Table 2.

Characteristics of the randomised-controlled trials included in the systematic review.

Reference	Participants Level	Intervention	Comparator	Outcomes	Compliance Rate	Reliability/SWC	Results	Comments
Gilchrist et al. 2008 [53]	1435 female soccer player (IG = 583, age: 19.88 years; CG = 852, age: 19.88 years) NCAA Division I	IG: PEP Program Duration: 12 weeks Frequency: 3/week Session duration: <30 min Training components: Stretching, strengthening, plyometrics, agilities, and avoidance of high-risk positions depicted on a video. Replacement exercises to alleviate boredom.	CG: Their customary warm-up.	Contact ACL injury, and non-contact ACL injury rate per 1000 AE.	72%	NA	↓ ACL injury rate in practice, and non-contact ACL injury rate in those with history of past ACL injury and late in season in IG. ↔ ACL injury rate and non-contact ACL injury rate in IG and CG.	Supervision: Certified athletic trainer. 8 dropouts in IG. Low compliance rate in IG. Lack of control the drills executed and of the uses of the program.
Steffen et al. 2008 [80]	31 adolescent female football players (IG = 17, CG = 14; age: 17.1 ± 0.8 years) Elite sport high school	IG: FIFA 11 Duration: 10 weeks Frequency: 3/week Session duration: ≈15 min Training components: 10 exercises focusing on core stability, neuromuscular control, eccentric hamstrings strength and agility.	CG: Regular warm-up (running and ball exercises)	Conventional H/Q ratio at 60 and 240 °/s and functional H/Q at 60 °/s. Frontal plane knee angles during CMJ and DVJ.	73%	NR/ NR	↔ No differences between groups in either H/Q ratios or valgus angle during CMJ and DVJ (p > 0.05)	Supervision: Project coordinator. Unbalanced groups. 2 dropouts in a small sample. Low power to detect differences.
Brughelli et al. 2010 [62]	28 soccer players (IG = 13, age: 20.7 ± 1.6 years; CG = 11, age: 21.5 ± 1.3 years). Professional	IG: Additional eccentric training Duration: 4 weeks Frequency: 3/week Session duration: 10–15 min Training components: 4–5 sets from 1–2 exercises, of 4 different eccentric exercises: Eccentric box drops, lunge pushes, forward deceleration steps, and reverse Nordic hamstrings.	CG: Regular field-based warm-up, but also training the Nordic hamstrings exercise (once a week, total of 2 sets of 6 reps)	H/Q ratio at 60 °/s	100%	Acknowledges another reliability data/ NR	↔ Q/H ratio at 60 °/s in both groups (p > 0.05)	Supervisor not specified. Drop of participants in CG (3). Low volume of additional training, and only 4 weeks.
Daneshjoo et al. 2010 [63]	36 male soccer players (IG1 = 12, age: 19.2 ± 0.9; IG2 = 12, age: 17.7 ± 0.4; CG = 12, age: 19.7 ± 1.6) Professional	IG1: FIFA 11+ Duration: 8 weeks Frequency: 3/week Session duration: ≈20–25 min Training components: (1) Running exercises; (2) strength, balance, muscle control and core stability; and (3) advanced running exercises. IG2: HarmoKnee Duration: 8 weeks Frequency: 3/week Session duration: ≈20–25 min Training components: (1) Warm up; (2) muscle activation; (3) balance; (4) strength; and (5) core stability	CG: Regular field-based warm-up	Error of proprioception test at 30, 45 and 60°. Distance excursion in SEBT. Time in the stork stand balance test, with open and close eyes.	NR	NR/ NR	↔ No significant difference between groups in either proprioception or static balance. ↑ Static balance with eyes opened in the 11+ (ESc = 2.25, p = 0.043) and HarmoKnee (ESc = 0.81, p = 0.011) and closed in the 11+ (ESc = 2.78, p = 0.027; HarmoKnee (ESc = 2.45, p = 0.022) in post- vs. pre-intervention. ↑ SEBT in the 11+ (ESc = 0.82, p = 0.004) and HarmoKnee (ESc = 0.91, p = 0.011) (time x group interaction: F = 3.767, p = 0.034).	Supervisor not specified.
