An estimated 80,000 anterior cruciate ligament (ACL) tears occur annually in the United States. The highest incidence is in individuals 15 to 25 years old who participate in pivoting sports. With an estimated cost for these injuries of almost a billion dollars per year, the ability to identify risk factors and develop prevention strategies has widespread health and fiscal importance. Seventy percent of ACL injuries occur in noncontact situations. The risk factors for non-contact ACL injuries fall into four distinct categories: environmental, anatomic, hormonal, and biomechanical. Early data on existing neuromuscular training programs suggest that enhancing body control may decrease ACL injuries in women. Further investigation is needed prior to instituting prevention programs related to the other risk factors.

Noncontact anterior cruciate ligament injuries: risk factors and prevention strategies References:

Noncontact anterior cruciate ligament injuries: risk factors and prevention strategies.

LEETUN, D. T., M. L. IRELAND, J. D. WILLSON, B. T. BALLANTYNE, and I. M. DAVIS. Core Stability Measures as Risk Factors for Lower Extremity Injury in Athletes. Med. Sci. Sports Exerc., Vol. 36, No. 6, pp. 926 –934, 2004. Introduction/Purpose: Decreased lumbo-pelvic (or core) stability has been suggested to contribute to the etiology of lower extremity injuries, particularly in females. This prospective study compares core stability measures between genders and between athletes who reported an injury during their season versus those who did not. Finally, we looked for one or a combination of these strength measures that could be used to identify athletes at risk for lower extremity injury. Methods: Before their season, 80 female (mean age 19.1 1.37 yr, mean weight 65.1 10.0 kg) and 60 male (mean age 19.0 0.90 yr, mean weight 78.8 13.3 kg) intercollegiate basketball and track athletes were studied. Hip abduction and external rotation strength, abdominal muscle function, and back extensor and quadratus lumborum endurance was tested for each athlete. Results: Males produced greater hip abduction (males 32.6 7.3%BW, females 29.2 6.1%BW), hip external rotation (males 21.6 4.3%BW, females 18.4 4.1%BW), and quadratus lumborum measures (males 84.3 32.5 s, females 58.9 26.0 s). Athletes who did not sustain an injury were significantly stronger in hip abduction (males 31.6 7.1%BW, females 28.6 5.5%BW) and external rotation (males 20.6 4.2%BW, females 17.9 4.4%BW). Logistic regression analysis revealed that hip external rotation strength was the only useful predictor of injury status (OR 0.86, 95% CI 0.77, 0.097). Conclusion: Core stability has an important role in injury prevention. Future study may reveal that differences in postural stability partially explain the gender bias among female athletes. Key Words: GENDER, HIP STRENGTH, TRUNK ENDURANCE, BASKETBALL, TRACK

https://www.marylloydireland.com/PDFSCANS/GAIT_RESEARCH/2004_ACSM_Core_Stability_Measures_as_Risk_Factors_for_Lower_Extremity_Injury_in_Athletes.pdf

Core stability measures as risk factors for lower extremity injury in athletes.

Core stability may provide several benefits to the musculoskeletal system, from maintaining low back health to preventing knee ligament injury. As a result, the acquisition and maintenance of core stability is of great interest to physical therapists, athletic trainers, and musculoskeletal researchers. Core stability is the ability of the lumbopelvic hip complex to prevent buckling and to return to equilibrium after perturbation. Although static elements (bone and soft tissue) contribute to some degree, core stability is predominantly maintained by the dynamic function of muscular elements. There is a clear relationship between trunk muscle activity and lower extremity movement. Current evidence suggests that decreased core stability may predispose to injury and that appropriate training may reduce injury. Core stability can be tested using isometric, isokinetic, and isoinertial methods. Appropriate intervention may result in decreased rates of back and lower extremity injury.

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Core stability and its relationship to lower extremity function and injury.

Background: Numerous factors have been identified as potentially increasing the risk of anterior cruciate ligament injury in the female athlete. However, differences between the sexes in lower extremity coordination, particularly hip control, are only minimally understood. Hypothesis: There is no difference in kinematic or electromyographic data during the single-legged squat between men and women. Study Design: Descriptive comparison study. Methods: We kinematically and electromyographically analyzed the single-legged squat in 18 intercollegiate athletes (9 male, 9 female). Subjects performed five single-legged squats on their dominant leg, lowering themselves as far as possible and then returning to a standing position without losing balance. Results: Women demonstrated significantly more ankle dorsiflexion, ankle pronation, hip adduction, hip flexion, hip external rotation, and less trunk lateral flexion than men. These factors were associated with a decreased ability of the women to maintain a varus knee position during the squat as compared with the men. Analysis of all eight tested muscles demonstrated that women had greater muscle activation compared with men. When each muscle was analyzed separately, the rectus femoris muscle activation was found to be statistically greater in women in both the area under the linear envelope and maximal activation data. Conclusions: Under a physiologic load in a position commonly assumed in sports, women tend to position their entire lower extremity and activate muscles in a manner that could increase strain on the anterior cruciate ligament. © 2003 American Orthopaedic Society for Sports Medicine

Differences in Kinematics and Electromyographic Activity between Men and Women during the Single-Legged Squat*:

Dynamics of force and muscle stimulation in human vertical jumping. Med. Sci. Sports Exerc., Vol. 31, No. 2, pp. 303-310, 1999.Purpose:The purpose of this study was to gain insight into the importance of stimulation dynamics for force development in human vertical jumping.Methods:Maximum hei

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Dynamics of force and muscle stimulation in human vertical jumping

