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Q: How fast should I perform my repetitions? One trainer said it didn’t matter as long as I was using good form, while another told me I should be doing them very slowly.


While both responses have some merit, neither answer is really correct. It is certainly essential to perform your reps with proper exercise form – that’s a given. But when it comes to rep speed, form is only one part of the equation. Performing reps too quickly – even with proper form – will inject momentum into the lift, reducing the workload on your muscles and thus diminishing results.

This is especially pertinent with respect to the eccentric portion of the repetition (i.e., the “negative”). Many people think of eccentric reps as inconsequential and simply focus on the concentric (i.e., positive) action. This strategy couldn’t be more misguided. In fact, the eccentric phase may very well be more important than the concentric component. You see, during eccentric reps, your muscles exert a braking action and preferentially recruit fast-twitch fibers to perform the majority of work. The significance here is that fast-twitch fibers are strength-related fibers that have the greatest capacity for hypertrophy (as opposed to endurance-based slow-twitch fibers, which are indefatigable but experience little in the way of growth). It should therefore come as no surprise that eccentric training has been shown to play a larger role in muscular development when compared to training concentrically. Hence, if you ignore the eccentric component and lower the weights haphazardly, you are missing out on more than half the benefit of the exercise.

On the other hand, it serves little benefit to perform your reps ultra slowly – and the ramifications of doing so actually can be detrimental, results-wise. The problem here is that in order to train in a super slow fashion, the weights used must be extremely light to compensate for the glacial speed of the lift. While this allows the concentric portion of the rep to be executed in the desired fashion, it takes away most of the muscular stress on the eccentric (i.e., negative) portion (muscles can handle significantly more weight on eccentric actions than on concentric actions). And since the eccentric component is essential in maximizing muscular development, results from super slow training will be suboptimal when compared to performing reps at a traditional cadence – a fact borne out by research.

In order to optimize results, you should follow the ABCs of lifting: always be in control. Control is directly influenced by gravitational force which, in turn, is dictated by the two phases of a repetition (concentric reps and eccentric reps).

Concentric reps involve lifting a weight against the force of gravity. For example, in the biceps curl, this involves flexing your arm from a fully straightened position. During the concentric phase, you shorten the target muscle until a contraction is achieved at the top of the movement. Here, significant exertion is required to complete the lift. Because of the effort involved, a slightly faster pace is necessary; take approximately one to two seconds to complete this phase.

Alternatively, eccentric reps move with the force of gravity. In the example of the biceps curl, this involves straightening your arm from a fully flexed position. During the eccentric phase, the muscle is lengthened and stretched at the end of the movement. Your focus here should be on using the target muscles to resist the pull of gravity so that momentum does not play a significant role in performance. On average, the negative phase should last twice as long as the positive, taking about three or four seconds to complete.

Brad Schoenfeld, Ph.D., CSCS, CSPS, FNSCA is an internationally renowned fitness expert and widely regarded as one of the leading authorities on training for muscle development and fat loss. He is a lifetime drug-free bodybuilder, and has won numerous natural bodybuilding titles. He has published over 60 peer-reviewed studies on various exercise- and nutrition-related topics. Brad is a best-selling author of multiple fitness books including The M.A.X. Muscle Plan (Human Kinetics, 2012), which has been widely referred to as the “muscle-building bible” and Strong and Sculpted (Human Kinetics, 2016), which details a cutting-edge, body-sculpting program targeted to women. Brad also has authored the seminal textbook Science and Development of Muscle Hypertrophy (Human Kinetics, 2016), the first text devoted to an evidence-based elucidation of the mechanisms and strategies for optimizing muscle growth. In total, Brad’s books have sold over a half-million copies. For more information, visit For more information, visit