Effects of Electrical Stimulation of the Calf Muscles

on Jumping Performance

Nagaoka Daichi

, Ogiso Kazuyuki

, Takenaka Mutsumi

and Tokui Masato

Faculty of education Kogakkan University, Ise, Mie, Japan

Department of Sport Science, Kyusyu Kyoritsu University, 1-8 Jiyugaoka, Yahatanishi-ku, Kitakyusyu, Fukuoka, Japan

1 OBJECTIVES

The calf muscles contract almost isometrically while

the Achilles tendon stretches and shortens during the

contact period when walking (Fukunaga et al.,

2001). This interaction between them makes it

possible for the muscles to exert a larger force and

for the tendinous tissue to function as a spring so

that walking can be performed more efficiently. In

addition, jumping requires an even larger force than

walking, and it is likely then that the functions of the

tendinous tissue influence performance

considerably. However, it is difficult to control the

functions of the tendinous tissue during jumping

because it is not innervated by afferent nerves. In

this study, therefore, to investigate the effects of

tendinous tissue on jumping performance, we

induced lengthening and shortening of the Achilles

tendon by forcibly contracting the calf muscles by

electrical stimulation.

2 METHODS

2.1 Subjects

Fifteen healthy men participated in this study (age,

21.1 ± 1.3 years; height, 173.5 ± 7.0 cm; weight,

69.0 ± 10.5 kg). All subjects were in good health,

with no orthopedic or neuromuscular abnormalities.

Subjects were fully informed of the nature and

possible consequences of the study before providing

written informed consent. The experiments were

conducted in accordance with the Declaration of

Helsinki. Approval was obtained from the Ethics

Committee of Kogakkan University.

2.2 Protocol

Subjects were instructed to perform 10 consecutive

two-legged jumps at maximum effort (100% jump)

and at 50% of the maximal jump height (50% jump).

Jumps were performed on a jump-measuring mat

(PH-1260, DKH, Tokyo, Japan) to measure jump

height, ground contact, and flight time. Subjects

were instructed to place both hands on their waist

and reduce ground contact time as much as possible.

Both normal and electrically stimulated jumps were

performed.

An electrical stimulus was applied over the calf

muscle during the jump at a frequency of 20 Hz

(ES20) or 60 Hz (ES60). Six sets of jumps were

performed with intervals of at least 5 min. Electrical

stimulation intensity was set to 20% of the

maximum ankle plantar-flexion torque, using an

electromyography / evoked potential measuring

system (MEB-2306, NIHON KODEN, Tokyo,

Japan). Two anodes and one cathode were placed on

the proximal and distal ends of the triceps surae

muscle, respectively. Reference marks were placed

on the right caput of the ossis metatarsalis V, ankle

joint, knee joint, greater trochanter, acromion,

tragus, and on the top of the subject’s head.

Jumping movements were filmed in the sagittal

plane with a high-speed camera (300 fps; EXLIM-

F1, CASIO, Tokyo, Japan) with 2 reference marks

placed on the ground at an interval of 2 m. The

subjects were questioned about their jump

performance and asked to rate the force required for

the jump and the ease of control on a 5-point scale

(5: very light or easy; 4: light or easy; 3: normal; 2:

heavy or difficult; 1: very heavy or difficult). In

addition, they were questioned about the extent (1:

none to 5: severe) and location of muscle soreness

each day for 6 days after the experiment.

2.3 Data Processing

The reference points in each frame were

automatically digitized (DARTFISH SOFTWARE,

DARTFISH, Fribourg, Switzerland), smoothed, and

converted to real coordinates. The ankle, knee, and

hip joint angles were computed during the ground

contact phase. Distances between the reference mark

Daichi N., Kazuyuki O., Mutsumi T. and Masato T..

Effects of Electrical Stimulation of the Calf Muscles on Jumping Performance.

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

on the ground in front of the subject and the right

caput of the ossis metatarsalis V (landing point)

were also computed to evaluate the stability of the

jump. The rebound jump index was computed using

the ground contact and flight times obtained from

the jump-measuring mat.

