Muscle Growth with Full Muscle Action Spectrum

We all want to make the most of our workouts, and several techniques can provide help packing tons of benefits into a short period of time in the gym. No single approach, however, provides as much benefit for our time invested as using the full muscle action spectrum.

Good lifting form has many dimensions, and, generally speaking, most people do a crummy job with their form.  Good form, among other things, helps us get the most muscle development from every single rep. And if we're looking to make the most of our gym time, it makes sense that we'd want to get the most from each rep.

One important aspect of good form is fully utilizing the three different actions that muscles produce on every rep, known as the muscle action spectrum. The three actions are as follows:

1) Eccentric Action: lengthening of the muscle while decelerating force
2) Isometric Action: holding muscle contraction equal to the force placed on it
3) Concentric Action: shortening of the muscle while accelerating force

Let's take the standard bicep curl as an example. How many times have you seen someone quickly curl the weight up, then just drop it down to their side? What just happened? Simple, they hit the concentric action and abandoned the isometric and the eccentric actions.

So why does using the full muscle action spectrum matter? It matters because our muscles work to produce force (concentric), to stabilize (isometric) and to reduce force (concentric), and by only producing force, we rob ourselves from development of the ability to stabilize force and to slow down force.

Think of how we move in everyday life. For example, imagine reaching and taking a heavy box off of a high shelf that's above our head. First, we slide the box toward us until it's no longer supported by the self. We're now holding the full weight of the box over our heads, this is isometric strength, or muscle contraction equal to the force placed on it. Next, we slowly lower the box down to the floor, this is eccentric strength, or reducing rate of force. And last, we put the box back up on the shelf, this is concentric strength, or contracting the muscle to accelerate force.

It's critical to understand this concept of full muscle action spectrum in terms of balanced muscular development because muscles must be able to, at different times, act as accelerators, as stabilizers, and as brakes.  Going back to our curl example, the upper arm (humerus) must be held stable by the shoulder to perform an effective curl, therefore our shoulder must have fully developed isometric strength to support our bicep development efforts.  Lacking this isometric shoulder strength would allow the upper arm to swing under momentum from the curl action, and we would lose our ability isolate the bicep for an effective curling action.  Therefore, lack of shoulder isometric strength would compromise our ability to develop bicep strength and size.

As you can imagine, this scenario is true for every exercise we do; for every muscle or muscle group we target with resistance training, we call on a complimentary muscle or group of muscles to isometrically stabilize, therefore lack of isometric strength costs us our ability to hold proper exercise form and to realize the greatest benefit from every rep. 

Additionally, eccentric action, or our ability to use muscles as a decelerator or brake against force, plays an important role in muscle growth and strength development.  In the gym this is referred to as a "negative rep".  Simply put, during negative reps our muscles recruit fewer fibers to decelerate than to accelerate, therefore we put greater stress on those fewer muscle fibers during eccentric action, stimulating greater muscle growth and strength. More importantly, much of what muscles do functionally in real life involves slowing down a force, either a weight or the weight and momentum of our own bodies. Think for example of how the quadracep acts as an eccentrice "brake" when we jump off of a box and land on the ground.

Our muscular systems work very dynamically to accelerate force, to hold force, and to decelerate force.  Simply focusing only on the concentric muscle action, or force acceleration, limits our ability to fully develop our bodies and additionally can even invite injury from creating strength imbalances within muscle groups and systems. By fully developing the muscle action spectrum of eccentric, isometric, and concentric strength we become more functional in the real world and create the potential for greater muscle size and strength gains overall for our time invested in the gym.