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Objectives: To compare long-lever squeeze testing using the ForceFrame and the Copenhagen 5-SecondSqueeze test (5SST) for assessment of hip adduction strength and provoked groin pain in elite male soccer players.Design: Cross-sectional study.Setting: Pre-season testing at facilities of a Danish professional 1st tier soccer club and academy.Participants: Elite male soccer players (n = 83, mean age; 16 +/- 2.7 years) from U13, U14, U15, U17, U19 and senior teams cleared for full training and match participation.Results: Hip adduction strength was 16% lower in the ForceFrame. A Bland-Altman plot showed a systematic bias (-0.47 Nm/kg, 95% CI [-0.57; -0.38]) and lack of agreement (95% limits of agreement: -1.31; 0.39 Nm/kg). In the ForceFrame, provoked groin pain was less intense (median NRS 0 [IQR: 0-1] vs. 555T: 1 [IQR: 0-3], p < 0.001) and reported by fewer players (NRS >0) (27% [n = 22] vs. 555T: 61.4% [n = 51], p < 0.001).Conclusions: The ForceFrame and the 5SST lack agreement and are not interchangeable methods. This may have implications when selecting a method for screening and detecting early groin problems in male soccer players. (C) 2022 The Authors. Published by Elsevier Ltd.

Objective: To test 1) if the 45-second Anterior Knee Pain Provocation Test (AKPP-test) could differentiate between adolescents with patellofemoral pain (PFP) and pain-free controls and; 2) whether improvements in the AKPP-test over 12 weeks were associated with improvements in self-reported knee function and pain. Design: Prospective cohort. Patients: 151 with PFP and 50 pain-free controls (age 10–14 years). Outcomes: The AKPP-test was performed at baseline, 4- and 12-week follow-up. Pain and function were collected using Knee Injury and Osteoarthritis Outcome Score (KOOS). Results: At baseline, the AKPP-test provoked pain to a median of 5 points (IQR: 3–7) on the 0–10 Numeric Pain Rating Scale in adolescents with PFP, compared to 0 (IQR 0-0) in controls. Higher pain during the AKPP-test was associated with worse KOOS-Sport/Rec (r = −0.33, P < 0.001), worse KOOS-Pain (r = −0.47, P < 0.001), and pain intensity (worst pain last 24 hours) (r = −0.39, P < 0.001) at baseline. Improvements in the AKPP-test over 12 weeks were associated with improvements in KOOS Pain (r = 0.48, P < 0.001) and KOOS Sport/Rec (r = 0.40, P < 0.001). Conclusions: Improvements in the AKPP-test were associated with improvements in self-report knee pain and limitations in sports, suggesting the AKPP-test may be a clinically responsive test of knee pain and sporting function in adolescents with PFP.

• OBJECTIVE: To compare pain, physical activity, quality of life, strength, and knee function in adolescents with patellofemoral pain (PFP) and Osgood-Schlatter disease (OSD) to those in painfree controls. • DESIGN: Cross-sectional study. • METHODS: Self-report questionnaires were used to describe pain, physical activity, knee function, and quality of life in participants with PFP (n = 151) or OSD (n = 51) and in pain-free controls (n = 50) between 10 and 14 years of age. Hip and knee strength were measured by handheld dynamometry. Physical activity levels were measured using wearable accelerometers. • RESULTS: Adolescents were highly active (accumulating greater than 120 minutes of vigorous physical activity per day), with no differences between the OSD, PFP, and control groups. Adolescents with PFP or OSD scored 22 to 56 points lower (P

This statement summarises and appraises the evidence on diagnosis, prevention and treatment of the most common lower extremity muscle injuries in sport. We systematically searched electronic databases, and included studies based on the highest available evidence. Subsequently, we evaluated the quality of evidence using the Grading of Recommendations Assessment, Development and Evaluation framework, grading the quality of evidence from high to very low. Most clinical tests showed very low to low diagnostic effectiveness. For hamstring injury prevention, programmes that included the Nordic hamstring exercise resulted in a hamstring injury risk reduction when compared with usual care (medium to large effect size; moderate to high quality of evidence). For prevention of groin injuries, both the FIFA 11+programme and the Copenhagen adductor strengthening programme resulted in a groin injury risk reduction compared with usual care (medium effect size; low to moderate quality of evidence). For the treatment of hamstring injuries, lengthening hamstring exercises showed the fastest return to play with a lower reinjury rate compared with conventional hamstring exercises (large effect size; very low to low quality of evidence). Platelet-rich plasma had no effect on time to return-to-play and reinjury risk (trivial effect size; moderate quality of evidence) after a hamstring injury compared with placebo or rehabilitation. At this point, most outcomes for diagnosis, prevention and treatment were graded as very low to moderate quality of evidence, indicating that further high-quality research is likely to have an important impact on the confidence in the effect estimates.

