Using BOSU to Alleviate Knee Pain

Many people suffer from mild to severe knee pain that prevents them from engaging in enjoyable activities such as hiking, playing tennis, or simply walking.  They blame the knee for their woes, yet the cause of the problem may not be the knees at all.

The muscles that help stabilize the knee during movement originate from either the foot and ankle, or from the lumbo-pelvic hip girdle.  Hence, if the foot/ankle or hip complex is not working correctly, then the soft tissue structures that provide support to the knee will be adversely affected.  As such, it is important to understand how the joints and muscles above and below the knees work, and to perform exercises that will keep these muscles strong and healthy.

Functional Anatomy of the Lower Kinetic Chain

There are many muscles in the lower and upper leg that are responsible for the functioning processes of the knee.  They work together to affect movement of the knee, but each has a specific task that contributes to healthy knee function.

The Feet and Ankles

The feet and ankles act as shock absorbers when the body interacts with a contact surface as well as assisting with the adaptation of the body to the terrain. Many muscles of the lower leg (e.g., the calfs, peroneals, anterior and posterior tibialis) assist with the functions of the foot and ankle as well as having direct impact on the knee.

The Calf Muscles

Most anatomy books identify that the soleus muscle assists in plantar flexing the ankle when the knee is bent.  Similarly, they also state that the gastrocnemius plantar flexes the ankle, and because it crosses the knee, it also assists in flexing the knee.  However, the function of these muscles become more complex when ground reaction forces are introduced.

When the heel strikes the ground during gait, lunging or a squat, the lower leg (tibia) continues to travel forward over the foot (dorsiflex) and the knee bends, causing the calf muscles (especially the soleus) to stretch (see Picture 1).  When the leg travels behind the hip into extension, the knee straightens and the gastrocnemius stretches (see Picture 2).  It is important to understand that these muscles are not loosening during the stretch phase. On the contrary, they are lengthening under tension as they slow down forces to the knee and ankle joints during the movement.

Picture 1. Increasing the tensile load to the soleus muscle as it lengthens	Picture 2: Increasing the tensile load to the gastrocnemius muscle as it lengthens

To better understand how these muscles function as they lengthen under load, imagine stretching a rubber band with your fingers.  The longer the band is stretched, the more tension there is in the rubber band.  Likewise, tension increases to protect the joints that the muscles cross from excessive wear and tear during the lengthen phase.  Therefore, the true function of the calf muscles is to decelerate forces during movement to the knee and ankle joints when the foot is in contact with the ground.

Tibialis Anterior and Tibialis Posterior

There are muscles on the inside and outside of the lower leg (i.e., tibialis anterior and posterior) that also help slow down forces to the foot and ankle (and, therefore, the knee) as the foot strikes the ground.  Most of these muscles wrap around and/or attach to the underside of the foot and some assist in holding up the arches of the foot.  When the foot pronates to help the body absorb shock, the arches of the feet flatten out.  The flattening of the arches helps to lengthen the muscles of the lower leg that wrap underneath those arches, thereby increasing tension in those muscles.  As a result, the lengthening of the tibialis anterior and posterior controls forces through and minimizes stress to the ankle and knee joints.

The Lumbo-Pelvic Hip Girdle

The lumbo-pelvic hip girdle is where the lower spine, pelvis, and top of the legs come together.  The main function of this area is to ensure the legs can move forward when walking, lunging or squatting and that the torso can follow along on a stable base of support.  Just as many of the muscles that attach to the foot control the lower leg (tibia), there are some larger muscles that originate from the lumbo-pelvic hip region (i.e., the gluteus maximus via the IT band and the hamstrings) which also control the tibia.

The Gluteus Maximus

Most anatomy books state that the gluteus maximus assists in hip/leg extension and outward rotation of the leg.  Keep in mind that the function of the gluteus maximus is completely different when ground reaction forces come into play.  When the foot comes into contact with the ground and pronates, the tibia rotates inwardly over the foot.  The inward rotation of the lower leg moves the insertion of the gluteus maximus (on the outside of the tibia) away from its origin (near the base of the spine and back of the pelvis).  This motion lengthens the muscle, thereby creating tension in it like a rubber band.  This tension helps slow down the internal rotation of the tibia.  Consequently, stress to the knee is kept to a minimum as it moves toward the midline of the body.

