Cumulative HR exertion primarily reflects accumulated external training volume, whereas HR exertion per minute is more closely related to locomotor and explosive action intensity in elite under-17 youth soccer training.
Key Findings
Results
HR exertion showed nearly perfect within-player associations with total distance covered and PlayerLoad.
Repeated-measures correlation between HR exertion and total distance covered: r = 0.921, p < 0.001
Repeated-measures correlation between HR exertion and PlayerLoad: r = 0.924, p < 0.001
These associations were classified as 'nearly perfect' by the authors
11 under-17 male elite soccer players were monitored across a nine-week in-season period with 266 player-session observations included
Results
HR exertion showed large within-player associations with high-speed running distance and explosive efforts.
Repeated-measures correlation between HR exertion and high-speed running distance: r = 0.662, p < 0.001
Repeated-measures correlation between HR exertion and explosive efforts: r = 0.621, p < 0.001
These associations were classified as 'large' by the authors, distinguishing them from the 'nearly perfect' associations seen with volume-based metrics
External training load was assessed using GPS units with integrated inertial sensors
Results
Total distance covered per minute and explosive efforts per minute were significant positive predictors of HR exertion per minute in the linear mixed-effects model.
A linear mixed-effects model was used to examine predictors of HR exertion per minute
Both total distance covered per minute and explosive efforts per minute were identified as significant positive predictors
These intensity-based (time-normalized) variables were examined separately from their cumulative counterparts
The model distinguished between cumulative external load variables and their time-normalized derivatives
Results
Cumulative HR exertion primarily reflects accumulated external training volume rather than training intensity in elite youth soccer.
The nearly perfect correlations (r > 0.90) between cumulative HR exertion and volume metrics (total distance and PlayerLoad) indicate that session duration and volume dominate cumulative internal load
Intensity-based metrics (per minute values) showed a different pattern of associations compared to cumulative metrics
The authors concluded that 'cumulative and intensity-based internal training load metrics' need to be 'interpreted separately in within-player training monitoring'
Internal training load was quantified using heart rate exertion derived from individualized HR zones
Methods
Within-player associations between external and internal training load were examined using repeated-measures correlations across a nine-week in-season monitoring period.
Sample consisted of 11 under-17 male elite soccer players
Monitoring period spanned nine weeks of in-season training
266 player-session observations were included in the analysis
GPS units with integrated inertial sensors were used to assess external load, capturing total distance, high-speed running distance, explosive efforts, player load, and their time-normalized derivatives
Repeated-measures correlation was selected specifically to examine within-player (rather than between-player) associations
What This Means
This research suggests that when monitoring how hard young elite soccer players are working during training, the way you measure 'internal load' (how the body responds to training, measured via heart rate) matters a great deal. When researchers simply added up heart rate stress over an entire session, that total was very strongly linked to how much total distance players covered and their overall movement load — in other words, longer or higher-volume sessions naturally produced higher cumulative heart rate stress, regardless of how intense the session actually was.
However, when the researchers looked at heart rate stress per minute (accounting for session length), a different picture emerged. This intensity-adjusted measure was more closely tied to how fast players were moving and how many explosive actions (like sprints and accelerations) they performed per minute. This suggests that per-minute heart rate metrics capture training intensity more faithfully than simple session totals, which are heavily influenced by how long a session lasts.
This research matters for coaches and sports scientists working with youth soccer players because it highlights a potential pitfall in training monitoring: using cumulative heart rate data alone could lead to the mistaken impression that a long, low-intensity session is equally demanding to a short, high-intensity one. The findings suggest that both cumulative and intensity-based internal load metrics should be tracked and interpreted separately to get a complete picture of how players are responding to their training programs.
Check Your Own Numbers
Upload your bloodwork. We'll cross-reference your results against this study and 4,700 others.
Havanecz K, Téglás T, Petridis L. (2026). Within-player associations between GPS-derived external training load and heart rate-based internal training load in elite youth male soccer training.. PloS one. https://doi.org/10.1371/journal.pone.0357176