Purpose: To investigate the differences in hip adductor and abductor muscle strength in elite male footballers from youth to senior level. Methods: We tested 125 players from the under-13-years (U’13) to senior squads of a Danish male professional football club in this cross-sectional design study. Hip adductor and abductor force (in newtons), torque (in newton meters), normalized torque (in newton meters per body mass), and adduction-to-abduction ratio were measured using handheld dynamometry. Results: Between U’13 and senior level, adductor force increased by 104%, torque by 127%, and normalized torque by 21%. Abductor force increased by 78%, torque by 126%, and normalized torque by 17%. For incremental differences between age groups, significant increases were observed between the ages of U’13 to U’14 (18%–39%) and U’14 to U’15 (19%–33%) for all strength measures (P ≤ .021). No incremental difference was observed for adductor-to-abductor ratio. Conclusions: The large increases in hip adductor and abductor strength occurring between the ages of U’13 and U’15 offer insight into the strength capabilities and stress demands in these players, which may relate to injury vulnerability, and facilitate clinicians in selecting best-suited exercise interventions.

This statement summarises and appraises the evidence on diagnostic tests and clinical information, and non-operative treatment of femoroacetabular impingement (FAI) syndrome and labral injuries. We included studies based on the highest available level of evidence as judged by study design. We evaluated the certainty of evidence using the Grading of Recommendations Assessment Development and Evaluation framework. We found 29 studies reporting 23 clinical tests and 14 different forms of clinical information, respectively. Restricted internal hip rotation in 0° hip flexion with or without pain was best to rule in FAI syndrome (low diagnostic effectiveness; low quality of evidence; interpretation of evidence: may increase post-test probability slightly), whereas no pain in Flexion Adduction Internal Rotation test or no restricted range of motion in Flexion Abduction External Rotation test compared with the unaffected side were best to rule out (very low to high diagnostic effectiveness; very low to moderate quality of evidence; interpretation of evidence: very uncertain, but may reduce post-test probability slightly). No forms of clinical information were found useful for diagnosis. For treatment of FAI syndrome, 14 randomised controlled trials were found. Prescribed physiotherapy, consisting of hip strengthening, hip joint manual therapy techniques, functional activity-specific retraining and education showed a small to medium effect size compared with a combination of passive modalities, stretching and advice (very low to low quality of evidence; interpretation of evidence: very uncertain, but may slightly improve outcomes). Prescribed physiotherapy was, however, inferior to hip arthroscopy (small effect size; moderate quality of evidence; interpretation of evidence: hip arthroscopy probably increases outcome slightly). For both domains, the overall quality of evidence ranged from very low to moderate indicating that future research on diagnosis and treatment may alter the conclusions from this review.

Purpose: Increasing age, high quadriceps strength, and low hamstring muscle strength are associated with hamstring strain injury in soccer. The authors investigated the age-related variation in maximal hamstring and quadriceps strength in male elite soccer players from under-13 (U-13) to the senior level. Methods: A total of 125 elite soccer players were included from a Danish professional soccer club and associated youth academy (first tier; U-13, n = 19; U-14, n = 16; U-15, n = 19; U-17, n = 24; U-19, n = 17; and senior, n = 30). Maximal voluntary isometric force was assessed for the hamstrings at 15° knee joint angle and for the quadriceps at 60° knee joint angle (0° = full extension) using an external-fixated handheld dynamometer. Hamstring-to-quadriceps strength (H:Q) ratio and hamstring and quadriceps maximal voluntary isometric force levels were compared across age groups (U-13 to senior). Results: Senior players showed 18% to 26% lower H:Q ratio compared with all younger age groups (P ≤ .026). Specific H:Q ratios (mean [95% confidence interval]) were as follows: senior, 0.45 (0.42–0.48); U-19, 0.61 (0.55–0.66); U-17, 0.56 (0.51–0.60); U-15, 0.59 (0.54–0.64); U-14, 0.54 (0.50–0.59); and U-13, 0.57 (0.51–0.62). Hamstring strength increased from U-13 to U-19 with a significant drop from U-19 to the senior level (P = .048), whereas quadriceps strength increased gradually from U-13 to senior level. Conclusion: Elite senior soccer players demonstrate lower H:Q ratio compared with youth players, which is driven by lower hamstring strength at the senior level compared with the U-19 level combined with a higher quadriceps strength. This discrepancy in hamstring and quadriceps strength capacity may place senior-level players at increased risk of hamstring muscle strain injuries.

