Pump & Burn

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The Pump

Immediately following a weight training exercise the muscle may seem full and tight for 15 to 30 minutes, or 'pumped'. The muscular 'pump' is caused by trapped plasma within the muscle. During muscular contraction the contractile elements exert a force inward upon themselves; the muscle diameter increases as it shortens. During intense muscular contraction, this force inward momentarily occludes the vasculature, backing up blood flow through that particular muscle group. A compensatory increase of blood pressure forces plasma from the congested capillaries into the interstitial spaces of the muscle cells.

Bodybuilders commonly perform pumping-up exercises before appearing on stage to make their muscles appear fuller. For most of us there is no real benefit from achieving a pump (except for boosting your ego). However, the inability to achieve a pump is one symptom of overtraining since fluid volume in the muscle, and possibly blood volume, decrease when glycogen stores are low. Intense cycling or swimming can also bring about a pump, or temporary fullness in the working muscles.

The Burn

Sled 45° Calf PressThe burning sensation during certain weight training exercises or high repetition training is caused by an accumulation of acid in the fatiguing muscle. Anaerobic glycolysis utilizes carbohydrates and produces water and acid, or free hydrogen ions. Lactate helps prevent muscle acidosis by transporting positive hydrogen ions out of the muscles. This acid does not clear sufficiently if blood flow is impeded. The vasculature within the muscle is temporarily occluded by the surrounding muscle when it is contracted intensely for a relatively prolonged duration. The excessive acid acts upon nerve receptors producing the localized burning sensation. Excessive acid accumulation also impedes muscular contraction. Acid interacts with calcium, rendering it unavailable for muscular contraction. If repeated regularly, the muscle will begin to adapt to this stress to become more efficient for later bouts. See types of muscular endurance and muscle fatigue & blood supply graph.

Many basic or compound exercises (e.g. squat, bench press, etc.) have a bell shaped resistance curves or shift the resistance through multiple muscle group throughout the exercise's range of motion allowing the muscles to momentarily relax between repetitions. This period of momentary relaxation between repetitions allows greater opportunity for momentary blood flow permitting the clearing of acid accumulation.

In contrast, auxiliary or isolated exercises (e.g., leg extensions, lever fly) tend to have relatively continuous resistance curves, such as experienced on variable resistance machines requiring the muscle to sustain contraction through the majority of the exercise's range of motion. This effect can be augmented by the use of cams and variable resistance levers which attempt to match the user's strength curve by a preset resistance curve. In time, after adequate adaptation, the muscle will be better able to deal with acid accumulation. Also see types of muscular strength.

Although the burning sensation may be indicative of the effectiveness of the exercise as it pertains to a specific type of muscular endurance, it does not efficiently promote strength, power, or muscle development. In actuality, an exercise that does not induce the burning sensation may be superior for the development of strength and, possibly, muscular size. For example, leg press (basic and compound) is noted to be superior for both strength and muscular size to leg extension (auxiliary and isolated) where the burning sensation is more prevalent. It is possible, however, to supplement compound exercises (e.g. leg press) with isolated exercises (e.g. leg extensions), in essence transferring muscular endurance to muscular strength.

Judging the effectiveness of an exercise on the burning sensation is fallacious. The burning sensation has nothing to do with fat burning as popular believed (See spot reduction myth).

It can also be misleading to judge an exercise's effectiveness on a particular muscle group based upon local muscular fatigue. For example, a common misconception is that leg raises exercise the lower abdomen since most exercisers feel a burning sensation in this area (see lower abdomen myth). Furthermore, beginners often feel muscular fatigue in unusual places until they become accustomed to that exercise. This is similar to the 'weak link' analogy (i.e. A chain is only as strong as its weakest link). Only after these 'weaker links' become conditioned will the 'chain' (target muscle and assisting muscles) be exercised more effectively.


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