There are less and less doubts about the need to keep adequate levels of strength and muscle mass for health. Scientific evidence is conclusive in this sense and strength restates its importance as a health marker, since there is a strong inverse association between strength levels and mortality for all causes, in healthy and pathological population.1–5 Over the years, people lose strength, making this situation more severe for 50-60 years old. This reduction in strength levels increases the risk of suffering from the well-known sarcopenia, meaning strength and muscle mass loss. In this case, strength training has shown to be a very effective alternative to minimise, and even revert strength loss related to age.

Strength training has been considered for so long as something exclusive for muscle men. However, during the last few years, this type of training has received special attention, especially, because of its benefits for health. Thus, while cardiovascular or aerobic training has been recommended by the main health institutions from the year 2000, strength training has been included in the guidelines of the American College of Sports Medicine, the World Health Organization and the American Heart Association, just over a decade ago, when they began to recommend strength training activities at least twice a week. 

Traditionally, this type of training has been performed until muscle failure (meaning, the inability to perform more repetitions due to fatigue) seeking a gain in strength that would happen in a concomitant way to an increase in muscle mass. The main physiological mechanism that would justify it is based on the fact that training to failure is necessary for full recruitment of high-threshold motor units, that mainly involve type II muscle fibres. Since these muscle fibres have a greater potential to increase strength6 and they are more susceptible to hypertrophy than type I fibres,7 training to muscle failure would be an essential stimulus to maximise muscle adaptations. However, this issue has been widely discussed in the last few years as, when the objective is strength and muscle mass gain, it seems that it is not really necessary to reach to failure.8–10 

In fact, a systematic review with meta-analysis published in the prestigious Sports Medicine, whose objective was to compare training to muscle failure versus training without reaching failure on muscle strength in people with prior experience in strength training and people without it, showed that (although slightly) training without reaching failure produced greater increases on strength than training to failure.11 Also, when the authors compared based on prior experience, trained individuals obtained greater benefits from training without muscle failure than untrained individuals.11 Moreover, Brad Schoenfeld, one of the greatest international experts on methodology of this type of training, led a study that compared the effect of strength training with high (70-80% of 1 maximum repetition [1 MR]) and low loads (30-50% 1MR) to muscle failure on muscle adaptation in trained people.12 The authors concluded that overtraining to failure, with both high and low loads, can increase muscle mass in these people, although high loads seem to produce greater benefits on maximum strength, while repetitions to failure with low loads do so on endurance strength.12 

More recently, a study has been published in which Dr. Schoenfeld has also participated, whose objective was to assess the training effects of strength with low and high loads, with and without reaching muscle failure, on mass and muscle strength in untrained individuals.13 In this case, 4 groups were formed (being training volume balanced in all of them):

• LL-RF repetitions to failure with low loads
• HL-RF repetitions to failure with high loads
• LL-RNF repetitions not reaching failure with low loads 
• HL-RNF repetitions not reaching failure with high loads 

After 8 weeks of training, the results showed that strength increased in groups that trained with high loads (+33,8% and + 33,4% in HL-RF and HL-RNF, respectively) compared to the groups that performed with low loads (+17,7% and +15,8% in LL-RF and LL-RNF, respectively).13 As for the effect on muscle mass, the groups HL-RF (+8,1%), HL-RNF (+7,7%) and LL-RF(+7,8%) increased the cross-sectional area of the quadriceps, while no changes were observed in LL-RNF (+2,8%). This means that greater benefits on strength were produced when training with high loads, regardless of reaching muscle failure or not, while muscle mass could also be improved with low loads reaching muscle failure.13

Conclusions

The first aspect to keep in mind is that results will vary depending on whether it is about trained or untrained individuals, since muscle adaptations will be different, so we have to consider the level of prior training, as well as the objective we are pursuing before prescribing this type of training. Also, the results do not seem to support a greater benefit when reaching muscle failure when seeking to improve strength, at least in trained individuals. This, plus the fact that reaching failure involves greater neuromuscular fatigue than not reaching failure14 and, therefore, will increase the risk of overtraining and injuries, makes us think that this training modality should be limited, at least in this population. However, it could be an effective strategy to produce different stimuli when training, in a timely manner to failure, restricting its use to the final series of each training, for example. Because of all this, it is important to remember that we should always pay attention to the principle of individualisation, given the variability of responses that occur in different individuals.

Javier S. Morales

References:

1. Ruiz, J. R. et al. Association between muscular strength and mortality in men: Prospective cohort study. Bmj 337, 92–95 (2008).
2. Ruiz, J. R. et al. Muscular strength and adiposity as predictors of adulthood cancer mortality in men. Cancer Epidemiol. Biomarkers Prev. 18, 1468–1476 (2009).
3. García-Hermoso, A. et al. Muscular Strength as a Predictor of All-Cause Mortality in an Apparently Healthy Population: A Systematic Review and Meta-Analysis of Data from Approximately 2 Million Men and Women. Arch. Phys. Med. Rehabil. 99, 2100-2113.e5 (2018).
4. Volaklis, K. A., Halle, M. & Meisinger, C. Muscular strength as a strong predictor of mortality: A narrative review. Eur. J. Intern. Med. 26, 303–310 (2015).
5. Artero, E. G. et al. A prospective study of muscular strength and all-cause mortality in men with hypertension. J. Am. Coll. Cardiol. 57, 1831–1837 (2011).
6. Tesch, P. A. et al. The influence of muscle metabolic characteristics on physical performance. Eur. J. Appl. Physiol. Occup. Physiol. 54, 237–243 (1985).
7. Fry, A. C. The role of resistance exercise intensity on muscle fibre adaptations. Sports Medicine vol. 34 663–679 (2004).
8. Sundstrup, E. et al. Muscle activation strategies during strength training with heavy loading vs. repetitions to failure. J. Strength Cond. Res. 26, 1897–1903 (2012).
9. Martorelli, S. et al. Strength training with repetitions to failure does not provide additional strength and muscle hypertrophy gains in young women. Eur. J. Transl. Myol. 27, (2017).
10. Nobrega, S. R., Ugrinowitsch, C., Pintanel, L., Barcelos, C. & Libardi, C. A. Effect of resistance training to muscle failure vs. volitional interruption at high-and low-intensities on muscle mass and strength. J. Strength Cond. Res. 32, 162–169 (2018).
11. Davies, T., Orr, R., Halaki, M. & Hackett, D. Effect of Training Leading to Repetition Failure on Muscular Strength: A Systematic Review and Meta-Analysis. Sports Med. 46, 487–502 (2016).
12. Schoenfeld, B. J., Peterson, M. D., Ogborn, D., Contreras, B. & Sonmez, G. T. Effects of low- vs. High-load resistance training on muscle strength and hypertrophy in well-trained men. J. Strength Cond. Res. 29, 2954–2963 (2015).
13. Lasevicius, T. et al. Muscle Failure Promotes Greater Muscle Hypertrophy in Low-Load but Not in High-Load Resistance Training. J. Strength Cond. Res. (2019).
14. Morán-Navarro, R. et al. Time course of recovery following resistance training leading or not to failure. Eur. J. Appl. Physiol. 117, 2387–2399 (2017).