Knowledge on how to optimise rehabilitation of athletes after an acute hamstring strain is progressing.1 Within the last 6 years, eight randomised controlled trials (RCTs) on this topic have emerged—conducted by many eminent clinician-scientists.1 Recent clinically relevant RCTs show that specific exercise-based interventions reduce time to return to sport and risk of re-injuries.1 In particular, lengthening contraction exercises compared with conventional exercises without such emphasis reduce time to return to sport,1 whereas a criteria-based programme including a more running-specific exercise focus, compared with the lengthening approach, seems promising for reducing the risk of re-injury.1 Furthermore, platelet-rich plasma injections provided no additional benefit to current exercise-based rehabilitation.1 This emphasises the importance of specific mechanical loading and progressive running exercises in athletes with hamstring strains—but can we rest on these laurels? This editorial points out common methodological shortcomings in the existing clinical hamstring trial literature that may help guide and improve scientific robustness of future trials. Based on these, we suggest four practical steps to advance the field by eliminating common errors: > “The aim of science is not to open the door to infinite wisdom, but to set a limit to infinite …

Background: Patellofemoral pain (PFP) affects 7% of adolescents, especially those who are highly active. Exercise-focused treatments show limited effect and overlook activity modification and load management. As many adolescents continue at high levels of sports despite pain, a new strategy addressing this problem is warranted. Purpose: To investigate the effects of a treatment strategy for adolescents that focuses on activity modification and load management. Study Design: Cohort study; Level of evidence, 2. Methods: Adolescents aged 10 to 14 years with PFP were included (N = 151). The 12-week intervention included 4 supervised sessions with a physical therapist, which adolescents and parents were required to attend. The intervention included activity modification (weeks 1-4) to reduce loading of the patellofemoral joint via an activity ladder and pain monitoring, home-based exercises (weeks 5-8), and return-to-sport guidance (weeks 9-12). Primary outcome was a 7-point global rating of change, ranging from “much improved” to “much worse.” Adolescents were considered to have a successful outcome if they reported “much improved” or “improved.” The primary endpoint was at 12 weeks, with additional follow-up at 4, 24, and 52 weeks. Secondary outcomes included the Knee injury and Osteoarthritis Outcome Score (KOOS), hip and knee torque, sports participation, satisfaction with treatment, and use of painkillers. Results: At 12 weeks, 87% completed the full questionnaire, of which 86% reported a successful outcome, as compared with 77% (95% CI, 68%-83%) at 6 months and 81% (95% CI, 73%-88%) at 12 months. There were large clinically relevant improvements in 3 KOOS subscales: Pain, Sport/Recreation, and Quality of Life (13-24 points). Hip and knee torque increased by 20% to 33%. In total, 68% were back playing sport after 3 months, which increased to 79% at 6 months and 81% at 12 months. The majority were satisfied with the treatment (90%) and would recommend it to a friend (95%). No specific patient characteristics were associated with prognosis. Conclusion: A treatment strategy focusing on activity modification and load management was associated with high rates of successful outcome among adolescents with PFP at 12 and 52 weeks. These short- and longer-term outcomes were supported by improvements in symptoms and objective measures of hip and knee torque. Registration: NCT02402673 (ClinicalTrials.gov identifier)