The Hamstrings

The hamstrings also affect knee function since they cross the knee.  (They originate on the ischium and insert below the knee on the back of the tibia.)  According to traditional text books, the hamstrings help flex the knee and extend the hips.  However, once the heel strikes the ground, the hamstrings actually lengthen to help prevent excessive stress to both the hip and the knee.  The tension generated in the hamstrings stops the hips from moving backward (which keeps the spine upright and prevents the body from falling forward causing stress to the knee).  They also retard flexion of the knee so that the knee joint does not experience excessive stress as it bends (see Picture 3).

Picture 3. Increasing the tensile load to the hamstrings as they lengthen

As demonstrated, the muscles of the upper and lower leg discussed in this article lengthen under load like a rubber band to help prevent unnecessary stress to the knee joint.  The reason many people experience knee pain is that one or more of these muscles are not functioning in an optimal manner and therefore are not able to adequately perform their specific role in maintaining healthy knee function.

How Can BOSU Help Alleviate Knee Pain?

Performing exercises on a flat surface limits the range of motion of the heel and foot.  The heel stops when it hits the floor and the foot pronates until it flattens to the ground.  However, performing exercises on a BOSU enables the heel to press down further as the dome surface of the BOSU gives.  Not only does this increase the foot and ankles’ ability to dorsiflex, but it also turns on both the calf and hamstring muscles so they can help protect the knee as it flexes.  Similarly, the soft dome of the BOSU allows the foot to pronate further than exercises performed on the ground.  This augmented range of motion in the foot and ankle results in an increased eccentric contraction for the muscles of the lower leg as well as more tension. The additional degree of pronation also helps boost tension on the gluteus maximus (as the tibia internally rotates) which can help protect the knee.

Using The BOSU To Train Muscles Effectively

The following exercises demonstrate three movements that are designed to increase the range of motion for the lower kinetic chain.  Putting the body through these movements will help activate those muscles that are directly responsible for slowing down forces to the knee, thereby helping to alleviate pain and improve function.

Multiplanar Lower Leg Stretch on BOSU

This is a dynamic stretch that supports an increased range of motion at the foot, ankle and knee which will prepare these structures for the weight bearing kinetic chain exercises that follow.

Position 1: Push the heel down into the BOSU as while bending the knee forward and pronating the foot.	Position 2: Push the heel down into the BOSU while straightening the knee and supinating the foot.

Lunge with Forward Reach on BOSU

This is a sagittal plane lunge designed to increase dorsiflexion at the ankle and increase knee flexion.  This will increase the tensile load to the posterior calf, hamstrings and quadriceps as the ankle and knee move away from each other.

Position 1: Begin in a split stance with one foot on the BOSU and the other foot on the floor.	Position 2: Lunge down and reach forward.  During the lunge, push the heel down, bend the knee and hip and transfer weight over the foot while reaching forward.  This will turn on the hamstrings, calves, quads and glutes.

Lunge with Transverse Reach across Body on BOSU

This is a transverse plane lunge designed to increase internal rotation of the tibia and femur and pronation at the foot and ankle.  This will increase the tensile load to the gluteus maximus, gluteus medius and gluteus minimus.

Position 1: Begin in a split stance with one foot on the BOSU and the other foot on the floor.	Position 2: Lunge down and reach forward across the front leg.  During the lunge, push the heel down, let the foot pronate and allow the knee to move toward the midline of the body.  This will create a counter balance for the cross-body arm reach action and will assist in the engagement of the gluteal complex.

Note: All of the above exercises can be performed in bare feet to increase the demand.  However, be aware that executing these exercises while barefoot will dramatically increase the range of motion at every joint so this is not recommended for users who typically wear orthotics or arch supports.

By utilizing the exercises illustrated in this article and applying the knowledge of the functional anatomy of the knee, you will be able to design and implement exercises that both prevent injury to the knee and correct imbalances of the lower kinetic chain.

References

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