The time a muscle is under tension is THE MOST IMPORTANT PART of resistance training. Time under tension will dictate everything else, including the weight, and number of sets you do. Ex) if each rep is performed with a 2 second count up and a 3 second count down that is 5 seconds a rep, 12 reps will take you 60 seconds the muscle is then under tension for 1min. The weight used will be determined by this because by the 12th rep it should be close to impossible to finish while maintaining ideal form. If this is true, it is the correct weight for endurance based training.

Remember to always warm up before you begin resistance training – just a 5 min warm up at 50-60% max heart rate is sufficient. Make sure to engage in a warm up that includes joints that will be used in the resistance session, for example if it is a leg day use the bike or treadmill. If your focus is on a  full body workout using an elliptical, rower, or doing a dynamic warm up are good options.  Follow every warm up with some dynamic stretches of the same joints about to be trained. Try to keep your workout comprised of no more than 20-24 sets total, as your body will often become too fatigued and energy stores too depleted to do much good doing more than this.