The serape effect gives yet another sign that our bodies evolved to perform certain tasks. They expect us to use them for traversing terrain by walking or running, pushing and pulling objects, and squatting to pick up and carry things. These all qualify as compound, free weight exercises.
Resisting movement at the core allows for these actions. The core muscles only work to prevent flexion, lateral flexion, extension, and rotation of the spine though. The powerful muscles of the upper and lower body are the true workhorses.
The core exists mostly to transmit forces and not to create it. This would allow, for example, the lower body to contribute to a throw or punch. Moving a load at the core is among the best ways to harm the lower back.
Origin
A serape is a blanket formed like a shawl. It is a popular piece of clothing worn by men throughout Mexico. It hangs over the shoulders and crosses diagonally in front of the body.
The muscles of the core arrange similarly to a serape. The fiber direction of the muscles here, such as the obliques and serratus anterior, have a criss-cross pattern. This orientation allows these core muscles to best prevent rotation.
Purpose
The serape effect occurs by resisting rotation, not causing it. Any contribution toward movement is small.
Sprinting demonstrates it. When running, notice that each side of your core alternates in tensing up and then briefly relaxing with each step. This allows a pre-stretch to occur in these muscles and maintains the optimal length-tension.
Sprinting fast had an evolutionary purpose. It allowed our ancestors to outrun a predator or close in on a prey. It makes sense then that a strong core served a purpose if it helped with speed.
It applies to other ballistic activities. These include throwing, kicking, swimming, and punching. In each case, a relationship forms between the right leg and left arm or vice versa. The shoulder and opposite hip then share a connection through the serape effect.
Misconceptions
Although we can rotate at the waist, this occurs unloaded during real tasks. This mobility exists for repositioning and not to handle a load, just like overhead movements for the hand and leg extension or leg flexion.
When speed is needed, as mentioned the core will transmit force with a pulse. This occurs through just a little range of motion.
Many functional training advocates will choose poor exercises such as chops using pulleys or medicine balls. These chops demand movement at the waist.
These chops would fit better if the movement occurs mostly at the shoulders instead of the core. This respects the true function of the core: to resist rotation and not to cause it. Better still, remove them all. These movements are redundant. If you sprint, squat, and row you address the core more than enough.
The serape effect certainly does not justify the endless assortment of goofy functional training exercises. These exercises allow balance and coordination to surpass fitness qualities like strength and endurance as the limiting factors. Using stability balls, resistance bands, and similar tools promote complexity along with other disadvantages.
It does defend sprinting or other options such as stairclimbing in your program.
Conclusions for the Serape Effect
No specific core work is natural or needed and may even harm you. Could you perform a sit-up or crunch while standing? Twisting also places harmful forces on the spine.
Do consider sprinting through intervals. This will address cardio and perhaps hit some stabilizers beyond what the push, pull, and squat used for lifting provide. It will work the core, as intended, through the serape effect.