The Weak Link – Off The Road Colum

by Russ Ebbets, DC, USATF Level 3 Coach

When you stand in single support (on one leg) you create a closed kinetic chain of the leg. Running is actually a cyclic series of small jumps from one foot to the other. To run properly it requires a degree of balance, timing, and coordination to produce a symmetric movement pattern. Anything that compromises one’s balance, timing or coordination will present with an insult or injury somewhere along the closed kinetic chain (Figure 1).

A closed kinetic chain is a series of joints where one joint affects the movement of the next and the next and the next joint along the chain. If you compare a closed kinetic chain to the Domino Effect (where one domino knocks down the next domino) you are not too far off. The “closed” part of the chain refers to the fact that one end of the chain is “fixed,” however momentarily, with the foot in ground contact. The leg that swings through, (the swing leg) is an open kinetic chain. The majority of leg injuries happen when the leg is in a closed kinetic chain.

The closed kinetic chain of the leg begins at the foot and proceeds to the ankle, knee, hip, SI joint and finally to the lumbar spine. Any weakness, instability, imbalance or asymmetric movement within the chain can present with a breakdown at that segment or contribute to a breakdown somewhere further along the closed kinetic chain.

For this analysis we’ll examine the joints of the closed kinetic chain of the leg individually, beginning with the toes and foot, progressing to the low back.

Toes and Foot

Although the toes are generally seen as a non-weight bearing appendage in stance, they do contribute to the movement of the running action. As the leg swings towards the ground the toes dorsiflex towards the shin allowing the outside of the forefoot to contact the ground, or on the outside of the heel, if you are a heel striker. Dorsiflexing the toes tilts the foot into this supinated position which makes the foot a rigid lever. The rigid lever of the foot allows the shock of ground contact to be transferred up the closed kinetic chain to the larger quad/hamstring/glut muscles to dissipate or manage the forces of forward movement that can momentarily be sizeable (4-7x bodyweight with jogging and running and up to 20x bodyweight with certain jumps).

As the body travels towards mid-stance pronation the foot transitions from a rigid lever to a mobile adapter. Foot pronation is a natural phase of the gait cycle but can be problematic when it happens too soon in the gait cycle, happens too fast or lasts too long. Foot pronation is controlled by an eccentric contraction (a lengthening contraction) of the posterior tibialis muscle. The posterior tibialis controls the “velocity of mid-foot pronation.” If this muscle is weak, improperly conditioned or fatigued the foot will flop into mid-stance in a state of pathologic pronation.

At toe-off the foot re-supinates, reverts to a rigid lever and with the powerful contraction of the gastric/soleus complex the body is driven forward. Once again, the action of the posterior tib helps invert the foot to a rigid lever. And again, any dysfunction of the posterior tib forces the Achilles/gastric complex to assume stability activities (in addition to propulsion) and creates the potential seeds of injury to these tissues.

The Knee

The knee is typically seen as a hinge joint, opening and closing in a forward/backward direction. While this is generally correct there is a slight amount of internal and external rotation that takes place within the knee. This internal/external rotation is called the Screw Home Mechanism. Just before heel strike the knee externally rotates. As the foot moves from supination to pronation the tibia (shin bone) internally rotates. Eighty percent of bodyweight of mid-stance is borne by the medial meniscus. Any pathologic pronation at the foot (too much, too soon or too fast) can cause excessive wear and tear with medial knee pain (at the medial meniscus) a characteristic first sign.

One of the structures that limits the internal rotation of the knee is the anterior cruciate ligament (ACL). Ligaments have a limited amount of elasticity, which in this case is important as the ACL checks the amount of internal rotation that can take place at the knee. But if the pathologic pronation at the foot is too great or the athlete does a “quick turn with deceleration,” as seen in basketball, and the limits of elasticity are exceeded, the ACL can tear. In truth this is more a female basketball player’s injury but can happen in running as seen at the Rio Olympics when Abby D’Agostino fell in the 5000m and tore her ACL.

The Hip

The hip is a multi-axial joint. That fact can be both good and bad. The fact that the hip can move in all directions can be problematic for a runner. Running, be it a 100m, a 5k or a marathon is done in a straight ahead manner. An unsteady gait, zig zagging to the left or right would be unproductive (wasted energy, loss of force production) and dangerous to other runners.

The straight ahead nature of the sport presents a problem biomechanically as the muscles that stabilize the multi-axial joint will atrophy, over the course of time, if effort is not taken to maintain a degree of conditioning to the dynamic stabilizer muscles of the hip, notably the adductor magnus, psoas and glut medius (Figure 2).

Muscular atrophy of these three dynamic stabilizers can cause a lateral sway with each step as seen in the orthopedic Trendelenburg Sign (Figure 3). Poor tone to these muscles can also cause the internal rotation caused by foot pronation to increase internal rotation at the hip and SI joints. This unchecked rotary movement combined with the SI’s ever present shearing forces can sprain the SI ligament when the leg is in single support.

The Pelvis

Three bones make-up the pelvis – the right and left ilia and the central sacrum. While there is limited movement to these bones there is a continuous movement from one step to the next. Again, anything that causes either too much or too little movement can injure the sacro-iliac joint. With each ground contact the weight of the body must be transferred through the SI joint. The stress at this joint is substantial as 2/3 of one’s bodyweight lies above the level of the navel. The vertical orientation of the joint surfaces makes it susceptible to shearing forces as opposed to compressive forces seen at the knee and hip.

Asymmetric gait patterns due to multiple factors (pathologic pronation, preferential leg dominance, a limp, inflexibility, fixation, pelvic rotation, poor shoes, road cant or camber, etc.) can lead to injury of the SI joint with a quick resolution to the problem difficult. The stresses to the SI joint are present with all upright movements from standing to simple walking.

