The Pump! The Potential of Cell Swelling to Enhance Muscle Growth

The hypertrophy trifecta of mechanical tension (heavy loading), muscle damage (breaking down muscle tissue), and metabolic stress (cell swelling – the pump) has been hypothesized to positively contribute to maximal increases in muscle growth.  Mechanical tension achieved with heavy load maximizes muscle activation, ensures overload, and is the primary impetus for the hypertrophic response.  Therefore, it is often recommended that increasing strength on heavy multi-joint movements should be foundational to a muscle-building program.  

While mechanical tension is important, exercise-induced metabolic stress can also be quite impactful in stimulating hypertrophy, and cell swelling is a main component of this process.  Cell swelling, aka “the pump,” refers to an increase in intracellular hydration and muscle fiber swelling, which may increase protein synthesis and decrease protein breakdown.  The degree at which this swelling phenomenon occurs is highly dependent on the type and intensity of training that is performed (as well as hydration, sodium intake, etc., but that is beyond the scope of this article).  
The pump is maximized with metabolic stressful training.  Said more eloquently, “The pump is magnified by resistance exercise that relies heavily on anaerobic glycolysis, particularly “bodybuilding-style training” that involves moderate to higher repetitions with limited rest intervals. Such exercise results in a substantial accumulation of metabolic byproducts including lactate and inorganic phosphate, which in turn function as osmolytes and thereby draw additional fluid into the cell.1” To achieve a pump, local muscle activation must be high enough to adequately restrict venous to allow for the blood to pool and not escape. Therefore, techniques that restrict venous return, such as tempo training, drop sets, constant tension (mid range hack squat vs. barbell squat), and blood flow restriction (BFR) training, can be used to enhance the pump. For example, BFR training can increase cell swelling compared to low-load free flow exercise when performed using the same amount of repetitions due to venous restriction, the pooling of blood, and the induction of overall metabolic stress.  Furthermore, type 2 muscle fibers (fast twitch) are highly sensitive to osmotic changes (changes in fluid balance) and display a superior potential for growth.  This means that cell swelling may “promote hypertrophy by favorably impacting net protein balance in these fibers1.”  

“Although these short-term effects of the pump are well documented, recent research suggests that the pump may, in fact, mediate long-term adaptive responses1.”

Do you add metabolic stress training into your regimen? Do you strictly #chasethepump?  Do you stick to heavy lifting?  Do you do a combination of the two?  What are your thoughts?  We’d love to hear from you!


1Schoenfeld, Brad J. PhD, CSCS, CSPS, NSCA-CPT1; Contreras, Bret MA2 The Muscle Pump, Strength and Conditioning Journal: June 2014 – Volume 36 – Issue 3 – p 21-25 doi: 10.1097/SSC.0000000000000021

****Remember, the decision to use BFR, or any treatment for that matter, should be based on the pillars of evidence-based practice.

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