Training to Failure: Repetitions, Fatigue, and Discomfort

The metabolic cost of training to failure

It is common to gauge a workout’s effectiveness by how difficult it feels, often pushing sets to the point where another repetition is impossible. However, when the goal is to accumulate training volume over the week, hitting muscular failure carries a disproportionate recovery cost.

A 2021 systematic review of 20 studies, with 12 included in its meta-analysis, comparing resistance training to failure against stopping short of failure found that training to failure leads to significantly greater acute fatigue. Specifically, taking sets to the limit resulted in a larger decline in biomechanical properties—such as jump height and movement velocity—and higher levels of muscle damage, indicated by elevated creatine kinase activity measured 48 hours post-exercise. Metabolic markers like blood ammonia concentrations were also significantly higher in the failure groups.

This severe fatigue does not necessarily buy more total work. In a 2021 randomized crossover trial involving 12 women, researchers compared four sets of high-velocity squats performed to momentary failure against sets that were stopped when the lifter's movement velocity dropped by more than 20 percent. While the participants lifting to failure completed an average of about four more repetitions in their first set, their performance dropped steeply as fatigue set in. By the final set, the group leaving repetitions in reserve was able to do more work. Ultimately, the total number of repetitions performed across all four sets was statistically similar between the two protocols. However, the failure group reported much higher ratings of perceived exertion and discomfort.

This trial supports considering a stopping rule before failure when acute fatigue and discomfort matter. It used a 20 percent velocity-loss threshold, not a fixed target of one or two repetitions in reserve. Its similar total repetitions across four squat sets should not be taken as a guarantee of equal workload in every exercise or program.

Upper body movements degrade faster under fatigue

When evaluating how fatigue impacts different types of training, it becomes clear that the body does not respond uniformly to muscular exhaustion.

In the exploratory analysis of the 2021 review mentioned earlier, researchers noted a distinction in how different muscle groups handle failure. They found that upper body exercises showed a more pronounced loss in movement velocity after training to failure than lower body exercises.

The review’s authors described this as an exploratory subgroup finding. It is not a rule that every upper-body exercise is more fatiguing than every lower-body exercise, and it does not directly compare a particular person’s bench press with their squat. The result is best treated as a reason to monitor how performance changes across sets rather than to impose a universal upper-body cutoff.

Acute fatigue is not the same as long-term progress

The review and squat trial address acute responses. They show that failure can carry greater immediate performance losses and discomfort, but they do not by themselves establish which approach produces the most long-term strength or muscle growth. When deciding where to use failure, the useful distinction is between the extra repetitions achieved early in a session and the fatigue that may affect the remaining work.