Gioftsidou et al. 2012 [68]	38 male soccer players (age: 22.7 ± 3.5 years) 1st Greek division	IG: Balance training program Duration: 6 weeks Frequency: 3/week Session duration: ≈20 min Training components: Four different soccer-specific (controlling, passing, heading) balance exercises performed on a hemi-cylindrical board and on an hemi-spherical board.	CG: Standard soccer training	Total (SI), anterior-posterior (API) and medial-lateral (MLI) index. Maintenance time for the anterior-posterior (APM) and medial-lateral (MLM) movements.	NR	ICC = 0.67–0.80/ NR	↓ SI (ESc = 0.67–0.70), API (ESc = 0.65–0.74) and MLI (ESc = 1.36–1.62) in both legs in IG. ↑ APM (ESc = 1.71–3.02) and MLM (ESc = 1.49–1.53) in both legs in IG	Supervisor not specified. No p values.
Impellizzeri et al. 2013 [73]	81 male soccer players (CG = 39, age: 23.3 ± 2.8; IG = 42, age: 23.7 ± 3.7 years) Amateur	IG: FIFA 11+ Duration: 9 weeks Frequency: 3/week Session duration: ≈20 min Training components: (1) Running exercises; (2) core and leg strength, balance and plyometric/agility; and (3) higher-speed running drills with cutting manoeuvres. The key element is promotion of proper technique.	CG: Traditional warm-up	SEBT. Time-to-stabilisation on a single leg during a jump-landing task. Unstable sitting posture test.	NR	SWD = 0,2*SD	↓ Core stability (8%) in CG. ↔ Core stability (1.5%) in IG. ↔ Time-to-stabilisation (1.5%) in CG. ↓ Time-to-stabilisation (−1.8%) in IG.	Supervisor: Fitness coach. Results rounded to decimals: Problematic to detect differences.
Silvers-Granelli et al. 2015 [56]	1525 male soccer players (IG = 675, age: 20.40 ± 1.66; CG = 850, age: 20.68 ± 1.46 years) NCAA Division I & II	IG: FIFA 11+ Duration: 1 competitive season Frequency: 3/week Session duration: ≈20 min Training components: (1) Running exercises that encompass cutting, COD, decelerating and proper landing techniques; (2) strength, plyometric and balance exercises that focus on core strength, eccentric control and proprioception; (3) running exercises.	CG: Typical soccer warm-up	ACL injury incidence per 1000 AE	Mean utilisation: 30.47 ± 12.16 sessions (considered moderate; total 18 games and 51/52 sessions)	NA	↓ ACL injury incidence rate (0.362/1000AEs vs. 0.085/1000AEs) in IG vs. CG. ↓ Likelihood of incurring an ACL injury (RR = 0.236 [0.193–0.93]; NNT = 70, p < 0.001)	Supervisor: Certified athletic trainer. Weeks of training not reported.
Dello Iacono et al. 2016 [65]	20 young male football players (IG = 10, age: 18.7 ± 0.67 years; CG = 10, age: 19 ± 0.063 years) Elite team national Israel league	IG: Core stability training Duration: 6 weeks Frequency: 5/week Session duration: ≈20 min Training components: The program consists of two parts: (1) improving balance and core stability, and (2) developing lower limb strength and neuromuscular control.	CG: Regular warm-up	H/Q conventional ratio at both 1.05 and 3.14 rad/s IA from GRF peak in a one-leg CMJ.	NR	95% limits of agreement: Isokinetic tests = −1.32–1.75 Jump tests = −2.12–1.96 ICC = 0.925–0.978/ NR	↑ H/Q ratio at 1.05 rad/s (ES = 0.61–0.75), and 3.14 rad/s (ES = 0.71–0.95) in both legs in IG. ↔ H/Q ratio at both velocities in CG. ↓ IA in IG (−71.4%, ES = 2.01). ↑ IA in CG (33.3%, ES = 1.28).	Supervisor: Researcher. Regular warm-up of the CG only consists of jogging, dynamic stretching and mobilisation.
