If you press the A button, when you have the Burst bar filled, you will exchange the bar for a PowerUp (which can be either Speed or Power). Otherwise, if you break the burst bar using the C button, you will fire a burst of energy Kind regards.
when you have the Burst bar filled, you will exchange the bar for a PowerUp (which can be either Speed or Power). 
Otherwise, if you break the burst bar using the C button, you will fire a burst of energy 