Figure 1. EMG Activity During PlyoPress and Squat Exercises
ABSTRACT:
Ongoing research in athlete training continues to reveal
new principles and training designs which strive to heighten athletic
performance and maximize athletic ability. One example of the
application of such research is the Plyo Press machine,
a patented device used in the Frappier Acceleration Program for
athletes. This device was specifically designed to combine strength
training with plyometrics to enhance speed and dynamic muscle
activity without the excessive low back stress of traditional
training methods. An EMG analysis of selected back and lower extremity
muscles was conducted in an attempt to provide information on
the levels of muscle activity and recruitment elicited by the Plyo Press, and thus verify the claims of its design. Four
different exercises were performed (Plyo Press leg press
and plyojump maneuvers, standing squat lift with weights attached
to a shoulder bar, and a vertical jump) and the EMG activity levels
compared with one another. This comparison revealed that the Plyo
Press does indeed provide a unique, safe, and specific method
of training for athletes, particularly in the enhancement of Vastus
Lateralis activity without excessive low back stress.
PURPOSE:
The Plyo Press was designed with several features
that were believed to maximize training benefits while minimizing
risks. Because of the novelty of the Plyo Press strengthening
device, no scientific investigations exploring the actual effects
this machine had on strength and power training. Therefore, this
study was needed to determine whether or not the claims made of
the Plyo Press device are valid. The main focus of this
study was three-fold: 1) to compare muscle activity and timing
of recruitment during the Plyo Press exercises, a free
weight squat lift, and a vertical jump, 2) to compare the use
of a pelvic stabilization belt during the Plyo Press exercises,
and 3) to determine whether or not prior training affects muscle
recruitment during Plyo Press activities.
METHODS:
Subjects. Ten healthy athletes participated as subjects
with an average age of 25 years. There were two groups of subjects:
1)Trained: utilized the Plyo PressJ
regularly in their training routines, and 2) Untrained: unfamiliar
with the Plyo PressJ. 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 Telemyo8J
transmitter/receiver. Procedure. The exercises performed were: 1) plyo-leg presses (with and
without a belt), 2) a plyo-jump, 3) squat lifting, and 4) a vertical
jump. Data Analysis. The EMG
data was analyzed using the MyoSoftJ
software package to compare normalized EMG values. Visual analysis
of the EMG recordings was also performed to determining muscle
timing patterns during the exercises.
RESULTS:
The results showed that the Plyo Press leg press elicited
less EMG activity than did the squat exercise (Fig. 1). However,
the Plyo Press machine appeared to selectively recruit
the VL. The highest level of activity during the Plyo Press plyo-jump occurred in the VL, whereas the highest level of
activity during the vertical jump occurred in the ES (Fig. 2).
With the use of the pelvic stabilization belt, there was an increase
in the activity of the VL (Fig. 3). During the Plyo Press leg
press, the BF and the VL were active throughout the entire exercise.
The ES was active only during the mid-portion of the exercise
and the GM was inactive.
Figure 1. EMG Activity During PlyoPress and Squat Exercises
Figure 2. EMG Activity During Plyojump and Vertical Jump Exercises
Figure 3. EMG Activity With and Without Stabilization Belt
CONCLUSIONS:
The Plyo Press appears to elicit significantly
less Erector Spinae activity during the leg press as compared
to the squat lift; and plyojump as compared to the vertical jump.
The Plyo Press appears to elicit increased dominant activity
levels of the Vastus Lateralis in both the leg press and the plyojump.
The use of a pelvic stabilization belt with the Plyo Press exercises does not appear to significantly effect levels of
muscle activity at loads equal to body weight. Task experience
related to the Plyo Press exercise maneuvers did not appear
to significantly effect the muscle lifting strategy used by the
subjects.