REF-178 · Hunter et al., 2024 · International Journal of Sports Physiology and Performance, · Paper · PubMed

The Relationship Between the Moderate-Heavy Boundary and Critical Speed in Running

Astrong evidenceMeasured on trained to highly trained athletesWritten before October 2026, being re-checked

Hunter et al. (systematic review with meta-analysis, 26 studies, n=527 runners) asked at what percentage of critical speed (CS, the heavy-severe boundary, estimable from habitual training) the first threshold T1 (the moderate-heavy boundary, which normally needs testing) occurs. Across all studies T1 occurred at 82.3% of CS (95% CI 81.1-83.6).

Studies were grouped by mean CS: low (11.5 km/h), medium (13.4 km/h) and high (16.0 km/h; 95% CI 15.7-16.3). In the medium- and high-CS groups T1 sat at a higher fraction of CS (83.2%, 95% CI 81.3-85.1, and 84.2%, 95% CI 82.3-86.1) than in the low-CS group (80.6%, 95% CI 78.0-83.2).

The authors note uncertainty in the fraction from inconsistent methods of determining both boundaries, and recommend testing where precision matters; the ratio is a foundation for remote analysis and prescription.

Key Findings (key figures)

T1/CS ratio, all studies: 82.3% (95% CI 81.1-83.6)
Low-CS group (mean CS 11.5 km/h): T1 = 80.6% CS (95% CI 78.0-83.2)
Medium-CS group (13.4 km/h): T1 = 83.2% CS (95% CI 81.3-85.1)
High-CS group (16.0 km/h): T1 = 84.2% CS (95% CI 82.3-86.1)
n = 527 participants, 26 studies

Practical Application

In 527 runners across 26 studies the first threshold (moderate-heavy boundary) sat at 82.3% of critical speed (95% CI 81.1-83.6), and fitter groups had it higher: 80.6% in the low-CS group (11.5 km/h) versus 83.2% (13.4 km/h) and 84.2% (16.0 km/h) in the medium- and high-CS groups (meta-analysis, Hunter 2024).
Estimate a runner's T1 from a known CS as roughly 82% of CS when no test exists; nudge it toward 84% for a fast runner and 80-81% for a slower one, and treat a measured T1 far outside ~78-86% of CS as a signal to re-check either the T1 or the CS estimate.
Testing is still recommended by the authors where precision matters: the ratio carries uncertainty from inconsistent methods of determining both boundaries across studies.
Inference, not tested: the same relationship is often transferred to cycling as LT1 ≈ 80-85% of CP, but this meta-analysis is running-only and reports no cycling data.

Limitations

From the design as the abstract reports it: a systematic review with meta-analysis of 26 studies (527 participants); the authors note uncertainty in the T1/CS fraction because the studies used inconsistent approaches to determine both boundaries.
Running only; no cycling data.
The CS groups are formed from study means, not from individual runners; the authors recommend testing for more precise applications.
How this entry was checked and changed
Content correction 2026-09-27
Group ratios corrected to the abstract: low-CS 80.6% (was "≈80%"), medium-CS 83.2% (was "≈82%"), high-CS 84.2% (was "≈84%"); confidence intervals added.
"Transfer to cycling: LT1 ≈ 80-85% of CP" relabelled as inference (running-only meta-analysis); Sport line "cycling, running" -> running.
2026-09-28: added Limitations from the abstract (Europe PMC/PubMed PMID 39048094).