Pump Up the Volume for Mass

The anabolic effects of “cell swelling.”
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You may recall how Arnold Schwarzenegger described the feeling he experienced when he got a pump in the documentary film Pumping Iron. Evidently, the former governor was very near a sexual climax at the very thought of picking up a weight. Talk about dedication! I can’t say that my pumps in the gym have given me the same “climactic” experience as they did Arnold, but then again, I’m no Arnold. Nevertheless, the swelling effects of a pump can be quite significant at times. For myself, my arms will increase a full half-inch with a good pump.

Although gym lore, fueled in no small part by films such as Pumping Iron, has always attributed muscle growth to the pump, I for the most part have dismissed this idea much in the same way I dismiss the importance of the temporary bump in hormones during a workout. The Strength and Conditioning Journal recently published an article discussing the plausibility of the pump actually contributing more to muscle growth than might otherwise be thought by academic folks like me.

First, some background. The article refers specifically to the anabolic effects of “cell swelling.” It is not the first attempt to attribute muscle growth to the pump. During muscle contraction water moves from the plasma into both the interstitial and intracellular spaces of the muscle. This redistribution of water and ions (sodium and potassium) between muscle fluid compartments causes ionic shifts between these compartments and a temporary influx of water into the cell. The main driving force causing a shift in water balance is the increase in intracellular osmolality due mainly to the hydrolysis of phosphocreatine as well as to the increase in lactate accumulation. Lactate accumulation is the greatest contributor to these osmotic changes and the resultant pump.

The authors of the paper admit there is no research looking specifically at the contribution of the pump during exercise to muscle growth, so much of this is just reasonable conjecture. It is true that cell swelling can cause an increase in protein synthesis in most cell types. It is also true that this likely involves mTOR and other signaling pathways shared by other stimuli. However, the cell swelling that occurs after muscle contraction lasts only a few minutes. This is because under in-vivo conditions, the ability to maintain homeostasis of cell volume is critical to the cell’s viability. This is why these reactionary changes in cell volume are very short, lasting only minutes. I concede, that cell swelling produces an anabolic reaction in cell culture studies, but the jury is still out as to the significance of this effect during training and how much it might contribute to growth in the real world when other factors such as altered genetic expression, growth factors, and satellite cells are known to play such a significant role. Having said all this, you can bet that I will continue to try to get the best pump I can every time I train. It’s just too satisfying in and of itself to ignore. - FLEX

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