Submaximal fatigue of the hamstrings impairs specific reflex components and knee stability.
ABSTRACT Rupture of the anterior cruciate ligament (ACL) is one of the most serious sports-related injuries and requires long recovery time. The quadriceps and hamstring muscles are functionally important to control stability of the knee joint complex. Fatigue, however, is an important factor that may influence stabilizing control and thus cause ACL injuries. The objective of this study was therefore to assess how submaximal fatigue exercises of the hamstring muscles affect anterior tibial translation as a direct measure of knee joint stability. While 15 test participants were standing upright with the knees in 30 degrees of flexion, anterior tibial translation was induced by a force of 315 N. Two linear potentiometers placed on the tibial tuberosity and the patella recorded tibial motion relative to the femur. Reflex latencies and neuromuscular hamstring activity were determined using surface electromyography (EMG). Muscle fatigue produced a significant longer latency for the monosynaptic reflex latencies, whereas no differences in the latencies of the medium latency component were found. Fatigue significantly reduced EMG amplitudes of the short and medium latency components. These alterations were in line with significantly increased anterior tibial translation. Our results suggest that hamstring fatigue is effectively associated with mechanical loss of knee stability. This decrease in joint stability may at least in part explain higher risk of ACL injury, especially in fatigued muscles. Furthermore, we discuss why the present findings indicate that reduced motor activity rather than the extended latency of the first hamstring response is the reason for possible failure.
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ABSTRACT: PURPOSE: The purpose of this systematic review was to identify the measurements that are used in clinical practice to assess the quantity and quality of functional performance in men and women more than 2 years after ACL reconstruction with bone patellar-tendon bone (BPTB) or semitendinosus/gracilis (STG) graft. METHODS: A systematic literature search was performed in Medline (Pubmed), EMBASE (OVID), the Cochrane Library and PEDro to identify relevant articles from 1990 up to 2010. Articles were included if they described functional performance after BPTB or STG reconstruction and had a follow-up of more than 2 years. Two authors screened the selected articles for title, abstract and full-text in accordance with predefined inclusion and exclusion criteria. The methodological quality of all articles was assessed by checklists of the Cochrane Library by two authors. Only the articles with good methodological quality were considered for further analysis. RESULTS: A total of 27 studies were included by full-text. According to their methodological quality six were rated as good. Different authors used different study designs for muscle testing which led to different outcomes that could not be compared. Besides strength, a single-leg hop for distance was used as a measurement for quantity of functional performance. No measurements for quality of functional performance were reported. CONCLUSIONS: Measurement of functional performance more than 2 years after ACL reconstruction consists of concentric or isometric strength, the single-leg hop for distance or a combination. The Limb Symmetry Index is used as the main outcome parameter to compare the involved leg with the uninvolved. In all studies the results of men and woman are combined. Based on our findings and previous studies that discussed additional important parameters a more extensive test battery to assess functional performance is suggested. LEVEL OF EVIDENCE: III.Knee Surgery Sports Traumatology Arthroscopy 05/2012; · 2.68 Impact Factor
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ABSTRACT: Anterior cruciate ligament (ACL) rupture ranks among the most common injuries in sports. The incidence of ACL injuries is considerably higher in females than in males and the underlying mechanisms are still under debate. Furthermore, it has been suggested that muscle fatigue can be a risk factor for ACL injuries. We investigated gender differences in hamstring reflex responses and posterior-anterior tibial translation (TT) before and after fatiguing exercise. We assessed the isolated movement of the tibia relative to the femur in the sagittal plane as a consequence of mechanically induced TT in standing subjects. The muscle activity of the hamstrings was evaluated. Furthermore, isometric maximum voluntary torque (iMVT) and rate of torque development (RTD) of the hamstrings (H) and quadriceps (Q) were measured and the MVT H/Q as well as the RTD H/Q ratios were calculated. After fatigue, reflex onset latencies were enhanced in women. A reduction of reflex responses associated with an increased TT was observed in females. Men showed no differences in these parameters. Correlation analysis revealed no significant associations between parameters for TT and MVT H/Q as well as RTD H/Q. The results of the present study revealed that the fatigue protocol used in this study altered the latency and magnitude of reflex responses of the hamstrings as well as TT in women. These changes were not found in men. Based on our results, it is conceivable that the fatigue-induced decrease in neuromuscular function with a corresponding increase in TT probably contributes to the higher incidence of ACL injuries in women.PLoS ONE 01/2013; 8(2):e56988. · 3.53 Impact Factor
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ABSTRACT: The ability to sustain brief high-intensity intermittent efforts (HIE) is meant to be a major attribute for performance in team sports. Adding changes of direction to HIE is believed to increase the specificity of training drills with respect to game demands. The aim of this study was to investigate the influence of 90[degree sign]-changes of direction (COD) during HIE on metabolic and neuromuscular responses. Eleven male, team sport players (30.5 +/- 3.6 y) performed randomly HIE without (straight-line, 2x[10x 22 m]) or with (2x[10x ~16.5 m]) two 90[degree sign]-COD. To account for the time lost while changing direction, the distance for COD runs during HIE was individually adjusted using the ratio between straight-line and COD sprints. Players also performed 2 countermovement (CMJ) and 2 drop (DJ) jumps, during and post HIE. Pulmonary oxygen uptake (VO2), quadriceps and hamstring oxygenation, blood lactate concentration (Delta[La]b), electromyography amplitude (RMS) of eight lower limb muscles and rating of perceived exertion (RPE) were measured for each condition. During HIE, CODs had no substantial effects on changes in VO2, oxygenation, CMJ and DJ performance and RPE (all differences in the changes rated as unclear). Conversely, compared with straight-line runs, COD-runs were associated with a possibly higher Delta[La]b (+9.7 +/- 10.4%, with chances for greater/similar/lower values of 57/42/0%)and either a lower (i.e., -11.9 +/- 14.6%, 2/13/85 for semitendinosus and -8.5 +/- 9.3%, 1/21/78 for lateral gastrocnemius) or equivalent decrease in electromyography amplitude. Adding two 90[degree sign]-CODs on adjusted distance during two sets of HIE is likely to elicit equivalent decreases in CMJ and DJ height, and similar cardiorespiratory and perceptual responses, despite a lower average running speed. A fatigue-induced modification in lower limb control observed with CODs may have elicited a selective reduction of electromyography activity in hamstring muscles and may induce, in turn, a potential mechanical loss of knee stability. Therefore, changing direction during HIE, with adjusted COD running distances, might be an effective training practice 1) to manipulate some components of the acute physiological load of HIE, 2) to promote long-term COD-specific neuromuscular adaptations aimed at improving performance and knee joint stability.BMC sports science, medicine and rehabilitation. 01/2014; 6(1):2.