EMG Pattern of Lower Extremity Muscle for iSAAC

a New Resistance Training Machine

Seiichi Yokoi

, Toyoyuki Honjo

, Naruhiro Shiozawa

, Toshiyuki Kurihara

Takatoshi Higuchi

and Tadao Isaka

Graduate School of Sports and Health Science, Ritsumeikan University,

1-1-1, Nojihigashi, Kusatsu, Shiga, 525-8577, Japan

Ritsumeikan Global Innovation Research Organization, Ritsumeikan University,

1-1-1, Nojihigashi, Kusatsu, Shiga, 525-8577, Japan

Keywords: EMG, Concentric Contraction, Lower Extremity Muscles, Resistance Training.

Abstract: Many researchers have investigated muscle contraction, often focusing on eccentric contraction. However,

some studies have revealed that concentric-only training contributes to increased concentric strength.

Moreover, eccentric contraction induces more muscle damage than concentric contraction. Even though

there is great demand for eccentric contraction in practice, concentric contraction is essential for an athlete’s

performance. To focus on concentric contraction exercise, we developed a concentric-only exercise machine

designated Intelligent System of Advanced Actuation for Concentric Training (iSAAC). In this study, we

compared the EMG patterns of squat (SQT), seated leg press (LP), and iSAAC. We observed a unique EMG

pattern and the generation of explosive power during knee extension with iSAAC. Therefore, iSAAC

enables athletes to enhance the concentric strength of their lower extremity muscles.

1 OBJECTIVES

Resistance training is essential to improve the

performance of athletes. Recent studies have shown

the effects of concentric and eccentric contraction.

Some researchers reported that eccentric contraction

induces greater muscle hypertrophy than concentric

contraction. However, it also causes greater muscle

damage than concentric contraction (Seger et al.,

1998). Concentric-only exercise causes a greater

increase in concentric strength than eccentric-only

exercise (Blazevich et al., 2007). Moreover,

concentric isokinetic training improves jumping

performance (Kovačević et al., 2013). Therefore,

concentric training is necessary for athletes to

improve their concentric strength and power. In

order to induce these concentric training effects, we

developed a concentric-only exercise machine

designated Intelligent System of Advanced

Actuation for Concentric Training (iSAAC).

The purpose of this study is to use surface EMG

for comparing lower extremity muscle activity

during iSAAC, back squat (SQT), and seated leg

press (LP). We selected these exercises because they

generate similar movements of the lower

extremities.

2 METHODS

2.1 Subjects

Five male college students participated in this

experiment. Their age, height, and mass were 21.2 ±

0.4 years, 171.2 ± 6.2 cm, and 65.0 ± 7.3 kg,

respectively.

2.2 Details about iSAAC

iSAAC provides cyclic concentric-only training of

the lower extremities. iSAAC adopts braking force

as resistance load. Because braking force is less than

or equal to human generated force, iSAAC is a safe

training machine. The timing of applying resistance

is determined by knee joint angle that is measured

by goniometer. Therefore, the iSAAC generates

Yokoi S., Honjo T., Shiozawa N., Kurihara T., Higuchi T. and Isaka T..

EMG Pattern of Lower Extremity Muscle for iSAAC a New Resistance Training Machine.

 2014 SCITEPRESS (Science and Technology Publications, Lda.)

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

activity with iSAAC and to investigate the short-

and long-term training effects of iSAAC.

ACKNOWLEDGEMENTS

This work was supported by a grant from JSPS

KAKENHI (No. 24300220).

REFERENCES

Baechle, T. R., Earle, R.W., 2000. Essentials of strength

training and conditioning, Human Kinetics,

Champaign, IL, 2

edition.

Blazevich, A. J., et al., 2007. "Influence of concentric and

eccentric resistance training on architectural

adaptation in human quadriceps muscles." J Appl

Physiol 103(5): 1565-1575.

Seger, J. Y., et al., 1998. "Specific effects of eccentric and

concentric training on muscle strength and

morphology in humans." Eur J Appl Physiol Occup

Physiol 79(1): 49-57.

Kovačević, Erol, et al., 2013 "The effects of concentric

isokinetic training on jumping performance." Homo

Sporticus 15.2: 29-34.