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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 ofU 13 toU 14 (18% 39%) andU 14 toU 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 andU 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.

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.

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.

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.