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How hard should you push yourself in the gym? Should you train until exhaustion, squeezing out every drop of performance your body has to give?

According to some trainers, coaches, instagurus, and athletes, the answer is absolutely. If you have read my articles before, you know anecdotal experience won’t satisfy my thirst for answers.

Training to failure

Before I jump into the study, I want to quickly cover the concept of training to failure. This implies you perform a set of exercise until you can no longer complete a full repetition. For some, they may elect technical failure, meaning a predetermined level of form or technique can no longer be achieved. Perhaps your row becomes a full-body pull. For others, failure only counts if the rep isn’t completed, regardless of form. This could be failing to lock out a deadlift or being unable to stand up from the bottom position of a squat, requiring help from spotters or you to bail and drop the bar (there are safe ways to do this).

For those who train short of failure, a common technique for predetermining exercise intensity and programming a workout is to use reps in reserve (RIR). RIR is a subjective calculation of how many reps you have left in the tank before you call quits on a set.

For example, you may determine you will perform 4 sets of squats with 2 RIR. When picking how much to load the barbell, you pick a rep range based on goals for your session or training block. If you are working on building muscle, you may want to complete 6–12 reps with 2 minutes of rest (there is no magic muscle building zone but this is a common range). The RIR provides flexibility for fluctuations in training performance that occur due to sleep, nutrition, and stress status (among other things).

I prefer this method over using the percent of one-rep max for the flexibility of autoregulation. Some days I feel better than others.

For the study I am about to share, they used RIR. For most literature assessing failure vs. non-failure, RIR is used. So, let’s take a look at the research.

Failure vs. non-failure

In this 2020 study, 14 trained men compared the effects of two training programs, each performed on one of their legs. Researchers compared changes in muscle growth, muscle architecture, and muscle activation in each quadriceps muscle following 10 weeks of training with unilateral leg press and leg extension exercises. One leg performed exercises to failure and the other performed them with 1–2 RIR. There was an even split of participants you trained the dominant leg to failure and the dominant leg with 1–2 RIR. They defined failure as being unable to perform the exercise with a full range of motion.

To control for volume and personalize the program, the researchers prescribed a 20% increase in each participant's quadriceps training volume from the week prior to the study. On average, participants performed 11.5 sets of leg press and 11.6 sets of leg extension per week over the 10 weeks, but the range was 4–25.

What did they find?

As expected, when training to failure, subjects performed 13.6% more repetitions (12.0 vs. 10.4) and 11.5% total volume (reps). Despite the greater volume of training from the failure group — keeping in mind volume is typically king when it comes to hypertrophy — the non-failure group had greater increases in muscle size (measured by cross-sectional area on ultrasound) and leg press one-rep max, at 4.6% and 4.4% respectively. Overall, the failure group increased muscle size 13.5% but the non-failure group increased 18.1%.

There were no differences between groups in the other measures.

How does this research stack up against previous research?

At first glance, the results may not make sense. How does less volume lead to greater muscle development? Well, this isn’t the only study to show that. Here is a sample of six articles for those interested in further reading (1, 2, 3, 4, 5, 6). As for the reason why, there are a couple of theories.

Regarding the need for training to failure, we see training short of failure stimulates sufficient motor unit recruitment and hormonal responses to trigger hypertrophy at equivocal levels as training to failure. Some studies show this occurs with up to 5 RIR. The difference may arise from molecular effects that have a net negative effect when pushing the body to failure.

Some research suggests training to failure may alter hormonal responses and create metabolic environments that inhibit muscle growth. First, muscle growth still happens, as the previous studies show, just not as muscle as stopping short of failure. Second, the data is largely theoretical.

So, while we don’t know the exact reason for non-failure trumping failure, we see the research largely supports it. A couple of final thoughts to keep in mind.

First, the differences between groups are small. If you prefer training to failure because you believe you get a better workout, it won’t crush your gains. Just be aware of the potential injury risk of pushing your body to its limit.

Second, you still have to train hard to build muscle. While there is debate about the optimal number of RIR, most studies operate in the 1–3 RIR range. You still need to push the body and provide sufficient rest between sets and recovery between lifts to continue exercising at a high intensity.

Third, know your goals of exercise. This study used RIR of 1–2 and showed improvements in strength and muscle growth. If you want to build strength, you need to work at high loads. It’s not just about training to failure, but training near your 1 rep max as well. Hypertrophy has a much wider range, as research shows you can train as low as 30% of your 1 rep max, provided you are near failure.

Lastly, this study used trained individuals. If you are not trained, meaning you don’t perform resistance training regularly, you will experience rapid improvements in strength and muscle growth regardless of the program you use. Novice lifters respond rapidly to resistance training, but they also require more rest for recovery. If you don’t have training experience, please don’t perform 5 sessions of training near failure a week. Gradually build up your capacity. The results will still come quickly.

In the end, don’t worry about training until the spotter needs to step in. You can safely leave a couple of reps in the tank and still reach your fitness goals.