Long Splice

Methods

Science and research

Every rule in Long Splice comes from a numbered row in its research files. Each row says what a study found, gives the numbers, grades how strong the evidence is and notes its limits. Here is what's in them, and how they shape your plan.

467
research papers behind the rules
1096
graded rules in the research files
67%
come straight from published research, 154 of them from trials
2006–2026
publication years, median 2021

The library

Fig. 1 The research library, by topic
Heat82Ultra running75Injury, load and recovery59Beginners, age and health34Strength training33Running after birth33Hills, speed and economy31Long runs, taper and pacing28Training and intensity23Food and weight22Coming back22Readiness18
Heat82Ultra running75Injury, load and recovery59Beginners, age and health34Strength training33Running after birth33Hills, speed and economy31Long runs, taper and pacing28Training and intensity23Food and weight22Coming back22Readiness18
Show the numbers
TopicPapers
Heat82
Ultra running75
Injury, load and recovery59
Beginners, age and health34
Strength training33
Running after birth33
Hills, speed and economy31
Long runs, taper and pacing28
Training and intensity23
Food and weight22
Coming back22
Readiness18

Papers behind the app's rules, grouped by subject. Most are open-access full texts on PubMed Central, read in full rather than from their abstracts. Strength has its own file, strength-rules.md, added in November 2026.

Fig. 2 How recent the evidence is
01223200620122014201620182020202220242026
0122320062014201820222026
Show the numbers
YearPapers
20062
20112
20121
20135
20143
20158
20165
20179
20189
201916
202018
202123
202218
202318
202415
202523
202621

Publication year of the papers with a known year. The median paper is from 2021, and 136 of 196 were published in 2020 or later.

Fig. 3 How strong the evidence is behind each rule
Training plans0: 41411: 1031032: 28283: 164: 25255: 102102Strength0: 19191: 24: 555: 2222Speed, hills and economy0: 13131: 11114: 335: 1818Long runs, taper and pacing0: 21: 19192: 14: 25: 2323Injury, load and recovery0: 661: 884: 13135: 1717Beginners, age and sex0: 331: 20204: 445: 1313Heat0: 771: 10104: 14145: 1919Training in the heat once used to it0: 661: 13134: 665: 1313Heat warnings people act on0: 13131: 15154: 775: 1313Food and weight0: 21211: 12124: 63635: 1515Running after birth0: 331: 14145: 2323Coming back after injury0: 31: 884: 20205: 2323Coming back after surgery or illness0: 441: 664: 885: 1212Readiness from your watch0: 10101: 10104: 335: 1414Ultras, 50 km to 50 mi0: 11: 43434: 445: 1616Ultras, 100 km to 100 mi0: 21: 62624: 25: 1919
  • Trials
  • Studies of runners
  • Top runners
  • Published plans
  • Expert reviews
  • Coaching judgement
Training plans0: 41411: 1031032: 28283: 164: 255: 102102Strength0: 19191: 24: 555: 2222Speed, hills and economy0: 13131: 11114: 35: 1818Long runs, taper and pacing0: 21: 19192: 14: 25: 2323Injury, load and recovery0: 661: 884: 13135: 1717Beginners, age and sex0: 31: 20204: 445: 1313Heat0: 771: 10104: 14145: 1919Training in the heat once used to it0: 661: 13134: 665: 1313Heat warnings people act on0: 13131: 15154: 775: 1313Food and weight0: 21211: 12124: 63635: 1515Running after birth0: 31: 14145: 2323Coming back after injury0: 31: 884: 20205: 2323Coming back after surgery or illness0: 441: 664: 885: 1212Readiness from your watch0: 10101: 10104: 35: 1414Ultras, 50 km to 50 mi0: 11: 43434: 45: 1616Ultras, 100 km to 100 mi0: 21: 62624: 25: 1919
  • Trials
  • Studies of runners
  • Top runners
  • Published plans
  • Expert reviews
  • Coaching judgement
Show the numbers
AreaTrialsStudies of runnersTop runnersPublished plansExpert reviewsCoaching judgement
Training plans41103281625102
Strength19200522
Speed, hills and economy131100318
Long runs, taper and pacing21910223
Injury, load and recovery68001317
Beginners, age and sex32000413
Heat710001419
Training in the heat once used to it61300613
Heat warnings people act on131500713
Food and weight2112006315
Running after birth31400023
Coming back after injury38002023
Coming back after surgery or illness4600812
Readiness from your watch101000314
Ultras, 50 km to 50 mi14300416
Ultras, 100 km to 100 mi26200219

Every rule in the research files is graded. Trials are randomised trials or meta-analyses. Coaching judgement marks a choice the app makes where no study tests it directly, and each one is anchored on the evidence rows it's built from.

