Changes in neck muscle electromyography and forward head posture during carrying of various schoolbags by children

Changes in Neck Muscle Electromyography

and Forward Head Posture During

Carrying of Various Schoolbags

by Children

Minhee Kim

The Graduate School

Yonsei University

Changes in Neck Muscle Electromyography

and Forward Head Posture During

Carrying of Various Schoolbags

by Children

A Masters Thesis

Submitted to the Department of Rehabilitation Therapy

and the Graduate School of Yonsei University

in partial fulfillment of the

requirements for the degree of

Master of Science

Minhee Kim

This certifies that the masters thesis of

Minhee Kim is approved.

Thesis Supervisor : Chunghwi Yi

Ohyun Kwon

Sanghyun Cho

The Graduate School

Yonsei University

Acknowledgements

“I love you, the Lord, all my strength.”

First of all, I must express my heartfelt thanks to God. He has heard my prayer and has encouraged me to write my masters thesis. I praise Him.

I want to express my gratitude to my parents and sister. They have given constant love to me. They have prayed to God for me everyday.

In process of writing my masters thesis, I would like to take this opportunity to express my appreciation to Professor Chunghwi Yi for his guidance and support. He has taught me as a director and took care of me like a father. I also deeply thanks to Professor Ohyun Kwon who gave me sincere advice to improve the quality of this masters thesis. He has impressed me as active attitude of not only a scholar but also a physical therapist. Professor Sanghyun Cho who is my teaching model has helped me to complete this masters thesis. I would also like to thank Professor Hyeseon Jeon and Professor Sung hyun You, for providing encouragement and for helping expand my knowledge.

I give my appreciation to all members of the department of rehabilitation therapy, and especially thank my senior, graduate student, Wongyu Yoo for his intellectual support and guidance. I also give thanks to Mr. Byungkyu Lee for administrative support.

Table of Contents

List of Figures ··· iii

List of Tables ··· iv Abstract ··· v Introduction ··· 1 Method ··· 4 1. Subjects ··· 4 2. Study Design ··· 5 3. Schoolbag Parameters ··· 6 3.1 Schoolbag Weight ··· 6 3.2 Backpack ··· 7 3.3 Double Pack ··· 8

3.4 Modified Double Pack ··· 9

4. Experimental Equipment ··· 10

4.1 Electromyography System ··· 10

4.2 3-D Motion Analysis System ··· 12

5. Statistical Analysis ··· 13

Results ··· 14

1. Neck Muscle Electromyography ··· 14

1.1 Upper Trapezius Electromyography ··· 14

1.3 Midcervical Paraspinals Electromyography ··· 15 2. Neck posture ··· 17 Discussion ··· 19 Conclusion ··· 23 References ··· 24 Abstract in Korean ··· 32

List of Figures

Figure 1. Carrying the backpack ··· 7 Figure 2. Carrying the double pack ··· 8 Figure 3. Carrying the modified double pack ··· 9 Figure 4. Neck muscle activation levels during carrying of schoolbags

in children ··· 16 Figure 5. Forward head posture (FHP) angles and distances during

List of Tables

Table 1. EMG activities during carrying schoolbags in children ··· 15 Table 2. FHP angles and FHP distances during carrying schoolbags

ABSTRACT

Changes in Neck Muscle Electromyography and

Forward Head Posture During Carrying of

Schoolbags by Children

Minhee Kim

Dept. of Rehabilitation Therapy (Physical Therapy Major) The Graduate School Yonsei University

This study tested the effects of three types of backpack on neck posture and neck muscle electromyography (EMG) in children. Independent variables were no pack, backpack (BP), double pack (DP), and modified DP (M-DP), and dependent variables were the neck muscle activities, forward head posture (FHP) angle, and FHP distance. Ten healthy boys and five healthy girls were asked to walk at a speed of 0.8 m/s on a treadmill and the data were recorded for 5-min. The electromyography and kinematics data were obtained from the last 30-sec of each 5-min data-collection

period. Repeated-measures analysis of variance (ANOVA) was used to test for differences in muscle activities, FHP angles, and FHP distances among the carrying of the various schoolbags. The EMG activity of upper trapezius (UT), sternocleidomastoid (SCM), and midcervical paraspinals (MPS) and the FHP angle and distance were significantly higher when carrying a BP than for the other conditions. When carrying a DP, the backward head posture was characterized by an increased FHP negative angle, decreased FHP distance, increased SCM EMG signal, and decreased MPS EMG signal. However, when carrying an M-DP, the FHP angle and distance decreased than carrying a BP and the backward head posture did not appear. These findings indicate that the M-DP minimizes the postural deviation due to the correct distribution of loading.

