"First, there is no clinical evidence or research data
whether published or not, of which I am aware (which of course
may simply mean I haven't come across it yet) that would lead
one to conclude (according to the accepted statistical methods
for the treatment of data to establish a correlation or causal
relationship) that squats performed on a Smith-machine apparatus
pose any inherent danger to either the knees or the spine when
performed correctly. If anyone can offer such evidence I would
greatly (and sincerely) appreciate him or her sharing it, or
letting me know where I can acquire it. Alternatively I would
also be interested in discussing any Biomechanical models that
he or she may have used to arrive at this conclusion. Anecdotal
accounts, opinion, and conjecture, regardless of the source or
the forum, do not constitute evidence.
Second, I would like to point out that if performing a squat
on a Smith-machine is to be classified as an "unnatural"
movement that the body was "not designed for" (and
I refrain from getting into the implications of that phrase because
I don't care to open a debate over evolution versus creation)
then this classification must also be applied to virtually every
other Strength Training movement existent. There is very little
that is "natural" about the majority of movements that
Strength Athletes utilize in the pursuit of their training in
so far as they do not occur outside of the training environment.
The argument within this context against the Smith-machine squat
of course tends to focus specifically on the fact that the bar
(or load) is restricted to a path of motion that is linear. Its
detractors argue that the "natural" motion produced
by movement of the body' s limbs is rotational and that the two
are therefore incompatible. This argument is completely erroneous
because it fails to consider that regardless of the path through
which the load is moved, the motion of the limbs about the axes
of the joints remains rotational in nature. This is because the
limbs are not capable in general of active linear motion (though
one portion of the body may be moved passively through space
on a linear path it is as a result of rotational motion occurring
about the axis of another joint e.g. the forearm and hand may
be pulled directly towards the body on a linear path via rotation
at the elbow and shoulder). Muscle complexes are activated to
produce linear forces that act on bones via connective tissue.
The linear muscle forces are translated into angular torque by
the lever systems formed through the articulation of the bones,
and expressed as rotational movement (provided there is a net
unbalanced force present) of the limbs about the joint axes.
Several of these rotational movements can then be combined and
coordinated to produce a variety of external movements both linear
and rotational in nature. The squat for example (whether using
a barbell or a Smith-machine) is a combination of rotational
movement at the ankle, knee, and hip joints, with minimal spinal
deflection at the articulation with the pelvis. The nature of
the final overt movement that is expressed in no way alters the
rotational nature of the movement of the limbs about the joint
axes that combine to produce it.
Third, I would like to emphasize that the performance of ANY
Strength Training movement without strict adherence to proper
form is inherently dangerous; and that the degree of risk is
in direct proportion to the load, and the percentage of momentary
volitional ability (your maximum capacity to perform) that is
applied. I will not dispute that a proportionally high number
of people who have at some point included Smith-machine squats
in their training program have experienced a variety of injuries
ranging from minor to catastrophic, and that low back discomfort
or strain is a common complaint because that has been my experience
as well. However, I have never encountered an instance where
the injury or discomfort was not preventable or correctable.
The vast majority of people get into trouble because they do
not understand how to perform the movement properly, and virtually
all of them make one or all of the following three mistakes.
By far the most common error, and the source of most complaints
about back strain, is that of allowing the pelvis to travel too
far to the rear as the trainee descends towards the bottom of
the exercise stroke such that the anterior angle between the
floor and the vertical axis of the trunk is greatly decreased.
