Brady Anderson chimes in:
The optimal pattern of motion for human body segments has been studied in a
variety of sports other than golf. In activities such as kicking, jumping and overhand
throwing, many authors have shown that a proximal to distal progression of motion
results in the highest performance. It is possible that this movement pattern is a natural
consequence of our mass distribution. Our bodies have evolved in such a manner that our
largest muscle groups are located near the body center. This is also the location of our
largest concentrations of mass. As we move away from the body center, segment
volumes decrease, segment masses decrease, and the length of long bones also decrease.
By the time we reach our hands and feet (our most distal endpoints); segment length,
mass and segment volumes have decreased to be a fraction of that near our core. In highspeed
movements therefore, it could be logical for humans to have evolved a movement
pattern that follows a proximal to distal sequencing, matching that of our segment mass
distribution.
In golf however, mass distribution is altered from that of other sports. A club is
added to the hands, and because of the handgrip used, this club segment hinges at the
wrist joints. The center of gravity of this external implement is located near its distal end.
The distance from the wrist joint to the club center of mass creates a large radius of
gyration, meaning that the club segment does not follow the progression of mass
distributions already found in the human body. For this reason, it is hypothesized that the
proximal to distal pattern that has evolved for high-speed human movement will not be
suitable for golf. The addition of an external element, with a large radius of gyration, to
the distal end of a human chain of linked segments should require a change in movement
pattern for optimal performance.
And he goes on:
Authors have argued over the optimal pattern of timing for joint angular velocities in a
linked system. Koniar (1973) has argued for what he called the “principal of
superposition of angular speeds in joints”. In order to achieve maximum performance for
a given action, Koniar said that all segments should reach a maximum angular velocity at
precisely the same moment. He measured 20 athletes with electro-goniometers and found
that subjects jumped highest when segmental angular velocities peaked simultaneously.
No mention was made as to the sampling frequency or smoothing methods used in this
investigation.
Koniar wasn’t the only author to describe this “principle” of simultaneous
segmental speed peaks. Gowitzke and Millner (1988) stated that “in theory, each joint
action should impart maximal linear velocity at the instant of release”. These authors
noted that this phenomenon wasn’t seen in hitting or throwing sports. They speculated
that it would be possible to estimate the degree of coordination for a given performance
by comparing peak end point velocity with a theoretical end velocity if all segments were
to peak at the same time.
Joris et al (1985) described a simultaneous maximality of body segment angular
velocities as “the Hocmuth Optimization Principal”. In a study of over hand throwing in
handball, those authors set out to determine if simultaneous peaking of segment angular
velocities actually improved performance. They found that this pattern could only be
possible in a purely theoretical, kinematic sense; that is, if the segments contained no
mass. Of course, this constraint does not hold true for real human movement. The authors
found that distal segments seemed to go through periods of highest acceleration when the
preceding segments underwent a deceleration. Joris et al stated that Newton’s third law
could likely explain the deceleration of proximal segments. Those authors reasoned that
“for every action on a more distal segment …” (i.e. joint torque) “there is an equal but
opposite reaction on the more proximal segment.” In their experiment, they found that
optimal performance was found when segmental angular velocities peaked in a proximal
to distal (P-D) fashion.
2.1.2 Proximal to Distal Sequencing of Body Segment Motion
Bunn (1972) was the original author to refute the concept of simultaneous peaking of
limb angular velocities. In his “guiding principles of human motion”, he stated that
optimum speed of a kinematic chain’s distal end point can only be reached when body
segment angular velocities peak in a P-D fashion. According to Bunn, “… movement of
each member should start at the moment of greatest velocity, but least acceleration of the
preceding member”. He reasoned that proximal joints could attain higher angular
velocities if their distal counterparts would remain flexed later in motion. Although he
did not provide equations to prove his work, Bunn argued that higher limb angular
velocities could be easier to attain if the radius of gyration of the linked system is kept
small (ie. when a joint is flexed). He felt it would be possible to capitalize on this
increased angular velocity by quickly lengthening the system’s radius of gyration preimpact.
He observed that the knee seemed to be flexed until late before ball contact for
maximum kicking velocity in human kicking motions.
Figure 2.1.2 shows hypothetical profiles of angular velocity for a planar, multisegment
chain. Figure 2.1.2 a) represents the motion pattern that Koniar referred to as the
Superposition of Angular Speeds. Figure 2.1.2 b) represents the Summation of Speed
Principal as described by Bunn (1972).
