George Vagenas

Intrinsic risk factors of non-contact quadriceps and hamstring strains in soccer: a prospective study of 100 professional players

Objectives To identify the intrinsic risk factors of non-contact strains in the hamstrings and quadriceps muscles of professional soccer players via a cohort prospective design. Methods A total of 100 professional soccer players (aged 19.4–27.8 years) from four professional teams underwent a composite musculoskeletal assessment at preseason. Intrinsic risk factors included dichotomies of asymmetries in muscle strength, flexibility, proprioception, anthropometry and knee joint stability, and of previous injuries. Muscle strains were prospectively monitored during the subsequent season using questionnaires. The data were analysed via binary logistic regression. Results Thirty-eight percent of the players sustained one or more lower-extremity muscle strains. Sixteen (42.1 %) and seven (18.4 %) of them were clinically diagnosed as having non-contact muscle strains at their hamstrings and quadriceps, respectively. Players with eccentric hamstring strength asymmetries (OR=3.88; 95% CI 1.13 to 13.23), functional leg length asymmetries (OR=3.80; 95% CI 1.08 to 13.33) and no previous hamstrings injuries (OR=0.15; 95% CI 0.029 to 0.79) were at greater risk of sustaining a hamstring muscle strain. Players with eccentric strength (OR=5.01; 95% CI 0.92 to 27.14) and flexibility asymmetries (OR=4.98; 95% CI 0.78 to 31.80) in their quadriceps as well as heavier (OR=10.70; 95% CI 0.73 to 156.37) and shorter players (OR=0.08; 95% CI 0.00 to 1.35) were at greater risk of sustaining a strain in this muscle group. Conclusions Professional soccer players with functional asymmetries possess a higher risk of sustaining hamstring strains. Previous injury seems not to constitute a risk factor. The systematic isokinetic evaluation of the lower extremities during the preseason period can provide therapists and trainers with valuable data regarding the predictive elements of non-contact hamstring strains in professional soccer players.

Hamstring weakness as an indicator of poor knee function in ACL-deficient patients

Anterior cruciate ligament (ACL) rupture causes instability to the knee joint which leads each patient to a different degree of disability. The purpose of this study was to examine the strength of the quadriceps and the hamstrings in ACL-deficient amateur soccer players at different levels of functional status. Thirty male amateur soccer players were separated into three groups according to their Lysholm score; the high-L1 (Lysholm ≥84), the intermediate-L2 (84> Lysholm ≥72) and the low-L3 (Lysholm <72) knee function groups. The control group consisted of 12 amateur soccer players. The strength of the quadriceps and hamstrings was assessed isokinetically at 60°/s. The quadriceps demonstrated significant deficits of the injured knee compared to the intact knee in all groups, whilst the hamstrings showed significant weakness only in the low function group. Respective percentage deficits in groups L1, L2 and L3 were 13.7%, 16.0% and 18.6% for the quadriceps and 2.4%, 5.6% and 19.2% for the hamstrings. All groups had significant quadriceps weakness which did not differ between the groups. In contrast, the strength deficit of the hamstrings was an indicator of poor knee function, since they were significantly weak only in group L3, which represented patients who clearly failed to compensate for instability symptoms. In groups L1 and L2 the side-to-side differences were within the area of asymmetry measured in the control group. Clinical importance of the results is discussed.

Intrinsic Risk Factors of Noncontact Ankle Sprains in Soccer A Prospective Study on 100 Professional Players

Background: Ankle sprain is an extremely common injury in soccer players. Despite extensive research, the intrinsic cause of this injury under noncontact conditions remains unclear. Purpose: To identify intrinsic risk factors for noncontact ankle sprains in professional soccer players. Study Design: Cohort study; Level of evidence, 2 Methods: One hundred professional soccer players were assessed in the preseason for potential risk factors of noncontact ankle sprains. The assessment included (A) ankle joint asymmetries (right-left) in isokinetic muscle strength, flexibility, proprioception, and stability; (B) somatometric asymmetries; (C) previous injuries; and (D) lateral dominance traits. Noncontact ankle sprains were prospectively recorded and diagnosed for a full competition period (10 months). Results: Seventeen of the players sustained at least 1 noncontact ankle sprain. Logistic regression revealed that players with (A) eccentric isokinetic ankle flexion strength asymmetries (odds ratio [OR] = 8.88; 95% confidence interval [CI], 1.95-40.36, P = .005), (B) increased body mass index (OR = 8.16; 95% CI, 1.42-46.63, P = .018), and (C) increased body weight (OR = 5.72; 95% CI, 1.37-23.95, P = .017 ) each had a significantly higher risk of a noncontact ankle sprain. A trend for younger players (OR = 0.28; 95% CI, 0.061-1.24, P = .092) and for players with ankle laxity asymmetries (OR = 3.38; 95% CI, 0.82-14.00, P = .093) to be at greater risk for ankle sprain was also apparent to the limit of statistical significance (.05 < P < .10). Conclusion: Functional strength asymmetries of the ankle flexors and increased body mass index and body weight raise the propensity for ankle sprains in professional soccer players. Age and asymmetries in ankle laxity are potential factors worth revisiting, as there was an indication for younger players and players with ankle instability to be at higher risk for ankle injury. Proper preseason evaluation may improve prevention strategies for this type of injury in soccer.

