To protect your underarm.
For a look at lunges done with a better camera and faster shutter speed, consider looking at Holly Buechel's video Speed of Fencing
"Signature for Rent"
Holly, damn good video. I love the focus and clarity and the super-duper slo-mo. Must have been hella hot under the bright lights to enable the 1ms shutter speed?
that's really cool
"I shall walk this way but once, therefore whatever good I may do, let me do it now, for I shall never walk this way again"- Unknown Poet