“External and Internal Load Measures During Preseason Training in Men Collegiate Soccer Athletes” [Article Review]

Introduction

This study was conducted by Jennifer B. Fields and colleagues from institutions including Springfield College, George Mason University, and others, and was published in the Journal of Strength and Conditioning Research. The researchers aimed to address the gap in understanding how various external and internal training load measures change across a collegiate soccer preseason period and how these markers relate to each other in predicting athlete readiness and performance. Collegiate athletes often experience high training volumes during preseason, making it crucial for practitioners to monitor both the work athletes perform (external load) and their physiological and psychological responses (internal load) to optimize both performance and health.​

Key Takeaways

The study observed 20 NCAA Division I men's soccer players over a two-week preseason, employing both GPS-based external load tracking (total distance, player load, high-speed distance, repeated high-intensity efforts) and internal load measures (heart rate variability, salivary hormones, wellness and RPE scales).

Results showed that external load and cortisol were highest in the first week, with significant reductions by week two, while testosterone and the testosterone-cortisol ratio increased. Despite these positive hormonal changes and a reduction in loads, negative mood states (anger, depression) increased and perceived energy and sleep quality decreased.

Bidirectional modeling revealed that morning hormonal levels predicted same-day afternoon external loads and RPE, while HRV predicted post-session RPE. Importantly, HRV did not change significantly, and its relationship with external load measures and perceived fatigue was limited.​

Conclusion

The study concludes that both external and internal load measures should be used in tandem to understand athletes’ stress responses to high-preseason loads.

External load appears to have delayed, cumulative effects on wellness, while hormonal shifts can be more immediate and sensitive to acute changes.

For applied sport performance, practitioners should pay close attention to mood and wellness status following periods of high load—using reductions in testosterone-cortisol ratio, HRV, energy, and sleep, alongside elevations in external loads, cortisol, and mood disturbances as signals to incorporate greater recovery strategies. This comprehensive and multi-domain approach enables more effective periodization and helps safeguard athlete health and performance through highly demanding training blocks like preseason.

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