Figure 2.1.2: Hypothetical segmental velocity profiles in a 3 link chain. In part a) all segments peak
simultaneously. Part b) shows a proximal to distal progression of angular velocity
peaks.
Putnam (1993) supported what she referred to as Bunn’s “summation of speed
principal”. She wrote that striking and throwing motions must follow a proximal to distal
progression. This is due to what Putnam refers to as “motion dependent interaction…
between links”. In a Lagrangian model of two-link motion, Putnam found that angular
kinematics of connected links did not solely depend on external moments applied (ie.
muscle torques); but also on resultant joint “interactive moments” between links. It is
speculated that these so called moments are actually due to reaction forces occurring at
the joints; and the virtual or inertial forces acting on the segment CG (center of gravity).
Putnam noted that the interactive moments were dependent on the relative angular
position, angular velocity, and angular acceleration of each segment in series. Putnam
found that interactive moments due to relative angular velocity were greatest when
segments were orthogonal. Conversely, interactive moments due to relative angular
acceleration were greatest when segments were co-linear. In both cases, interactive
moments caused the proximal segments to slow down while the distal segments sped up.
In any case, Putnam showed that the kinematics of inter-segmental movement had an
interdependent relationship with the loading of those segments.
Herring and Chapman (1992) carried out a 2D, three segment, over-hand
throwing optimization. In the study, relative timing and direction of external joint torques
were manipulated to find an optimal strategy for the longest possible throw. They found
that a proximal to distal (P-D) sequencing was essential in obtaining the highest overall
distal end point velocity. This was not only true of the onset timing of torques, but also in
timing and magnitude of segmental angular velocities. The authors also found that
negative torques applied to proximal segments can enhance distal end speed if applied
just prior to release. Of note, Herring and Chapman found that P-D sequencing was a
very robust solution for optimal segmental movement. Their optimization tended towards
this type of movement pattern for a wide range of limb lengths, inertial properties, and
applied muscle torques. They concluded that the linked, segmental nature of human limbs
predisposes our movement systems to P-D sequencing.
Feltner and Dapena (1989) created a 3D, two segment, over-hand throwing
model. They attempted to address the “cause-effect” interdependent mechanisms that link
segment kinematics and kinetics. The purpose of their investigation was to show resultant
joint forces and torques as a function of relative segment kinematics. They also showed
how segment kinematics can be determined as a function of joint forces / torques in
addition to gravity and neighbouring segment kinematics. The authors showed that
kinematics of a double pendulum represent an extremely multifaceted, interdependent
system that does not rely solely on external impulses alone.
In summary, there have been two generalized motion patterns introduced that
attempt to predict an optimum solution for speed generation in multi-segmented
movement. Koniar (1973) introduced the concept of simultaneous peaking of angular
velocities between body segments to reach optimum speed generation. Bunn (1972)
presented a contrasting solution. He stated that segments should peak in a proximal to
distal manner to achieve maximal distal end point velocity. Since these concepts were
established, only Koniar’s own study has quantitatively supported the concept of
simultaneous peaking. The papers of Gowitzke and Millner (1988) and Joris et al (1985)
supported the concept of simultaneous peaking in theory, but their results showed that
humans displayed a pattern of P-D peaking in real movement.
Simulation work has gone on to support the concept of P-D patterning in
segmented human movement. Putnam (1993) showed this pattern to be a function of the
inertial property of our limbs. Simulation work by Herring and Chapman (1992) showed
that a P-D pattern of segmental motion was a robust solution for a wide range of system
parameters in their speed optimization study. Finally, the simulation work of Feltner and
Dapena (1989) showed that a system involving 3D motion in linked segments is
extremely complex and interdependent; and cannot be defined by external loading alone.
It seems that a pattern of P-D peaking in segmental human motion has been
established as an optimal solution for speed generation. However, previous studies in the
literature have shown that humans seem to have evolved to use this type of patterning in
movements such as kicking, jumping and throwing. In these movements, there are no
external implements involved as a part of the dynamic, segmented chain. This is an
important distinction. In general, human segments decrease in mass as you move along
the body in a proximal to distal manner. In golf, the system may be slightly different. The
club is an external implement that is swung as to be another segment in the dynamic
linkage. Although the mass of the club is most likely less than that of the arms segment,
the length of the club requires a large radius to be created between the club CG and the
focus of club rotation. The result of this is a distal segment that may have more inertia
than what humans have evolved to move optimally. Therefore, it remains to be seen
whether a P-D pattern of segmented motion exists in the golf swing.
