How Hard Should You Train?

By Aadam | April 4, 2024

There are several ​factors and variables​ you need to consider when designing a training program. But none of these matter if you’re not training hard enough. Broadly speaking, training “hard enough” can be grouped into two categories:

You’ll note one common thread between these two approaches: Proximity to failure. To explore why this matters, imagine you’re in the gym doing a set of bicep curls.

At first, the weight moves quickly, and the reps feel easy. But as you keep curling away, you reach a point where the weight feels heavier, and your reps start slowing down. Eventually, you’ll hit the point where completing another rep takes everything you have before you can’t physically complete another rep.

So what happened here?

When you began the set of bicep curls, your body began recruiting motor units. As the set progressed and you got closer to failure, there was a progressive increase in the recruitment of higher-threshold motor units, exposing type II muscle fibres (the fibres with the highest potential for growth) to greater mechanical tension–the key stimulus for muscle growth.

Therefore, the idea is if you take each set to failure, you’re able to recruit all motor units, which will lead to more muscle growth.

However, it seems you don’t need to pay Jesus a visit to reap the muscle growth benefits of a set.

A recent meta-analysis looked at 15 studies on the effects of training to failure vs not training to failure and found that while training to failure did have a ‘statistically significant’ impact on muscle growth, the actual size of the effect was trivial. 1

In other words, training to failure did increase muscle growth, but the real-world implications were practically insignificant.

Further, there seemed to be a non-linear relationship between failure and muscle growth––i.e., as you get close to failure, muscle growth seems to increase, but there’s no further benefit to muscle growth once you hit failure.

One reason for the non-linear relationship between failure and muscle growth could be due to neuromuscular fatigue, which could then impact your ability to maintain your performance across sets.

In any case, the researchers concluded that:

There is no evidence to support that resistance training performed to momentary muscular failure is superior to non-failure resistance training for muscle hypertrophy.

However, the researchers pointed out that while training to failure might not be necessary, there’s no universally accepted definition of ‘failure’, making it hard to discern just how close to failure you need to go to maximise muscle gains.

Moreover, many studies on the topic have defined failure in binary terms––the participants are either training to failure or not to failure. This fails to capture the nuances of training in the real world, where proximity to failure lives on a spectrum; you might train one, two, or three reps shy of failure or you might take a set to complete failure.

Well, a brand new study decided to do something about that.

The researchers wanted to see how proximity to failure, as defined by reps in reserve (RIR), impacted muscle growth compared to training to failure. 2

What did the researchers do?

12 men and 6 women with an average of seven years of resistance training experience were recruited for the study. Each participant served as their own control, with one leg randomly assigned to the FAIL condition and the other leg assigned to the RIR condition.

This illustration took way too fucking long. And I expect my inbox to be flooded with messages telling me how great it is. Thanks.

Some other quick takes regarding the study design for those who happen to give a damn–

  • Participants trained 2x/week with each leg either training to failure or RIR separated by 3 days.
  • The set volume for each participant was individualised based on what they habitually performed in their previous training, and this was increased by 20% in week 5 of the study. Over the course of the study, the participants performed between 10-17 sets for the quads per week (which is in line with the general recommendation of ​10-20 sets per muscle group/week​).
  • While the participants were allowed to perform additional moderate-intensity resistance training involving muscle groups other than the quads (hams, glutes, calves, and upper body), the researchers limited the hamstring and glutes to specific exercises to reduce quadriceps engagement. For example, the participants could perform leg curls but couldn’t perform squats or lunges.
  • Muscle thickness of the quads (rectus femoris and vastus lateralis) was assessed via ultrasound at baseline and following the 8-week RT intervention.
  • Additionally, the researchers also looked at neuromuscular fatigue via
    • Changes in lifting velocity in weeks one, four, and eight
    • Reps completed from the first to the final set
    • Volume load (sets x reps x load)
    • Repetition volume (sets x reps)
  • Finally, each participant was tested for RIR accuracy before the study began. Each participant was able to report RIR with high accuracy (on average, less than one repetition from the 1– and 3-RIR target on both exercises).

Basically, the researchers didn’t fuck around––seriously, this was a very well-done study. Hell, they even uploaded sample set footage of one of the participants performing a set to failure and 2 RIR.

What did they find?

