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A 1978 report of research by McLaughlin, Lardner &
Dillman, titled "Kinetics of the parallel squat," suggests
that there are deficiencies in the squat as an exercise for
developing quadriceps strength. I suggest that the ScrumTruk
may be a more efficient apparatus for this purpose.
McLaughlin and his colleagues investigated torques and
joint forces generated during the parallel squat by studying
nationally-ranked and world-class powerlifters competing at
the U.S. Senior National A.A.U. Powerlifting Championships.
Although now very dated, the study is important given that, as
with other complex joint movements, the study of the kinetics
of the squat exercise has been virtually neglected. The
research involved a cinematographic analysis to calculate
joint forces and muscular torques for the shank, thigh and
trunk, i.e., at the ankle, knee and hip joints,
respectively.
Subjects were classified as world-class, high-skilled or
less-skilled. This delineation of ability was used in order to
isolate trends in technique. It was assumed that the
most-skilled subjects “would exhibit efficient patterns of
performance,” so that they were, in effect, used as a
reference group in assessing the performance of those in the
other subgroups. By comparing the techniques of lifters in
each group, the researchers hoped to identify possible general
trends in performance for individuals relatively unskilled in
the squat.
Figure 1 is a schematic of the squat movement reproduced
from the article, indicating the points at which the muscular
torques were computed and the muscle groups involved.
Technique differences between highly-skilled and
less-skilled lifters
Previous studies by McLaughlin alone and by the three
authors jointly (McLaughlin, 1975; McLaughlin, Dillman &
Lardner, 1977) had found that less-skilled subjects “leaned
forward more and moved the knees frontward to a greater extent
during the descent, and ... moved the hips backward more in
the early ascent while also increasing trunk lean." The degree
of forward lean during the lift appears to increase the torque
for the trunk extensors and reduce those of the thigh
extensors.
The 1978 study confirmed these findings. One of its major
observations was “a general trend for the high-skilled
subjects to exhibit more extensor-dominant thigh torques than
the less skilled." In particular, the three world-class
subjects had the greatest extensor-dominant thigh torques.
With respect to trunk torque, it was noted that it
"increased linearly the more a subject’s trunk angle
decreased.” The angle referred to was that between the trunk
and the horizontal at the hip joint. The 1977 study found the
mean trunk angles to be smaller for less-skilled subjects than
for the high-skilled. The most recent study verified the
related trend for less-skilled subjects to exhibit greater
trunk torques than more highly-skilled subjects. "It would
appear from the data that high-skilled subjects attempt to
minimize the trunk torque, and do so largely by reducing
forward trunk lean." It was noted that among the subjects, the
then world super heavy weight champion maintained the greatest
trunk angle of all subjects and, despite his much greater bar
load, had a lower trunk torque than many smaller, less-skilled
subjects.
It was suggested that the magnitudes for trunk torque
greatly affect the magnitude and dominance of the thigh torque
values. As mentioned above, the high-skilled subjects
demonstrate larger trunk angles, lower trunk torques and more
extensor-dominant thigh torques. "It therefore appears that
the high-skilled subjects strive to use the leg extensors to a
greater extent than do less skilled subjects. This greater
emphasis on the leg extensors is obtained by a minimization of
the trunk torques by the high-skilled subjects (achieved by
maintaining more erect trunk positions)."
Implications of the study results
Although the parallel squat has been generally regarded as
primarily a leg-extensor activity, the results of this study
show that trunk extensors play a very significant and perhaps
even a dominant role. The muscular torques for the trunk
extensors were found to be substantially greater than the
thigh and shank torques across a wide range of trunk-angle
positions.
The authors conclude that the widespread recommendation of
the squat as one of the primary exercises for developing
quadriceps needs to be altered in the light of their findings.
Those recommending the exercise primarily for quadriceps
development should either ensure that a high trunk angle is
maintained or suggest other exercises that more directly
involve the quadriceps.
In practice, of course, given the observed tendency of
inexperienced lifters to move their hips backwards and lean
forward more when coping with heavy loads, it is unlikely that
the squat is a generally effective exercise for development of
the quadriceps group.
