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
(㎜) 27.08±7.24 43.31±17.89 9.04±13.35 31.39±14.41 0.001
NP BP DP M-DP
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
아동에게아동에게
아동에게아동에게 다양한다양한다양한다양한 책가방책가방책가방책가방 적용적용적용적용 시시시시 목주변근의목주변근의목주변근의목주변근의 근전도와
근전도와근전도와
근전도와 전방머리자세의전방머리자세의전방머리자세의전방머리자세의 변화변화변화변화
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.