Muscle growth

There was a similar increase in quadricep thickness between FAIL (+6.96%) and RIR (+6.98%) or about a 0.18 cm (~0.1″) increase in both groups. So training to failure wasn’t more effective for muscle growth than stopping a few reps short.

individual (coloured circles) and average (horizontal bars) changes in quadriceps muscle thickness for FAIL and RIR.

Volume load + repetition volume

Average volume load (sets x reps x load) and repetition volume (sets x reps) were similar across both groups suggesting that stopping a few reps short of failure doesn’t affect the total ‘work’ completed vs going to failure.

Average volume load and average reps completed by each group for the leg press and leg extension across the study

Neuromuscular fatigue

There was a greater increase in neuromuscular fatigue in FAIL vs RIR––the group training to failure experienced greater decreases in lifting velocity and greater repetition loss. However, the gap between the groups in terms of lifting velocity and repetition loss decreased by the eighth week, suggesting a potential adaptation to the training stimulus.

So what does this all mean?

There’s enough data at this point to be quite confident in suggesting that training a few reps shy of failure is just as effective (if not more effective, considering the smaller decline in performance) as training to failure.

Sure, this study was the first of its kind to quantify proximity to failure via RIR, but the results jive with the rest of the research on the topic. Fuck yeah I said jive. Anyway, let’s keep it moving.

To Cliff Notes the findings for those who jumped to the end:

👉🏼 The group who trained with 1-2 reps in reserve experienced similar muscle growth as the group who trained to failure.

👉🏼 Further, the FAIL group experienced greater neuromuscular fatigue as measured by changes in lifting velocity and repetition loss across the entire study compared to the RIR group.

Now, there was some indication that participants in this study ‘adapted’ to failure training over time.

While that might be true, it’s important to consider these findings outside of a research setting and how they might differ in the real world.

For one thing, fatigue tolerance is highly individual. And while some people may be able to push to failure a bit more regularly and recover ok, this might not be the case for everyone.

Additionally, the participants were allowed to continue training outside of the study (as long as they didn’t use exercises that hit the quads) and were told to train at a ‘moderate intensity’. The researchers didn’t specify what ‘moderate intensity’ meant in a training context, but I’m going to assume they weren’t training to failure (otherwise, that would have impacted the study results).

So, in reality, the participants were only really taking two exercises to failure (the leg press and leg extension, the exercises performed during this study). And, taking two exercises to failure is very different from taking every exercise in a program across the week to failure.

Exercise selection can also influence how much fatigue you experience. In this study, the participants performed the leg press and leg extension, which are far less fatiguing than multiple hard sets of, say, the barbell back squat or deadlift. Don’t get me wrong, pushing to failure on the leg press isn’t exactly a walk in the park but it’s still less fatiguing than a comparatively hard set of the back squat. So, people might adapt to higher training intensities over time, but this will likely be exercise– and context-dependent.

In any case, considering that training a few reps shy of failure leads to the same amount of muscle growth as training to failure, with considerably less fatigue, most of your training should occur around 1-3 RIR (i.e. 1-3 reps from failure), with failure training used sensibly and under the right contexts (see image below).

Key points

  • As you get closer to failure, more motor units are recruited, which exposes type II muscle fibres to greater mechanical tension––the key stimulus for muscle growth. Thus, the reasoning for taking sets to failure is that you’re able to recruit all muscle fibres, which will lead to more #gainz.
  • However, the research seems to suggest you can get the muscle growth benefits stopping a few reps shy of failure. While this might be true, research quantifying proximity to failure and muscle growth is still limited.
  • A new study–the first of its kind in this area of research–quantified proximity to failure using the RIR model and investigated how training 1-2 reps from failure vs taking a set to failure impacted muscle growth and fatigue.
  • There was no difference in muscle growth between the group training to failure and the group training 1-2 reps in reserve. On average, both groups saw a ~7% increase in their quads.
  • The failure group experienced higher neuromuscular fatigue measured by changes in lifting velocity and repetition loss. However, there was some indication the failure group adapted to the stimulus over time.
  • But while some people might adapt to higher training intensities, this is highly individual, and it might not be the case for you.
  • Considering that muscle growth seems to be similar when training to failure vs stopping a few reps short of failure, it’s probably a good idea to keep the majority of your training around a 1-3 RIR.
  • This doesn’t mean training to failure is bad or dangerous, it just needs to be used properly (refer back to the image above).

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