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Table 2 Characteristics of included studies

From: The Association Between Training Load and Injury Risk in Elite Youth Soccer Players: a Systematic Review and Best Evidence Synthesis

Study Follow-up Population Injury definition Workload
Internal External
Bacon and Mauger [26]
2017
UK
2 seasons N = 41
Mean age 17.8 ± 1.1 yrs
Overuse injuries—no definition described n.a. Total distance (m); weekly and whole season training/match averages
High speed running (m); weekly and whole season training/match averages
Bowen et al. [27]
2017
UK
2 seasons N = 32
Mean age 17.3 ± 0.9 yrs
A non-contact/contact injury was defined as one that caused any absence from future football participation n.a. Total distance (m); this includes walking, jogging, fast running, and sprinting
High speed distance (m); total distance > 20 km/h
Total load (au); acceleration along x, y, and z axes
Accelerations (n); a change in GPS speed data for at least half a second with maximum acceleration in the period of at least 0.5 m/s/s
Brink et al. [28]
2010
Netherlands
2 seasons N = 53
Mean age 15–18 yrs
Any physical complaint sustained by a player that results from a soccer match or training, resulting in time loss (unable to take full part in future soccer activities) or medical attention (> 1 day but still able to take full part in future soccer activities)
Traumatic injuries resulted from a specific, identifiable event. Overuse injuries resulted from repeated microtrauma without a single identifiable event
Rate of perceived exertion; global intensity of each training session rated on Borg 15-point scale
Psychosocial stress and recovery; Recovery Stress Questionnaire for athletes (RESTQ-Sport)
Physical stress (min); duration of training sessions and matches
Training load; product of the session-RPE and the physical stress
Monotony; daily mean training load divided by the SD of the daily mean training load over a 1-week period
Strain; product of weekly training load and monotony
Delecroix et al. [29]
2019
France
4 (U19) and 5 (U21) seasons U19: n = 52; mean age 16.8 ± 0.9 yrs
U21: n = 70; mean age 20.1 ± 0.3 yrs
Any physical complaint sustained by a player that resulted from a football match or training, that made the player unable to participate in a future football training or match Rate of perceived exertion; global intensity of each training session and match rated on a 0–10-point scale Workload (au); product of the session-RPE and duration of training session and matches
A:C ratio (au); 1-week workload divided by the average workload of the last 28/21/14 days
Week-to-week load changes; 1-week load divided by accumulated load of previous 7 days
Raya- González et al. [30]
2019
Spain
1 season N = 22
Mean age 18.6 ± 0.6 yrs
A non-contact injury that occurred during a scheduled training session or match that caused absence from the next training session or match Rate of perceived exertion; global intensity of each training session and match rated on a 0–10-point scale Workload (au); the sum of load (RPE*duration) for all training sessions and matches for each week
A:C ratio; sum of the current week’s load (acute load) divided by the average weekly training load over the previous four weeks (chronic load)
  1. yrs years, n.a. not applicable, m meters, km/h kilometers per hour, GPS Global Positioning System, au arbitrary unit, n number, min minutes, RESTQ Recovery Stress questionnaire, SD standard deviation, RPE Rate of Perceived Exertion, A:C ratio acute to chronic workload ratio