As far as ive heard, this isnt a good kind of bruise. Forget about the effects on your body, when your trail leg hits the pole on the swing, thats a huge loss of energy in your swing.
I think this could be happening in two ways:
it could be a result of your bottom arm too much to the opposite side of your body. That would make the bend of the pole right under your trail leg, and you could hit it when you swing. To fix this, think about both hands directly over your head. I was taught to aim your bottom (left) arm to the top of the left standard before you swing. That will get the bend slightly to the left (dont overcompensate by bringing your bottom arm completely to the side of your body; not until you are completely inverted). This should leave a clear path for your trail leg.
Another way this might be happening, and i would think more likely way:
You might be swinging your left trail leg back and to the left. Then when you swing, your leg swings upward and to the right. This is probably happening because you are trying to NOT hit the pole with your trail leg, and maybe wanting to keep it to the left as much as possible. But when you swing back and to the left, just like a pendulum on a clock, its going to come back direcly the way it came, and up to the right. To fix it, go back to some short run or even pop-ups, and bring your trail leg directly behind you, and then directly in front of you. It would be best practiced on the rings first. If you swing straight through and aim your left hand to the left standard, its physically impossible to hit the pole with your shin.
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