High intensity or high volume: Which one for maximum muscle?
There is an age-old debate about which is more important: intensity or volume. Before we get into that, the term intensity needs a little bit of clarification. I prefer not to use the word intensity at all, primarily because it confuses people who associate it with fatigue (one-set-to-absolute-failure mentality) and not weight loads. Rather than intensity, I like the term load or load-stress. Load-stress more accurately describes the importance of using enough weight. The question of whether or not to take each set to failure is a different issue.
How Heavy Is “Heavy Enough”?
Now, about that research; when looking at a broad sample of studies examining the impact of load (i.e., intensity) versus volume, we do see some basic principles emerge. Data from more than 70 different muscle hypertrophy studies was collected by Wernbom and colleagues and published in the journal Sports Medicine in 2007.(1) In general, the rate of hypertrophy in these studies was greatest when the loads were 65%–85% of an athlete’s one-repetition maximum (1RM). It is of interest that you don’t see a linear dose-response by increasing the weight from 65%–85%. The seemingly equivalent results from widely varying weight loads demonstrate a “threshold” effect. As with other threshold-type models, once the threshold is crossed, you see diminishing returns as you push things higher. The same is true for weight; heavier doesn’t necessarily mean more effective. The only time heavier equals better is when you haven’t reached the effective load-stress threshold for your level of conditioning.
But what about volume? The controversy about the optimal number of sets stems from a large number of studies that show little difference (and a significant number that do) between one set and multiple sets in producing hypertrophy. When we take a closer look at these studies, the reason for the conflicting data becomes clear. The overwhelming majority of studies showing no difference in growth between one set and multiple sets use untrained subjects. This means that their muscles’ load-stress threshold was very low, allowing very little volume to induce measurable growth. In addition to using untrained subjects, nearly all studies showing no difference were short-term, lasting no longer than 14 weeks. What these researchers demonstrated was that in these untrained individuals, the threshold for triggering growth was adequately met using only one set. As expected, once the threshold was reached, any additional “work” failed to produce measurably greater anabolic effects.(2)
There were many who questioned the validity of such a one-size-fits-all, low-volume conclusion. What about well-trained populations? This skepticism rises from anecdotal evidence that once you have been training a few years, just dropping by the gym to do one set and then packing up and going home is not going to get you very far. Indeed, later research utilizing longer training periods and altering the loads to accommodate tissue conditioning have demonstrated superior gains from multiple-set training.(3,4) We can think of volume in ways other than total sets, though. Counting the “total reps” per session is a way of quantifying volume as well. Counting total reps is probably a more accurate way of estimating time under load. Most of the training scenarios considered thus far used anywhere from 8 to 12 total reps for single-set training and 24–36 total reps for multiple-set training. Referring again to Wernbom’s analysis of 70 different studies, it’s clear that measurable hypertrophy can be achieved using a wide variety of set and rep combinations; nevertheless, the greatest anabolic response was obtained when using 30–60 total reps per muscle group per session.
Best of Both Worlds
In the end it isn’t either high intensity or high volume, it is the right combination of both for your particular situation. In a nutshell, you can be confident that if you use 75% to 85% of your 1RM and perform enough sets to equal 30 total reps per upper-body muscle group and 60 total reps for leg muscle groups, you will be pretty close to the ideal combination of intensity and volume for maximum gains.
References: 1) M. Wernbom et al., Sports Med., 37(3):225–64, 2007. 2) V. Kumar et al., J. Physiol., 587(Pt 1):211–7, 2009. 3) S. Marzolini et al., Med. Sci. Sports Exerc., 40:1557–64, 2008. 4) B.R. Rønnestad et al., J. Strength Cond. Res., 21:157–63, 2007.