It is easy to assume that harder training always produces better results. In resistance training, which includes lifting weights or using resistance machines, taking every set to the point where you cannot complete another repetition may create more fatigue without producing better results.
A repetition, or rep, is one complete movement of an exercise. A set is a group of repetitions performed without a long rest.
Training to failure means continuing a set until you cannot complete another full repetition with acceptable technique, despite making your best effort. This is sometimes called momentary muscular failure.
An alternative is to stop while you could still perform one or more repetitions. This is described as repetitions in reserve, or RIR. If you could complete ten repetitions but stop after eight, you have two repetitions in reserve, usually written as 2 RIR.
Why might training close to failure help?
Muscles are made up of individual cells called muscle fibres. These fibres are broadly classified as type 1 or type 2 fibres and are controlled by the nervous system. The type 2 fibres produce more force and can grow more than type 1 fibres.
A light load is generally one that you could lift for more than 15 repetitions, whereas a heavy load limits you to completing fewer than 10 repetitions. When lifting a light load, the type 1 fibres are active. As the set approaches failure, the nervous system activates type 2 fibres to keep the weight moving.
Lifting a heavy weight activates type 2 muscle fibres from the beginning of the set. With a light weight, type 2 fibres only become activated as the type 1 fibres fatigue later in the set. Light-weight sets therefore need to be completed reasonably close to failure if the aim is muscle growth.
The final possible repetition does not appear to provide a special muscle-building effect. Research suggests that a hard set ending shortly before failure can stimulate muscle growth while causing less fatigue.
What are the drawbacks?
Taking a set to failure produces more immediate fatigue than stopping earlier. A systematic review and meta-analysis, which combines the findings of several studies, found that failure training caused larger reductions in strength, movement speed and power immediately after exercise. It also produced greater feelings of effort and more signs of temporary muscle disruption.
This fatigue can affect the rest of the workout. If the first set of an exercise is taken to failure, the lifter may complete fewer repetitions with good technique on remaining sets. Research comparing failure and non-failure training has also found that recovery can take longer after sets performed to failure.
The effects of training to failure depend partly on the weight and the exercise. Sets using light weights involve more repetitions, last longer and usually cause more breathlessness and the feeling of muscle burn. That discomfort may make the workout less enjoyable or harder to maintain.
Exercise choice also affects safety. A machine leg extension or biceps curl is relatively easy to stop when the muscles fatigue. A technical exercise like a squat or bench press requires more balance, coordination and control. As fatigue increases, technique may deteriorate and the lifter may be unable to finish the repetition safely. Failure training during these exercises is best avoided unless suitable safety equipment or a competent spotter is available.
What does the research show?
A 2022 systematic review and meta-analysis found no significant overall difference between failure and non-failure training for strength or muscle growth. The authors noted that the studies used different programmes and did not always match training volume, meaning the total amount of load lifted during a training session was different.
A later review examined 15 studies of muscle growth. It found no evidence that reaching failure produced more growth than stopping earlier. The researchers concluded that training closer to failure may increase the muscle growth stimulus up to a point, but every additional repetition does not necessarily provide the same extra benefit.
A 2024 analysis found that failure was not necessary for improving strength as it improved across a wide range of stopping points. Muscle growth tended to improve as sets ended closer to failure, although the researchers could not identify an exact number of repetitions in reserve that was optimal.
The American College of Sports Medicine’s 2026 review of resistance-training evidence reached a similar practical conclusion. Regular training with sufficient effort is more important for healthy adults than following a complicated programme or taking every set to failure.
How close to failure should you train?
For many gym users, finishing most sets with about one to three repetitions in reserve is a useful starting point rather than a fixed rule. The final repetitions should feel difficult and the weight should be moving more slowly than it was at the start of the set.
Training closer to failure may be more useful when using light weights, completing only a very short training session, or performing the final set of a technically simple exercise. Occasionally taking a suitable exercise to failure can also help you learn how many repetitions you genuinely have left.
Judging repetitions in reserve takes practice. Research has found that people often underestimate how many repetitions they could still perform, particularly when using lighter weights.
Beginners have little reason to take every set to failure. They can make progress while learning exercises and gradually increasing the weight or number of repetitions. Experienced lifters may use failure selectively when it suits their programme and recovery.
You do not need to take every set to failure to become stronger or build muscle. Sets still need to be challenging, especially when lighter weights are used. Stopping shortly before failure can preserve technique and reduce fatigue while providing an effective training stimulus. For most people, keeping roughly one to three repetitions in reserve offers a sensible balance between effort and recovery.
Paul Hough does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.
