When we observe function, the execution of the desired movement does not occur from a static position. Rather, a combination of joint motions creates a movement that is “opposite” of what is desired. The “opposite” movement lengthens and loads the muscles. This load is transformed into the desired movement. We LOAD to EXPLODE. To jump up, we go down. To throw forward, we reach back.
The same muscles that lengthen during the LOAD, will shorten during the EXPLODE. Eccentric muscle activity decelerates the loading motions. During this deceleration energy is stored. The stored energy is then used to transform the eccentric into a concentric acceleration of the joints to produce the desired movement. Certain movements lengthen muscles in all three planes during the LOAD, followed by a shortening in each of the three planes of motion during the EXPLODE.But lengthening and shortening in three planes is often not the functional truth. Functional movements create complex muscle actions at multiple joints simultaneously.
During the loading movement, individual muscles may lengthen in one or two planes while shortening in two planes or one plane. Also, very commonly muscles that cross more than one joint will shorten at one joint while lengthening at another. At Gray Institute®, this functional type of muscle contraction is called econcentric – eccentric and concentric at the same time. In many cases it is more accurate to describe the muscle function as an econcentric LOAD transformed into an econcentric EXPLODE.
These econcentric actions are not rare; in fact, they are very common. When they do occur, there is often a physiological / mechanical advantage. The physiological advantage can be seen during a squat. When the person goes down to LOAD, the hip flexes, the knee flexes, and the ankle dorsiflexes in the sagittal plane. The hamstrings lengthen at the hip and shorten at the knee. The rectus femoris shortens at the hip and lengthens at the knee. The gastrocnemius shortens at the knee and lengthens at the ankle. When a multi-joint muscle lengthens and shortens at the same time, it can stay in its most effective force generating range while energy is stored in the tendon and connective tissue. And this get more exciting when we consider other planes!
The mechanical advantage is exemplified during gait when the subtalar joint is trying to supinate / invert to lock up the foot for propulsion. This EXPLODE from the everted position is created by the tibialis posterior, soleus, and gastrocnemius. Lifting the arch against gravity requires a lot of force from the leg muscles (and elsewhere in the body). These same muscles are being lengthened by the ankle dorsiflexion. This lengthening in the sagittal plane creates power to assist the shortening in the frontal and transverse planes. Econcentrics at work, once again.
Econcentrics is not limited to multi-joint muscles. The LOAD and EXPLODE of the gluteus maximus can be all eccentric and concentric for some functional activities. However, if hip flexion is combined with abduction or external rotation then the gluteus maximus is lengthening in the sagittal and shortening in one of the other planes. It is the required motions that dictate the combination of lengthening and shortening. Our job as movement practitioners is to create movements / tasks that require the joint motion combinations that are part of the desired activity.A better EXPLODE starts with a better LOAD. The 3DMAPS® (3D Movement Analysis & Performance System; https://www.grayinstitute.com/courses/maps) movements for analysis and training employ global movements made up of joint motions that create a LOAD before the EXPLODE. Focus on the LOADING motions if you want to engage and train the muscles functionally.