Introduction

Proper posture is considered to be a state of musculoskeletal balance that involves a minimal amount of stress of strain to the body (Griegel-Morris et al. 1992). Kendall, and McCreary (1983) described a standard for normal alignment involving the theoretical straight line formed by the point of reference consisting of the lobe of the ear, the seventh cervical vertebra, the acromion, the greater trochanter, just anterior to the midline of the knee, and slightly anterior to the lateral malleolus. Deviation from normal alignment (i.e., postural abnormalities) suggests the presence of imbalance and abnormal strain on the musculoskeletal system (Braun 1991).

The forward head posture (FHP) of cervical musculoskeletal abnormalities is usually associated with shortening of the posterior neck extensor muscles and tightening of the anterior neck muscles (Fernandez-de-las-Penas et al. 2005). Also, FHP implies a relatively extended upper cervical spine and a relatively flexed lower cervical spine (McKenzie 1983). FHP has been associated with neck and shoulder pain (Haughie, Fiebert, and Roach 1995). Cureton (1941) found that the mean sagittal plane head posture angle (also called the craniovertebral angle) in more than 600 men was 53.6°, and Raine, and Twomey (1997) reported the value to be 48.9° in 160 adults. A decrease in this angle increases neck and shoulder pain (Moore 2004).

The epidemiological and clinical literature identifies strong associations between spinal posture and backpack (Di Palma, Ferrantelli, and Medici 2005; Jull et al.

2002). Backpacks of various types are widely used by hikers, soldiers, and schoolchildren. Recreational hikers commonly carry subsistence and shelter items in backpacks (Fletcher 1974), and foot soldiers often walk for long distances carrying extremely heavy backpack loads (McCaig, and Gooderson, 1986). Especially in military situations, many studies of the carrying of backpacks have focused on the physiological, biomechanical, and medical aspects (Christie, and Scott 2005; Knapik, Reynolds, and Harman 2004). Many researchers have studied various backpack types and designs with the aim of preventing injuries associated with prolonged load carriage in hikers and soldiers, but few have focused on schoolchildren (Chansirinukor et al. 2001).

Repetitive static and dynamic loading of the spine constitutes a risk factor for low-back, shoulder, and neck pain not only in adults but also in children (Balague, Troussier, and Salminen 1999; Chansirinukor et al. 2001; van Gent et al. 2003). Pascoe et al. (1997) found that the prolonged carrying of heavy backpacks could lead to symptoms of body soreness, aches, pains, and tiredness in children. The adolescent spine differs from the adult spine in two important respects: (i) a child’s skeleton has large amounts of cartilage that is susceptible to repetitive micro trauma, weakness of which decreases soft-tissue flexibility, induces muscle imbalances, and can also lead to injury (Micheli, and Fehlandt 1992); and (ii) the highest rate of growth occurs in schoolchildren when they are 10–15 years of age (Rowland 1996), and they are thought to be less able to withstand stresses that the adult spine can cope with (Grimmer, and Williams 2000).

Recognition of the importance of studies involving children has led to reports on the effects of backpacks on postural changes and musculoskeletal impairments (van Gent et al. 2003). However, many of these studies have focused on the back segments, such as trunk forward lean (Cottalorda, Bourelle, and Gautheron 2004), back-muscle activities (Motmans, Tomlow, and Vissers 2006), and back pain (Skaggs et al. 2006), and there have been few reports on neck posture and muscle activities whilst carrying a backpack. Both back and neck segments are influenced by backpack loads (Grimmer, Nyland, and Milanese 2006). Abnormal postural changes due to the carrying of a backpack may induce round shoulder, FHP, changes in neck muscle activities, and muscle fatigue. Moreover, Brattberg (2004) reported that risk factors such as load carriage, abnormal neck posture, and neck muscle fatigue may induce headache in schoolchildren.

Based on this background, this study assessed the electromyography (EMG) activities of the three neck muscles, the FHP angle, and the FHP distance in children aged 9–11 years while they were carrying three types of schoolbag: backpack (BP), double pack (DP), and modified DP (M-DP).

Method

1.