2.4 Statistics

Data are presented as the means ± SD. One-way

analysis of variance was used to analyze the

differences in jumping performance, movement, and

5-grade evaluations of jumping performance and

muscle soreness. Fisher’s post hoc comparison was

performed when significance was found. The

probability level accepted for statistical significance

was p<0.05.

3 RESULTS

Jump height was significantly lower in the 100%

jump with ES60 than in the 100% normal jump. No

significant differences in jump height were observed

between the other conditions (Fig. 1).

Figure 1: Jump height. * and ## denote significant

differences (p<0.05 and p<0.01, respectively) among

jump conditions and between 100% and 50% jumps,

respectively.

Stability of the jump increased significantly in

the 50% jump compared with the 100% jump.

Electrical stimulation had no effect on stability (Fig.

2). The results of the self-evaluations were as

follows: jump performance was rated significantly

lower for 60ES than for 20ES in both the 100% and

50% jumps; force required was rated as high at 20

Hz and almost the same at 60 Hz compared with the

normal jump; whereas ease of control was rated

almost the same at 20 Hz but lower at 60 Hz

compared with the normal jump (Fig. 3).

No obvious differences were observed in angular

displacement of the lower joints during jumps

between the normal, ES20, and ES60 jumps.

Significant differences were observed only in hip

flexion in the 50% jump and in ankle plantar-flexion

in both the 100% and 50% jumps between the

normal and ES60 jumps (Fig. 4).

After the experiment, all subjects reported severe

muscle soreness at the myotendinous junction of the

gastrocnemius muscle. However, it gradually

decreased day by day (Fig. 5).

Figure 2: Distances between the reference mark and

landing point during jumps. # and ## denote significant

differences (p<0.05 and p<0.01, respectively) between

100% and 50% jumps.

Figure 3: Results of self-evaluations on jump performance

by assessing the force required for the jump and ease of

control. * and ** denote significant differences (p<0.05

and p<0.01, respectively) between ES20 and ES60.

4 DISCUSSION

In this study, the intensity of the electrical

stimulation applied to the calf muscle during

jumping was adjusted so that that the calf muscle

could generate 20% of the maximum torque at

frequencies of 20 Hz and 60 Hz. However, electrical

stimulation at 60 Hz did not increase jump height;

instead it significantly decreased it when the jump

was performed at full effort. This may be related to

the difficulty in controlling jumps stimulated at 60

Hz, as revealed by the results of the self-evaluation

on ease of control. This implies that jump height was

sacrificed to stabilize the landing point and may be

supported by the significant decreases in ankle

plantar-flexion during the late contact phase of

jumps stimulated at 60 Hz. On the other hand, for

the electrical stimulation at 20 Hz, subjects reported

performing the jump with less effort, although jump

height remained unchanged. This suggests

appropriate use of the tendinous tissue elasticity

during these jumps.

Figure 4: Angular displacement of flexion and extension

of each joint during the jumps. * denotes significant

differences (p<0.05) among jump conditions.

Subjects reported severe muscle soreness after

the exercise. Since they performed only 6 sets of 10

consecutive two-legged jumps with sufficient

intervals, the pain was likely due to the electrical

stimulation applied to the calf muscle. Muscle

soreness was concentrated at or near the

myotendinous junction of the gastrocnemius muscle.

Muscle strain injury that is caused by combining a

large force with substantial stretch (Garrett, 1990)

has been reported to occur at or near the

myotendinous junction (Tidball et al., 1993), and a

clinical report revealed that most muscle strain

injuries occur at or near the myotendinous junction

during high-intensity or explosive voluntary

movements such as sprint and quick turn (Okuwaki,

2009). Therefore, forced contraction of the calf

muscle by electrical stimulation might induce a large

force with substantial stretch at or near the

myotendinous junction during jumping. However, it

is not clear which experimental condition in the

jump exercise induced the muscle soreness reported

in this study. Further studies are needed to perform

jumps with electrical stimulation applied to the

muscle to ensure safe and appropriate training of the

myotendinous units.

Figure 5: Change in muscle soreness. * and ** denote

significant differences (p<0.05 and p<0.01, respectively)

among days after the experiment.

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