How a plan is built

Fig. 4 One marathon plan, week by week
03162.5W1W3W5W7W9W11W13W15W17W19
  • Base
  • Build
  • Race prep
  • Taper
03162.5W1W5W9W13W17W19
  • Base
  • Build
  • Race prep
  • Taper
Show the numbers
WeekPhasekm
1Base39.5
2Base41.5
3Base43
4Base, lighter week32
5Base45
6Base45
7Base48
8Build, lighter week33
9Build50
10Build52.5
11Build53
12Build, lighter week41
13Race prep57.5
14Race prep61.5
15Race prep62.5
16Race prep62.5
17Taper44
18Taper38
19Taper25

Weekly distance from a real plan the engine builds for a middle-volume runner, race week excluded. Each week rises by at most the larger of 3 km or 9% (rule P-D1) [1]. Every 4th week drops about 30% (P-D3, the faded bars) [2]. The taper shrinks distance but keeps a quality session, which is what trials found works (T-D1 to T-D4) [3][4].

Fig. 5 How hard the running is, by time
Published plans, high0: 8282%1: 1010%2: 88%Published plans, middle0: 7676%1: 1818%2: 66%Published plans, low0: 7878%1: 1717%2: 5Long Splice, marathon0: 7878%1: 1616%2: 66%Long Splice, half0: 7878%1: 1414%2: 88%Long Splice, 10K0: 8080%1: 1010%2: 1010%Long Splice, 5K0: 8080%1: 88%2: 1212%
  • Easy
  • Moderate
  • Hard
Published plans, high0: 8282%1: 1010%2: 8Published plans, middle0: 7676%1: 1818%2: 6Published plans, low0: 7878%1: 1717%2: 5Long Splice, marathon0: 7878%1: 1616%2: 6Long Splice, half0: 7878%1: 1414%2: 8Long Splice, 10K0: 8080%1: 1010%2: 1010%Long Splice, 5K0: 8080%1: 82: 1212%
  • Easy
  • Moderate
  • Hard

Roughly four fifths of the running is easy, in published marathon plans at every volume (D-4) [1] and in world-class runners (D-5) [5]. In trained runners no one split, polarised or threshold, has been shown to beat the others (D-1) [6], so the app uses one sensible mix and shifts it by race distance (D-D3).

Fig. 6 Tapering and marathon time
Strict, 3 weeks4.16 minStrict, 2 weeks3.68 minStrict, 4 weeks3.67 minRelaxed, 3 weeks2.97 minStrict, 1 week2.43 minRelaxed, 2 weeks2.32 minNo taper0 min
Strict, 3 weeks4.16 minStrict, 2 weeks3.68 minStrict, 4 weeks3.67 minRelaxed, 3 weeks2.97 minStrict, 1 week2.43 minRelaxed, 2 weeks2.32 minNo taper0 min
Show the numbers
TaperMinutes faster
Strict, 3 weeks4.16
Strict, 2 weeks3.68
Strict, 4 weeks3.67
Relaxed, 3 weeks2.97
Strict, 1 week2.43
Relaxed, 2 weeks2.32
No taper-0.06

Minutes faster than a relaxed one-week taper, in 158,117 marathon runners (T-8) [4]. Strict means every week lower than the one before. The app tapers a marathon over a strict 3 weeks. This is an association, and faster runners may simply taper more.

Strength

Fig. 7 Load through the leg on every stride, at an easy 10 km/h
Achilles tendon7.3×8.2×8.7×Quadriceps6.3×6×5.1×Kneecap joint5.4×5.2×4.3×
  • Heel strike
  • Midfoot
  • Forefoot
Achilles tendon7.3×8.2×8.7×Quadriceps6.3×6×5.1×Kneecap joint5.4×5.2×4.3×
  • Heel strike
  • Midfoot
  • Forefoot
Show the numbers
StructureHeel strikeMidfootForefoot
Achilles tendon7.38.28.7
Quadriceps6.365.1
Kneecap joint5.45.24.3

Peak force as a multiple of body weight (ST-2) [7]. The Achilles takes the most, whichever way you land, which is why every strength session has a calf move and moves it to one leg early. Tendons only got stiffer under loads above about 70% of maximum effort (ST-16) [8].

Fig. 8 Which strength training improves running economy
Heavy and jumping combined0.43Heavy, 80% of max or more0.27Jumping alone0.12
Heavy and jumping combined0.43Heavy, 80% of max or more0.27Jumping alone0.12
Show the numbers
MethodEffect sizeSignificant
Heavy and jumping combined0.426Yes
Heavy, 80% of max or more0.266Yes
Jumping alone0.122No

Effect size on running economy, larger is better (S-ST-2) [9]. Heavy work and heavy work combined with jumping both helped; jumping alone didn't reach significance (the grey bar). Across trials strength made running 2 to 8% more economical and races up to 10 km 2 to 4% faster (S-ST-1) [10].

Rules in the app

A sample of what the engine does, with the rule it follows. Rule IDs match the research files, and each session in the app cites its own in How & why.

