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 a boost of one's 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.
burning sensation as experienced during (1) certain weight training
exercises, (2) high repetition training, or (3) particular advanced
training techniques, 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.
After several regular workouts, the muscle(s) become better adapted
to deal with acid accumulation. See types
of muscular endurance and muscle
fatigue & blood supply graph.
Many basic or compound exercises (e.g.
press, etc.) have a dynamic, or bell
shaped resistance curve or they shift the resistance through
multiple muscle groups throughout the exercise's range of motion,
both 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, many auxiliary or isolated exercises
fly) tend to have relatively continuous resistance curves,
particularly when performed 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
resistance levers which attempt to match the user's strength
curve by a preset resistance curve.
or not locking out can be used to restrict the range
of motion on either compound or isolated exercises. These
techniques also evoke intercellular acidosis by preventing the
muscle to relax at the top and/or bottom of the movement, keeping
it continuously contracted throughout the set.
Some evidence suggests that the resulting burning sensation
may promote muscle development by via sarcoplasmic
hypertrophy. Interestingly, mechanically occluding the venous
return while moving relatively light loads can elicit metabolic
changes and promote sarcoplasmic hypertrophy (Loenneke 2012).
It is thought that hypoxia and intracellular acidosis of the
muscle cells stimulate certain metabolic changes that are responsible
for this effect.
Although using particular exercises or training techniques
which bring about the burning sensation may be an effective means
for training for sarcoplasmic hypertrophy or a particular type of
muscular endurance, it does not appear to be the most effective
method for developing strength, power, or myofibrillar hypertrophy.
It can be argued that compound exercises that do not induce
burning sensation as readily, appear to more effective than isolated
exercises in development of strength and muscular size. For example,
press (a basic
and compound exercise)
is superior in developing both strength and muscular size compared
extension and hip
extension (both auxiliary
and isolated exercises)
where the burning sensation is far more prevalent. In fact, isolated
exercises may not provide additional benefits in the way of strength
or muscular size in untrained men. (Gentil 2013)
Judging the effectiveness of an exercise on the burning sensation
can be fallacious. 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 (eg: neck fatigue during crunches). 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, can the 'chain' (target muscle and assisting muscles)
be exercised more effectively. In addition, the burning
sensation has nothing to do with fat burning as popularly believed
(See spot reduction
Gentil P1, Soares SR, Pereira MC, Cunha RR, Martorelli
SS, Martorelli AS, Bottaro M (2013). Effect of adding single-joint
exercises to a multi-joint exercise resistance-training program
on strength and hypertrophy in untrained subjects. Appl Physiol
Nutr Metab. 38(3):341-4.
Loenneke JP1, Wilson JM, Marín PJ, Zourdos MC, Bemben
MG (2012). Low intensity blood flow restriction training: a meta-analysis.
Eur J Appl Physiol. 2012 May;112(5):1849-59.