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Table 5 Results of the best evidence synthesis concerning non-contact and overuse 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
Internal load parameters
 Psychosocial stress and recovery Brink et al. [28] General stress
Emotional stress
Social stress
Conflicts/pressure
Fatigue
Lack of energy
Physical complaints
Success
Social recovery
Physical recovery
General well-being
Sleep quality
Disturbed breaks
Emotional exhaustion
Fitness/injury
Being in shape
Personal accomplishment
Self-efficacy
Self-regulation
1.03 (0.75–1.43)
1.24 (0.85–1.82)
1.07 (0.74–1.53)
0.94 (0.70–1.27)
0.96 (0.70–1.30)
1.07 (0.75–1.52)
1.02 (0.71–1.45)
0.76 (0.55–1.04)
0.94 (0.71–1.26)
0.89 (0.66–1.19)
0.93 (0.68–1.26)
0.86 (0.64–1.16)
1.00 (0.73–1.37)
0.92 (0.69–1.23)
1.46 (1.091.96)
0.84 (0.64–1.09)
0.90 (0.68–1.20)
0.97 (0.74–1.27)
0.82 (0.66–1.02)
No
No
No
No
No
No
No
No
No
No
No
No
No
No
Yes
No
No
No
No
Insufficient
External load parameters
 Total distance Bacon and Mauger [26] 2-week cumulative loads    Insufficient
Moderate (2-, 3-, 4-week cumulative loads)
   TD—normal load
TD—low load
TD—high load
3-week cumulative loads
TD—normal load
TD—low load
TD—high load
4-week cumulative loads
TD—normal load
TD—low load
TD—high load
(ref.)
1.26 (0.16–9.77)
0.67 (0.40–1.14)
(ref.)
0.69 (0.29–1.64)
0.95 (0.44–2.05)
(ref.)
0.69 (0.29–1.64)
0.95 (0.44–2.05)
No
No
No
No
No
No
 
Bacon and Mauger [26] TD (low, normal, high) 0.0029 (0.0029–0.003) Yes
Bowen et al. [27] Accumulated 1/2/3/4-week loads   
TD—low
TD—moderate-low
TD—moderate-high
TD—high
TD—very high
0.30/0.61/0.67/1.01
1.45/0.95/0.87/0.77
0.83/1.19/1.08/1.06
1.64/1.37/1.65/1.55
3.04/3.35/2.79/2.30
Yes/no/no/no
No/no/no/no
No/no/no/no
No/no/no/no
No/no/no/no
 High speed running Bacon and Mauger [26] 2-week cumulative loads .   Insufficient
Conflicting (2-, 4-week cumulative HSD loads)
Moderate(3-week HSD loads)
HSR—normal load
HSR—low load
HSR—high load
3-week cumulative loads
HSR—normal load
HSR—low load
HSR—high load
4-week cumulative loads
HSR—normal load
HSR—low load
HSR—high load
(ref.)
0.99 (0.38–2.59)
0.58 (0.33–1.02)
(ref.)
0.51 (0.21–1.21)
1.05 (0.54–2.03)
(ref.)
0.51 (0.21–1.21)
1.05 (0.54–2.03)
No
No
No
No
No
No
Bacon and Mauger [26] HSR (low, normal, high) 0.065 (0.064–0.067) Yes
Bowen et al. [27] Accumulated 1/2/3/4-week loads   
HSD—low
HSD—moderately low
HSD—moderately high
HSD—high
HSD—very high
0.54/0.26/0.68/0.94
1.10/0.95/0.79/0.61
1.73/1.42/1.40/2.14
0.65/1.75/1.42/0.68
0.00/0.00/0.00/0.59
No/yes/no/no
No/no/no/no
Yes/no/no/yes
No/no/no/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
0.47/0.60/0.69/0.95
0.77/0.96/0.68/0.72
1.03/1.27/1.29/1.02
2.25/1.10/1.47/1.64
1.31/4.25/5.11/4.25
No/no/no/no
No/no/no/no
No/no/no/no
Yes/no/no/no
No/yes/yes/yes
 Duration Brink et al. [28] Duration (min) of training sessions and matches 1.07 (0.98–1.18) No Insufficient
 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
0.31/0.59/0.55/0.80
1.40/1.17/0.85/1.04
0.79/1.13/1.37/0.94
2.20/1.45/1.41/1.64
0.00/0.00/1.39/1.07
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
1.50/0.29/1.19
0.96/1.12/0.62
1.45/1.43/1.53
1.05/1.28/1.51
0.00/–/–
0.60/0.63/1.20
0.88/0.88/0.81
1.33/0.85/2.09
1.39/2.55/0.47
–/–/–
1.22/0.31/1.37
0.81/1.32/0.63
1.52/1.23/1.49
1.41/1.30/1.54
–/–/–
1.20/0.50/0.98
0.84/0.84/0.79
1.87/1.55/1.93
0.87/1.16/0.53
–/–/–
No/no/no
No/no/no
No/no/no
No/no/no
No/n.a./n.a.
No/no/no
No/no/no
No/no/yes
No/yes/no
n.a./n.a./n.a
No/no/no
No/no/no
No/no/no
No/no/no
n.a./n.a./n.a
No/no/no
No/no/no
Yes/no/no
No/no/no
n.a./n.a./n.a
Combined internal/external load parameters
 Workload Brink et al. [28] Product of the session-RPE and duration 1.01 (1.00–1.02) No Insufficient
 Monotony Brink et al. [28] Daily mean training load divided by the SD of the daily mean training load over a 1-week period 0.84 (0.25–2.76) No Insufficient
 Strain Brink et al. [28] Product of weekly training load and monotony 1.00 (1.00–1.01) No Insufficient
  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 Chronic Workload Ratio, n.a. not applicable, RPE rate of perceived exertion, SD standard deviation
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