Thigh Muscle Weakness in Acl-deficient Knees Persists without Structured Rehabilitation

We evaluated whether quadriceps and hamstrings weakness depended on chronicity in amateur athletes with anterior cruciate ligament deficiencies. We hypothesized that the weakness would not recover to the level of healthy control subjects without structured rehabilitation. Secondarily, we asked whether quadriceps and hamstrings side-to-side percent asymmetry in strength was consistent at different stages of chronicity. Thirty-six male amateur athletes forming equal groups of short, intermediate, and long chronicity (mean, 4, 12, and 56 months, respectively) were tested isokinetically against control subjects at 60° per second. Weakness was substantial in both muscle groups and at all times ranging from 32% to 21% compared with the control subjects. However, side-to-side deficits revealed a linear trend of lessening with time. The quadriceps had greater side-to-side asymmetry that ranged from 23% to 10%, whereas the hamstrings asymmetry ranged from 14% to almost 0%. Acquiring symmetric strength earlier than 1 year after injury only occurred in the hamstrings. It can be inferred that participation in organized rehabilitation would minimize the detrimental effects of anterior cruciate ligament rupture on thigh muscle strength.Level of Evidence: Prognostic Study, Level II. See the Guidelines for Authors for a complete description of levels of evidence.

Anthropometric, flexibility, strength-power, and sport-specific correlates in elite fencing.

This study investigated selected structural correlates of fencing performance. 33 elite fencers were tested on (a) selected anthropometric, flexibility, and strength-power related parameters, and (b) specific lower extremity functional fencing tests. Multiple regression showed that drop jump and thigh cross-sectional area were best predictors of lunge time and distance of squat jump on the shuttle test. When the two performance variables were expressed per Lean Body Mass, lunge time was significantly predicted only by the performance on the arm-driven counter-movement jump, while time on the shuttle test was best predicted by three noncollinear significant predictors: squat jump performance, thigh circumference, and percent body fat. Lunge time and time on the shuttle test were predicted by explosive power, while none of the nontrainable anthropometric measures or years of training seemed to be important in performance of fencing-related skills.

Eversion and inversion muscle group peak torque in hyperpronated and normal individuals.

BACKGROUND Excessive subtalar pronation causes significant changes in the biomechanics of the lower leg, adversely influences proprioceptive feedback and neuromuscular reflex behavior and consequently, affects stability of the foot. However, the changes in muscle strength, caused by hyperpronation are unclear. OBJECTIVES The purpose of the present study was to compare the evertor and invertor peak torque between hyperpronated and normal individuals as well as between their dominant and non-dominant foot. METHOD 20 healthy male participants volunteered for this study. Leg dominance was assessed on the basis of a questionnaire and navicular drop measurements were used to classify participants into two groups: hyperpronated (> or =10 mm) and normals (5-9 mm). Isokinetic concentric eversion and inversion muscle group strength was tested at 30 degrees and 120 degrees/s using the Con-Trex MJ isokinetic dynamometer. RESULTS In all cases, inversion peak torque was greater than eversion peak torque and declined with increasing angular velocity. No significant differences were found for inversion and eversion concentric strength at both speeds tested, neither between normal and hyperpronated individuals neither between their dominant and non-dominant foot. CONCLUSIONS These results indicate the need re-evaluation of navicular drop values in order to identify normal and abnormal subtalar pronation. The assessment of eccentric contractions is also proposed when examining invertors and evertors isokinetic strength.

Leg and vertical stiffness (a)symmetry between dominant and non-dominant legs in young male runners.

Biomechanical findings show that running is asymmetric in many kinetic properties. Running stiffness is a vital kinetic property of yet unknown pattern of lateralization. The aim of this study was to examine the degree and variability of lower limb dominance specific asymmetry of running in terms of leg stiffness, vertical stiffness, contact time, flight time, maximal ground reaction force during contact, vertical displacement of the center of mass, and change in leg length. Leg and vertical stiffness was estimated by the sine-wave method in 22 young males during treadmill running at 4.44 m/s. Lower limb dominance was determined by the triple-jump test. Asymmetry was expressed as dominant - non-dominant, and indexed by the absolute asymmetry index. Significant asymmetry was found only in flight time (3.98%) and in maximal ground reaction force (1.75%). The absolute asymmetry index ranged from 1.8% to 6.4%, showed high variation between subjects (0-31.6%), and differentiated among the 7 analyzed variables. Leg and vertical stiffness in treadmill running of moderate pace (4.44 m/s) should be considered symmetric.