or below 30% ensures that no single session dominates the training week. Your other runs — your speed work, your tempo efforts, your easy recovery runs — still have room to provide their specific stimulus without being undermined by excessive long-run fatigue.
Recovery Weeks: The Built-In Reset
Volume caps limit how fast you build. Recovery weeks limit how long you build before backing off.
Pacewright builds in planned recovery weeks using a periodization cycle:
- Standard (most runners): 3 build weeks, then 1 recovery week
- Conservative (beginners, older runners, injury-prone): 2 build weeks, then 1 recovery week
During a recovery week, your volume drops to 60-70% of your recent training load. Intensity drops too. The purpose isn’t to stop training — it’s to give your body the time it needs to consolidate the adaptations from the previous build cycle.
This is where the actual fitness improvement happens. Banister’s foundational work on the fitness-fatigue model showed that training produces both a fitness signal and a fatigue signal. During build weeks, fatigue accumulates alongside fitness. During recovery weeks, fatigue dissipates faster than fitness — so when you return to full volume, you’re genuinely fitter than when you started the cycle.
Skipping recovery weeks feels productive in the short term. Over 8-12 weeks, it leads to stagnation, persistent fatigue, and often injury. The planned reset is how you build sustainably.
How the Guardrails Work Together
No single cap tells the whole story. What makes the system work is that all the guardrails operate simultaneously on every plan update:
- Weekly volume cap checks whether your planned mileage for next week exceeds the mileage-dependent limit.
- Stability bonus adjusts that limit based on how long you’ve been at your current volume.
- Single-session spike guard checks whether any individual workout exceeds 110% of your recent longest run.
- Long run limit checks whether your long run exceeds 30% of the week’s total.
- ACWR checks whether your 7-day training load is spiking relative to your 28-day average.
- Periodization determines whether this is a build week (progress) or a recovery week (consolidate).
A workout might pass five of these checks and fail one. That one failure is enough to trigger an adjustment. The explanation tells you exactly which guardrail caught it and why:
“This week’s planned volume of 32 miles exceeds your cap. You’re currently at 26 miles/week (15-30 tier, 15% max increase). Maximum allowed next week: 29.9 miles. Your plan has been adjusted to 29 miles.”
Or: “Saturday’s long run of 11 miles exceeds your single-session limit. Your longest run in the past 30 days was 9.5 miles. Maximum allowed: 10.45 miles. Your long run has been adjusted to 10 miles.”
Every adjustment is visible. Every number is yours to examine. The guardrails aren’t hidden rules that silently modify your plan — they’re transparent constraints that you can see, understand, and track over time.
Why Constraints Make You Faster
It seems contradictory. If the goal is to get faster, why is the app limiting how much you can run?
Because the goal isn’t to run as much as possible this week. It’s to run as much as possible this year — and the year after that, and the year after that. The research is unambiguous: the runners who improve the most over time aren’t the ones who had the biggest individual training weeks. They’re the ones who stayed consistent, stayed healthy, and built gradually.
A 10-week training block with 8 good weeks and 2 weeks lost to injury produces less fitness than 10 weeks of slightly lower but uninterrupted volume. The volume caps exist to keep you in that second scenario. The constraints aren’t limiting your potential — they’re protecting it.