ABSTRACT:
Strength training is a primary
factor in athletics and rehabilitation. Lower extremity strength
training has traditionally consisted of free weights,
biomechanically designed weight machines, or plyometrics. The
PlyoPress is a machine that is currently being utilized in the
Frappier Acceleration Program for athletes. It is specifically
designed for lower extremity strength training in combination
with plyometrics. The principle behind its design is to build
strength in the most effective way to enhance speed and dynamic
activity without the stress to the low back or legs that is
present with the use of free weights. However, there has been
limited research conducted on the machine to validate the
manufacturer’s claims. Therefore, the purpose of this study
was to compare muscle recruitment during, 1) a leg press in the
PyloPress leg machine, 2) a plyo-jump in the PlyoPress, and 3) a
traditional squat lift. An EMG analysis was performed on selected
trunk and lower extremity muscles in order to provide information
on the muscle activity and recruitment pattern evoked by the
three activities. Sixteen, healthy, trained, male subjects were
loaded down with 80% of their previously determined one
repetition maximum and performed three repetitions of each
exercise. An analysis of the normalized EMG data was conducted
using the Myosoft and Norquest software package. The results of
the study revealed that the PlyoPress appeared to specifically
recruit the vastus lateralis muscle during each of the exercises.
The PlyoPress appears to offer the advantage of specifically
training the vastus lateralis with less recruitment of other
lower extremity and back muscles relative to a squat lift.
PURPOSE:
The purpose of
this study was to compare the trunk and lower extremity muscle
activity during a PlyoPress leg press, a plyojump, and a
traditional free weight squat.
METHODS:
Subjects. Sixteen, healthy, trained athletes participated as subjects.
The average age of the subjects was 22 years. All the subjects
were currently engaged in a training program at least one or more
times per week, and were able to safely squat a weight equal to
80% of their 1 repetition maximum. All subjects were using the
PlyoPress in their weight training program. Instrumentation. EMG activity was recorded from the erector spinae (ES),
gluteus maximus (GM), vastus lateralis (VL), and biceps femoris
(BF). The EMG data was recorded using the Noraxon Telemyo8 transmitter/receiver.
Procedure. The exercises
performed were: 1) a PlyoPress leg press, 2) a plyo-jump
performed in the PlyoPress, and 3) a traditional squat lift. Each
subject performed three repetitions of each exercise using a
weight equivalent to 80% of their one repetition maximum. Data Analysis. The EMG data
was analyzed using the MyoSoft and Norquest software packages. A
comparison was made of the normalized EMG values recorded during
the three exercises
RESULTS:
The results
showed that the leg press elicited less EMG activity than did the
traditional squat exercise (Fig. 1). The highest level of muscle
activity during the leg press occurred in the VL; whereas the
highest level of activity during the squat occurred in the ES.
Both the leg press and the squat produced the least amount of
activity in the biceps femoris. The plyo-jump caused more
activity in all of the muscles than did the leg press. The
plyo-jump caused more activity in the VL than did the squat, but
the squat recruited the ES to a greater extent than did the plyo-jump.
Figure 1. Comparison of PlyoPress, PlyoJump and Squat exercises.
CLINICAL IMPLICATIONS:
The
PlyoPress appears to elicit less Erector Spinae activity during
the leg press as compared to a squat lift. However, both the leg
press and the squat lift recruited high levels of activity in the
vastus lateralis and erector spinae. There seems to be some
evidence to suggest that the leg press causes less erector spinae
recruitment which may be beneficial for preventing back muscle
strain.