VAN ZANDWIJK, J. P., M. F. BOBBERT, M. MUNNEKE, and P. PAS. Control of maximal and submaximal vertical jumps.Med. Sci. Sports Exerc., Vol. 32, No. 2, pp. 477‐ 485, 2000. Purpose: It was investigated to what extent control signals used by human subjects to perform submaximal vertical jumps are related to control signals used to perform maximal vertical jumps. Methods: Eight subjects performed both maximal and submaximal height jumps from a static squatting position. Kinematic and kinetic data were recorded as well as electromyographic (EMG) signals from eight leg muscles. Principal component analysis was used analyze the shape of smoothed rectified EMG (SREMG) histories. Jumps were also simulated with a forward dynamic model of the musculoskeletal system, comprising four segments and six muscles. First, a maximal height jump was simulated by finding the optimal stimulation pattern, i.e., the pattern resulting in a maximum height of the mass center of the body. Subsequently, submaximal jumps were simulated by adapting the optimal stimulation pattern using strategies derived from the experimental SREMG histories. Results: SREMG histories of maximal and submaximal jumps revealed only minor differences in relative timing of the muscles between maximal and submaximal jumps, but SREMG amplitude was reduced in the biarticular muscles. The shape of the SREMG recordings was not much different between the two conditions, even for the biarticular muscles. The simulated submaximal jump resembled to some extent the submaximal jumps found in the experiment, suggesting that differences in control signals as inferred from the experimental data could indeed be sufficient to get the observed behavior. Conclusions: The results fit in with theories on the existence of generalized motor programs within the central nervous system, the output of which is determined by the setting of parameters such as amplitude and

/pdf/control-of-maximal-and-submaximal-vertical-jumps-1mcjzpevsx.pdf

Control of maximal and submaximal vertical jumps

In models describing the excitation of muscle by the central nervous system, it is often assumed that excitation during a tetanic contraction can be obtained by the linear summation of responses to individual stimuli, from which the active state of the muscle is calculated. We investigate here the extent to which such a model describes the excitation of human muscle in vivo. For this purpose, experiments were performed on the calf muscles of four healthy subjects. Values of parameters in the model describing the behaviour of the contractile element (CE) and the series elastic element (SEE) of this muscle group were derived on the basis of a set of isokinetic release contractions performed on a special-purpose dynamometer as well as on the basis of morphological data. Parameter values describing the excitation of the calf muscles were optimized such that the model correctly predicted plantar flexion moment histories in an isometric twitch, elicited by stimulation of the tibial nerve. For all subjects, the model using these muscle parameters was able to make reasonable predictions of isometric moment histories at higher stimulation frequencies. These results suggest that the linear summation of responses to individual stimuli can indeed give an adequate description of the process of human muscle excitation in vivo.

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From twitch to tetanus for human muscle: experimental data and model predictions for m-triceps surae

The effect of muscle stimulation dynamics on the sensitivity of jumping achievement to variations in timing of muscle stimulation onsets was investigated. Vertical squat jumps were simulated using a forward dynamic model of the human musculoskeletal system. The model calculates the motion of body segments corresponding to STIM(t) of six major muscle groups of the lower extremity, where STIM is muscle stimulation level. For each muscle, STIM was allowed to switch "on" only once. The subsequent rise of STIM to its maximum was described using a sigmoidal curve, the dynamics of which was expressed as rise time (RT). For different values of stimulation RT, the optimal set of onset times was determined using dynamic optimization with height reached by the center of mass as performance criterion. Subsequently, 200 jumps were simulated in which the optimal muscle stimulation onset times were perturbed by adding to each a small number taken from a Gaussian-distributed set of pseudo-random numbers. The distribution of heights achieved in these perturbed jumps was used to quantify the sensitivity of jump height to variations in timing of muscle stimulation onsets. It was found that with increasing RT, the sensitivity of jump height to timing of stimulation onset times decreased. To try and understand this finding, a post-hoc analysis was performed on the perturbed jumps. Jump height was most sensitive to errors in the delay between stimulation onset times of proximal muscles and stimulation onset times of plantar flexors. It is explained how errors in this delay cause aberrations in the configuration of the system, which are regenerative and lead to relatively large jump height deficits. With increasing RT, the initial aberrations due to erroneous timing of muscle stimulation are smaller, and the regeneration is less pronounced. Finally, it is speculated that human subjects decrease or increase RT depending on the relative importance of different performance criteria.

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Sensitivity of vertical jumping performance to changes in muscle stimulation onset times: a simulation study

In guided leg movements (e.g., in cycling or wheelchair propulsion), the kinematics of a limb are determined by the object on which a force is applied. As a consequence, the force direction can vary and may deviate from the movement direction, that is, the effective direction. In the present study, the relation of effective force application and maximal power output was examined. Subjects (n = 5) performed guided leg tasks on a special dynamometer. They were instructed to exert a maximal force against a moving forceplate in the direction of the movement, as if they were pushing the plate away. Three different movement directions were tested: perpendicular to the horizontal, rotated 30° backward, and rotated 30° forward. For each trial, force and position data were recorded. The results of the experiments showed that in the extreme movement directions (both 30° conditions), the force vector deviated significantly from the direction of the movement. Apparently, maximal power output was achieved wit...

J P van Zandwijk

Papers

Dynamics of force and muscle stimulation in human vertical jumping

Control of maximal and submaximal vertical jumps

From twitch to tetanus for human muscle: experimental data and model predictions for m-triceps surae

Sensitivity of vertical jumping performance to changes in muscle stimulation onset times: a simulation study

On the Effectiveness of Force Application in Guided Leg Movements