“In fact, a recent study (I can try to dig it out) found just that: light/moderate loads are more effective when done to failure but heavier loads show no benefit between going to failure or stopping 1-2 reps short.”
This is some info from Christian Thibadeau about training to failures and heavy vs medium weights.
"The benefit of failure is seen mostly with lighter and moderate weights (under 70% of your 1R’M). The reason is that with these loads you are not recruiting all of your fast-twitch fibers right from the start (and FT fibers have the most growth potential).
With light loads, as fatigue accumulates your strength diminishes and the load represents a heavier load relative to your capacity at the start of the rep (there is a 2-3% strength decrease/fatigue per rep). So when working with light or moderate weight you must go to failure, or close to it, to get a significant number of reps utilizing the fast-twitch fibers.
FT fibers start to be recruited when the amount of force you have to produce to lift the weight represents 80% of the maximum force you have available at the beginning of that rep (remember, strength decreases 2-3% per rep).
If you stop way short of failure with light-moderate loads, the hypertrophy stimulus is much weaker because you don’t impose a big stimulus on the growth-prone fast-twitch fibers.
Now, when using loads of, or above, 80% the need to go to failure is lowe because right from the start of the set, you are involving the fast-twitch fibers.
In fact, a recent study (I can try to dig it out) found just that: light/moderate loads are more effective when done to failure but heavier loads show no benefit between going to failure or stopping 1-2 reps short."