Should we train to failure to maximize muscle hypertrophy? A key consideration is how we define muscular failure. The authors of this study define momentary muscular failure as “when an individual cannot complete the concentric portion of a given repetition with a full range-of-motion without deviation from the prescribed form of the exercise.” This definition still leaves room for interpretation.
A prescribed form can allow for some variability. Performing a true 1 rep max will look different than a lesser load. There will be some level of compensation and some muscles will fail before others (e.g., rounding of the back during deadlifts). Some deviations are more apparent than others (large back extension during a row or hitching a bar up during deadlifts) while others are subtle. If we are too strict with form, we will likely impede potential training adaptations.
The goal of training close to failure is to maximize mechanical tension to stimulate hypertrophy. This, however, comes with a cost. If the body is taxed too much, it may not recover enough prior to the next session, leading to overtraining and potential injury. Limiting our viewpoint to training to failure does not account for the total training load, the velocity of contractions, or recovery strategies. So should you train your patients to failure?
This recent systematic review and meta-analysis assessed the overall effect of training to failure versus non-failure on hypertrophy. They looked at momentary muscle failure, set failure (defined as anything other than the definition of momentary muscular failure), and high-velocity loss. The final analysis included 15 studies. There was a statistically significant advantage to training to set failure versus non-failure on muscle hypertrophy, however, the difference was trivial in magnitude [ES = 0.19 (95% CI 0.00, 0.37), p = 0.045].
Given the wide variety of definitions of failure and the minimal differences, it does not appear training to failure yields a worthwhile benefit in most cases, especially when taking into account the increased risk of overtraining. In some cases, it may be worth it. For example, on the final set for a muscle group or if the overall training volume is low (< 5 sets per session or only training 1–2 sessions per week). If someone is a novice with little resistance training experience, I would forgo training to failure. It is likely best reserved for trained individuals performing low-load isolated movements (e.g., leg extension instead of squats).