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Figure 2: EMG patterns of vastus lateraris muscle (VL) during a motion of SQT, LP, and iSAAC (one subject). All other
muscles display similar EMG patterns in each exercise. When the knee is extended, the knee joint angle is 0°.
training resistance only while subjects extended their
hip and knee joints. This machine is also able to
calculate the joint torque using sensory information.
In addition, the resistance during exercise could be
varied by control inputs from PC.
2.3 Procedures
Before the execution of the experimental tasks, all
subjects performed 1RM of LP, SQT, and iSAAC.
The value of each 1RM was determined by
gradually increasing the mass of the weight until the
participants thought that they were able to lift no
more than three repetitions. After 3 min of recovery,
they continued lifting until they were unable to lift
the weight; then, we calculated their 1RM by using a
1RM prediction equation (Baechle et al., 2000).
During the experiment, subjects performed eight
repetitions with 70% of their 1RM for each exercise.
Each exercise was performed twice by all subjects.
While subjects were performing the exercise, we
measured the muscle activity of rectus femoris,
vastus lateralis, vastus medialis, biceps femoris,
gluteus maximus, and joint angle of the knee.
Muscle activity was measured using wireless surface
electrodes. The data were collected using Vital
Recorder. Knee joint angle was measured by using a
goniometer. When the knee was fully extended, the
knee joint angle was 0°. The data were collected by
Powerlab and Labchart. The sampling rates of
surface electrodes and goniometer were 1 kHz.
2.4 Data Analysis
We analyzed EMG data using KineAnalyzer. EMG
data were rectified after a filtering process. The data
included one motion of each exercise and one
motion consisting of ascent and descent phases. The
measured data for each subject were normalized to
their movement cycle and averaged.
3 RESULTS
The averaged EMG of vastus lateralis muscle and
knee joint angle in each exercise are shown in Figure
2. Five measured muscle displayed similar EMG
patterns in each exercise. However, these three
exercises display unique EMG patterns. In SQT, all
muscles contracted throughout the motion. On the
other hand, LP and iSAAC displayed peaks during
knee extension. The difference between LP and
iSAAC is that LP displayed another peak during the
descent phase. In iSAAC, all muscles tended to
reach one large peak in the beginning. In addition,
there was no remarkable muscle activity during the
descent phase in iSAAC. This result showed that
these muscles had almost no eccentric contraction in
iSAAC.
4 DISCUSSION
According to the EMG data, LP and SQT featured
muscle activity in both eccentric and concentric
phases. On the other hand, iSAAC featured a brief
period of muscle activity in the concentric phase.
Because iSAAC training required the generation of
explosive concentric power, this training machine is
suitable for sports that requires explosive power
such as football, rugby, and wrestling. Although
iSAAC is a squat-like exercise, result indicates
differences between iSAAC and squat. Further
studies are required to quantitatively analyze muscle