Training intensityIntensity · Percentage of 1RM
How heavy a load is, usually expressed as a percentage of your one-rep max.
Training intensity is how demanding the work is, and the word means two different things depending on which room you are standing in. In strength training it usually means load as a percentage of your one rep max. In endurance training it means effort as a percentage of maximum heart rate, VO2max or threshold pace.
That ambiguity causes genuine confusion, since a high intensity set of three heavy singles and a high intensity interval session are demanding in almost unrelated ways.
On the strength side, intensity trades against volume. Heavy work at high percentages drives maximal strength through largely neural adaptations; moderate percentages taken close to failure drive size; and you cannot do a great deal of either at once, which is what programmes are managing.
The more useful daily measure is effort rather than percentage. Your true maximum moves with sleep, stress and fatigue, so RPE and reps in reserve describe what a set actually cost you on the day in a way a fixed percentage cannot.
On the endurance side, intensity distribution across the week matters more than any single session. The evidence favours most of the volume being genuinely easy with a smaller amount genuinely hard, and the common failure is a moderate rut in the middle that is too hard to recover from and too easy to drive adaptation.
For growth specifically, load turns out to matter less than proximity to failure: light and heavy sets taken close to failure produce similar hypertrophy, with heavier work producing more strength.
In practice, estimate percentages with our one rep max calculator, regulate day to day by RPE, and set endurance bands with the heart rate zone calculator.