Rate of repetition is typically one of the first questions you receive working as any sort of exercise technician. When performing a rep of an exercise for the first time, I often get “Is this too fast? Is it better to go slow?” As with all principles we discuss in this blog, there is no right or wrong, however there is always a more EFFICIENT way to do something based on your goals. In efforts to remains consistent in our discussion, let’s continue to focus on body composition and weight loss resistance training when examining the rate of repetition.
Before understanding which rate of repetition is most important for weight loss, we must understand how a muscle contracts and the velocity-tension relationship. To put it in layman terms, our muscles act as sliding filaments. Skeletal muscle is comprised of two different types of filaments, a thick (myosin) and a thin (actin) filament, which bind to one another and cause contraction upon stimulus. For those who are visual, view the image below to get a better idea of how a muscle contracts (McArdle, Katch & Katch, 2010).
Now onto the velocity tension relationship. The slower a muscle contracts the more binding of actin and myosin can occur, therefore more force is generated. It is important to understand that in order for binding to occur, calories must burned. Vice versa, the quicker a muscle contracts, the less binding occurs. Therefore at first glance, we can assume a slower muscle contraction would be more beneficial since more fibers are being used, and ultimately the more calories you burn and weight you will lose!
Not so fast! No pun intended. It is important to always identify the practical application of an Exercise Physiology principle. The slower the movements, the less repetitions you complete in a given hour. The less repetitions you complete, the less calories you burn due to decreased amount of work in that hour. So unless you have an extra hour in the day, on top of the hour you already set aside for exercise, you may find yourself spending much more time in the gym due to slower training.
To conclude, there are several benefits to slower training for resistance exercise. However, it suggested to start with a moderate pace to assure an adequate amount of work is completed in a timely manner. This appropriate pace would be 2-4 second range per repetition. Certainly be sure to integrate sets of slower training into your workout, to increase muscle fiber utilization, however avoid fast training as it may lead to inappropriate compensation and ultimately injury.
McArdle, William D., Frank I. Katch, and Victor L. Katch. Exercise physiology: nutrition, energy, and human performance. Lippincott Williams & Wilkins, 2010.