Multi Planar Stretching for the Two-Joint Flexors

By: Anthony Carey, MA, CSCS, CES

I realize it is called the BOSU® Balance Trainer. Of course it provides an environment in which to challenge balance mechanisms in a variety of ways. However, the same design and materials that have become synonymous with balance also have a hidden benefit.

At Function First, we work with a population of clients that deal with long-term musculoskeletal challenges such as joint, soft tissue and/or neurological pain. Associated with these challenges are movement dysfunctions that are either an underlying cause of pain, or a resulting effect of pain avoidance and compensation.

In either event, a common dysfunction found is a limitation in functional flexibility. A critical area in most people is the hip flexor. In our society, it is no big secret that the hip flexors have a tendency to be short and tight. A major contributor to this condition is the propensity towards sitting frequently during everyday life. For most people, this situation is not going to change. Therefore, it is our responsibility as health professionals to see that clients, athletes or patients are given the appropriate tools to maintain functional flexibility. 

Ample exercises are available and practiced for the purpose of addressing hip flexor length. The limitation with most of these programs is that the flexibility strategy only addresses the sagittal plane component of this muscle group. Since all muscles have a multi-planar function, all planes should ultimately be included to comprehensively address the flexibility issue.

Both the shape and surface of the BT allows us to address flexibility in multiple planes. The shape of the BT gives the client an effective pre-stretch of the involved muscles in the plane each are most commonly associated with. In the case of the hip flexors, this is the sagittal plane.

Two Joint Hip Flexors

In most discussions about hip flexors, the two-joint hip flexors are often forgotten, especially in regard to the iliopsoas, or ilacus and psoas mucles. Both muscles attach on the inner-upper thigh area. The iliacus originates from the anterior aspect of the pelvis, whereas the psosas originates from the sides of the lower vertebrae. A two-joint muscle (or biarticular) is one that crosses two joints. Many are familiar with the rectus femoris as a two-joint hip flexor because it crosses both the hip and knee joint. However, the rectus femoris is not alone in this function. The sartorius and gracilis cross both the hip and knee joints as well. Both attach very close to one another on the medial aspect of the proximal tibia, or lower leg. Another overlooked muscle as it relates to both the knee and hip is the tensor fascia latae. This muscle is a secondary hip flexor, but also acts on the knee via the iliotibial band. Mechanically, the two-joint hip flexors are commonly lengthened (in the sagittal plane) with the knee flexed and hip extended. This lengthening can easily be accomplished using the BT.

Like single joint hip flexors, lack of mobility in this group (two joint hip flexors) can add stress to the lower back because it limits hip extension. If the hip is limited in extension, the lumbar spine must provide additional motion in the sagittal plane with increased extension. If the increased extension occurs with walking or lunging, it adds additional components of rotation and lateral flexion in amounts the spine cannot tolerate over time. This can lead to low back injuries in the lumbar region.

Furthermore, because the biarticulate (two joint) hip flexors cross the knee, their lack of mobility can affect patellar tracking in all three planes. By using the BT, health professionals can effectively improve mobility of this muscle group in all three planes of movement by taking a traditional stretch and making it better.

The following are corrective stretching techniques using the BT. To begin, place one knee near the base/rim of the BT with the shin resting on the upward slope of the dome, and the top of the foot resting on the top of the dome. This position places the ankle joint in plantar flexion which is important to maintaining length through the entire anterior myofascial chain, or from toe extensors to hip flexors.

Place the other foot flat on the floor in front of the BT with knee and hip flexed. Each knee should be in alignment with its respective hip joint. Initially, it may be advantageous to use external support so that the flexibility component is prioritized over the balance component.

While in this position, body weight will cause compression to the BT dome surface, producing additional flexion at the knee (Note: It is important that knee placement does not cause knee to "bottom out" to the base/rim of the BT. If this occurs, move knee further back from the base/rim.)

Once stable, posteriorly tilt the pelvis. The hip extension created by this rotation combined with knee flexion should create lengthening of the two joint hip flexors in the sagittal plane. It is at this point where full advantage can be taken of the compressive surface of the BT. By gently creating a weight shift with the knee on the BT dome, additional and varying muscle fiber lengthening of the two joint hip flexors is emphasized. In tighter individuals, a similar response may be experienced with the quadriceps.

For example, say a client has the left knee on the BT dome. A gentle weight shift to the left while in the frontal plane produces left hip ADduction and relative internal hip rotation. This immediately changes the relationship of the distal and proximal attachments of the two joint hip flexors. As a result, different groups of muscle fibers are emphasized more as other fibers are lengthened in the frontal and transverse planes, and not just the sagittal plane. If a client is asked to produce the opposite movement, or a gentle weight shift to the right while in the frontal plane, it produces hip ABduction and relative external rotation.

Why stop there? By introducing anterior diagonal patterns in the transverse plane, other groups of fibers are emphasized. This is achieved by having the client move the pelvis on an anterior or medial diagonal. While doing this, the hip extends more and the knee flexes more with coupled motions occurring in the frontal and transverse plane.

These corrective stretching techniques may be utilized during static or dynamic stretching protocols. Also, it is very easy for a client to become familiar with the start position, and then seek out his/her personal areas of greatest need. This allows the client to be in control, take advantage of the surface of the BT and have a tool for self care.


Anthony Carey, MA, CSCS, CES, was named 2009 Personal Trainer of the Year by Personal Fitness Professional magazine. He is an internationally recognized expert in musculoskeletal function, holds a master's degree in biomechanics and athletic training, and is the owner of Function First in San Diego, CA. Carey is the author of The Pain-Free Program: A Proven Method to Relieve Back, Neck, Shoulder and Joint Pain which was recommended by Time magazine. His work has received national attention, including the New York Times, Shape and O, The Oprah Magazine. His clientele includes professional athletes, entertainers, physicians, chiropractors, physical therapists, acupuncturists, moms, dads, sons, daughters and heads of industry. Carey presents and writes internationally for the fitness community on biomechanics, corrective exercise, functional anatomy and motor control and their relationships to musculoskeletal pain and function. He was a Top 10 Finalist for the ACE's Educator of the Year in 2005 and 2006.

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