To gain muscle mass, the classic range of 8 to 12 repetitions at an intensity between 70 and 85% of 1RM has often prevailed. However, for several years now, scientific evidence has been accumulating and confirming that muscle hypertrophy is possible with a very wide range of load intensities from 30% to over 70% of 1RM.
According to the size principle established by Henneman in 1957, during an effort, the motor units are recruited in an orderly fashion : the smallest first and then the largest. In practice, this translates into the initial recruitment of type I muscle fibres, and then during the course of the effort, with the onset of fatigue, to that of type II fibres. All this is done to maintain force production. From this observation, the idea of training for muscular failure appeared. Muscle failure consists of performing a set with as many repetitions as possible (without stopping to rest). Failure is defined as the point at which no further repetitions can be performed. For some, this way of training is optimal for hypertrophy and muscular strength since such a set assumes that all available motor units are recruited. However, with loads above 70% of 1RM, a high level of muscle activation can be achieved without resorting to muscle failure.
However, the results of studies on the subject diverge because the protocols often forget to take into account the training volume (which plays a primordial role for gains in muscle hypertrophy and strength), which distorts the results. It therefore seems important that training volume be equalised in training protocols in order to understand the role of muscle failure in muscle adaptations, regardless of load intensity.
This is what a team of Brazilian and American researchers did by comparing the gains in muscle mass and strength obtained as a function of training with light and heavy loads, with or without muscle failure.
To do this, the researchers recruited 25 untrained participants and divided them into two groups : one group (n=13) trained with a heavy load (80% of 1RM) and the other group (n=12) with a light load (30% of 1RM). For 8 weeks, the participants practiced leg extension twice a week. To determine the impact of muscle failure on strength and hypertrophy, all participants trained unilaterally. Thus, one lower limb was trained to failure and the other was not. For example, one person in the light group trained one leg until muscular failure and the other leg without failure. For the training until failure, the participants performed 3 sets with a maximum number of repetitions. To equalise the volume, for the non failure participants, additional sets were performed. A rest of two minutes was taken between each set.
The leg extension 1RM was assessed at the start of the training protocol, after 4 weeks to adapt the training loads and after 8 weeks, at the end of the protocol. To measure muscle hypertrophy, the muscle cross-sectional area of the thigh (at 50% of the femur length) was measured by MRI, before and after the 8-week protocol. Finally, after each session, participants reported their perceived exertion level on a Borg scale (CR10), with 0 representing no exertion and 10 representing maximal exertion.
The main results of this study show that with light load, training until failure is necessary to achieve hypertrophy gains comparable to those obtained at high load. However, training until failure did not confer any additional benefit for participants training with heavier load for either strength or hypertrophy. Finally, regardless of load, training until failure was the most intense in terms of perceived effort.
These results show that in order to achieve gains with relatively light loads (30% of 1RM), it is important to train to failure. Simply increasing the volume of training will not be sufficient to achieve hypertrophy results. Failure increases metabolic stress, and according to two hypotheses in the scientific literature on the subject, the accumulation of metabolites stimulates anabolism or generates more fatigue in the muscle fibres, which makes it possible to recruit the largest motor units.
On the other hand, training until failure did not bring any additional benefits during training with a high load (80% of 1RM), either in hypertrophy or in strength. It is probable that the muscle fibres are sufficiently stimulated by the intensity of the load.
Finally, all conditions resulted in strength gains, and training until failure did not result in greater gains. The results show that high load training clearly leads to better results : 33.8% and 33.4%, for high load training at failure and without failure, respectively, compared to 17.7% and 15.8%, for low load training at failure and without failure, respectively. For strength, a threshold training volume would be preferred over muscle failure.
Training until failure is particularly useful if you want or have no choice but to train with relatively light loads. You will be able to achieve similar gains in hypertrophy as you would with heavier loads, while gaining slightly in maximal strength (but much less than with heavier loads). If you train with moderate to high loads, training until failure will not provide any additional benefit except perhaps greater perceived difficulty, and therefore greater fatigue. In the case of advanced practice, a few sessions of training until failure can be a good way to give a boost without necessarily increasing the loads, but in long-term practice, it could be counter-productive.
For beginners, the RPE being systematically greater when the series are performed to failure, this type of training could induce unnecessary fatigue between sessions, alter recovery, which could lead to less pleasure during the sessions and therefore to a lower adherence to the training, and in fine, a greater risk of drop out.
Regarding limitations, this study did not take into account the nutritional aspect, and none of the participants were followed up. However, the nature of the study itself (the two thighs of the same person following two different training principles) allows the negative impact of this phenomenon to be limited. Although it could be argued that people training with heavier loads will have wanted to pay more attention to their nutrition without telling the researchers... Secondly, the participants in this study were men, beginners. What about women, seniors, teenagers and trained men ? Finally, only a single joint lower body exercise was used in this protocol. A study with a real-life programme will therefore be necessary to confirm or refute these results.
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