To build strength endurance it is recommended to use light weight and perform about 15-20 reps. You will lift quickly on the concentric move and slowly on the eccentric. Example: while performing bicep curls, the concentric is the upward movement and eccentric is the downward. NOTE: it is very important to spend more time under tension in the eccentric part of the exercise in order to build up strength endurance! Knowledge is power, safe lifting folks!