Irene McClay Davis

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

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.

Gender differences in lower extremity mechanics during running.

OBJECTIVE To compare differences in hip and knee kinematics and kinetics in male and female recreational runners. DESIGN Gait analysis of 20 men and 20 women recreational runners. BACKGROUND Female runners are reported to be more likely to sustain certain lower extremity injuries compared to their male counterparts. This has been attributed, in part, to differences in their structure and it has been postulated that these structural differences may lead to differences in running mechanics. It was hypothesized that females would exhibit greater peak hip adduction, hip internal rotation, knee abduction and decreased knee internal rotation compared to their male counterparts. It was also hypothesized that females would exhibit greater hip and knee negative work in the frontal and transverse planes compared to males. METHODS Comparisons of hip and knee three-dimentional joint angles and negative work during the stance phase of running gait were made between genders. RESULTS Female recreational runners demonstrated a significantly greater peak hip adduction, hip internal rotation and knee abduction angle compared to men. Female recreational runners also demonstrated significantly greater hip frontal and transverse plane negative work compared to male recreational runners. CONCLUSION Female recreational runners exhibit significantly different lower extremity mechanics in the frontal and transverse planes at the hip and knee during running compared to male recreational runners. RELEVANCE Understanding the differences in running mechanics between male and female runners may lend insight into the etiology of different injury patterns seen between genders. In addition, these results suggest that care should be taken to account for gender when studying groups of male and female recreational runners.

Lower extremity stiffness: implications for performance and injury

BACKGROUND Lower extremity stiffness is thought to be an important factor in musculoskeletal performance. However, too little or too much stiffness is believed to increase the risk of musculoskeletal injury. PURPOSE To provide a current update of the lower extremity stiffness literature as it pertains to both performance and injury. SUMMARY It appears that increased stiffness is beneficial to performance. As well it appears that there may be an optimal amount of stiffness that allows for injury-free performance. There is some evidence that increased stiffness may be related to bony injuries and decreased stiffness may be associated with soft tissue injuries. Further investigations should evaluate the relationship between stiffness and injury prospectively. Initial reports suggest that stiffness can be modified in response to the external environment or verbal cues. RELEVANCE A greater understanding of the role of stiffness in both performance and injury will provide a stronger foundation for the development of optimal training intervention programs.

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

&NA; 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.

High-arched runners exhibit increased leg stiffness compared to low-arched runners

Leg stiffness between high-arched (HA) and low-arched (LA) runners was compared. It was hypothesized that high-arched runners would exhibit increased leg stiffness, increased sagittal plane support moment, greater vertical loading rates, decreased knee flexion excursion and increased activation of the knee extensor musculature. Twenty high-arched and 20 low-arched subjects were included in this study. Leg stiffness, knee stiffness, vertical loading rate and lower extremity support moment were compared between groups. Electromyographic data were collected in an attempt to explain differences in leg stiffness between groups. High-arched subjects were found to have increased leg stiffness and vertical loading rate compared to low-arched runners. Support moment at the impact peak of the vertical ground reaction force was related to leg stiffness across all subjects. High-arched subjects demonstrated decreased knee flexion excursion during stance. Finally, high-arched subjects exhibited a significantly earlier onset of the vastus lateralis (VL) than the low-arched runners. Differences exist in leg stiffness and vertical loading rate between runners with different foot types. Differences in lower extremity kinetics in individuals with different foot types may have implications for new treatment strategies or preventative measures.

