Ideal Repetition Speed And Rest Periods for Muscle Growth

If you’ve read my previous articles, you’ll know that when it comes to muscle growth, I lean towards time under tension and adequate rest periods as being the culprit to eliciting muscle growth for bodybuilders. Even Arthur Jones, one of the pioneers in exercise science who advocated low volume, high intensity training, used time under tension to promote maximal exercise intensity (isokinetic movements). However with that being said, periodization is also a fundamental principle in exercise science and it can be used to incorporate workouts with faster rep speeds/shorter rest periods into your routine.

However, with high intensity exercise, it is very important to prevent periods of overtraining as a result of over stimulating the central nervous system. The one thing many gym enthusiasts forget in their quest to meet their goals is that your mind and your muscles are at risk of being over trained.

Periodization is a recurring idea in strength and conditioning because it is the best way to push for progression in your routines. Your body has a tremendous ability to adapt to workouts, so it makes sense that sticking to one specific training style year round will lead to your body developing adaptations to that training style and peaking in progression.

For example, you are born with a pre set number of Type I (slow twitch) to Type II (fast twitch) muscle fibers ¹; however, if you are involved in distance running the Type II muscle fibers in your major muscles will begin to take on Type I ‘characteristics’ in an attempt to cope with the increase in aerobic activity.² So with this in mind, why would you stick to once specific style of training year round?

In my article Volume vs. Intensity, I discuss how using both training techniques are to your advantage. Both the volume and intensity groups have bodybuilders who have achieved success with either training style.

Slow vs. Fast Repetition Speed

A very recent study from the Journal of Strength and Conditioning determined that a faster lifting tempo increased IGF-1 (Insulin-like Growth Factor, a hormone similar to insulin responsible for growth) and the subject's one repetition maximum also increased with the faster tempo.² While it is already known that a quicker tempo (2 seconds up, 2 seconds down vs. 2 seconds up, 4 seconds down) is better for increasing strength, the higher levels of IGF-1 were interesting since this hormone is most directly related to growth (when using anabolic substances IGF-1 is increased and is directly responsible for growth.)

So does this mean that a faster lifting tempo is the only way to go? Not quite. While it does provide validity to that fact that different training styles have a positive effect on the body, it doesn’t supersede the research done by Dr. Goldberg and his team at the University of London. They found that constant tension and overload induced hypertrophy in the absence of testosterone (the rats were castrated) by way of IGF-1 as well.⁴

So despite this great study for the validity of faster repetition speeds for strength and growth, focusing on the eccentric phase (the lowering portion) of a lift has more of a research history. In the book Cells & Tissue Research it was concluded that repeated bouts of high tension causes structural changes in muscle fibers, particularly Type II muscle fibers (which have the greatest potential to hypertrophy, or grow).⁵

Related: 5 Reasons To Add Eccentric Training To Your Routine

In the European Journal of Applied Physiology, they compared eccentric oriented training to concentric training.⁶ The training methods used were isokinetic, meaning that variable resistance was used so that no matter how much force was applied, the speed would be fixed. They found that eccentric training was superior for hypertrophy as compared to concentric training at fast and slow speeds.

However, they found that fast eccentric training was superior for strength and they hypothesized that it may be superior for hypertrophy, too. They didn’t have any conclusive evidence for this in the study, and there is much evidence for slower, loaded eccentric training for hypertrophy (which they were able to conclusively discover in their study).

So what does all this mean for the appropriate repetition speed? The best conclusions that can be drawn based on available evidence point to incorporating slower and faster repetitions into your routine to prevent adaptations to either style of training and to take advantage of the research behind both showing increases in IGF-1 and muscle growth.

Long vs. Short Rest Periods

Another hot debate in the bodybuilding world is centered around the ideal rest periods during exercise. It was originally thought that the ideal rest periods for bodybuilding were 30-60 seconds because of the anabolic hormones that were released in response to the stress caused by these short rest periods. However, with rest periods this short, the amount of weight and tension time that can be put on a given muscle group are limited.

Then came the research that showed that the acute hormone response to exercise was ideal for fat loss but had no connections with protein synthesis. What quickly followed was the trend of research and information pointing to adequate (1½- 2 minutes) rest periods and tension time for increasing IGF-1 and the growth response.

However, thanks to advancements in research, the validity behind lower workloads at higher intensities is making a comeback. The latest research method to determine the influence of anabolic hormones and training with lower levels of oxygen is being done through a method called vascular occlusion. This involves limiting blood flow (almost like using a blood pressure cuff) to a given muscle group while training it to cause an acute hormonal response as a result of the added stress.

Related: Kaatsu Training: A Techinque for Enhanced Muscle Growth

What was discovered is that fast twitch (Type II) muscle fibers had higher rates of activation (most likely as a result of the fact that these fibers have less of a reliance on available oxygen for activation).⁷ Vascular occlusion was also shown to increase strength and muscle mass in a study done just last year in the International Journal of Sports Physiology Performance.⁸

Despite these findings for the effectiveness of training in low oxygen states, these positive findings weren’t compared to a group doing tension time oriented training; they were compared to a control group doing unrestricted training at similar rep ranges. In another study that compared intermittent (rest periods) leg training to continuous (without rest periods) leg training, the leg that was trained with limited rest periods experienced greater gains in muscle mass and strength.⁹ However, once again, these results were not compared to tension focused training protocol, although they were positive.

In the end, the take home message based on the latest research re validating the use of shorter rest periods and faster movements is that there is sufficient evidence to warrant keeping these in your routine if your goal is hypertrophy. However, there isn’t enough evidence to warrant tossing out some of the current accepted protocols for hypertrophy like time under tension methods.

Another important factor to keep in mind when it comes to the increases in hormones and recruitment of fast twitch fibers as a result of training with short rest periods, is that these same responses can be achieved when you start your workouts with compound, free weight, multi-joint exercises like the squat, deadlift, or barbell row. So do incorporate new rep speeds and lower rest periods into your routine, but don’t think that research is going to come along to validate only once training style that will allow you to train for growth within a comfort zone.

Dustin Elliott is the Head Formulator for Betancourt Nutrition.