Resistance training must challenge muscles close to failure to stimulate muscle growth.

“And in order to do that, we need to challenge the muscle in a way that is a sufficient stimulus for growth. So, if we think about a full body training program, we want to target all of the major muscle groups and a challenging load will differ depending on the exercise and and the muscle groups that we're targeting. And we can train in low, moderate, or high rep ranges, but we need to train close enough to failure. Meaning, if we can only do 10 and not an 11th, that's failure. So, we can stop at maybe eight or nine and that's an appropriate stimulus. But if we finish that set of 10 and we could easily do another 10, then that load is too light.”