The mechanical effect of this is the same as that of leaning
too far forward when squatting with a barbell in as much as the
moment arm (perpendicular distance between the applied force
vector [in this case that of gravity acting vertically downward
on the bar] and the axis of rotation) in the lever system consisting
of the spinal column, the pelvis, and their articulation is greatly
increased, which multiplies the resulting torque acting about
the joint axis. This amplified torque must not only be overcome
in order to reverse the motion of the bar and execute the positive
phase of the exercise stroke, but must also be continuously matched
in order to maintain proper spinal alignment. Though there is
nothing inherently wrong with bending forward at the waist while
under load (as in a stiff legged deadlift, hyperextension, or
good-morning) the loads typically utilized when squatting are
far beyond the abilities of most people to safely handle in this
way. Few trainees posses the strength and control in the muscles
of their lower backs to produce sufficient force and to maintain
it without any interruption for long enough to fatigue their
leg and hip extensors in this fashion. The squat (barbell or
otherwise) should always be performed while keeping the torso
as vertical as possible. If you are unable to descend into a
full squat without leaning forward excessively (especially on
the machine) then you need to work on ankle flexibility rather
than cheat by leaning further forward.
The next most common mistake (and this applies to barbell
squats, and just about every other exercise as well) is loading
the bar with a weight that far exceeds your ability to perform
the movement properly. Now I'm not speaking of occasionally challenging
yourself with an extra 5 or 10 lbs, but of trying to push a weight
so large you have no option but to cheat and use momentum from
the first repetition. Most people who are having trouble with
Smith- squats will find that some (if not all) of their problems
can be alleviated simply by reducing the load to the point where
they are able to regain control of it. Most of us know first
hand the dangers of using a load that is beyond our abilities,
and those that don't will learn one way or another, and probably
sooner than later. A good test to see if the weight is too heavy
is to ask yourself if someone were to suddenly yell stop at any
point throughout the range of motion of any movement would you
be able to comply immediately. If you could not then the load
is too heavy for you to control safely.
The third mistake, which is often coupled with the second,
is that of moving too rapidly through the transition between
the negative and positive stroke, i.e. bouncing out of the bottom.
The problem (briefly because it is a topic unto itself) is that
the impact forces which occur in that instant when the motion
changes from negative to positive can be far in excess of the
stabilizing forces that hold the joint together (the force of
the muscles on the joint and surrounding tissues, hydrostatic
pressure within the joint, and all of the resulting action/reaction
force couples) even when combined with the stretch reflex that
occurs, such that the excess kinetic energy is transferred to
the joint structure itself where it momentarily becomes stored
potential energy (assuming the tissues can withstand the force
and do not simply snap or tear). Though the release of this stored
potential energy from the joint does allow you to push more weight
out of the bottom position it can also contribute greatly to
both acute and chronic knee injuries (just as is would with barbell
squats). You should always move slowly and under control, particularly
when approaching a maximum load or you are asking for injuries
regardless of what movement you are performing.
There are a host of other smaller mistakes, many of which
are related to an individuals biomechanical configuration or
just plain sloppy lifting habits such as foot placement, pelvic
tilt and yaw, hip alignment, shoulder position, the placement
of the bar across the upper back, body segment and limb proportions,
proper breathing, etc. that can also have an effect on how comfortable
(relatively speaking) a trainee will be when performing the movement.
Most of these however, are easily correctable when recognized,
but require a certain amount of experience to pick up on.
The bottom line is that the Smith-machine squat does not pose
any inherent dangers to either the knees or the spinal column
provided it is performed correctly, and no one to my knowledge
has ever proven otherwise either in theory or through clinical
trials (though "expert" opinions abound); but I invite
anyone to do so if they can. However if you do not adhere to
proper form when performing this or ANY other exercise you will
in all likelihood encounter problems. The Smith machine has long
been a viable alternative for those who wish to perform squats
and pressing movements at or near the upper limits of their abilities
with safety and confidence at times when a capable spotter or
a power rack is not available. It has also served well those
who are attempting to learn such movements but do not yet possess
the balance to feel confident even within a good sturdy power
rack. I realize that this post is not likely to change many opinions,
most people will continue to believe as they do simply because
they want to. In all likelihood most will simply dismiss it as
"too technical" or just a bunch of "pseudo-science".
About this I harbor no delusions. Perhaps however it will cause
a few to think beyond what they have heard at the gym, or read
in their favorite muscle-comic."