Lying Leg (Knee-joint) Curl

Lying Leg (Knee-joint) Curl

The Lying Leg Curl exercise represents the most fundamental Hamstring movement and offers
opportunity to work the hamstrings with a variety of foot positions. The exercise can be potentially
harmful to the sometimes delicate hamstring muscle group as well as the lower back. Light resistance
should be utilized in effort to reduce the injury risks associated with the lying leg curl movement.

Considerations for Machine Selection
The lying leg curl exercise is performed on a lying leg curl machine. The machine may be either a
combination thigh extension / leg curl machine which as outlines earlier would feature a flat bed, or
a specific lying leg curl lying leg curl machine which could feature either a flat or angled bed. The flat
bed accentuates the upper area of the hamstring muscles as well as the gluteals due to the angle of
pull of the muscles during the movement application. The angled bed allows for greater accentuation
of the hamstrings throughout their range of motion due to the more advantageous angle of pull and
the relationship of the force vector and the gravitation forces experienced during the movement.

The angled bed provides a more natural movement application. Because the semtiendonosis and
the semimembraneosous cross both the knee and the
hip joints the movement application of the leg curl
forces the hips to rise off the flat bed. The resulting
raising up off the bed action exposes the lower back
to potential injury. As well, rising up off the bed reduces
the effectiveness of the exercise due to mechanical
disadvantage of the force vector and its relationship
with gravity.

The angled bed allows for a natural positioning of
the torso with the hips in a slightly raised and thus
natural position for the movement application. The
angled bed allows for contact between the torso and a
solid base of support. The movement application is
performed with the body in a more advantageous position
with respect to the relationship between the
force vector and the gravitational forces.

In addition, the flat bed encourages a lifting of
the head and a rising of the chest off the bed. This
flaw in posture creates an arcing in the back exposing
the lower lumbar region to injury risk. The angled bed
discourages the raising of the head and even if there is
experienced a rising of the chest off the bed, there is a
compensatory base-of-support provided at the hips as
well as a superior angle of application.

Considerations for Feet Displacement
One of the foremost considerations attributed to
proper exercise execution of the leg curl are those
related to feet position and displacement. The feet
should be spaced about 7-9 inches apart (depending
upon the width of the hips), in order to maximize the
effectiveness of the exercise and reduce injury risk. If
the feet are spaced too far apart there will be a severe
reduction in the natural application of the movement
throughout the entire ROM of the hamstring muscles.
In addition wide placements could invoke stress upon
the inner region of the knees.

Conversely, exaggerated close feet placements can
produce great stress upon the spine. In addition,
closed feet placements discourage the activation of
the inner portion of the posterior thigh and encourage
the accentuation of the powerful biceps femoris. The
result is that the hamstrings are not provided with an opportunity for full and even development.
In addition to the considerations given to the displacement of the feet are those areas of concern
related to the basic positions of the feet. The reference here is to:

Feet straight-ahead
This position encourages the incorporation of all three major hamstring muscles.

Heels-in position
This position accentuates the activation of the stronger outer or lateral position of the posterior
region of the thigh, notably the biceps femoris muscle. As outlined earlier the accentuation upon the
powerful biceps femoris muscle discourages a balanced development of the rear thigh.

Heels-out position
This position encourages the involvement of the inner portion of the posterior thigh. The difficulty
experienced with this position is that the weaker region is accentuated during the movement
while the powerful biceps femoris muscles are discouraged from becoming involved in the movement.
This would be an effective position to use if you have been abandoning the inner region and
over-emphasizing the outer portion of the posterior thigh.

It should be noted that the hamstrings as a group are not only called upon to provide support for
the knee joint during the actions of knee-joint flex on and knee-joint extension but to serve to provide
impetus for the action of external rotation of the leg. This action creates the twirling sensation
during the concentric and then eccentric contraction phases of the movement application.

As you go through your set, the heels are encouraged to come inside even more with the result
that increased emphasis is being placed upon the biceps femoris muscle. If you find that the heels are
being forced in too much during the completion of a set (you might want to ask a partner to watch
for the movement of the heel), then simply reduce the weight and focus on maintain the straightahead
position of the feet. It should be noted that when too much resistance is applied, there is a
natural response of the pelvic girdle to rise up from the bed in order to provide for a more optimal
angle-of-pull for the muscles to complete the lift.

This raising of the hips action (hip-joint flexion), is a natural mechanism of the body to alter the
upper attachment of the hamstring muscles so that they can now function more effectively as kneejoint
flexors. This is why the angled bed is more effective in providing for a more natural movement
application. Due to the natural tendency of the pelvic girdle to raise up off the bed during flat-bed
applications of the lying leg curl movement the trainee is exposed to high risk of injury to the lower
lumbar region due to the hyperextended posture of the back.

Dorsi Flexion vs. Plantar Flexion
Another major question that needs to be answered is that of which ankle-joint position should
the trainee assume when applying the leg curl movement? The considerations given to dorsi flexion
applications are that more resistance can be utilized and there is a greater feeling of comfort during
the movement application. The reason for the “appearance” of being able to work with greater loads
is that the calf muscles are greatly activated during the dorsi flexion application.

