We’ve literally rewritten the book on hypertrophy training in the past five years.  A collection of studies has now shown that variations in training intensity [1-4], tempo [5] and rest intervals [4,6-9] impart little to no hypertrophic benefit over any of the other possible combinations. 

Consistent with that human desire to simplify everything, we tend to view strength training adaptations as a binary system, responding to variations in either intensity or volume.  If we’ve established that comparable growth can occur at opposing poles of the intensity continuum [1-4], then surely it must be volume in the hypertrophic driver’s seat? 

The problem with establishing volume as the prime determinant of muscle hypertrophy is that we don’t use the same terms to define what volume is.  Comparing one set at the same intensity to multiples is a clear-cut comparison of differing volumes, favoring multi-set protocols to a point [10,11].  Unfortunately, defining volume as simply the number of sets is woefully inadequate, as drastically different work outputs can occur dependent on the training intensity.  Completing three sets to concentric failure at 90%-1RM and three sets at 30%-1RM will have much more work completed in the low intensity condition [12].  Even this is an over simplification, as cumulative training volume is the result of the interaction of load, sets, reps, number of exercises, and if you consider work, distance as well. 

Muscle growth at widely varying volumes

Many took the recent investigations of the comparable growth that occurs with training at different intensities as telling solely on the relationship between training intensity (%1RM) and growth [1-4].  There is nothing wrong with this; it’s the obvious conclusion, and one I’ve written about previously. 

But these studies also tell us about the role of volume, or work, on muscle hypertrophy.  When training to concentric failure at either high or low intensity, work output varies significantly, being much higher at low training intensities [12].  And yet, when training studies have been completed comparing low and high intensity, comparable growth has been shown across various muscle groups in both trained and untrained individuals.  In these cases, not only did training intensity differ between the groups, but work (volume) as well. 

In fact, the ability of low intensity training to stimulate comparable hypertrophy may actually depend on completing more work.  When you equate volume between conditions (high and low intensity), not only do we see a failure of low-intensity training to stimulate an acute protein synthetic response [12], there is a hypertrophic advantage to higher load training [13,14].  There may be a threshold to this relationship, as Schoenfeld et al [4] recently demonstrated comparable hypertrophy at matched volume loads when training with either 3RM or 10RM loads.  This is consistent with previous data from Campos et al [14], who found comparable growth without significant differences in training volume between what they deemed to be heavy (3-5RM) and intermediate (9-11RM) loads. 

Ultimately, understanding the relationship between the variables matters most.  When training at lower intensities, work must increase to achieve a comparable hypertrophic response, yet it’s possible that there is a threshold to this response.  At this time, it’s impossible to really say where that threshold is, as much of the literature has compared extremes (80-90%-1RM to 30%-1RM), with relatively few testing narrow intensity ranges [4,14]. 

What do our recommendations actually mean? 

As practitioners, when we tell someone that they must focus on training volume to satisfy their hypertrophic desires, what are we actually saying? 

Are we favoring multi-set over single set, without consideration for intensity?  Or are we really just saying, in a round-about way, that you don’t need to focus on load to grow [15]? 

Given the vagueness of the recommendation, and that we’ve done a poor job of defining optimal volume ranges (outside of the number of sets), it’s probably time to reevaluate our practices when it comes to volume recommendations for hypertrophy training.