Mike Mentzer conceded that 100% intensity may not be required to stimulate muscle hypertrophy. Maybe 85%, 90%... is sufficient. But how do you measure it? How do you know you are at 85% or 95% intensity? One can only reasonably and somewhat accurately (motivation, force of will, being driven, cognitive effort, are also variables that affect performance) measure only two states of intensity: 0% intensity and 100% intensity.