"For rugby players, who usually
have inexpert technique in the squat, the ScrumTruk appears to
be a much more efficient vehicle for developing and
strengthening the quadriceps."
Is the ScrumTruk
a useful alternative?
At the low point of the squat movement, the exerciser has
completed the eccentric or lowering phase and is switching to
the concentric or rising phase. This is occurring in a region
of high mechanical disadvantage. At this point the injunction
to keep the hips forward and the trunk near upright is
unlikely to be followed if a relatively inexperienced lifter
is struggling with a near-limit weight and worried about the
implications of failure.
The corresponding scenario with the ScrumTruk involves the
exerciser allowing the push truck to roll back towards them in
the eccentric phase then generating the shove for the
concentric or pushing phase. If they are not confident about
coping with the weight they can simply allow the push truck to
come to rest against the bumper stops. They have no need for a
spotter to take some of the load.
Even more importantly, the horizontal trunk position
adopted with the ScrumTruk is intuitive, comfortable and
involves no strain on the lumbar spine. Athletes find no
difficulty in maintaining a horizontal trunk throughout a set
of repetitions.
Figures 2 and 3 provide a comparison of the orientation of
the trunk relative to the direction of weight force for the
squat and ScrumTruk respectively. In Figure 2 it is obvious
that there is quite a long moment arm from the fulcrum point
at the hip joint to the vertical line of force from the weight
bar. This moment arm increases as the trunk angle decreases
and the hips are moved back.
The exerciser in Figure 3 is in the typical starting point
for pushing the ScrumTruk. The included angles for both hip
and knee joints are approximately 90°. It can be seen that the
moment arm from the hip joint to the horizontal weight force
is negligible.
Range of movement
In scrummaging the conventional range of movement in terms
of included angles for both hip and knee joints is 90° to
130-40°. This relationship is readily replicated using the
ScrumTruk. Further, when the exercise range is extended to
“lock-out” or full extension, hip and knee joints basically
move in unison from 90° to 180°. Thus the hip and knee
extensors share more or less equally the distribution of the
load, with the result that the quadriceps group, as knee
extensors, are fully engaged.
As noted, there is the tendency with the squat for
excessive trunk lean. To the extent that this occurs, at the
lowest point of the squat the included angle at the hip joint
is significantly less than that at the knee joint.
Consequently, rising to “lock-out” or 180° extension involves
a much greater range of angular movement for the trunk than
the thighs. Crucially, observation of actual lifters suggests
that much of this greater relative movement tends to occur
when the lifter is moving from a horizontal thigh position
through the "sticking point," which McLaughlin and his
colleagues estimated at around 30° above horizontal. Thus the
trunk extensors, principally the gluteus maximus, bear the
bulk of the serious loading while the quadriceps is not fully
taxed.
Given that the ScrumTruk is a very recent invention which
is just coming out of the development stage, there have not
yet been any systematic studies of its operation or effects.
However, the most common observation from players in Sydney
University Football Club’s Elite Development Squad who have
been making extensive use of the ScrumTruk in out-of-season
training, is a very definite “pump” or “burn” in the
quadriceps when performing heavy sets. When queried, they
report no similar effect from the squat which they are
simultaneously performing.
Conclusion
For rugby players, who usually have inexpert technique in
the squat, the ScrumTruk appears to be a much more efficient
vehicle for developing and strengthening the quadriceps.
Given its ease, comfort and efficiency of use, the
ScrumTruk is likely to offer similar advantages over the squat
for athletes in other sports or for other people pursuing
strength and fitness. Its use is certainly indicated where
there is a history of back or knee problems or where the
person’s limb geometry makes it difficult to maintain good
form in the squat.
References
McLaughlin, T.M. A kinematic analysis of the parallel squat
as performed in competition by national and world class
powerlifters. Microform Publications. Eugene: University of
Oregon, College of Health, Physical Education and Recreation
1975
McLaughlin, T.M., Dillman, C.J. & Lardner, T.J. A
kinematic model of performance in the parallel squat by
champion powerlifters. Medicine and Science in Sports, 9,
128-33 1977
McLaughlin, T.M., Lardner, T.J. & Dillman, C.J.
Kinetics of the parallel squat. The Research Quarterly, 49,
173-89. 1978
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