When one stands in single support on the right leg the pelvis tilts slightly backwards. This action is due to the hip joint being anatomically more forward on the pelvis than the SI joint. This backward tilt of the pelvis causes the sacro-iliac joint to tilt the sacrum down and anterior creating an uneven base for the 5th vertebrae. This uneven base causes the body of the 5th vertebrae to rotate right. The whole process is repeated as one steps to the left leg. Any of the asymmetries mentioned above will cause asymmetric movements of the SI joint or in the lumbar spine which can in turn injure a disc or impact a spinal nerve that may take months to heal or correct. Rehabilitation recommendations may include no running and present with psychological upset. Low back injuries can potentially shorten one’s running career and certainly participation in one’s activities of daily living (see Figure 1, letters E, F, G).

Remedies

Fortunately, with a little planning and forethought training strategies can be devised that can address potential problem areas within the closed kinetic chain of the leg that will not only lessen the chances of repetitive motion injury but also improve performance by better coordinating the system. Listed below are six training ideas or practices that can accomplish one’s goals with minimal expense, time or space necessary to achieve significant results.

A Dynamic Warm-up – A dynamic warm-up is a 10-20 minute time period at the beginning of one’s practice session where a variety of stationary and movement exercises are performed. These exercises can be done in quick succession and mixed in terms of order creating a “different” challenge each day they are done. The movements may be a series of spiral or circular movements, short hops, jumps or skips, or exaggerated movements using the arms and legs. YouTube offers a plethora of choices. Which one is best? The answer is simple - the one you will do. Check out this link to get you started:  The 5 Minute Dynamic Warm Up for Running | Week 34 | Movement Fix Monday | Dr. Ryan DeBell - YouTube

The 6 Foot Drills – The six foot drills exaggerate the different ranges of motion of the foot and ankle. While there is some strength created by walking on the inside/outside, toe-in/toe-out, backwards and heel walks, the greater benefit is that these different gait patterns challenge and clarify the nerve pathways from the brain to the foot thereby improving one’s balance and proprioception. The recommendation is to do the six foot drills daily, for 25 meters each at the beginning of a practice. They take about three minutes to complete from shoes off to shoes back on. You can check out this YouTube link for details: The Six Foot Drills - YouTube

Lower Core Stability – The lower core is where the leg attaches to the torso. The area of potential great instability is the hip joint. The multi-axial nature of the hip joint, the numerous muscles involved in controlling movement combined with the forces of ground contact and the linear nature of running form a volatile mix of potential problems.

The Europeans refer to core stability as pillar stability with the psoas muscle and the erector spinae muscles that run parallel to the posterior spine representing the four “pillars” (Figure 4). Traditional sit-up and push-up planks can help stabilize the area but one must also consider side planks and back extension exercises to develop the four muscles equally around the spine. One need not go overboard here, the goal should be to tone the muscles as opposed to any degree of hypertrophy or visually obvious development.

Balance and Proprioception – Improvements in balance (eyes open) and proprioception (eyes closed) will come about with strength improvements, be that at the foot or lower core. The ability to stand on one leg for 15 seconds with the eyes open or closed signifies a degree of development that one should strive for. Poor balance, either static or dynamic is an age marker and also a marker of a healthy body. Performing a simple lunge step for 10-12 strides will improve one’s running balance.

Quad Strength – The quads are under tremendous stress with the running action. A twice weekly routine of leg extensions will tone the muscles adequately to sustain the shock of ground contact and stabilize the knee joint for continued trauma. Ideally 1-2 sets of 10 reps twice weekly is preferred on a leg extension machine. In the absence of resistance equipment one can do “wall sits” for 10-30 seconds at various knee angles (i.e. - 90°, 100°, 120°) to condition the muscles.

The Dynamic Stabilizers – The dynamic stabilizers allow one to hold a desired position while moving. The posterior tibialis in the lower foreleg is the primary dynamic stabilizer for the foot and ankle. Conditioning the muscle can be done with the foot drills.

The dynamic stabilizers for the hip are the adductors, psoas and glut medius (Figure 2- See above). The preferred method is to use a total hip machine, but again in the absence of a resistance machine one can do side leg raises, squeezing a basketball sized exercise ball between the knees and the lower core sit-ups to address conditioning concerns for this area.

Summary

One’s running technique is visible and may be more easily corrected with conscious attention to leg lift, torso tilt and arm actions. The machinations of foot pronation, the Screw Home Mechanism, dynamic stability of the hip or the tilt of the sacrum with leg to leg ground contact are not under our volitional control. Nonetheless they all represent potential “weak links” in a kinetic chain that is at the essence of the sport.

The use of corrective drills and making an effort for “all-around” fitness becomes a crucial concern the deeper one gets into a running career. Presented here are some simple ideas that can be implemented with minimal time or monetary expense but will reap benefits in terms of enjoyment and healthful participation in one’s avocation whether one’s intent be recreation, a socio-emotional outlet or performance based training.


1-RussEbbetsFinalEnd.jpegRuss Ebbets, DC is a USATF Level 3 Coach and lectures nationally on sport and health related topics. He serves as editor of Track Coach, the technical journal for USATF. He is author of the novel Supernova on the famed running program at Villanova University and the sequel Time and Chance. His book, A Runner’s Guide, a collection of training tips and running articles was a 2019 Track and Field Writers of America Book of the Year finalist. His Runner’s Guide 2 was published in February 2023. Books are available from Amazon.com. His USATF Niagara High Performance presentation on Career Longevity and the Masters Athlete can be found at – USATF Niagara HP Zoom. He can be contacted at spinedoctor229@hotmail.com.


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