A kettlebell swing requires requires sufficient hip flexion and extension ROM to successfully be completed without dumping compression force into the lumbar spine.
1. Without requisite hip flexion, this compression may be anterior to the disc, causing a potential posterior bulge either during initiation of the movement or during the backswing (A). To explain, when the forward hinging action of the hips is restricted the athlete compensates for this lack of "hip" ROM by allowing the lumbar spine to flex and sacrifice integrity.
This same type of bulge can occur if the swing technique is grossly incorrect (B).
2. Without requisite hip extension, the compression force may be posterior to the disc resulting in an anterior disc bulge. This would hypothetically occur at the end of the concentric phase of the swing.
Pictured to the far left, an athlete demonstrates sufficient hip extension (A), bringing her skeletal system into good postural alignment. In the adjacent photo (B) the athlete displays the less desired movement dysfunction, stopping short of full hip extension and using her lumbar erectors to reach a vertical torso position. Hip extension vs. Lumbar extension.
If an athlete or client repeatedly dumps either anterior or posterior (or both) compression forces into the lumbar spine sooner or later that pressure will likely rupture the disc wall (herniation).
One of my All time favourite Kettlebell sport videos. This weight is Over 50lbs. Watch to the end to see her launCh the bell when her grip finally gives!
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