Boost power output by lifting faster...
When contracting muscle is first stretched (prestretch) and then
immediately allowed to shorten, it generally exhibits higher contractile
performance than it does without prestretch, e.g., enhanced productions
of mechanical work and power in isokinetic and isotonic conditions,
respectively.
Such a phenomenon is seen most frequently in the form of a countermovement.
The countermovement consists of an initial lengthening of muscle
(eccentric action) and a subsequent, rapid reversal of the movement
to produce shortening of muscle (concentric action).
This rapid deceleration of the eccentric action gives rise to the
generation of large force and thereby makes the following concentric
action stronger.
Researchers from the University of Tokyo studied a group of five
men who performed squatting exercises with a countermovement at
varied deceleration rates before lifting the load [1].
The experiments were carried out with well-trained athletes because
the generation of large eccentric force was thought to be dangerous
for untrained subjects. In addition, some preliminary measurements
with untrained subjects exhibited no reproducible enhancement in
power output with the increase in peak eccentric force, suggesting
that a certain level of skill for resistance-exercise training is
required for obtaining consistent results.
The men performed squatting exercises on a force plate, using
a barbell weighing 50% of the mens 1-repetition maximum. In the
exercise without a countermovement, the subjects squatted at a
knee angle of 90°, stayed still for 2-3 s, and then stood
up to the upright position at their maximal effort.
The lowest hip position was recognized by the subjects correctly
and reproducibly with the aid of a height-adjustable stool placed
behind them. In the exercise with the countermovement, they squatted
until their hip touched the stool, and at this moment, they reversed
the motion as rapidly as possible to return to the upright position.
When an intense deceleration was taken at the end of downward movement,
large eccentric force was developed, and the mechanical power subsequently
produced during the lifting movement was consistently larger than
that produced without the countermovement.
Numerous structural abnormalities are evident in muscle after exercise,
especially exercise that involves eccentric contractions. These
abnormalities include sarcolemmal disruption, dilation of the transverse
tubule system, distortion of myofibrillar components, fragmentation
of the sarcoplasmic reticulum, lesions of the plasma membrane, cytoskeletal
damage, changes in the extracellular myofiber matrix, and swollen
mitochondria.
Accompanying these changes, there can be a gradual increase in
the soreness of the involved muscles that peaks 24-48 hours after
the exercise. This effect is known as delayed-onset muscle soreness.
It occurs frequently after the performance of unfamiliar exercises
that include eccentric contractions and is attenuated as the exercises
are repeated in subsequent sessions.
The short- and long-term consequences of including eccentric contractions
in an exercise program can be to induce structural adaptations in
muscle, to activate an inflammatory response, and to modify the
neural commands used to control the movement. Whereas these adaptations
can also be induced by other types of contractions, they seem to
be maximized by eccentric contractions.
Reference
1. Takarada Y, Hirano Y, Ishige Y, Ishii N. (1997). Stretch-induced
enhancement of mechanical power output in human multijoint exercise
with countermovement. Journal
of Applied Physiology, 83, 1749-1755
2. Enoka, R. M. (1996). Eccentric contractions require unique activation
strategies by the nervous system. Journal
of Applied Physiology, 81, 2339-2346
3. Nardone, A., Romano, C., & Schieppati, M. (1988). Selective
recruitment of high-threshold human motor units during voluntary
isotonic lengthening of active muscles. Journal
of Physiology, 395, 363-381
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