The heel wedge has been used as a tool with the squat for different reasons, such as: to get more gluteal involvement, more quadriceps recruitment, because it is easier on the knees or back, or because clients have difficultly getting into a good squat position. Whatever the reason, it is vital the trainer understand the rationale for the use of a heel wedge when implementing the tool. For example, if the wedge is being used because the client has difficulty getting into good squat position, the trainer must ultimately evaluate what is the limitation that inhibits this movement pattern in the first place. Those limitations can then be addressed rather than simply placing a “Band-Aid” on the movement. The view of this article is not to express opinion of the heel wedge usage, but to inform the trainer of the biomechanical reaction changes that occur due to its use.
The Mechanics of Deceleration/Acceleration
En route to exploring the mechanics of the squat, we must first understand a few noteworthy principles. The discussion of human motion actions and positions of bony structures are described in terms of the position of the distal bone in relation to the proximal bone. As motion transforms from the ground up, the distal bones move slightly faster than the proximal bones, therefore providing the described relative position of structures. For instance in gait, in foot pronation, the chain reaction causes the tibia to rotate slightly faster than the femur. Since the tibia is distal to the femur and is internally rotated to a greater degree than the femur during pronation, the knee can be described as internally rotated.
Table 1, created by Gary Gray, P.T., clearly describes the positions/actions of the joints from the foot through the hip. This table shows the tri-plane functions of these joints in supination and pronation. If the trainer studies this grid, they will understand the chain reactions that occur from the ground up in human movement.
Table 1 - with permission from Gary Gray, P.T
The actions of pronation are important to note, as these actions produce absorption of forces and deceleration of the motions of the body. During pronation, the metatarsals dorsiflex, the subtalar joint of the foot abducts, the calcaneal everts, ankle dorsiflexion causing tibial, femoral, and hip internal rotation. The results of these actions are knee and hip flexion to some degree. (Refer to Figure 1c) These are the same actions that happen when squatting, lunging, going down stairs, sitting, or preparing to jump. In the squat, the mere fact that pronation must transpire requires the trainer to gain an understanding of the chain reaction stages of the squat. If the client is not attaining the desired effect through the squat, the fitness professional should be able to ascertain where the limitations are, the compensations that have developed, and the net resultant movement pattern. For example, if the gluteals are tight, this can inhibit the ability to flex the hip in the sagittal plane, or internally rotate the hip in the transverse plane. When either of these motions is inhibited, the squat will be limited through the range of motion. Yet on the other hand, if a client has a tight calf, this will inhibit the ability to achieve dorsiflexion which will not allow an adequate knee and hip flexion and a resultant limited range of motion of the squat movement pattern.
Figure 1:Foot Position
Through human motion, supination accelerates the body. It is force producing, shortening of muscles, propulsive, and concentric muscle action. The act of supination involves reactions from the foot up and can be described as calcaneal inversion in the frontal plane, subtalar joint adduction in the frontal plane, the ankle is in relative plantar flexion in the sagittal plane, and the tibia, femur, and hip are externally rotated in the transverse plane. (Refer to Figure 1a) Supination is the extension out of the squat, stair climbing, rising from a chair, leaping in the air after the loading phase, or plantar flexion, knee and hip extension during gait. The common thread of all these activities is a concentric, propulsive aspect to the motion. Efficient supination depends upon adequate pronation, which lengthens and decelerates motion. If inadequate pronation is present due to limited range of motion at a site or sites in the kinetic chain, this can create excessive force production and overuse of concentric forces. This will prolong the supination phase and can lead to overuse injuries to the overused tissues.
The beauty of human motion is ever-present when analyzing the squat. As the body goes from the extended upright position into the squat position, tremendous eccentric loading occurs in all three planes of motion. Starting at the foot and working upward, the metatarsals dorsiflex and abduct as the ankle goes into dorsiflexion. This motion transforms simultaneously with subtalar joint abduction, causing calcaneal (heel) eversion (the relative position of the heel turns outward). Pronation of the foot and ankle can be described as forefoot abduction, metatarsal dorsiflexion, calcaneal eversion. Further up the chain, the tibial reaction to the foot in pronation is internal rotation. The femur, likewise will internally rotate, causing knee flexion in the sagittal plane, knee abduction in the frontal plane, and knee internal rotation in the transverse plane. This reaction will cause the hip to internally rotation in the transverse plane, flex in the sagittal plane, and hip adduction in the frontal plane. (refer to photo 1)
As these motions occur, there is increased deceleration or eccentric loading of all the muscles of the foot, leg, and hip to control the actions and degree of triple flexion (foot and ankle dorsiflexion, knee and hip flexion). Foot and ankle pronation require the calf musculature to lengthen in three planes of motion. Likewise, as the knee flexes, the range of motion of the quadriceps, calf, and hip control the depth of the action. When the hip flexes, the actions and limitations of the hip will affect its range of motion as well. The interesting and exciting relationships that occur from the study of human motion does not stop at the local joint, but the impact adjacent joints have upon the local joint.
