Question 27

Do pacing changes follow distance or elapsed time?

For runners whose first slow section ended at 15.53 mi, median arrival there was 98 minutes in the under-4-min/mi early-pace group and 178 minutes in the 6-min/mi-or-slower group. Distance and elapsed time describe different aspects; these observations do not identify the cause of slowing.

The timing mats locate the first slow section, not the exact instant the pace changed. This descriptive comparison cannot identify a distance-driven or time-driven cause.

2,253,478 eligible finishes

How we measured it. Define the first section after 12.43 mi whose average pace is more than 10% slower than 3.11–12.43 mi. Look only through 24.85 mi so all tested sections are 3.11 mi long. Group runners using their observed 3.11–12.43 mi pace.

Full methodology & sources

Among runners with such a section, plot the distribution of its end distance. For each distance and early-pace group, show median elapsed arrival at the start and end of that section. The medians bound a typical observation interval; they are not confidence limits. This broader 10% section definition is separate from the sustained slowdown definition.

Use complete, strictly increasing elapsed checkpoints at 3.11, 6.21, 9.32, 12.43, 15.53, 18.64, 21.75, 24.85 and 26.22 mi. Clock strings must parse as H:MM:SS or M:SS. No missing splits are interpolated.

Remove exact duplicate race records, ignoring database IDs, ingestion timestamps and source URLs. Retain finishes from 90 minutes to 12 hours with every section between 3.22 and 32.19 minutes/mi. These quality filters can exclude genuine unusual performances; the analysis describes this eligible cohort, not every entrant.

Full source records are available in public GitHub Releases. These chart tables require at least 100 eligible observations per cell for estimate reliability. Counts refer to finishes, linked pairs or event observations as specified in that answer.

These are observational results. Fitness changes, intentions, training, selection into the dataset and unmeasured conditions can explain differences. Outcome percentiles describe variation among performances, not confidence intervals or advice about the best strategy.

Apply the reviewed source-quality edition exclusions for this exact export after the timing checks. Known invalid split grids, incomplete ingestion, unreconciled HOLD editions and a selected top-finisher field do not contribute to the analyses or prior benchmarks. Report source exclusions separately; an already invalid timing row is not counted twice. Missing age or recorded gender alone does not exclude an otherwise eligible finish from the overall cohort. Other sparse editions are not declared incomplete merely from their size.

Marathons, years and recorded data. Chart samples may be smaller than the eligible analysis cohort.

Method and data coverage (JSON)First slow section by early-race pace (CSV)Elapsed time at the two timing mats (CSV)Study methodology

First slow section by early-race pace

Percent (%)

3.11–12.43 mi pace

2520.3%

3027.6%

3530.9%

4021.3%

View exact values and sample sizes

Section ends at (mi)	First slow section by early-race pace	Observations
25	20.3%	848,232
30	27.6%	848,232
35	30.9%	848,232
40	21.3%	848,232

Elapsed time at the two timing mats

Minutes

3.11–12.43 mi pace

At section startAt section end

At section start111.6 min

At section end144.4 min

At section start140.2 min

At section end172.5 min

At section start167.8 min

At section end199.9 min

At section start194.8 min

At section end226.4 min

View exact values and sample sizes

Section ends at (mi)	At section start	At section end	At section start: Observations	At section end: Observations
25	111.6 min	144.4 min	172,153	172,153
30	140.2 min	172.5 min	234,051	234,051
35	167.8 min	199.9 min	261,754	261,754
40	194.8 min	226.4 min	180,274	180,274