Subjects

Fifteen children were recruited for this study (ten boys and five girls, aged 10.3 years) from a local elementary school. The subjects were healthy and reported no acute problems that would interfere with their performance in our experiments. The mean body weight and height of the subjects were 33.64 ㎏ and 142.67 ㎝, respectively. All subjects were right-handed. Before the schoolbag testing, the subjects and their parents were informed about the purpose, procedures, and applications of the study, and parental agreement was obtained.

2.

Study Design

The neck muscle activity and neck posture during the carrying of schoolbags were studied in the four trials involving the subjects walking on a treadmill: no pack (NP), BP, DP, and M-DP. The subjects wore lightweight short-sleeve shirts, socks, and sports shoes. In the starting position on the treadmill each subject stood comfortably erect with the knees extended and the feet separated by approximately the shoulder width. All subjects were asked to walk at a speed of 0.8 ㎧, which is a comfortable walking speed for children, and to keep their head looking straight ahead whilst the following gait parameters were recorded for 5-min: (i) the amplitudes of the EMG signals of the upper trapezius (UT), sternocleidomastoid (SCM), and midcervical paraspinals (MPS); and (ii) the positions of markers attached to the C7 spinous process and tragus of the ear (for motion analysis). The EMG and kinematics data were obtained from the last 30-sec of each 5-min data-collection period, since this interval was determined as the interval to analysis because of the significant difference between the first 30-sec of 5-min and the last 30-sec of 5-min by one-way ANOVA in a pilot study. The test order was assigned randomly to prevent any test order effect, and a 10-min rest interval between trials for each subject was provided to avoid muscle fatigue. Before trials, all subjects were given ample time to familiarize themselves with the treadmill walking.

3.

Schoolbag Parameters

3.1 Schoolbag Weight

The schoolbag load weight used in this study was 15% of the body weight (BW), since the load-weight percentage carried by school-age children reportedly varies from 10% to 20% (Grimmer, and Williams 2000; Limon, Valinsky, and Ben-Shalom 2004; Sheir-Neiss et al. 2003; Whittfield, Legg, and Hedderley 2001). Preparative books and weights (1 ㎏) used to achieve this load weight.

3.2 Backpack

The center of the commercially available BP used in this study was between levels T11 and T12 in each subject (Korovessis et al. 2005). The subjects adjusted the shoulder straps of the schoolbag according to their personal comfort preferences.

3.3 Double Pack

The DP consisted of a front pack and a BP of the same type, each weighing 7.5% of the BW. The center of the front pack was positioned at the umbilicus of abdomen, and the subjects adjusted the shoulder straps according to their personal comfort preferences.

3.4 Modified Double Pack

The M-DP was especially made for this study and consisted of two types of packs, with the BP and front pack weighing 10% and 5% of the BW, respectively. The front pack was half the size of the BP, and was attached to the adjustable shoulder straps of the BP by the primary researcher. The front pack was positioned on the sternum (not the abdomen), and its center was located at the xiphoid process of the sternum.

4.

Experimental Equipment

4.1 Electromyography System

EMG data were collected using a Biopac MP100WSW (Biopac System, Santa Barbara, CA, USA) data acquisition system and a Bagnoli EMG system (Delsys, Boston, MA, USA). Ag-AgCl surface EMG electrodes were positioned at an interelectrode distance of 20 ㎜. Electrode sites were prepared using skin abrasion and by cleansing the area with an alcohol. The active surface electrodes were aligned approximately parallel to the direction of the muscle fibers. The electrode sites were located on each subject’s dominant right side as follows (Cram, Kasman, and Holtz 1998): (i) UT, 2 ㎝ lateral to the midline drawn between the C7 spinous process and the posterolateral acromion; (ii) SCM, 2 ㎝ distal to the muscle insertion at the mastoid process; and (iii) MPS, 2 ㎝ lateral to the midline of the spine approximately at the C4 level.

All EMG signals were amplified, bandpass (20 ㎐ to 450 ㎐) and bandstop (60

㎐) filtered, and digitized at 1000 ㎐ using AcqKnowledge software (Biopac System,

Santa Barbara, CA, USA). The root mean square (RMS) values of the raw data were calculated, with the amplitude normalized to reference voluntary contractions (RVC) rather than to the maximal voluntary contractions so as to reduce the risk of injury or residual muscle soreness, especially in the neck and shoulder (Harms-Ringdahl, and Ekholm 1986). The reference contractions of the SCM and MPS were determined

whilst the subjects looked straight ahead whilst keeping the neck in line with the spine in the supine position (Babski-Reeves, Stanfield, and Hughes 2005). The UT reference contractions were determined by holding with arms abducted 90° in the frontal plane and parallel to the floor (Babski-Reeves, Stanfield, and Hughes 2005). Subjects completed three 5-sec exertions with a 1-min rest period between contractions. EMG data collected during walking on the treadmill for 5-min are expressed as the %RVC.