Gonzalez-Jurado et al. 2016 [69]	18 male soccer players (IG = 9, age: 25,89 ± 3.85; IG2 = 10, age: 23.33 ± 3 years) 2nd Spanish division	IG1: Proprioceptive training on stable surface Duration: 5 weeks (5 phases of one week each) Frequency: 5/week (first 4 phases) and 3/week (last phase) Session duration: ≈5 min (estimated) Training components: Monopodal proprioceptive training exercises on a stable surface, adapted to football, and executed using a 4-station circuit.	IG2: Proprioceptive training on unstable surface Duration: 5 weeks (5 phases of one week each) Frequency: 5/week (first 4 phases) and 3/week (last phase) Session duration: ≈5 min (estimated) Training components: Monopodal proprioceptive training exercises on different unstable surfaces (soft mat, Freeman Dish, Fit-sit Platform and Dyn-air), adapted to football, and executed using a 4-station circuit.	Star Excursion Balance Test (maximum distance reached in 8 directions)	NR	NR/ NR	↑ Front left, Ant-Lat left, Lat right, Back right, and Ant-Med right (ES = 0.13–0.55) in IG1 and Front right and left, Ant-Lat left, Lat left, Post-Lat right, Post right and left, Post-Med right and left, Med right, and AntMed left (ES = 0.06–0.43) in IG2 ↑ AntMed right in IG vs. IG2 (intergroup analysis)	Supervisor not specified. Low sample size in each group. Daily training too short (5 min?).
Silvers-Granelli et al. 2017 [57]	1525 male soccer players (IG = 675, age: 20.40 ± 1.66; CG = 850, age: 20.68 ± 1.46 years) NCAA Division I & II	IG: FIFA 11+ Duration: 1 competitive season Frequency: 3/week Session duration: ≈20 min Training components: (1) Running exercises that encompass cutting, COD, decelerating and proper landing techniques; (2) strength, plyometric and balance exercises that focus on core strength, eccentric control and proprioception; (3) running exercises.	CG: Typical soccer warm-up	ACL injury incidence per 1000 AE	NR	NA	↓ ACL injury incidence rate (RR = 0.24 [0.07–0.81], p = 0.021) and non-contact ACL injury incidence rate (RR = 0.25 [0.06–1.15], p = 0.049) in IG vs. CG. ↔ Contact ACL injury incidence rate (RR = 0.21 [0.03–1.74], p = 0.148) in IG vs. CG.	Supervisor: Certified athletic trainer. Low number of ACL injuries. High amount of lost follow ups in the IG (100 players). Per protocol analysis.
Ayala et al. 2017 [60]	41 male youth football players (age: 16.8 ± 0.7 years) Amateur	IG1: FIFA 11+ Duration: 4 weeks Frequency: 3/week Session duration: ≈20–25 min Training components: (1) Running exercises; (2) strength, balance, muscle control and core stability; and (3) advanced running exercises. IG2: HarmoKnee Duration: 4 weeks Frequency: 3/week Session duration: ≈20–25 min Training components: (1) Warm up; (2) muscle activation; (3) balance; (4) strength; and (5) core stability	CG: Regular field-based warm-up	Y-Balance test. Ankle and hip ROM. Single hop for distance (asymmetry). Triple hop for distance (asymmetry).	NR	Acknowledges another reliability data/ NR	↑ Triple hop LSI score (very likely substantial difference [98%]), anterior distance (likely substantial difference [89%]), and posteriomedial distance (possibly substantial difference [60%]) in FIFA 11+ vs. CG ↔ No main effects in ankle ROM, LSI during single hop, posterolateral and composite score in FIFA 11 vs. CG and in all variables (possibly/likely trivial) in HarmoKnee vs. CG).	Supervisor: Trained rehabilitation specialist. Low sample of each group.
