For all of us health and fitness enthusiasts, we understand the term “pump”. Who doesn’t like looking in the mirror during their workouts to see the intensified vascularity and definition of their muscles? We all do it. I was reading through some of my old notes and textbooks when I came across a topic I used to teach in my classes, so I wanted to delve into this a bit from a physiological standpoint for those of you that may be interested. As for you who are not interested in putting forth the legwork to learn and grow, feel free to stop reading here..

What causes these pumps? Most will say an increase in blood flow. That is correct. However, there are other aspects at play outside of NO2. These aspects in a nutshell are a combination of accumulating metabolic waste by-products and cellular energy depletion, which yield the end result of “contractile failure.”

It begins with cellular energy depletion. You’ll hear me say time and again how ‘the body’s desired source of energy is carbohydrates’. This is because carbs are the raw materials needed for synthesizing the primary fuel source for muscular contraction – ATP.

Without getting too deep into the biomechanics here, our ATP reserves are very limited. When they are exhausted a chain reaction occurs metabolically that essentially converts stored glycogen into ATP in order for muscular contractions to continue. Although this is a somewhat elaborate process to explain, I want to give a summary to hopefully lend perspective to a later point.

Every molecule in the human body is made up of a specific assortment of atoms that are bound together. A molecule of glucose is made up of 6 carbon atoms and several oxygen and hydrogen atoms. (keep in mind, I’m not trying to give a chemistry lesson here, but bare with me) Although glucose is the raw material for ATP synthesis, the molecule itself is too complex. Therefore, it must be broken down by a catabolic reaction called glycolysis.

During glycolysis, the 6-carbon glucose molecules are split in ½ by an enzyme to form two 3-carbon molecules called pyruvate. Pyruvate is then broken down by the mitochondria of the muscular cells to make ATP. However, in order for a molecule to be broken down, a bond must be broken and an atom released. Everytime a glucose molecule is split (glycolysis), a hydrogen atom is released.

Wait a sec, D.. I thought you were trying to keep it simple? This process is actually a bit more complex that this, but everything I have mentioned above is leading up to this: LACTIC ACID BUILDUP

When the muscle is contracted, it becomes impervious, which means that nothing is able to cross the cellular membrane (nothing in or out of the muscles’ cells). That includes the hydrogen atoms that are released during glycolysis. While performing high rep sets, the rate of glycolysis outstrips the mitochondria’s’ capacity for converting pyruvate to ATP, simultaneously increasing the rate of glycolysis. This rapid rate of glycolysis produces abundant pyruvate and releases more hydrogen atoms more rapidly. Because the contracted muscle doesn’t allow the freed hydrogen atoms to escape the cell, they begin binding with the accumulating pyruvate molecules, thereby changing their chemical structure and forming lactic acid.

Now we’re getting somewhere: CONTRACTILE FAILURE! The accumulation of lactic acid (and subsequent drop in pH) in the muscles produces the burning sensation and fatigue commonly associated with high rep sets. See, it isn’t so much the energy depletion that causes contractile failure in the high rep sets; it’s the accumulation of metabolic by-products – LACTIC ACID

So where does this tie into the pump?

As the muscle continuously contracts and the lactic acid builds up, the muscle cells begin to increase in circumference. As the muscle cells swell, they begin to apply pressure to the capillaries within that muscle, which subsequently restricts the amounts of nutrient- and oxygen-rich blood available to the working muscles. In a sense, it’s a lot like kinking a garden hose. Once the set is complete and the muscle is allowed to relax, the back pressure of blood in the capillaries is relieved; like removing the kink in the garden hose. This rush of blood into the working muscles will make them appear much larger but will subside shortly after completing the workout. In addition, this tremendous amount of blood re-entering the capillaries will be perfused into the interstitial spaces between the muscle cells where it will exert pressure against the cell membranes. This will prolong the presence of intercellular lactic acid, causing premature failing of the muscle in following sets. This is known as the “pump” and should be avoided.

Understanding your body’s processes allows you to harness its full potential. Never train in a manner that inhibits you from reaching your potential. Hope this was helpful. Now time to grub on a grilled tuna steak, brown rice, and beans!