4.2 3-D Motion Analysis System

A 3-D ultrasonic motion analysis system (CMS-HS, Zebris, Medizintechnik, Isny, Germany) was used to measure the FHP angle and the FHP distance of the head. The positions of the two markers were sampled at 20 ㎐ during walking on the treadmill for 5-min. The markers were visible to the measuring sensor, which consisted of three microphones used to record the ultrasonic signals.

The FHP angle was defined as the angle between a horizontal line at C7 and a line from the tragus of the ear to the spinous process of C7 (Fernandez-de-las-Penas et al., 2005). The measured angles were normalized to 0° degrees relative to the starting position, namely neutral position, where a larger positive FHP angle than 0° degrees indicated an increase in the FHP, and a larger negative FHP angle than 0° degrees indicated an increase in the backward head posture. The FHP distance was defined as the distance between X-axis positions of the markers on the C7 and the tragus, with an increased value of this distance compared with the starting position indicating the presence of FHP. The collected kinematics data were analyzed by Win-data software (ver. 2.19, Zebris, Medizintechnik, Isny, Germany).

5.

Statistical Analysis

To test for differences in muscle activities, FHP angles, and FHP distances among the carrying of the various schoolbags, repeated one-way analysis of variance (ANOVA) was used to determine if there was a significant effect of muscle and posture. For the significant main effect, Bonferroni’s correction was performed to identify the specific mean differences. Differences were defined as significant at

Results

1. Neck Muscle Electromyography

1.1 Upper Trapezius Electromyography

The normalized EMG data are presented in Table 1. The EMG activity was significantly higher while carrying the BP, DP, and M-DP then when walking with NP (p<0.05) (Table 1) (Figure 4). The EMG activity did not differ significantly among the BP, DP and M-DP (Figure 4).

1.2 Sternocleidomastoid Electromyography

As can be seen in Table 1, the SCM EMG activity increased when the load was carried by the BP or DP than by the NP (p<0.05), and was significantly lower for the M-DP than for the BP or DP (p<0.05) (Figure 4). In addition, the difference of SCM EMG activity was not significant between the NP and the M-DP (Figure 4).

1.3 Midcervical Paraspinals Electromyography

The normalized EMG activity of the MPS, shown in Table 1, increased in order of DP<NP<M-DP<BP, with the increase being most significant for the BP (p<0.05) and with the decrease being most significant for the DP (p<0.05) (Table 1). There was no significant difference between the M-DP and NP (Figure 4).

Table 1. EMG activities during carrying schoolbags in children (N=15) EMG (%RVC, mean±SD)

No pack Back pack Double pack Modified DP p

UT a 23.48±2.35 33.25±4.25 39.50±12.20 35.23±6.46 0.000 SCM b 14.04±7.11 22.76±12.53 24.50±11.21 17.66±10.50 0.001 MPS c 26.40±9.36 37.99±14.96 22.23±7.49 28.36±11.45 0.000 a UT : Upper Trapezius. b SCM : Sternocleidomastoid. c MPS : Midcervical Paraspinals.

UT SCM MPS 0 10 20 30 40 50 60

No pack Backpack Double pack Modified DP

*

*

*

*

*

*

*

% R V C

Figure 4. Neck muscle activation levels during carrying of schoolbags in children (Bonferroni’s correction). UT: upper trapezius, SCM: sternocleidomastoid, MPS: midcervical paraspinals. *Significantly different from NP (padj<0.05/6).

2. Neck Posture

Table 2 shows the FHP angle and FHP distance. The one-way ANOVA revealed significant overall changes. The mean FHP angle was most increased significantly when carrying the BP (p<0.05) (Figure 5). The mean FHP angle was lowest for the DP, and its value was of opposite sign (Table 2). Carrying the M-DP had the smallest effect as compared with carrying the NP (p>0.05) (Figure 5). The mean FHP distance increased more for the BP was than for NP and the DP and M-DP (Table 2). The mean FHP distance for the DP was smaller than for the NP, at nearly zero (p<0.05) (Figure 5). There was no significant difference between the NP and the M-DP.

