Q&A: Exercise Volume And Metabolic Versus Mechanical Work

Question: A reader asked for my opinion on an article in which the author claims, “…multiple sets are a must if you want to maximize your muscular potential.” I’ve written about this before, but since this is a subject a lot of people are still obviously confused about I’m going to break it down here and explain it as simply as I can.

Answer: Like most things, the answer is “it depends.” You do not need multiple sets to maximize your muscular potential, but for single set training to be effective you have to do it right. And, if you are doing it right, performing more than one set can quickly result in overtraining and slow or stop your progress.

To better understand this it helps to think of exercise volume in terms of metabolic rather than mechanical work. The stress on your body and stimulus for adaptation has little to do with how many times you lift and lower the weight, and a lot to do with the tension and metabolic demand placed on your muscles. Because of this, it is more appropriate to define exercise volume in terms of the magnitude and duration of muscular force application (force x time) than reps and sets. This is why isometric training methods like static holds and timed static contractions effectively build muscular strength and size without any mechanical work performed.

It also helps to keep in mind that different people have very different ideas about what a set is and how it should be performed, and this often determines how many they believe is necessary. For example, a person who performs four sets of ten repetitions of an exercise at a typical cadence – lifting the weight in a second then lowering it just as quickly – would have a cumulative time under load (TUL) for that exercise of eighty seconds (4 sets x 10 reps x 2 seconds per rep = 80 seconds). A person who performs just one set of ten repetitions of an exercise at a moderately slow and controlled cadence – lifting the weight in four seconds then lowering the weight in four seconds – would also have a TUL for that exercise of eighty seconds (1 set x 10 reps x 8 seconds per rep = 80 seconds). Although the first person performed four times as much mechanical work, assuming the same resistance the metabolic work would be roughly equal.

If you perform an exercise at a fast cadence – quickly throwing the weight up and dropping it – with typical repetition ranges your TUL per set would be very low and you would be able to perform more sets without overtraining. Even if your intensity of effort is very high you might need to perform multiple sets for optimal results if each of the sets is very short.

On the other hand, if you perform an exercise at a slower cadence – lifting, lowering, and reversing direction under strict control – with typical repetition ranges your TUL per set would be very long, and attempting multiple sets in this manner would result in overtraining.

There are a lot of examples of people who have gotten big and strong using both methods, and on the surface it might not seem to make much of a difference whether you perform multiple shorter sets or a single longer one if the cumulative TUL per muscle group is the same, but there are several disadvantages to performing multiple sets at a faster cadence.

The faster you move during an exercise the greater the force encountered when you reverse direction between lowering and lifting, where the muscles under load are most vulnerable. The more mechanical work you perform the more wear on your joints. The faster you move during exercise the less you are capable of maintaining proper body positioning and control over the path of movement. These all increase your risk of injury or developing joint problems over time. Additionally, the faster you move during exercise the less weight you can lift.

It could be argued that despite your muscles being able to produce more force at slower concentric contraction speeds dividing the TUL of an exercise into multiple, shorter sets with a few minutes of rest in between would allow the use of heavier weights. However, since most people do not train to failure on each set when performing multiple sets and your results from exercise have more to do with your intensity of effort than load, this wouldn’t appear to be any more effective than a single, longer set performed to muscular failure.

Of course, if you want to go as heavy as possible you can still do it with slower repetitions by performing rest-pause, with lower risk of injury and less wear on your joints.

While it probably makes little difference in muscular strength and size gains whether you perform multiple shorter sets or a single longer one provide the intensity of effort and TUL are similar, when it comes to safety and efficiency HIT style single sets are the clear winner.

While a lot of training methods can be highly effective if done hard, progressively, and consistently, not all methods are equally safe or time efficient. If you have to choose between multiple methods capable of producing the same strength and conditioning improvements over time (which is limited by your genetics, regardless of the methods used), it makes sense to choose the method that is least likely to injure you or undermine your long term joint health and functional ability, and requires less time in the gym. Effectiveness alone is not enough. An exercise program should also be safe and time efficient.

The goal of exercise is to stimulate the body to produce improvements in all the trainable factors of functional ability, to improve your physical capabilities, appearance, and health. Even if a program effectively stimulates the body to do so, if it is likely to cause you injury it is going to undermine your functional ability and health in the long run.

The ultimate reason for exercising, for wanting to improve your physical capabilities, appearance, and health is to better enjoy your life. None of us knows how much time we have, and once we die that’s it. Unless you really enjoy hanging out at the gym (and some people do) spending any more time working out than necessary is a waste.

Although the cumulative TUL of many HIT workouts is comparable to that of many multiple set bodybuilding workouts, because the work is more condensed they take much less time to complete. For example, if you perform a HIT workout consisting of ten exercises each performed for a single set of six to ten reps at a 4/4 cadence and rest a minute between exercises, your cumulative TUL would be a little over ten minutes and your total workout time would be around twenty minutes. Consider that many people who do HIT use even shorter rest periods and might complete the same workout in under fifteen minutes. Compare this with a typical bodybuilding workout consisting of a dozen exercises performed for three to four sets of eight to twelve reps at a 1/1 cadence and with a two to three minute rest between sets. Although the cumulative TUL would be about the same the total workout time would be one and a half to two hours because of how the work is distributed. Additionally, condensing the same cumulative TUL into a shorter workout increases the work to rest ratio and the effectiveness for cardiovascular and metabolic conditioning, making it unnecessary to spend more time performing other activities for that purpose.