A heavy enough weight along with a high effort at the end of a set recruits the fast-twitch muscle fibers and develops the most tension.
These fibers affect muscle growth the most and the high tension makes them grow. The intent to move fast is more important than the actual speed. Ultimately, effort matters more than how slow or fast you go. At the end of a set, you will move slow due to fatigue, which allows you to work hard yet stay in control.
Exercise speed in the past received little thought. Moving weights smoothly without counting rep speed or duration under a load provided a good guideline for most trainees. Nonetheless, some disadvantages exist to moving too fast or too slow. You should strike a middle ground in the slow reps vs. fast reps debate.
Too fast occurs when the speed exceeds the muscle’s ability to contract, occurs so quickly the antagonists contract, and feel out-of-control.
- Avoid very fast reps that jerk the weight.
Lifts that require you to move explosively are always dangerous.
This often occurs during purposely explosive movements. These include a power clean, push press, or any Olympic lift. Most exercises that allow you to control the speed can only be lifted too fast with very light weights.
Too fast allows momentum to take over the motion. This places high external forces on the body, especially the joints, due to the spikes in force. With a fairly heavy weight though and the right exercises, you should struggle to move the weight fast enough for this to happen.
This also creates a pre-programmed impulse from the nervous system. This fails to allow feedback since it takes place so quickly. The rep simply occurs too fast to correct the motion if something feels wrong. It feels difficult to stay tight with too fast of a rep speed.
If using sets of very high reps such as 30 or more, you may want to avoid using your utmost effort until the final reps of each set. Otherwise you may move the weight dangerously fast early in the set. Very high reps may be unwise though due to other reasons related to fatigue.
- Never drop heavy weights.
You should always feel some tension in the muscles.
Dropping releases tension stored while lowering weights. This relaxes the muscles and you have to catch the weight at the bottom, reducing the elastic energy that aids performance. If you fail to catch the weight you could also strain a muscle, collapse a lung, and otherwise get horribly hurt due to the sudden need for force to deal with a heavy falling resistance.
This also ignores the most useful portion of the exercise for gaining strength, the lowering or negative phase.
- You fail to take advantage of the pre-stretch.
This pre-stretch allows more time to develop tension, less inhibition, passive tension to overcome the sticking point, and an overall stronger positive contraction.
Without a pre-stretch, the sticking points of an exercise become pronounced. This makes you vulnerable in these weak positions, decreasing safety and results.
- It encourages a poor mindset for intensity.
Very slow speeds could blunt effort since the trainee may adopt a mindset that encourages a less than full effort at the end of an exercise, when they should attempt to move as fast as possible.
Do We Need to Move at All?
When you understand the length-tension relationship, you may question why we even need to move it all.
Since the midpoint of any motion creates the most tension for stimulating size and strength, why not just hold a heavy weight there?
This idea has some flaws though. Trainees may lack motivation due to the lack of clear feedback without a moving weight. Moving involves the nervous system more deeply too which boosts performance. This would also ignore negative movement and the pre-stretch.
Slow Reps Vs. Fast Reps
Every repetition of every set of most exercises should be performed as fast as possible – consistent with proper form and safety considerations.
– Arthur Jones
Lift and lower as fast as possible but never throw, bounce, jerk, yank, or drop a weight. Most importantly, you must try to push the final reps as quickly as possible even when the speed slows. This allows for muscle growth.
Beginners may wish to choose a slower rep speed until they grow more experienced. The lowering phase especially should remain slow since it very high forces. For many trainees, this will mean lowering for about 2 seconds and then lifting a bit more quickly. As the weight gets heavier, you may find yourself slowing down far too much on the negative. Resist this urge and keep a cadence, knowing that going too slowly will reduce your effort.
Use a rep speed that allows you to stay safe yet feel powerful. A natural cadence that feels right to you and allows you to exercise safely will work best. Ignore the endless debate on slow reps vs. fast reps and concentrate instead on effort at the end.