Table 2. FHP angles and FHP distances during carrying schoolbags in children (N=15) Forward head posture (FHP, mean±SD)

No pack Back pack Double pack Modified DP p

Angle

(°) 4.10±3.49 7.53±5.34 -0.70±5.06 5.02±3.43 0.004 Distance

NP BP DP M-DP -10 -5 0 5 10 15

*

*

No pack Backpack Double pack

Modified double pack

A F H P a n g le ( d e g r e e s) NP BP DP M-DP 0 10 20 30 40 50 60 70 No pack Backpack Double pack

Modified double pack

*

*

B F H P d is ta n c e ( m m )

Figure 5. Forward head posture (FHP) angles and FHP distances during carrying of schoolbags in children (Bonferroni’s correction). *Significantly different from NP (padj<0.05/6).

Discussion

The purpose of this study was characterize the neck muscle activity, FHP angle, and FHP distance for NP (control) and when carrying the BP, DP, and M-DP. The measured EMG activities of three muscles (UT, SCM, and MPS) were significantly higher for BP than when carrying the NP. Moreover, the FHP angle and FHP distance increased significantly for the BP, which reflects the induction of FHP. The COG of the upper body is normally located slightly forward of the lumbosacral joint. However, the addition of a load on the back results in the combined COG of the body plus pack shifts backward and creates extension moments (Bobet, and Norman 1984), which is counterbalanced by both a forward trunk lean and a forward head shift (Goh, Thambyah, and Bose 1998).

Theoretically, an anterior shift in the COG of the head elicits the head and neck postural reflexes involving the vestibulocollic (Wilson et al. 1995), cervicocollic (Peterson et al. 1985), and cervical-facet mechanoreceptors. These respond to the forward head position of the postural stimulation by actively orienting the trunk’s COG under the head’s COG (Morningstar, Strauchman, and Gilmour 2004). Although this postural change maintains efficient body locomotion by minimizing the energy expenditure (Adkin et al. 2000), when sustained this abnormal posture induces musculoskeletal pain.

For the DP, the UT and SCM electrical activities were significantly higher than for NP and the M-DP. The FHP angle was significantly increased for the DP, but this was in the opposite direction. This indicates that the head was shifted backward relative to the starting position. As the head moves backward, beyond the neutral position, it was considered that the SCM activity increased greatly to counteract the head backward movement.

Motmans, Tomlow, and Vissers (2006) reported that the trunk posture was shifted backward while carrying a front pack and Fiolkowski et al. (2006) reported that carrying a front pack resulted in the head being moved backward relative to control (i.e., no BP). Similarly, the results of the present study for the DP are consistent with the results of these front pack study. This can be explained by moments, which are the forces acting over a distance (moment ＝ force × distance). The distance between the front pack (at the abdomen) and spine is greater than that between the BP and the spine, so the flexion moment is larger than the extension moment for an equivalent weight loading. This would result in a backward head posture to compensate the flexion moment when carrying the DP, same as the effect of carrying a front pack. The associated trunk and pelvis posture accompanied by changes in the head and neck may result in a response. However, we found only changes in the head and neck, and hence future investigations should focus on from the head and neck to the trunk and pelvis.

The M-DP investigated in this study was designed to minimize gravity-induced stresses on body tissues and changes in the COG. The M-DP was designed to

improve the restriction of the abdomen of the DP. Knapik, Reynolds, and Harman (1997) reported that the DP could result in movement inhibition, respiratory ventilation reduction, and discomfort due to restriction of the abdomen.

We found that UT EMG activity significantly increased, SCM and MPS EMG activity was slightly increased, not significantly, for the compared with the NP condition. The UT was exposed to a constant load in all conditions, resulted in increased muscle activity and the induction of fatigue. The mean FHP angle and FHP distance were significantly lower for the M-DP than for the BP, and were slightly increased (but not significantly) relative to the NP condition. As a result, it was showed that carrying the DP was made little FHP, but this difference with the M-DP was less than the forward head with the BP and than the backward head with the DP. This represents evidence that M-DP minimized FHP, but even so this indicates that carrying heavy load included M-DP for long time may cause the postural abnormality.

These observations can be attributed to two factors when using the M-DP. First, distributing the pack weight to the back and front in the ratio 2:1 resulted in the correct moment being maintained between the back and front. In children, 9-11 yrs in this study, there was protruded abdomen and not well developed breast. The decreased distance between the center of a front pack and spine due to shift the load from on the abdomen to on the sternum further improved the moment balance (Grimmer et al. 2002). Second, the smaller size of the front pack of the M-DP resulted in it not pressing against the abdomen, which therefore may did not cause

discomfort due to restriction of the abdomen. Lloyd, and Cooke (2000) reported that the presence of comfort and safety during walking may effect an upright posture.

