Gene Calantoc, Semper Fit personal trainer, uses a pilates ball during an abs class at the Marine Corps Recruit Depot San Diego Semper Fit Center Oct. 6 . Calantoc leads participants through a variety of abdominal exercises using different equipment, like medicine balls and weights, to target different core muscles. The class is held Monday through Thursday at the Semper Fit center. - Gene Calantoc, Semper Fit personal trainer, uses a pilates ball during an abs class at the Marine Corps Recruit Depot San Diego Semper Fit Center Oct. 6 . Calantoc leads participants through a variety of abdominal exercises using different equipment, like medicine balls and weights, to target different core muscles. The class is held Monday through Thursday at the Semper Fit center.