The jerk is divided into five phases,
combined into three periods. (recovery
from split and final fixation of bar are not
included).
The first period consists of one phase, the half squat.
Phase one begins the instant the knees begin to flex
and ends the instant the barbell reaches its maximum
downward velocity. This period contains only one
phase because at the start, the bar is already bent.
The bar straightens as its center is lowered , so the
"athlete-barbell" system is already moving. This
obviates the need for an additional phase. The
objective of phase one (as in the snatch and clean) is
to create a rigid interaction between the links of the
"athlete-barbell" kinematic chain and to lower the bar
vertically.
The second period consists of two phases; the
"braking" (phase two) and the final acceleration or
thrust (phase three).
Phase two begins the instant the
bar reaches its maximum downward velocity and
concludes with the largest degree of flexion in the
knee joints. At the end, the bend in the bar is
maximum. The objective of phase two is to switch
from flexing the knees to straightening them as quickly
as possible and to maintain support in the middle of
the feet.
Phase three lasts from maximum knee flexion to
maximum extension in these same joints. The object
of phase three is to create maximum speed of leg and
arm extension.
The third period includes two phases, the squat under
(non-support and support phases).
Phase four is the time period from maximum
extension in the knees until the bar reaches its
maximum speed. The athlete vigorously rearranges
the legs in the saggital plane (fore and aft) during this
phase. The object of phase four is to rearrange the
legs with maximum speed and to correctly position the
arms, torso, and legs.
Phase five lasts from the instant the barbell reaches
its maximum speed up until it is fixed in the squat
under position. The object of phase five is to switch
from extension to squat under as quickly as possible
and to create a rigid interaction between the links of
the "athlete- barbell" kinematic chain,to land with the
support uniformly on the legs and to solidly fix the
barbell in the squat under position.
Some additional comments on the
jerk:
Phase two, the "braking" phase is the key to a
successful jerk. The faster one switches from the half
squat to the thrust, the greater the elastic potential
created in the muscles and consequently the higher
the working effect. The greater the vertical support
reaction, the greater the maximum barbell speed
which ultimately enables one to jerk the weight to a
greater height.
The most basic requirement during the execution of
the half squat is not to "separate" from the barbell but
rather become a unified whole with it.However,one
should not slow down this part of the movement. The
artificial slowing of phase one will not allow the bar to
bend sufficiently but on the other hand, executing
phase one with excessive speed will cause the
"unified interaction" of the athlete and the barbell to be
lost. This in turn will result in a prolonged execution of
the braking phase ,insignifigant forces against the
support, and a low barbell speed. Consequently, the
speed of the half squat should be optimized for each
athlete.
by Jim O’Malley