In addition, the activation of the hip joint also encourages the involvement of the gluteal muscles.
In fact it is very difficult to isolate the neural-impulsing into the hamstring muscles when the
dorsi flexion ankle-joint position is used. Conversely, when plantar flexion applications are utilized,
the emphasis in the hamstring area is more readily realized. This is due to the fact that the calf muscles
are relaxed and not activated nearly as much during the movement application.

As well, due to the plantar flexion position of the ankle-joint the gluteals are discouraged from
taking as much of an active role. It should be noted however, that the trainee must concentrate fully
on directing the neural impulses into the hamstring muscles in order to provide optimal growth and
development opportunity. While the trainee would experience a reduction in the amount of resistance
that would be used, he/she would be comforted by the fact that the burden would be taken up
by the hamstrings and not by the support muscle groups. With reference to the “comfort factor”
there is feeling of a pulling action experienced throughout the posterior region of the thighs and less
of a “squeezing” sensation felt in the calves which offers a feeling of discomfort at the outset. However,
with a little practice, the comfort experienced with the strong activation of the calves will be
realized with the control being exerted with the hamstrings. More significantly, the benefits that will
be realized will far outweigh the considerations for comfort. You may want to experiment with both
ankle-joint positions in order to gain a full appreciation of the sensations attributed to each position.

Considerations for Additional Injury Risks
You will want to be extremely careful not to allow for any “bouncing” to occur at the completion
of the eccentric contraction phase of the movement. The bouncing effect creates a hyperextension
effect upon the knee joint which could lead to serious injury to the popatella ligament located
in the front of the knee. As well, bouncing at the bottom of the eccentric contraction phase of
the movement encourages a resulting lifting of the upper torso off the bed. This is particularly evident
during applications on the flat bed. As the head is raised there is a resulting exaggerated arching
of the back which creates a jamming of the facet joints in the lower lumbar region.

This flaw in exercise execution is frequently illustrated when too much resistance is attempted. If
you cannot perform the movement without rising off the bench if effort to provide required momentum
then reduce the resistance before you injure yourself. It is difficult to avoid rising off the bed
when performing the leg curl exercise on a flat bed machine. This is due to the fact that the hip flexors
are attached to the lumbar vertebrae. As the movement is being performed, the hip flexors pull
with great force upon the femur bones of the upper legs driving them into the bed of the machine
which induces a natural lifting of the head which creates a great arching in the back. You may want to
place a cushion or a towel under the hips to provide a base of support in manner of alleviating the
pressure upon the lower lumbar region.

If during the completion of a set, you notice that you are beginning to rise off the bed, then
simply abort the set, reduce the resistance and pump out a high-rep set of perfectly performed repetitions.
Remember, the hamstrings are a comparatively-sensitive muscle group and as such extreme
care must be taken to avoid injuries to the muscles as well as their connective ligaments and tendons.

Particularly vulnerable is the tiny but prominent popliteal muscle located directly behind the
knee. The popliteal muscle is highly susceptible to injury and once injured (even slightly) it can plague
the trainee for a lifetime. Also at risk are the highly-visible, lateral and medial cruciate ligaments
which provide the support for the knee. These ligaments form the chord-like connections on the
outside and inside portions (respectively), of the posterior region of the knee joint.
In addition, the hamstring muscles themselves can become inflamed and stretched, pulled, or
even tom with poor technique and improper weight selection. Always utilize slow speed-ofcontraction
and highly-synchronized movement applications and use a high degree of common sense
when selecting your resistance on the hamstring curl exercise. You would be well-advised to strive
for the “feel” in the muscle on this exercise one rather than testing yourself on how much weight you
can move.

Summary of Correct Exercise Execution
- Assume a face-down prone position on the leg press machine with the head held to one side or
chin touching the bed. If a straight bed is used use the cheek-to-one-side posture to further discourage
any resulting arching of the back.
- Grip the sides of the bed and make certain the rollers are placed across the Achilles tendon of
the foot. You will want to avoid having the rollers come too far up the calves as this would reduce
the effectiveness of the exercise and could result in knee strain due to the inappropriate angle
of exertion associated with the rollers riding up too high. Conversely you will want to make
sure not to place the rollers too far down on the heels as they could slip off resulting in potential
dangerous alteration in pressure that could damage the knee joints.
- Slowly raise the weight upward by utilizing knee-joint flexion. You will want to be sure to raise
the weight through the muscle’s full ROM before pausing for two counts while squeezing the
weight. You will need to: concentrate fully in order to avoid blasting the weight up too quickly
and bouncing the rollers off the gluteals as rapid movement applications on the concentric contraction
phase of the movement could provoke injury to the knees.
- Once at the fully-extended concentric contraction phase of the movement following the twocount
pause, slowly return the weight to the starting position. You will need to avoid the general
pitfall of allowing the weight to return too quickly by utilizing strong neural impulsing to provide
well-controlled muscular contractions.

Keys to the Lift
- Make certain to keep the bead down throughout the movement application
- Utilize slow speed-of-contraction applications
- Exercise caution in selecting the resistance to be used in this movement