Squat as described in ExRx can be used as an alternative
exercise to to the barbell
squat. For novices, it can used to familiarize oneself with
the squat movement, particularly with a trainer's assistance.
For more advanced weight trainers, it can be implemented periodically
after the squat has become stale
(yielding less progress as when originally performed). I'm not
aware of any scientific study suggesting Smith squats are not
as safe as regular barbell squats.
has argued that the path is unnatural and that the machine prevents
the body from determining its groove. I assume they feel linear
or lever machines are not as effective or not as safe as free
weights. Although this argument warrants consideration, I am
not aware of any scientific or empirical evidence to support
this claim. Free weights certainly offer more variety of exercises
than machines, but why restrict yourself to just free weights,
particularly since greater progress can be obtained from exercises
you are not accustomed to. See Restimulating
Progress by Changing Exercises.
Machines seem to be as safe as free weights; even physical
therapists commonly use linear machines for rehabilitation. One
closed-chain exercise used for knee rehabilitation is the Sled
Lying Leg Press. Is someone suggesting physical therapists
are doing more harm than good by locking the body into the machine's
The Smith squat can be adapted to accommodate individuals
that may feel pain on the barbell squat. A center of gravity
does not need to be maintained between the forefoot and heel
since the machine can prevent you from falling over. Using a
similar method we used earlier to examine
the barbell squat, we can compare the torque forces of the
Smith squat to the variations of the barbell squat.
Using the form recommended by the trainer mentioned in the
the knees do not travel as far forward and the depth of squat
is restricted. Both factors result in less torque force in the
knees and lower back. Regarding placing the feet slightly forward
during the Smith squat, concern has been expressed there is additional
stress on the knees as the feet wants to slide forward but doesn't
because of the friction from the floor surface. I would argue
there is actually less stress on the knee and this stress is
not necessarily unnatural. The foot and lower extremity endure
far greater forces during running or jumping forward; the
feet want to slide forward but don't because of the friction
from the ground.. You can calculate these vector forces using
certain physics calculations. Many of our readers have probably
calculated these forces in a biomechanics, or kinesiology class.
You would be hard-pressed (pun intended) to find a leg press
exercise that did not place the lower extremity in a force some
consider 'unnatural'; the feet want to slide forward but don't
because of the friction. Again analyze the Lunge
or the Sled
Lying Leg Press. Just try dowsing the bottom of your feet
with Vaseline® (petroleum jelly), hop on your favorite leg
press machine and see which way your feet slip. I must warn you,
though, make sure the leg press machine has a safety catch unless
you want some hospital staff to have to remove it from the insides
of your rear end.
Incidentally, if an attempt was made to lower the feet on
Lying Leg Press so they would not encounter the questioned
stress the feet want to slide forward but don't because of
the friction, the knee would endure far greater torque forces
just as if the back were too vertical
on the squat or smith squat. The rounding of the back is encounter
when the limitations of hip flexibility are taxed on most any
squat or leg press exercise. See Squat
analysis. This can be controlled by the depth of the squat
if hip flexibility
I do agree that a stance with the feet forward beyond what
is necessary can be less than desirable. I recommend a form similar
to that of the barbell squat: knees and hips moving forward and
backward the same distance respectively, weight distributed between
the forefoot and heel. If modifications are made, perhaps to
emphasize the glutes or avoid pain in a bad knee, I recommend
only subtle changes from standard form; move feet forward just
a couple inches forward or the minimum modification that will
accommodate the intended goal.
Although greater relative intensities can be applied to specific
muscles by emphasizing one muscle over another (auxiliary
exercises), greater absolute intensities can be achieved
when agonist muscles
work together with similar intensities (basic
This freedom of movement during the Smith squat could also
invite unexpected problems. During a Smith squat with the feet
under the bar the back can be inadvertently positioned much more
vertically that what would be possible on a regular barbell squat.
This is accompanied by the knees traveling much more forward
than they are probably accustomed to. The heel can consequently
raises from the floor adding to the already exaggerated torque
forces of the knee. This is particularly true when there is inadequate flexibility
of the ankle. This is the situation I believe you and others
are referring to when you say Smith squats places more stress
on the knee. This problem can be easily remedied using a similar
technique as with the barbell squat.
The muscles and joint structures can adapt to most any stress.
If any of the factors outline on the ExRx site are not adhered
to, injury can result. See adaptation
criteria. The potentially excessive freedom of motion during
a Smith squat (discussed above) may result in inconsistent stresses
to the knee joint that make it difficult for adequate adaptation.
This assessment may seem ironic given machines are typically
viewed as more restrictive in motion.
Generally speaking, the Smith squat is a safe exercise when
guidelines are observed.