Mixed
Training to muscle failure is not required for maximizing muscular strength or hypertrophy gains compared to training non-failure, provided training volume is equated.
You do not need to train to absolute muscular failure on every set to build maximum strength or muscle size. As long as you are close to failure (e.g., 1-3 reps in reserve) and you match the total number of reps/sets (volume) between your failure and non-failure groups, your results will be statistically identical. Prioritize non-failure training to reduce joint stress and improve recovery, unless you are a highly trained individual where failure might offer a slight hypertrophy edge.
Training to muscle failure does not seem to be required for gains in strength and muscle size. However, training in this manner does not seem to have detrimental effects on these adaptations, either.
Why this rating
Systematic review and meta-analysis of 15 randomized controlled trials with moderate-to-good methodological quality.
Source
Effects of resistance training performed to repetition failure or non-failure on muscular strength and hypertrophy: A systematic review and meta-analysis
Jozo Grgić et al. · Journal of sport and health science/Journal of Sport and Health Science · 2021
This is one finding among thousands. Every one is graded and traced to its source, so you can see what the evidence actually supports. Browse the research →