Strength training programs have a variety of goals, although the two main ones for most athletes are to increase strength or muscle mass. The goal is often to produce improvements in only one of these factors. For example, in sports where it is important to avoid excessive gains in body weight, athletes may seek to increase strength without increasing muscle mass. So, when scheduling strength training we need to be clear about the goals in order to modulate the different training variables in a way that achieves the desired adaptations. Specifically, two of the variables that most affect the adaptations produced with strength training are intensity (e.g. high or low loads, high or low speeds) and volume (e.g. number of repetitions performed, time under tension).

Volume vs intensity to increase strength

Several studies have sought to analyse how high or low loads affect levels of muscle mass and strength, and the results have been shown to be complex. In a meta-analysis published by Dr Brad Schoenfeld, one of the leading experts in strength training, 21 studies were analysed that had compared training protocols with high loads (>60% of the maximum weight that can be lifted [1RM]) vs low loads (<60%). The results showed that both low and high loads can produce the same benefits in terms of muscle mass, although high loads produce greater improvements in strength.¹  

These results suggest that intensity (i.e. the load used) is a key factor for producing gains in muscle strength. This is probably because strength is largely dependent not only on muscle mass, but also on other factors such as neuromuscular factors (e.g. fast twitch fibre recruitment) that benefit more from explosive and high load actions. In fact, volume seems to play a lesser role in strength gains. For example, in another recently published study in which Dr Schoenfeld also participated it is shown that performing a single series per exercise (8-12 repetitions to muscle failure) for 3 days a week may be enough to increase muscle strength, while increasing the number of series did not produce greater benefits.²

Volume vs intensity to increase muscle mass

However, unlike what happens with muscle strength, training volume does seem to play a key role in muscle hypertrophy. Nevertheless, in the aforementioned study by Dr Schoenfeld et al. it was observed that the more series are performed, the greater the gains in muscle mass.² Furthermore, a meta-analysis that included 15 studies concluded that performing a greater number of series per week produced a greater increase in muscle mass (4% more on average) than lower training volumes, with each additional training series increasing muscle mass by 0.4%.³ These results show that training volume (number of repetitions or series) is a very important factor when it comes to producing muscle mass gains, while the load used could be less important. Specifically, it seems that the same gains in muscle mass can be achieved regardless of the load being high or low, as long as muscle failure is reached (i.e. such high levels of fatigue are produced when we are unable to perform any more repetitions in each series). For example, one study showed that both low loads with high repetitions (20-25 repetitions with 30-50% RM) and high loads with few repetitions (8-12 repetitions with 75-90% RM) caused the same gains in muscle mass. if both protocols were performed until muscle failure.⁴

Conclusions

The benefits of training with strength and muscle mass loads will largely depend on the intensity and volume performed. Specifically, intensity (load used) seems to play a key role in strength gains, with greater benefits being obtained with high loads as opposed to low loads. However, the evidence shows that the same benefits in muscle mass can be obtained with low or high loads as long as high levels of fatigue are reached (reaching muscle failure), in which case training volume is the main modulator of the adaptations produced.

Pedro L. Valenzuela

References:

1. Schoenfeld BJ, Grgic J, Ogborn D, Krieger JW. Strength and hypertrophy adaptations between low- vs. High-load resistance training: A systematic review and meta-analysis. J Strength Cond Res. 2017;31(12):3508-3523. doi:10.1519/JSC.0000000000002200
2. Schoenfeld BJ, Contreras B, Krieger J, et al. Resistance Training Volume Enhances Muscle Hypertrophy but Not Strength in Trained Men. Med Sci Sports Exerc. 2019;51(1):94-103. doi:10.1249/MSS.0000000000001764
3. Schoenfeld BJ, Ogborn D, Krieger JW. Dose-response relationship between weekly resistance training volume and increases in muscle mass: A systematic review and meta-analysis. J Sports Sci. 2017;35(11):1073-1082. doi:10.1080/02640414.2016.1210197
4. Morton RW, Oikawa SY, Wavell CG, et al. Neither load nor systemic hormones determine resistance training-mediated hypertrophy or strength gains in resistance-trained young men. J Appl Physiol. 2016;121(1):129-138. doi:10.1152/japplphysiol.00154.2016