The first group ( n = 15 ) received a 0 W/cm2 ultrasound treatment ( placebo ) ; the second group ( n = 16 ) received a 1.0 W/cm2 continuous ultrasound treatment and the third group ( n = 15 ) received a 1.0 W/cm2 1:4 pulsed ultrasound treatment 5 days a week for a total of 15 sessions .