The mizuno synchro concept is the optimised combination of two different midsole compounds to guarantee cushioning guidance and smoothness during the ride while the upper midsole uses a denser material to ensure maximum stability the lower midsole uses u4icx foam to provide incredible cushioning smoothride fluid motion at every step of your runsmoothride begins working the moment your foot touches the ground flex grooves in the heel promote natural movement from the back of your foot to t