When you purchase the ISSA course, you receive online access to the free digital version What type of muscle contraction maintains constant tension in the muscle as the length changes? The NSCA is the worldwide authority on strength and conditioning and this manual was been developed to help you start your journey into the area of strength training and conditioning with some of the foremost coaches in the world ISSA Unit– Strength; ISSA Unit– Cardiovascular Training; ISSA Unit– Flexibility Train