Do I need to train to failure to grow?

No, but you do need to train close to it. Stopping roughly one to three reps short of failure produces similar growth to going all the way, with much less fatigue, which lets you do more quality work across the week.

What "close to failure" means

Reps in reserve is the usual way to describe it. Two reps in reserve means you stop believing you could have completed two more with good technique. Beginners tend to overestimate how close they are, often stopping five or more reps short while feeling like they are at the limit. Filming a set to failure once or twice calibrates this quickly.

The cost of true failure

• Fatigue rises steeply on the final rep while the growth signal barely changes.
• Technique degrades exactly when the load is heaviest, which is where most training injuries happen.
• Performance on subsequent sets and exercises falls, reducing your total quality volume.
• Recovery between sessions takes longer, which can reduce weekly training frequency.

Where failure is still useful

Isolation and machine exercises are the sensible place for it: A leg extension or a cable curl taken to failure carries little risk and produces almost no systemic fatigue. Occasional failure sets are also useful for recalibrating your sense of effort, and for the final set of the final exercise when nothing follows it.

Where to avoid it

Heavy compound lifts such as back squats and Romanian deadlifts, and anything explosive or technical, should stay well clear of failure. Grinding a maximal squat is a poor trade in every direction.

A practical rule

Aim for one to three reps in reserve on the large majority of sets, allow the last set of an isolation exercise to reach failure if you want, and make sure the effort is real. The most common problem is not going too hard; it is a whole programme of comfortable sets that never approach a challenging effort.

How effort interacts with volume is discussed further in Hypertrophy and Muscle Growth.