The Adductor Magnus and its role in Squatting: Part II – Issues of form, strength, and safety
When performed properly, squats utilize/work several agonists. Of all the muscles utilized we can narrow down the most important to include the Hamstrings, Glutes (Maximus), Quads, and Adductor Magnus…..that’s right….Adductor Magnus. I often tell my patients (who I regularly coach on proper lifting form) that a good way to know that you have performed your squats correctly is to feel DOMS in your adductors a day or two later.
The obvious question is “why would an adductor come into play during a clearly saggital plane movement?” Before I answer this question, I will first talk about a recently published case that provides striking evidence proving that indeed the Adductor Magnus muscle is utilized when squatting.
An articles published in the journal Clinical Nuclear Medicine (March 2005, 30;3) by Graves et al. describes a case of a 45-year old man with a history of performing heavy squatting exercises 1 week prior to a bone scan that was ordered for an unrelated reason. A Bone scan, or bone scintigraphy is a nuclear scanning test to find certain abnormalities in bone, which are triggered in the bone’s attempts to heal. The test will also pick up active healing in
metabolically active tissue such as muscle (when inflamed, or during intense cellular reproduction/healing). The test is performed by injecting a patient with a small amount of radioactive material and then scanning them with a gamma camera, a device sensitive to the radiation emitted by the injected materials. In other words, the injected ‘dye’ will be attracted to metabolically active tissues that will show up on the scan as dark black areas. As can be seen in figure one, there is a large amount of uptake in the adductor magnus muscles bilaterally indicating that following the squatting, the tissue underwent damage (as occurs when weight training) which was in the healing process at the time of the scan. In other words, out of all of the agonists mentioned, it seemed would seem by these figures that the Adductor Magnus played a major role in the lift.
Now that I have demonstrated that the Adductor Magnus is an important contributor to the movement, I will attempt to explain why. Further, I will explain why certain biomechanical considerations should emphasized when teaching squatting to ensure that the person is utilizing this muscle for proper execution. The reasons can be divided into those concerning safety, and those concerning strength generation.
In terms of squat depth, a full squat is where the hips drop below level with the top of the patella. Any squat that is not deep, the ‘partial’ squats, stress the knee and the quads without stressing the glutes, the adductors, and the hamstrings. The hamstrings (and Gracilis…an adductor), when under the tension required for proper form exert a posterior tension on the tibia by way of their distal attachments, and the net effect of the anterior quadriceps tendon insertion is an anterior force against the tibial plateau. With sufficient depth (where hamstring/adductor tension is maintained during the lift), anterior and posterior forces on the knee are balanced. Thus the total shear force on the knee is nil. In partial squats, the anterior shear is allowed to occur without being ‘checked’ by the posterior pull of the hamstrings.
Another important consideration is the alignment between the knees over the toes during the movement. The correct position of the knees during the squat is to be in line with the toes. The toes should be angled outwards approximately 30 degrees, this will ensure that enough subtalar pronation is able to occur
in order to achieve proper squat depth as noted above (Figure 2). If the feet are not angled outwards, dorsiflexion of the ankle will be limited at the ankle mortise joint (due to the larger anterior half of the talus) which will prevent the proper depth from being achieved (Figure 3). In addition to the stresses that this causes on the knees, this will also force the person to lean anteriorly thus shifting
the weight away from the centre of balance (the weight should remain in line with the midfoot). This in turn causes incorrect back, hip, and knee angles that will lead to damaging shearing forces in each area. As for the knees, if they do not track in line with the feet, but instead travele anteriorly, this will in effect increase the Q-angle (the angle formed by a line drawn from the ASIS to central patella and a second line drawn from central patella to tibial tubercle) which leads to an abnormal laterality of patellar tracking (thus leading to patellofemoral problems) (Figure 4).
What does this have to do with the Adductor Magnus?? If the feet and knees are in the proper position during the squat, this will lead to a lengthening of the Adductor Magnus by way of its insertions (see part 1 of this blog for an anatomy review of this muscle) thus engaging it in eccentric contraction during the decent, and allowing them to contribute to hip extension when performing the concentric portion of the lift (“coming out of the basement”). If the knee’s track forward, and proper depth is not reached (see Figure 3), the muscle will remain slackened and thus cannot significantly contribute to the lift.
In terms of force development, improper form and insufficient depth will over utilize only the Quadriceps group. Thus the force generating capacity is limited to that group alone. When achieving proper depth, contraction of the Gluteals, Hamstrings, and Adductor Magnus can contribute to overall force production thus allowing the athlete to lift more weight….not to mention making the exercise more effective in developing strength by training several muscles at once (Figure 5).
*IN THE PICTURES: JARED HEFT – Head Coach of CrossFit Vaughan (CrossFitVaughan.ca)
– Partial squats cause damaging shearing forces on the knees.
– To achieve proper depth the feet must angle out approximately 30 degrees and the knees must stay in line with the toes to prevent an increased Q-angle
– Improper knee tracking will cause a shift of the weight anteriorly thus increasing stress on the knees, low back, and hip.
– By performing full depth squats, this will call the Glutes, Hamstrings, and Adductor Magnus into play by lengthening them under the load (thus allowing them to store potential energy which can be used in the lift (when converted to kinetic energy)
– By calling more muscle groups into play one can generate more force and thus strength.
In the next entries on this topic, I will discuss how tightness, or lack of strength in the Adductor Magnus can lead to improper squatting form resulting in decreased force development and potential injury.