Purpose: To investigate the association between hamstring muscle peak torque and rapid force capacity (rate of torque development, RTD) vs sprint performance in elite youth football players. Methods: Thirty elite academy youth football players (16.75 [1.1] y, 176.9 [6.7] cm, 67.1 [6.9] kg) were included. Isometric peak torque (in Newton meters per kilogram) and early- (0–100 ms) and late- (0–200 ms) phase RTD (RTD100, RTD200) (in Newton meters per second per kilogram) of the hamstring muscles were obtained as independent predictor variables. Sprint performance was assessed during a 30-m-sprint trial. Mechanical sprint variables (maximal horizontal force production [FH0, in Newtons per kilogram], maximal theoretical velocity [V0, in meters per second], maximal horizontal power output [Pmax, in watts per kilogram]) and sprint split times (0–5, 0–15, 0–30, and 15–30 m, in seconds) were derived as dependent variables. Subsequently, linear-regression analysis was conducted for each pair of dependent and independent variables. Results: Positive associations were observed between hamstring RTD100 and FH0 (r2 = .241, P = .006) and Pmax (r2 = .227, P = .008). Furthermore, negative associations were observed between hamstring RTD100 and 0- to 5-m (r2 = .206, P = .012), 0- to 15-m (r2 = .217, P = .009), and 0- to 30-m sprint time (r2 = .169, P = .024). No other associations were observed. Conclusions: The present data indicate that early-phase (0–100 ms) rapid force capacity of the hamstring muscles plays an important role for acceleration capacity in elite youth football players. In contrast, no associations were observed between hamstring muscle function and maximal sprint velocity. This indicates that strength training focusing on improving early-phase hamstring rate of force development may contribute to enhance sprint acceleration performance in this athlete population.

OBJECTIVE: The preseason Nordic Hamstring Protocol (NHP) reduces hamstring strain injuries in football players. Despite persisting injury rates, elite clubs are reluctant to apply the NHP often over concerns of negative impacts on performance. This pilot study investigated if sprint or jump-performance outcomes tended to increase or decrease following implementation of the NHP in elite male soccer-players.RESULTS: Nineteen male soccer players from the Danish 1st division were randomised to perform NHP (27 sessions) during pre-season, or to control group (CG). Sprint performance (30 m with 5 and 10 m split times) and countermovement jump (CMJ height) was measured before the mid-seasonal break and again after 10 weeks of performing the NHP at the end of pre-season. Dropouts were due to transfers and injuries unrelated to performing NHP (NHP = 0, CG = 5). Sprint performance on the short split distances improved for most players in the NHP (6 out of 9 improved, median changes for 5 m split: - 0.068 s; 10 m split: - 0.078 s), but not CG (2 out of 5 improved, median changes for 5 m split: + 0.1 s; 10 m split: CG: + 0.11 s), but both groups had small declines at 30 m sprint (NHP: 7 out of 9 declined, median changes: + 0.116 s; CG: 4 out of 5 declined, median changes: + 0.159 s). CMJ height mostly improved in both groups (NHP: 6 out of 9 improved, median changes: + 2.1 cm; CG: 4 out of 8 improved, median changes: + 0.55 cm). Performing the NHP in elite soccer players did therefore not seem to negatively affect sprint and vertical jump performance outcomes in the present study, while in fact showing some promise for the more explosive characteristics such as the short 5 and 10 m split-times and maximal CMJ height, which all are highly relevant performance parameters in elite football.

OBJECTIVE: To investigate the effect of FIFA injury prevention programmes in football (FIFA 11 and FIFA 11+).DESIGN: Systematic review and meta-analysis.ELIGIBILITY CRITERIA FOR SELECTING STUDIES: Randomised controlled trials comparing the FIFA injury prevention programmes with a control (no or sham intervention) among football players.DATA SOURCES: MEDLINE via PubMed, EMBASE via OVID, CINAHL via Ebsco, Web of Science, SportDiscus and Cochrane Central Register of Controlled Trials, from 2004 to 14 March 2016.RESULTS: 6 cluster-randomised controlled trials had assessed the effect of FIFA injury prevention programmes compared with controls on the overall football injury incidence in recreational/subelite football. These studies included 2 specific exercise-based injury prevention programmes: FIFA 11 (2 studies) and FIFA 11+ (4 studies). The primary analysis showed a reduction in the overall injury risk ratio of 0.75 (95% CI 0.57 to 0.98), p=0.04, in favour of the FIFA injury prevention programmes. Secondary analyses revealed that when pooling the 4 studies applying the FIFA 11+ prevention programme, a reduction in the overall injury risk ratio (incidence rate ratio (IRR) 0.61; 95% CI 0.48 to 0.77, pCONCLUSIONS: An injury-preventing effect of the FIFA injury prevention programmes compared with controls was shown in football. This effect was induced by the FIFA 11+ prevention programme which has a substantial injury-preventing effect by reducing football injuries by 39%, whereas a preventive effect of the FIFA 11 prevention programme could not be documented.TRIAL REGISTRATION NUMBER: PROSPERO CRD42015024120.