ST. PETERSBURG — A treadmill at the LA Fitness at 5900 Fourth St. N caught fire overnight and caused minor fire and water damage to the gym, according to St. Petersburg Fire Rescue.The treadmill caught fire for unknown reasons around 11 p.m. Wednesday night, said St. Petersburg Fire Rescue Lt. Steve Lawrence. The last employee had already left for the night.The fire was discovered by an employee when they showed up for work around 5 a.m. Thursday. Two treadmills were destroyed, a window suffered minor damage and soot had spread throughout the building. The gym was also doused in water released by the automatic sprinkler system that was activated during the fire.The damage left the gym closed Thursday. Lawrence said the LA Fitness was being cleaned up and it should be open again in two to three days.The sprinklers likely saved the gym from more extensive damage, he said."The fire suppression system did do its job," he said. "It was limited fire damage. The water damage can be cleaned up."