What the app doesRuleEvidenceSource
Weekly distance rises by at most 3 km or 9%P-D1Coaching judgement[1]
Every 4th week is about 30% lighterP-D3Coaching judgement[2]
At most one hard session in any 48 hoursD-D2Coaching judgement[1]
Easy runs are set by feel, with pace as a guide onlyZ-D2Coaching judgement[11]
Marathon taper: strict, 3 weeks, quality keptT-D1Coaching judgement[4]
Strength: 2 sessions a week, 1 in race prep, none in the last 10 daysS-D15Coaching judgement[10]
Strength moves stay for 3 weeks, then step upST-D12Coaching judgement[12]
Calf work in every strength sessionST-D4Coaching judgement[7]
Jumping counted in foot contacts by level and ageST-D13Coaching judgement[13]
Strength kept 2 days from the long run where it can beST-D17Coaching judgement[14]
No run more than 10% longer than your longest in the past monthBA-D3Coaching judgement[15]
Run-walk adds at most 10% running a session, building to 30 minutes in 8 weeksBA-D1Coaching judgement[15]
Under 18: up to a half marathon; under 16: 10K; at 13: 5KBA-D7Coaching judgement[16]
Heat stress from temperature and humidity sets five bands of adviceHT-D2Coaching judgement[17]
After a break, the first week back is about 25% lighterIL-D11Coaching judgement[18]
Marathon goals checked against half marathon time × 2.17LP-D16Coaching judgement[19]

What the app doesn't claim

Some running advice is repeated so often it sounds settled. These are the claims the evidence didn't support, so the app doesn't make them.

Common claimWhat the evidence saysRule
The 10% a week ruleNothing in the library supports it for weekly totals. Published plans add 2 to 3 km a week. The 10% limit the app does use is on single runs (BA-D3). [1]N-1
Strength work prevents running injuryNot shown. The strength reviews didn't measure injury, so the app recommends strength for performance only. [20]N-9
Lighter weeks reduce injuryNo trial has tested it. The app keeps them because trained runners' plans use them. [21]N-2
Polarised training is bestIn trained runners it was no better than other mixes for race performance. [6]D-1
Cycling can stand in for runningSmall trials found no difference, which isn't the same as showing they're equal. [22]N-8
Ice baths, massage or compression speed recoveryNo recovery method was consistently better, so the app doesn't schedule any. [23]P-8

Limits

Most trials are small, short and run on trained men, and many findings come from studies that show an association rather than cause. Where no study tests a choice directly, the app labels it as coaching judgement. No doctor, physio, dietitian or coach has reviewed the plans. They're general information, not medical advice.

References

  1. Knopp M 2024. Quantitative Analysis of 92 12-Week Sub-elite Marathon Training Plans.. PMC11065819
  2. Filipas L 2022. Effects of 16 weeks of pyramidal and polarized training intensity distributions in well-trained endurance runners.. PMC9299127
  3. Wang Z 2023. Effects of tapering on performance in endurance athletes: A systematic review and meta-analysis.. PMC10171681
  4. Smyth B 2021. Longer Disciplined Tapers Improve Marathon Performance for Recreational Runners.. PMC8506252
  5. Haugen T 2022. The Training Characteristics of World-Class Distance Runners: An Integration of Scientific Literature and Results-Proven Practice.. PMC8975965
  6. Silva Oliveira P 2024. Comparison of Polarized Versus Other Types of Endurance Training Intensity Distribution on Athletes' Endurance Performance: A Systematic Review with Meta-analysis.. PMC11329428
  7. 2025, Achilles, plantar fascia and patellofemoral loads by foot strike. PMC12590200
  8. Bohm 2015, tendon adaptation meta-analysis. PMC4532714
  9. Llanos-Lagos C 2024. Effect of Strength Training Programs in Middle- and Long-Distance Runners' Economy at Different Running Speeds: A Systematic Review with Meta-analysis.. PMC11052887
  10. Blagrove RC 2018. Effects of Strength Training on the Physiological Determinants of Middle- and Long-Distance Running Performance: A Systematic Review.. PMC5889786
  11. Emig T 2020. Human running performance from real-world big data.. PMC7538888
  12. Baz-Valle 2019, random exercise variation RCT. PMC6934277
  13. Eihara 2022, heavy vs plyometric training meta-analysis. PMC9653533
  14. de Carvalho e Silva 2022, acute effects of strength training on running, meta-analysis. PMC9385928
  15. Frandsen 2025, high-risk running sessions in 5,205 Garmin runners (BJSM). PMC12421110
  16. Athletics Australia FIT model, minimum age recommendations for road distance events, updated January 2025.
  17. Grundstein 2019, Falmouth heat stroke, WBGT and race pace. PMC7739836
  18. Girardi 2020, detraining effects prevention (perspective). PMC7593778
  19. Vickers 2016, race times and prediction in 2,303 recreational runners. PMC5000509
  20. Wu H 2026. Associations between training behaviors and injuries in performance-oriented parkrunners using traditional statistical methods and machine learning.. PMC13489425
  21. Costa P 2019. A Randomized Controlled Trial Investigating the Effects of Undulatory, Staggered, and Linear Load Manipulations in Aerobic Training on Oxygen Supply, Muscle Injury, and Metabolism in Male Recreational Runners.. PMC6646634
  22. Menges T 2026. Cross-training between running and cycling: effects on VO<sub>2</sub>max and running performance-a systematic review and meta-analysis.. PMC13243379
  23. Li S 2024. Effectiveness of Recovery Strategies After Training and Competition in Endurance Athletes: An Umbrella Review.. PMC11098991