Delextrat et al. 2018 [64]	21 female soccer players (IG1 = 10, age: 21.8 ± 4.0; IG2 = 11, age: 23.7 ± 7.2) Amateur.	IG1: Strength endurance Duration: 7 weeks Frequency: 3/week Session duration: 10–15 min Training components: 6 sets of 12–20 rep progressing by decreasing the inter-set rest period (90 to 45s) of two hamstring strength exercises: (1) seated hamstrings curl, and (2) stiff-legged deadlifts.	IG2: Strength Duration: 7 weeks Frequency: 3/week Session duration: 20–25 min Training components: 6–10 sets of 6RM progressing by increasing load (80 to 100% of 6RM), with 3-min inter-set rest, of two hamstring strength exercises: (1) seated hamstrings curl, and (2) stiff-legged deadlifts.	H/Q functional ratio before and after BEAST90 test	NR	Acknowledges another reliability data/ NR	↔ Functional H/Q ratio before and after BEAST90 post-intervention only in IG1 in dominant leg (p = 0.045, n: 0.38) (intervention x match interaction) ↑ Functional H/Q ratio before BEAST90 post-intervention in both IG2 (+14.6%, d = 0.73, p = 0.01) and IG1 in dominant leg (+4.9%, d = 0.25, p = 0.039)	Supervisor: Experienced S&C coach. IG1 did not change the decline before/after BEAST90, but probably because the increase in the H/Q post- was higher than in IG2.
Rey et al. 2018 [78]	23 male soccer players (age: 24.7 ± 3.8 years) Amateur	IG: FIFA 11+ Duration: 6 weeks Frequency: 3/week Session duration: ≈25 min Training components: Fifa 11+ consisting on 3 parts: (1) 6 running exercises at low speed; (2) 6 exercises targeting strength, balance, neuromuscular control and core stability with 3 levels of increasing difficulty; (3) running exercises at moderate/high speed.	CG: Standard warm up with jogging, ball exercises and active stretching.	FMS score, divided into FMSmove, FMSflex and FMSstab.	NR	Inter-rater: ICC = 0.899 Intra-rater: ICC = 0.991/ NR	↔ No between groups differences.	Supervisor: Fitness trainer. No p values shown.
Riela et al. 2019 [81]	30 male soccer players (IG = 15, age: 23.80 ± 4.6; CG = 15, age: 24.78 ± 2.08 years) Italian 2nd division	IG: Movement-based program Duration: 8 weeks Frequency: 3/week Session duration: ≈30 min Training components: 15 min of exercises aimed at improving mobility and flexibility and 15 min of stability and posture, and strength with the use of elastic bands, medicine balls and foam rollers.	CG: Standard technical-tactical routing of warm up.	FMS score, divided into advances movement, mobility and stability	NR	NR/ NR	↑ Advanced movement (F(1,28) = 14.43, p = 0.03) and mobility (F(1,28) = 3.89, p = 0.50) in IG.	Supervisor: Specialised trainer. No p values. No counterbalanced the intervention with the two groups.
Whalan et al. 2019 [58]	806 male soccer players (IG1 = 398, age: 24,8; IG = 408, age: 23.8 years) Sub-elite	IG1: Rescheduled FIFA 11+ Duration: 1 season (28–34 weeks) Frequency: 2/week (+ Parts 1 and 3 before matches) Session duration: ≈20–25 min Training components: 2 parts of the Fifa 11+ performed at the start of the warm-up (parts 1 and 3), and one part performed at the end of training during the cool down period (part 2). In Part 2, players remained at level 1 for a minimum of 2 weeks, and progressed to level 3 after a minimum of 6 weeks	IG2: FIFA 11+ Duration: 1 season (28–34 weeks) Frequency: 2/week (+ Parts 1 and 3 before matches) Session duration: ≈20–25 min Training components: 3 parts of the Fifa 11+ performed at the start of the warm-up. In Part 2, players remained at level 1 for a minimum of 2 weeks, and progressed to level 3 after a minimum of 6 weeks.	Non-contact ACL injury incidence per 1000 h of AE.	IG1 = 18.9 (doses), 32.7% (doses/sessions) IG2 = 29.1 (doses), 57.7% (doses/sessions)	NA	↔ Non-contact ACL injury incidence (p = 0.238) in IG2 (IR/1000h = 0.06 [0.01–0.2]) compared to IG1 (IR/1000h = 0.15 [0.01–0.4])	Supervisor not specified. Weeks of season not specified.

ACL—anterior cruciate ligament, FMS—functional movement score, GRF—ground reaction force, AE—athlete exposures, SWC—smallest worthwhile change, IG—intervention group, CG—control group, NR—non-reported, d—Cohens’d, ES—effect size, ESc—effect size calculated through Hedge’s g, CMJ—countermovement jump, DVJ—drop vertical jump, NA—non-applicable, ↓—decrease, ↑—increase, ↔—no change.