The Influence of Humidity, Ambient, and Apparent Temperature on Match-Running Performance in International Men's Soccer
International journal of sports physiology and performance · 2026
Elite match running starts dropping off at surprisingly mild heat/humidity combos, long before conditions feel extreme.
Part of: Training load and injury risk: what the evidence says · Endurance performance and physiology: training the aerobic engine
The paper
Observational cohort using GNSS tracking, n=91 international-level male soccer players across FIFA-regulated matches, 2018-2024.
What they found
Match-running metrics declined non-linearly once temperature passed early breakpoints: total distance fell by up to -1.44%/°C under moderate-high humidity, high accelerations by up to -8.65%/°C, high-speed running by up to -2.61%/°C, with the steepest drop-offs at 25-40°C apparent temperature or 22-35°C ambient temperature combined with 60-80% humidity; maximal velocity was largely preserved (-0.08%/°C).
Study design
Retrospective observational cohort analysis of GNSS match data from 91 male international players, modeled with generalized additive mixed models (GAMMs) and breakpoint/segmented-regression analysis. This sits low on the hierarchy, it is correlational field data, not an experiment, akin to a large, well-modeled cohort study.
Methodology
The strength here is the modeling: GAMMs with subject-level random effects handle repeated measures per player, and breakpoint analysis lets effects vary rather than forcing a straight line. The weaknesses are typical of observational match data: no control for opponent quality, score state, tactical role, pitch/altitude, match importance, or heat acclimatization status, all of which plausibly confound running output alongside temperature. Humidity was held at fixed values (40/60/80%) as a modeling convenience rather than observed interaction, so those tri-level curves are model-derived, not raw comparisons. A clinician trusting the specific thresholds would need to see the breakpoint confidence intervals and model fit diagnostics, which aren't in the abstract.
The appraisal
The direction (heat and humidity suppress high-intensity actions, with acceleration/deceleration load dropping hardest) is biologically plausible and consistent with known thermoregulatory physiology, but this is an association from a GAMM, not a causal test, so 'breakpoints' are descriptive features of a curve fit rather than proven physiological thresholds, and breakpoint detection itself is exploratory and sensitive to model choices. The magnitudes matter more than the p-values here: a slope of -8.65%/°C in accelerations at its steepest point is a large practical effect worth planning around, even though that rate is local to the breakpoint and doesn't compound linearly across a wider temperature range, whereas the -0.08%/°C change in max velocity is clinically trivial despite being 'significant' in a model sense.
The gap
No data on player acclimatization status, which is probably the single biggest effect modifier in heat-performance research, two players in identical conditions can respond completely differently depending on prior heat exposure. Without stratifying by that, the 'universal' breakpoints are averaged over an unmeasured and highly variable factor. The cohort is also restricted to international men's matches, so these exact breakpoints shouldn't be assumed to transfer directly to domestic league, academy, or women's soccer populations without their own data.
Landmark context
This extends the existing heat-and-soccer literature built around work like Mohr et al.'s heat studies from hot-climate tournaments (e.g. Qatar), which showed reduced high-intensity running in heat, by applying modern GNSS data, a larger multi-year international sample, and nonlinear breakpoint modeling rather than simple hot-vs-moderate comparisons.
What to do Monday
For national-team and tournament-prep staff (notably relevant with 2026 World Cup venues in hot, humid US cities), this supports planning cooling strategies, substitution windows, and load expectations specifically once apparent temperature nears 25°C or ambient temperature with high humidity nears the low-to-mid 20s°C, rather than waiting for extreme heat alarms. It does not change day-to-day clinical management for individual patients.
In practice
This applies to national-team and tournament-prep staff heading into hot-humid fixtures (the 2026 World Cup's US venues are the obvious case), and to physios managing players returning to play within those windows. On the S&C floor, build heat-humidity triggers into periodisation and substitution planning once apparent temperature is approaching the mid-20s°C or ambient temperature sits in the low-to-mid 20s°C with high humidity, rather than waiting for a day that 'feels' dangerous, and expect accelerations/decelerations to be the metric that falls off hardest, not top speed. In the clinic, this doesn't change rehab programming for an individual patient, but it should sharpen expectations for a player coming back from injury into a hot fixture, their planned high-intensity exposure likely won't be delivered as programmed, so build in a buffer rather than assuming the session plan equals the match reality. The caveat in applying it: these breakpoints are averaged over players with unknown heat-acclimatization status, so don't use them as a fixed rule for a player arriving from a cold climate, that player needs an individualized heat protocol well before the group threshold.
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