The Effectiveness of External Support on Hip Abduction Strength in Subjects with Insufficient Core Stability

The importance of function of the central core of the body for stabilisation and force generation in all sports activities is being increasingly recognised. 'Core stability' is seen as being pivotal for efficient biomechanical function to maximise force generation and minimise joint loads in all types of activities ranging from running to throwing. However, there is less clarity about what exactly constitutes 'the core', either anatomically or physiologically, and physical evaluation of core function is also variable. 'Core stability' is defined as the ability to control the position and motion of the trunk over the pelvis to allow optimum production, transfer and control of force and motion to the terminal segment in integrated athletic activities. Core muscle activity is best understood as the pre-programmed integration of local, single-joint muscles and multi-joint muscles to provide stability and produce motion. This results in proximal stability for distal mobility, a proximal to distal patterning of generation of force, and the creation of interactive moments that move and protect distal joints. Evaluation of the core should be dynamic, and include evaluation of the specific functions (trunk control over the planted leg) and directions of motions (three-planar activity). Rehabilitation should include the restoring of the core itself, but also include the core as the base for extremity function.

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. 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. 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). 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.

Prospective, single-group, repeated-measures design. To identify exercises that could be used for strength development and the exercises that would be more appropriate for endurance or stabilization training. The exercises analyzed are often used in rehabilitation programs for the spine, hip, and knee. They are active exercises using body weight for resistance; thus a clinician is unable to determine the amount of resistance being applied to a muscle group. Electromyographic (EMG) analysis can provide a measure of muscle activation so that the clinician can have a better idea about the effect the exercise may have on the muscle for strength, endurance, or stabilization. Surface EMG analysis was carried out in 19 males and 11 females while performing the following 9 exercises: active hip abduction, bridge, unilateral-bridge, side-bridge, prone-bridge on the elbows and toes, quadruped arm/lower extremity lift, lateral step-up, standing lunge, and using the Dynamic Edge. The rectus abdominis, external oblique abdominis, longissimus thoracis, lumbar multifidus, gluteus maximus, gluteus medius, vastus medialis obliquus, and hamstring muscles were studied. In healthy subjects, the lateral step-up and the lunge exercises produced EMG levels greater than 45% maximum voluntary isometric contraction (MVIC) in the vastus medialis obliquus, which suggests that they may be beneficial for strengthening that muscle. The side-bridge exercise could be used for strengthening the gluteus medius and the external oblique abdominis muscles, and the quadruped arm/lower extremity lift exercise may help strengthen the gluteus maximus muscle. All the other exercises produced EMG levels less than 45% MVIC, so they may be more beneficial for training endurance or stabilization in healthy subjects. Our results suggest these exercises could be used for a core rehabilitation or performance enhancement program. Depending on the individual needs of a patient or athlete, some of the exercises may be more beneficial than others for achieving strength.