By Brad Schoenfeld, Ph.D. Flex
If you’ve seen Pumping Iron, you may recall Arnold saying the following: “The most satisfying feeling you can get in the gym is the pump. Let’s say you train your biceps. The blood is rushing into your muscles. Your muscles get a really tight feeling, like your skin is going to explode any minute. It’s like somebody blowing air into your muscles. There’s no better feeling in the world.” Ever since, training for the pump has become synonymous with bodybuilding.
What is not as well understood is how the pump works from a physiological standpoint. Here’s the short course: When you lift, the veins taking blood from the working muscles become compressed from the force of muscular contractions. At the same time, blood continues to be delivered to the muscle by the arteries. This creates an increased concentration of blood within the muscle, causing plasma to leak from the capillaries and into the interstitial spaces. Upon completion of the set, a pressure gradient caused by accumulated extracellular fluid triggers a phenomenon called reactive hyperemia, where blood is drawn back into the muscle. The net effect is that the working muscles become engorged with blood, temporarily swelling the muscles far beyond their resting girth.
Okay, perhaps you’re questioning the value of being swole for a few hours post-workout. After all, the goal is to pack on real muscle that lasts 24/7, right? Well, contrary to popular belief, the effects of the pump aren’t necessarily confined to the immediate post-workout period. Emerging evidence suggests that getting a good pump could actually help promote greater long-term growth as well.
Studies clearly show that cell swelling—as occurs with the pump—initiates both anabolic and anti-catabolic effects. Specifically, it promotes a significant increase in protein synthesis with a corresponding decrease in protein breakdown. Since muscle growth is predicated on the protein balance, this translates into a hypertrophy home run! Moreover, type II muscle fibers have been shown to be particularly sensitive to osmotic changes, conceivably due to their high concentration of specialized water transport channels. The significance here is that type II fibers are theorized to have the greatest hypertrophic potential, suggesting that pump training might be particularly effective in stimulating their growth.
Although the underlying processes aren’t entirely clear, it is believed that cell swelling acts on the body’s survival mechanisms. Similar to an overfilled water balloon, the increased pressure from swelling against the fiber membrane is perceived as a threat to the cell’s integrity. In response, volume sensors within the swollen muscle initiate an anabolic signalizing cascade in an attempt to strengthen the ultrastructure of the fiber. The upshot: bigger, stronger fibers.
To maximize cell swelling, it’s essential to keep working muscles under constant tension so that the veins remain continually compressed, and then maintain the venous compression long enough for blood to pool within the muscle. The pump is further enhanced by training in a manner that creates a substantial amount of metabolic stress. The associated buildup of metabolic by-products, such as lactate, function as osmolytes that draw additional fluid into the muscle cell. Thus, both exercise selection and how you perform the movement are important considerations when training for the pump.
A couple of different strategies can be employed to maximize pump-related gains. One approach is to train with moderate to high reps and take short rest periods between sets. For example, perform 3–5 sets for a given exercise for 10–20 reps with no more than a minute of rest in between sets. Another option is to incorporate Dropsets whereby a heavy set is performed to fatigue after which the load is immediately reduced by ~25–50% and then repped out until failure. Double dropsets where the load is decreased a second time can heighten the effect even more. To optimize results, you should employ exercises that maintain tension throughout the set. Traditional single-joint machine-based exercises such as the pec deck, reverse pec deck, leg extension, and seated leg curl exercises are generally good choices for pump training due to the constant tension they place on the target musculature.
Lastly, pump training when performing exercises in a continuous manner ensures that the target muscles are not allowed to relax. Research shows substantial reductions in local muscle oxygenation—consistent with heightened cell swelling—when training is performed without a relaxation phase as compared with a one second relaxation between repetitions. When combined with the strategies previously mentioned, the result is a skin-splitting pump and potentially greater muscular gains.