There are data indicating that sustaining the head in protraction leads to pain over the dorsal aspect of the cervical and upper thoracic spine (Harms-Ringdahl, and Ekholm 1986). This may be explained by the increase in stress due to the neck shifting forward of its normal posture, with the compressive forces on the neck increasing due to the additional weight of the head. When the head moves forward, the body COG will shift anteriorly to compensate for the weight shift, and the upper trunk will drift backward. Besides, to complete the compensatory changes in posture, an anterior tilts will appear in the pelvis (Fiolkowski et al. 2006). So, the presence of FHP can cause pain not only in the head and neck, but also in the lumbar spine and pelvis.

The use of the treadmill in this study allowed a consistent walking speed and simulated the environment of walking in the street. In general, the kinematics data and EMG activity obtained at both slow and fast speeds do not differ between treadmill walking and floor walking (Myrray et al. 1985). However, there are limited data on the similarity between treadmill walking and ground walking. Also, our data were obtained during short recording time from small sample size, so we cannot explain longer duration changes in the neck muscle EMG and the FHP appearance. It is need to study recruited many schoolchildren and to record the EMG and postures for long duration.

Conclusion

In this study, we have found that the backpack (BP) was increased the maximal forward head posture, and the double pack (DP) was induced the backward head posture beyond the neutral. However, modified double pack (M-DP) decreased the deviation of head and neck posture in children. It is considered that the M-DP minimizes the forward head posture by redistributing the carried loads and by reducing the load size. Many schoolchildren carry heavy schoolbags for long periods, and hence it is recommended that they use the M-DP.

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국문 요약

아동에게

아동에게

아동에게

아동에게

_다양한

다양한

다양한

다양한

_책가방

책가방

책가방

책가방

_적용

적용

적용

적용

_시

시

시

시

_{목주변근의}

목주변근의

목주변근의

목주변근의

근전도와

근전도와

근전도와

근전도와

_{전방머리자세의}

전방머리자세의

전방머리자세의

전방머리자세의

_변화

변화

변화

변화

연세대학교 대학원

재활학과(물리치료학 전공)

김 민 희

본 연구는 아동이 3 가지 종류의 책가방을 착용했을 때 나타나는 목주변근의 근전도와 전방머리자세의 변화를 평가하기 위해 시행되었다. 독립변수는 가방을 메지 않은 상태(대조군), 뒤에만 가방을 멘 상태, 뒤와 앞에 가방을 멘 상태, 앞 가방의 무게와 크기를 뒤에 멘 가방의 2 분의 1 로 줄여 앞과 뒤에 가방을 멘 상태로 4 가지 조건이었고, 종속변수는 목주변근의 근활성도, 전방머리자세 각도, 그리고 전방머리자세 거리였다. 연구대상자는 15 명의 초등학생들이었으며 책가방을 메고 트레드밀 위에서 0.8 ㎧의 속도로 5 분 동안 걷게 하였다. 5 분의 데이터 중 구간별

차이분석을 통해 유의한 차이를 보인 마지막 30 초의 데이터를 분석에 사용하였다. 각 조건에서의 차이를 알아보기 위해 반복측정된 일원분산분석을 하였으며, 본페로니 수정법을 통해 사후검정을 하였다. 연구 결과, 등에만 가방을 착용했을 때 모든 종속변수에서 유의한 증가를 보여 전방머리 각도 변화량이 가장 크게 나타났다. 뒤와 앞에 가방을 착용했을 때 전방머리자세 각도는 음의 값을 보였고, 전방머리자세 거리는 감소하였으며, 목빗근의 근활성도가 뚜렷한 증가를 보여 후방머리자세가 유발되었음을 알 수 있었다. 앞 가방의 무게와 크기를 줄여 앞에 착용하고 기존의 가방을 뒤에 착용하게 한 조건에서는 뒤에만 가방을 멘 조건보다는 전방머리자세가 유의하게 감소하였다. 이러한 결과는 책가방을 장시간 착용하는 아동들의 적절하고 바른 가방 착용을 위한 기초자료로 사용될 수 있을 것이다. 핵심되는 말: 근전도, 아동, 전방머리자세, 책가방.