A popular way to alter exercise / repetition intensity is to increase the amount of time a muscle is held under tension (or load). This can be thought of as the total duration of the set. Such changes can be done at specific points in a particular movement, such as only increasing the amount of time held at the bottom of a squat exercise (as seen in a pause squat variation), or, by slowing down the descent of the squat in order to accentuate the eccentric (or slow, controlled) portion of the movement. In either scenario, this is often referred to as altering repetition tempo. Increasing the total time of the set through slowing down both the eccentric and concentric actions is usually just colloquially referred to as altering time under tension. SO, we (should) know that changing set and repetition tempo can make an exercise more difficult and induce adaptation, right? However, many questions should still come to mind. Questions like how long is enough?, is one better for muscle growth or strength than the other?, and most importantly, why would I even want to alter rep tempo?
In order to start answering these questions we first have to look at a basic principal of resistance training, known as specificity. One of the more simple principles to understand, “specificity” essentially states that the most effective adaptations will occur if training mimics the target activity. Or in other words, “practice how you play”. Research has given us a continuum of 1 to about 70 seconds of total time under tension for a given set and that can be superimposed over a standard repetition spectrum. We (researchers) can now see that the left end of 1 to about 20 seconds makes up our strength range (1-5 reps), and on the right from about 40 to about 70 seconds (15+ reps) we can achieve mostly muscular endurance, and, that hypertrophy not only holds fast in the middle but blankets the entire spectrum. So, if altering time under tension is an appealing idea to you, you merely have to ask yourself, what is my goal? If absolute strength is your goal, for example, I would recommend steering clear of sets lasting over a minute (which we can see in the literature that subjects training for super slow tempos throughout their sets could not perform as well in 1RM testing when compared to their traditional tempo counterparts). BUT, this is great news because it falls in line with what we know and what the principal of specificity tells us (since a 1RM is much more similar to a traditional tempo (think control down, fast up)). It makes sense that these subjects performed better than the slow adapted group.
So, vastly increasing total time under tension may not be ideal for making improvements in strength. However, staying on the topic of strength training, we know we don’t want to spend minutes performing a single set, However, what if we just increased the amount of time in one spot through altering the rep tempo? Again, we have to ask “why?”. Why would we want to increase time even only at a single point if taking too long in total can be detrimental? The answer lies with the principle of the stretch shortening cycle, (which, by the way is a great topic for another article in order to explain it in its entirety), but for now I’ll try an analogy for the sake of time. Think of your legs housing a flaccid rubber band that extends from hip to knee, and as you descend in the squat this band gets stretched and as you spring up all that wonderful stored energy starts to release as the band returns to its original shape and propels you out of the bottom. That process is essentially what we call the stretch shortening cycle. Great, right? Well sort of, from a performance stand point we want it in order to lift the most weight possible, and conveniently it happens to occur in the bottom of a rep where we are generally the weakest in many exercises. So, think of it like taking over the counter ibuprofen for a broken arm. It helps to get us out of the weak spot, but we’re not actually addressing and strengthening that weakness. So, enter repetition tempos, and more specifically pause repetitions. The stretch shortening cycle works by capitalizing on a quick transition from eccentric to concentric, so, by sitting in that transition point (i.e. the bottom of a squat) we effectively lose tension in our “rubber bands” and eliminate the spring effect. Over time this stimulus will in turn force the body to undergo adaptations as we do with strength training and voila altering tempo has allowed us to make ground in the ever on going battle that is strength training.
Okay enough analogies, what if your goal is hypertrophy/muscle growth? Well, at best, the results weigh increased time under tension equally to traditional resistance training. Tanimoto et al. put subjects through a 13 week, whole body training protocol with one group performing three second eccentrics and three second concentrics, one group performing one second for each, and then a sedentary control group. Both slow and fast groups increased muscle thickness above their respective baseline and above the control. Shepstone et al, utilizing inter subject reliability found that overall cross sectional area was greater in their fast tempo group when compared to the slow. They also found significant difference in size of type IIa and x fibers in the fast over the slow tempo groups. Since these are our high end force output fibers that would make sense, and due to the inherent capacity of these fibers to grow larger and quicker than type I we can most likely assume that they are responsible for the increased cross sectional area. However, Shepstone et al. also found that the slow tempo group presented significantly lower oxygen levels post training. This hypoxic environment creates greater metabolic stress on the muscle which can induce hypertrophy, now keep in mind the fibers geared towards aerobic action are the fatigue resistant type I’s which would be the most likely candidates to adapt due to this type of stressor therefore hypertrophy would be limited in this regard.
FINALLY, to recap, we can see that by increasing time under tension/repetition tempo we can improve our strength and maybe some muscle growth. To make it simple, you might want to alter repetition tempo if.... strength is your goal because by eliminating help from the stretch shortening cycle you can stimulate that area to adapt, or you are interested in increasing metabolic stress on your muscles through hypoxia. Otherwise, just sticking to traditional resistance training (using a controlled eccentric and forceful concentric) can net plenty of gains in either the strength or hypertrophy realms. And if you do decide to change your tempos just remember to keep total set time in line with your goals.
Thanks for reading, stay strong!
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