Researchers at the University of Alberta studied the effects of weight training and cardio on backaches. Unless you have severely injured your back and the doctor has ordered bed rest, staying active, particularly lifting weights, will help you in recovery. Study participants who weight-trained three times per week decreased their pain by 63% compared to participants who did cardio only and reduced their pain by 6%. Resistance training targets both upper and lower body muscles, whereas cardio targets mainly lower-body muscles. You should continue with some cardio to avoid putting on unwanted bodyfat during recovery from injury, and do whatever strength training exercises you can handle with poundage that will not make your injury worse. You do not want to overdo it to find yourself sidelined and out of the gym indefinitely.