The length-tension relationship establishes that the midpoint of a good exercise allows the most contraction sites to form. More sites allow more tension from the muscles. Tension is the main stimulus for more size and strength. It makes sense then to focus on the midpoint.
You may question though, why move at all? Why not just hold the weight at the midpoint for some length of time? This would seem to maximize the desired effect. While compelling at first thought, it appears that every phase of the rep serves a purpose, especially the lowering portion.
How much range of motion to use depends on the exercise and trainee in question. Nonetheless, you should strive to feel at least some stretch in the muscles. This allows you to benefit from the pre-stretch. Too much of a stretch though will place you in too weak of a position. Avoid stretching to the point that you ever feel it in the joints.
A pre-stretch boosts your performance. It also keeps you safer, minimizing the time you spend in a bad position and returning you quickly to the tougher but more productive midpoint.
To activate the pre-stretch, you need to move quickly but smoothly from the bottom back into the rep. This gives one reason why moving too slowly can harm your results just as moving too quickly will too.
The Stretch-Shorten Cycle
Try to learn something about everything and everything about something.
– Thomas Huxley
When jumping as high as possible, notice that an athlete will perform a counter-movement. By swinging the arms downward along with bending the hips, knees, and ankles, he or she stores elastic energy. If the athlete swiftly transitions out from the bottom of the movement, this stored energy releases and allows the athlete to jump higher.
This transition is known as the stretch-shortening cycle. This occurs without thought in many athletic movements, even when simply walking. Punching, swinging, and sprinting all involve a pre-stretch.
Some experts would tell you to avoid it while lifting. They fear the consequences of you moving too quickly and assume its application is relevant only to sports. This is not true. It seems the pre-stretch improves strength not just through the stretch reflex and the release of elastic energy but by other mechanisms too. It helps the muscle to produce more force through a variety of possible reasons:
- It gives more time for active tension to develop.
- It may blunt inhibitions which relax a muscle when sensing high tension.
- The stretch itself may aid active tension by reinforcing the contraction sites, preventing the components from dissembling.
- The stored elastic energy allows you to overcome sticking points more easily.
The Stretch-Shorten Cycle Applied to Lifting
A pre-stretch works the same as it would for an unloaded, athletic movement though it does occur more slowly. A smooth but quick transition from the negative to the positive activates the pre-stretch on any exercise. This boosts positive strength and in turn allows more negative work.
If the trainee performs the exercise at an artificially slow speed, they will have no stored energy. They may get stuck or at least pause at the bottom, a position of weakness for both the joints and the muscles.
Keep in mind that going too quickly is foolish too. Never yank, jerk, or bounce heavy weights. If you drop the weight instead of actively lowering it, you will fail to hold the elastic energy anyway. This drop also activates the antagonist muscles to catch the weight at the bottom, which again harms performance. The force spikes can lead to a muscle tear or joint injury. The speed gives you little time to respond to any problems. Always stay in control.
If you cannot enter the stretched position smoothly, you will slow down too much. Tight muscles with poor flexibility will not allow a good pre-stretch to take place among other problems. Perhaps non-intuitively, this explains why stretching before a workout, if not overdone, will help.
Use the Stretch-Shorten Cycle in Lifting
Lift smoothly but quickly. I am reluctant to recommend an exact cadence, but it should take you at least 1-2 seconds lowering the weight and perhaps a second or less to lift. An exercise like a squat with more range of motion may require 2-3 seconds lowering and 1-2 seconds lifting.
Err toward more slowly if unsure. The speed of the transition from the lowering phase to the lifting phase matters more than the overall speed. Stay cautious on the negative, due to the high tension. Push up hard though once you reach the bottom.
Consider stretching the muscles before any workout. You will know they need loosened up if you feel too much of a slowdown on the warm-up sets. You should feel powerful and not tight. Stretching pre-workout can further warm you up as well.
Use this to stay safer and achieve more on your lifts.