Effect of inverted orthoses on lower-extremity mechanics in runners

INTRODUCTION Foot orthoses are recommended for individuals with injuries associated with abnormal lower-extremity mechanics. However, the biomechanical effect of these devices is not completely understood. Most clinicians and researchers believe that foot orthoses are effective in reducing some aspect of rearfoot motion. This is important as many injuries are suggested to be the result of increased pronation. Inverted orthoses are a more aggressive treatment in those whose symptoms do not respond to standard orthotics. They are likely to alter motion in all planes. However, no three-dimensional studies have assessed lower-extremity mechanics in individuals wearing inverted orthotics. PURPOSE The purpose of this study was to compare the three-dimensional kinematics and kinetics of the rearfoot and knee during running while varying orthotic intervention. METHODS Eleven subjects were initially fitted with standard foot orthoses and then with inverted orthoses. Three-dimensional kinematic and kinetic data were collected for conditions of no orthoses, standard orthoses, and inverted orthoses. RESULTS There were no differences between conditions in peak rearfoot eversion or rearfoot eversion excursion. Peak rearfoot inversion moment and work were significantly reduced (P = 0.045 and P < 0.001, respectively) in the inverted orthotic condition suggesting a decreased demand on the soft tissue structures that control eversion. Significant differences were seen in tibial rotation (P = 0.043), knee adduction (P = 0.035), and knee abduction moment (P < 0.001) in the inverted orthotic condition, suggesting alterations were made further up the kinetic chain. CONCLUSIONS The differences in kinetic parameters at the rearfoot may result in fewer injuries of the rearfoot soft tissue structures when using inverted orthotics. These alterations in lower-extremity mechanics associated with inverted orthoses provide clinicians some evidence for prescribing this device.

A comparison of four methods of obtaining a negative impression of the foot.

Four methods are currently available for taking a negative impression of the foot for the purpose of fabricating an orthotic device: nonweightbearing plaster casting, partial-weightbearing foam impressions, and partial-weightbearing and nonweightbearing laser scanning. This study compares the reliability and accuracy of these methods. Each impression method was performed three times on each foot of 15 subjects. Measures of rearfoot and forefoot width, forefoot-to-rearfoot relationship, and arch height were obtained from the negative impressions. Additionally, rearfoot and forefoot width and forefoot-to-rearfoot relationship were measured clinically for each subject. This study found that 1) foot measures are significantly influenced by the method used to obtain a negative foot impression; 2) the methods differ in reliability; and 3) plaster casting may be preferable to the other three methods when it is important to capture the forefoot-to-rearfoot relationship, as in fabricating a functional orthosis.

Dual-function foot orthosis: effect on shock and control of rearfoot motion.

Orthoses have been designed that claim to both reduce shock and control rearfoot motion. It was hypothesized that the dual-purpose soft orthosis would reduce shock and control rearfoot motion greater than a no-orthotic condition. Three-dimensional kinematic and kinetic data were collected along with tibial acceleration while subjects ran in no-orthotic, the dual-purpose orthotic, and a rigid orthotic condition. Variables of interest were eversion excursion, peak eversion, eversion velocity, peak positive acceleration, loading rate, and leg stiffness. None of the evaluated variables were significantly different (p = .05) between the three conditions. These data suggest that shock attenuation and rearfoot motion cannot be controlled by the orthoses used in this study for a group of healthy runners.

The effect of a single treatment of the Protonics™ system on biceps femoris and gluteus medius activation during gait and the lateral step up exercise

INTRODUCTION Patellofemoral pain, a frequent complaint among women, is attributed in part to excessive femoral internal rotation, leading to patellofemoral malalignment. The Protonics resistive dynamic knee orthosis was designed to facilitate hamstring activation, leading to a less anteriorly tilted pelvis and less femoral internal rotation. This decrease in femoral internal rotation is thought to improve patellofemoral joint alignment, thereby reducing knee pain. In this position, the gluteus medius (GM) would be more effective against the force of gravity. Therefore, this studys purpose was to determine the effects of a single application of the Protonics orthosis on knee pain and biceps femoris (BF) and GM activation. METHODS 21 females (23.4+/-3.1 years, 1.66+/-0.05 m, 65.3+/-20.4 kg) with a history of chronic PFP participated in the study. Data were collected during level walking and a lateral-step up exercise in three conditions: pre-treatment (PRE), a placebo condition collected after the orthosis was set at zero resistance (PLAC), and post-treatment (POST). PLAC and POST were performed after the orthosis had been removed from the subjects leg. Percent of gait cycle activated, integrated EMG (IEMG), and level of pain (VAS scale) were measured in each condition. An ANOVA was used to determine significance between conditions (alpha=0.05). RESULTS Use of the Protonics orthosis did not result in any change in the level of knee pain, IEMG or duration of activation for the BF or GM. SUMMARY Our results do not support an increase in hamstring activation or decrease in GM activation following a single treatment with the Protonics orthosis.