The spikes are also used for the purpose of intimidation. from CCosgames's blog

Usagi finishes her cosplay with Chun-Li’s trademark hairstyle and additionally the ones spiked steel bracelets that Chun-Li wears to help tone and workout her frame whilst performing her kicking movements,   Cosplay Costume    consisting of supporting stabilize her centre of gravity throughout a Hyakuretsukyaku and restriction her at some point of supers including the Senretsukyaku to keep away from overexerting her muscle tissues. The spikes are also used for the purpose of intimidation.    Spider Man Costume