For instance, if the ankle cannot dorsiflex fully due to calf tightness, this will not allow the knee and hip to attain their full range of motion. If tightness is in the hip, the tight gluteal can inhibit the calf from achieving its full range of motion. Further up the chain, tightness of the back musculature can inhibit full motion sought after in the squat. It is for these issues, an understanding of the chain reaction and flexibility relationships will enrich the trainer’s knowledge and understanding of the intricate associations of muscle function.
Upon the ascent phase of the squat, the foot begins to supinate and tibial, femoral, and hip external rotation ensues as this is the propulsive action. Supination involves the rigid girding of the foot so forces may ascend through the lower extremity to the hip and back. The rigidity of the foot causes propulsive reaction, while conformity of the foot is conducive to deceleration. (refer to photo 2)
Key Considerations of Actions
In the scenarios described above, I have seen many trainers place a heel wedge under the client’s rear foot so they may be able to attain greater depth for increased tension on the legs. Is this defeating the purpose of the mechanics of the squat? When a wedge is placed under the rear foot, the foot is now placed in a relatively plantar flexed position. This will create a chain reaction of relative calcaneal inversion and tibial external rotation. Yet, as the client squats, pronation must occur, which creates calcaneal eversion, tibial, femoral, and hip internal rotation. Where does the conflict seem to take place in the chain? Quite possibly the knee, as the tibia “wants” to internally rotate when ankle dorsiflexion and knee flexion occurs, yet the tibia is placed into a relatively externally rotated position with a heel wedge; while during the squat, the femur internally rotates as the hip flexes.
The mechanics of the knee requires the “cooperation” of the tibia and femur to allow proper internal and external rotation. In flexion, the tibia will internally rotate slightly faster than the femur. Yet with a heel wedge, the internal rotation will be compromised, and the mechanics of the squat are now altered. Limitations in range of motion of the calf, quadriceps, gluteals, or back can create limited motion during the squat. The remedy may not necessarily be the heel wedge, rather an integrated assessment of the entire kinetic chain of the client. I suggest the trainer become familiar with the Reebok Movement Screen Squat Assessment and the Total Body Functional Profile, by Gary Gray, P.T. These two tools can assist in assessing the client’s range of motion and a personalized flexibility program can be implemented to assist the client’s idiosyncrasies in relation to joint and muscle group tightness.
Chain Reaction Modifications
As stated in the opening comments of this article, it is not my intention to comment if a heel wedge is correct for the client’s program and trainer’s toolbox. This article is to bring attention to the fact the heel wedge is often used as a device to mask many issues of kinetic chain dysfunction. If the trainer is attempting to modify the squat to get certain muscle responses, the following are some common chain reaction tendencies:
Slower movements produce less of an elastic tendency of muscles and reduce the eccentric loading actions of the soleus, gastrocnemius, and posterior tibialis and increase the quadriceps concentric loading in knee extension and external rotation especially in movements where the hip does not move over the knee.
To accomplish more quadriceps action, have the client perform a lunge using dumbbells. Slow the movement to reduce the elastic tendency of the other muscle groups, and therefore, increase the demand upon the quadriceps. The goal in this instance is to reduce the assistance of the calf and gluteals when executing this movement pattern. In essence, the client should do the lunge straight up and down limiting the amount of dorsiflexion and hip flexion during the movement pattern. The caution to this approach is the loading of the “friends” of the quadriceps, i.e. calf and gluteals are being minimally loaded. If the quadriceps is weak, this increases eccentric load to the patellar tendon.
Tight rectus femoris creates increased anterior pelvic tilt, which inhibits gluteus maximus and hamstrings, creating kinetic chain compensation leading to tightness and strain to external hip rotators, often referred to as the piriformis.
It is critical the trainer stretch the tight, inhibited areas prior to commencing with the strengthening phase of training. This can be done through passive movement patterns and gently lengthening as the movement becomes deeper and more dynamic. When the structures are lengthened, this enhances firing to the antagonistic muscle group.
Decreased ankle dorsiflexion reduces the eccentric loading of the posterior calf group, therefore, the ability to extend the knee is decreased and the quads have to concentrically be overloaded for knee extension.
For proper hip action to occur, there must be adequate range of motion of the calf group. If the calf is tight, this has a high degree of range of motion limitation in at least one plane of motion through the chain reaction. A tight calf can limit foot and action, thus limiting tibial, femoral, and hip function. These accumulative reactions can cause improper squat technique.
Through understanding of human motion and careful assessment, the trainer can now critically view each of the client’s movement patterns. With practice and appreciation of the human body, we can provide a fix to problems rather than the limiting issues.
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