Lee SP, Powers CM. Individuals with diminished hip abductor muscle strength exhibit altered ankle biomechanics and neuromuscular activation during unipedal balance tasks. Gait & Posture 2014, 39: 933-938.
This study investigated the relationship between hip strength and foot function during tasks while standing on one leg. They studied static standing and a dynamic task requiring reaching with the non-stance leg. The subjects were 45 females who were divided into three groups based on isometric hip abduction strength. Strength was tested in standing based on a protocol used in a previous paper. The 15 subjects with the highest strength values were considered “strong” while the 15 with the lowest values made up the “weak” group. Kinematic, kinetic, and electromyography data was compared between the strong and weak groups.
This blog will focus on the results from the dynamic task. This task required a forward reach with the opposite limb until touching a surface below with the heel (step down and return). The height difference was normalized at 10% of subject height. The average hip abductors value for the weak group was 21 Newtons / kilogram (N / kg) compared to 30 N / kg for the strong group. The medial to lateral shift of the Center of Pressure was 39% greater for the weaker group (136 – 98 mm). The weak group also demonstrated greater invertor moments and greater activation of the peroneus longus muscle, presumably to control the invertor moments.
Why are these findings important to function? First, it is further proof of the Chain Reaction® basis of human movement. Hundreds of research articles now support the Principles of Applied Functional Science® (AFS) that have been taught by Dr. Gary Gray for over 30 years. Second, it speaks to Strategies for assessment and training / rehabilitation that address the body as an integrated system rather than a collection of isolated joints. The specific movements / exercises are the Techniques dictated by the Strategy. The Principles – Strategies – Techniques process serves as the foundation of AFS.
Using the “weak” subjects in this study as the target population for our example, let’s consider some movements to rectify the deficits in strength and the resulting postural instability. The majority of movement practitioners, based on their educational training, would position the patient / client on his / her side and have him / her abduct his / her leg against gravity. This will improve abductor strength, but lacks two essential “ingredients”: proprioceptor activation of the muscles during weight-bearing, and integration of the knee and foot. At Gray Institute®, the “test is the exercise.” So the dynamic step down and return task used in this study could be a great training movement. But how do we prepare the body to be more successful (functional)?
For this example, let’s consider the right hip abductor muscles as the target of the intervention. Lunges with the right leg will turn on the hip abductor muscles. The direction of the lunges can be sequenced to require more effort from the abductors. Lunges with the left leg will also create the hip motions on the right side. Frontal plane lunges, both Same Side Lateral and Opposite Side Lateral, will create the motion of right hip adduction that requires the right abductor muscles to fire without conscious activation. Single leg balance movements with resistance (pulley or elastic band) attached to the left leg require the right hip muscles to be activated by the proprioceptors based on the direction of leg movement. To challenge the right abductors the resistance would be attached pulling the left leg to the right. After success with these movements, the step down and return testing movement can be utilized for training with tweaks of the direction of the reaching leg. These are just a few of the training movements that would emanate from the Principle-based Strategy.
Research continues to provide proof of the truth that has been known for hundreds of years: the body is a reactive integrated system that desires to be trained and rehabilitated as such.
For more information on the Chain Reaction® of the body, please take a look at 3DMAPS® (3D Movement Analysis & Performance System)