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Table 6 Results of the best evidence synthesis concerning all injuries

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

Risk factor Study Specification of independent variable Outcome OR/RR (95% CI) Best evidence synthesis
Presence of association Level of evidence
External load parameters
 Total distance Bowen et al. [27] Accumulated 1/2/3/4-week loads    Insufficient
TD—low
TD—moderately low
TD—moderately high
TD—high
TD—very high
0.25/0.62/0.53/0.89
1.38/0.76/1.23/0.73
0.95/1.55/1.36/1.19
1.57/1.27/1.31/1.64
2.59/2.88/2.37/1.29
Yes/no/no/no
No/no/no/no
No/yes/no/no
No/no/no/yes
No/no/no/no
 High speed running Bowen et al. [27] Accumulated 1/2/3/4-week loads    Insufficient
HSD—low
HSD—moderately low
HSD—moderately high
HSD—high
HSD—very high
0.38/0.30/0.67/0.79
1.16/0.81/0.84/0.73
1.73/1.72/1.15/1.56
0.59/1.45/1.66/1.26
0.82/0.00/0.33/0.33
Yes/yes/no/no
No/no/no/no
Yes/yes/no/yes
No/no/yes/no
No/no/no/no
 Acceleration Bowen et al. [27] Accumulated 1/2/3/4-week loads    Insufficient
ACC—low
ACC—moderately low
ACC—moderately high
ACC—high
ACC—very high
0.35/0.51/0.63/0.93
1.01/0.92/0.77/0.82
1.00/1.21/1.32/1.01
1.83/1.37/1.38/1.66
3.06/3.19/3.84/2.37
Yes/no/no/no
No/no/no/no
No/no/no/no
Yes/no/no/yes
Yes/yes/yes/no
 Total load Bowen et al. [27] Accumulated 1/2/3/4-week loads    Insufficient
TL—low
TL—moderately low
TL—moderately high
TL—high
TL—very high
0.27/0.50/0.55/0.75
1.45/1.07/0.98/1.01
0.98/1.38/1.39/1.12
1.65/1.03/1.09/1.20
2.00/1.93/1.59/1.84
Yes/no/no/no
No/no/no/no
No/no/no/no
Yes/no/no/no
No/no/no/no
 ACWR Bowen et al. [27] Overall/low chronic/high chronic    Insufficient
TD—low
TD—moderately low
TD—moderately high
TD—high
TD—very high
HSD—low
HSD—moderately low
HSD—moderately high
HSD—high
HSD—very high
ACC—low
ACC—moderately low
ACC—moderately high
ACC—high
ACC—very high
TL—low
TL—moderately low
TL—moderately high
TL—high
TL—very high
1.00/0.28/0.91
1.25/1.43/0.98
0.97/0.97/1.19
1.13/1.76/1.21
2.09/–/1.80
0.47/0.47/1.52
1.10/0.86/1.11
1.32/1.30/1.27
0.98/1.82/0.50
0.95/–/1.63
0.85/0.29/0.71
1.16/1.49/1.04
1.15/0.94/1.25
1.44/1.70/1.10
2.09/–/2.71
0.84/0.37/0.81
1.15/1.15/1.22
1.34/1.16/1.34
1.01/1.59/0.43
1.17/–/2.67
No/yes/no
No/no/no
No/no/no
No/no/no
No/n.a./no
Yes/no/no
No/no/no
No/no/no
No/no/no
No/n.a./no
No/yes/no
No/no/no
No/no/no
No/no/no
No/n.a./no
No/no/no
No/no/no
No/no/no
No/no/no
No/n.a./no
Combined internal/external load parameters
 Workload Delecroix et al. [29] U19    Insufficient
Moderate (1-week workload)
1-week workload
2-week cumulative workload
3-week cumulative workload
4-week cumulative workload
U21
1-week workload
2-week cumulative workload
3-week cumulative workload
4-week cumulative workload
1.11 (0.84–1.50)
1.03 (0.77–1.38)
0.97 (0.74–1.28)
1.00 (0.76–1.33)
1.18 (0.92–1.52)
1.28 (0.97–1.69)
1.39 (1.041.84)
1.40 (1.061.86)
No
No
No
No
No
No
Yes
Yes
Raya-Gonzálaz et al. [30] Sum of load (RPE*duration) for all training sessions and matches for each week 1.00 (0.99–1.00)a No
 ACWR Delecroix et al. [29] U19    Insufficient
Moderate (4-week A:C workload)
2-week A:C workload
3-week A:C workload
4-week A:C workload
Week-to-week workload changes
U21
2-week A:C workload
3-week A:C workload
4-week A:C workload
Week-to-week workload changes
0.99 (0.90–1.09)
1.01 (0.95–1.06)
1.01 (0.96–1.07)
1.00 (0.96–1.04)
0.86 (0.58–1.29)
0.88 (0.66–1.16)
0.89 (0.71–1.13)
1.00 (0.95–1.06)
No
No
No
No
No
No
No
No
Raya-Gonzálaz et al. [30] Sum of the current week’s load (acute load) divided by the average weekly training load over the previous four weeks (chronic load) 0.16 (0.01–1.84)a No
  1. In bold are statistically significant (p < 0.05) associations
  2. OR odds ratio, RR risk ratio, CI confidence interval, ref reference, TD total distance, HSD high speed distance, ACC acceleration, TL total load, HSR high speed running, min minutes, ACWR acute to chronic workload ratio, n.a. not applicable, RPE rate of perceived exertion, SD standard deviation, U19 under 19 years squad, U21 under 21 years squad, A:C acute to chronic
  3. a90% confidence interval
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