Author: Jan Ekstrand et al
Journal: The American Journal of Sports Medicine (2019)

AI generated summary

🎯 Purpose

To examine whether the number of preseason training sessions completed by elite European soccer teams is associated with:

• Injury burden
• Severe injury incidence
• Player training attendance
• Player match availability
• Injury incidence

The dataset included 44 teams across 244 team-seasons in UEFA Champions League and Europa League clubs over 15 years.

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📈 Key Findings

1️⃣ More preseason sessions → lower in-season injury burden

For every +10 preseason training sessions, teams had on average:

• –22 layoff days per 1,000 hours exposure (whole season)
• Effects strongest Jan–May, not Aug–Dec

This is shown in Figure 1 (top-left scatterplot), where the trend line slopes downward.

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2️⃣ More preseason sessions → fewer severe injuries

For every +10 sessions:

• –0.20 severe injuries per 1,000 hours

Shown in Figure 1 (top-right), also with a negative slope.
Effect significant for the whole season and the second half of the season.

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3️⃣ More preseason sessions → higher training attendance

Teams completing more sessions showed:

• +1.4% higher team training attendance (per +10 sessions)

Displayed in Figure 1 (bottom-left).
Higher attendance = more players consistently available.

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4️⃣ More preseason sessions → higher match availability

For every +10 sessions:

• +1.0% higher match availability

Visible in Figure 1 (bottom-right).
Even a small improvement matters greatly in elite environments.

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5️⃣ No significant effect on overall injury incidence

Although trends were negative (fewer injuries), the associations were not statistically significant.

This emphasizes that injury burden and availability are better indicators than raw incidence.

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🧠 Interpretation & Practical Meaning

✔ Preseason matters — but effect size is modest

The regression models explain 1–3% of injury outcomes.
So preseason volume is a contributing factor, not the main determinant.

✔ Why might preseason reduce injuries?

• Improved chronic load tolerance (“protective effect of fitness”)
• Better physical robustness before fixture congestion increases
• More players conditioned to high-speed and match-intensity demands

✔ Strongest benefits appear in the second half of the season

Suggesting preseason builds resilience that “shows up” later in the year.

✔ Cannot identify type/intensity of sessions

Only the number of sessions was analyzed—not duration, intensity, RPE, high-speed load, strength work, etc.

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📌 Practical Takeaways for Coaches

1. A “bigger” preseason (more sessions) is generally beneficial

Even an extra 10 sessions can meaningfully help reduce injuries and increase player availability.

2. Focus on building robust physical qualities early

Aerobic capacity, strength, speed, and repeated-sprint qualities are linked to lower injury risk in other work cited by the authors.

3. Preseason quality matters as much as quantity

The study could not measure training composition; however, modern practice emphasizes:

• progressive high-speed running
• eccentric hamstring load
• neuromuscular warm-up (FIFA 11+)
• strength and CMJ profiling
• load progression tailored to player histories

4. Integrate preseason lessons into in-season microcycles

A strong preseason doesn’t override poor load management later.