Resistance training is an effective method for building muscle mass and increasing strength (hypertrophy). Maximizing muscle growth requires high training intensity. One technique used to ensure sufficient intensity is “training to failure,” where a set is pushed to the absolute limit of the muscle’s capacity. This approach maximizes the stimulus for adaptation but must be applied strategically to manage fatigue.
Defining Training to Failure and Intensity
Training to failure, or momentary muscular failure, is the point during a set where a lifter cannot complete another concentric repetition with strict, controlled form. Concentric failure means the muscle is unable to shorten and overcome the resistance for one more rep, despite maximal effort. This differs from technical failure, which occurs when a lifter can no longer maintain the desired form, often resulting in compensatory movements.
For muscle growth, lifting should continue until at least technical failure is reached to ensure the targeted muscle is adequately stimulated. A common method to quantify intensity without always going to failure is the Reps in Reserve (RIR) scale. RIR measures how many more repetitions a lifter believes they could complete before reaching momentary muscular failure. For example, 0 RIR indicates the set was taken directly to failure, while 2 RIR means the lifter stopped two reps short.
The Physiological Rationale for Training to Failure
The primary mechanism driving muscle hypertrophy is the mechanical tension placed on the muscle fibers. Training close to or at failure reliably ensures that all muscle fibers, including high-threshold motor units, are recruited and fatigued.
During a set, the body recruits motor units following the size principle, starting with smaller units and progressing to larger ones as fatigue increases. Pushing a set close to failure exhausts the smaller motor units, forcing the nervous system to activate the high-threshold units to maintain force production. This maximal recruitment and subsequent fatigue provide a strong stimulus for the muscle to adapt and increase its size. This intense effort also generates metabolic stress, which contributes to the overall muscle-building signal.
Determining Optimal Sets Taken to Failure
Reaching momentary muscular failure is not required for every set, as similar muscle growth results can be achieved by stopping just 1 to 3 repetitions short of failure. This proximity to failure (0-3 RIR) is considered the effective intensity zone for maximizing hypertrophy. Avoiding failure on every set is necessary because of the significant increase in systemic fatigue and recovery time that accompanies this intense effort.
The majority of total weekly sets for a muscle group should fall within the 0-3 RIR range. For intermediate or advanced trainees, the optimal range of total working sets per muscle group per week is often cited as 10 to 20 sets. Only a small fraction of these sets needs to be taken all the way to 0 RIR to reap the benefits. A practical recommendation is to take only the final one to three sets per muscle group per workout to true failure, providing maximal stimulus while managing accumulated fatigue.
Practical Considerations and Application
Selecting the right exercises is important when incorporating training to failure due to safety and recovery concerns. Exercises involving significant balance, coordination, or a high risk of injury should be avoided for true failure training. Heavy, compound movements like the barbell squat, deadlift, or overhead press carry a high systemic fatigue cost and risk of form breakdown.
Isolation exercises, such as bicep curls, lateral raises, or machine-based movements like leg extensions, are better suited for momentary muscular failure. These movements isolate the target muscle, produce less overall systemic fatigue, and are safer to perform when the muscle reaches its limit.
When performing any exercise to failure, having a spotter or utilizing safety equipment like a power rack is essential to prevent injury. Training to failure is a high-stress technique and should be used sparingly by intermediate and advanced lifters who have mastered proper form and understand their recovery capacity.