1. INTRODUCTION:

This indicates that ambulance workers are working in a very inadequate environment, as compared to people in other duties. Although ambulance workers are in a special condition that requires strong physical strength, their safety and health are at risk and they suffer from various symptoms. These factors can reduce their physical strength and have a huge negative effect on their health¹.

Shin conducted a survey of musculoskeletal symptoms among 167 ambulance workers in the Gangnam fire station in Seoul. According to the results of the survey, the prevalence rate was high in the shoulders (35%), back (34%), neck (26%), and legs/feet (25%). On the scale from 0 to 10, the pain was rated 5.62 in the back and 5.33 in shoulders^2,3. Also, Kim stated that ambulance workers have twice to three times higher prevalence rate of back pains than people in other duties. The prevalence rate for each body part was 16.1% for the back and 11.1% for shoulders⁴. Kang also reported that ambulance workers have a higher rate of musculoskeletal symptoms, as compared to people in other jobs. He mentioned that 49.4% of ambulance workers suffer from musculoskeletal symptoms. The prevalence rate was the highest in back the (33.2%), 22.0% in shoulders, and 15.1% in the neck^5,6.

Since emergency medical technicians must wear helmets in every mission, some of them suffer from musculoskeletal symptoms in the neck or shoulders. Although the weight of the helmet is ca. 2 or 3kg, substantial pressure is loaded on fine muscles around shoulders and the neck. Since emergency medical technicians need dynamic movements with the helmet, such as running and carrying, rather than static movements, the load can be greater than the weight of the helmet^7,8.

Although there are many studies on musculoskeletal disease of emergency medical technicians, most of them are conducted with questionnaires. Therefore, it is difficult to investigate objective causes of the disease.

In order to assess muscle activity, Subjective Discomfort (Bong's CR-10 Scale) assessment method is nowadays used. However, we do not have sufficient EMG research that objectively analyzes muscle activity and movement analysis objectively. Moreover, there has been no research of transferring patients using stretchers with or without helmets^9,10.

Therefore, this study seeks to investigate the difference in muscle activity of ambulance workers, with and without helmets, through the analysis of their muscle activity. We will also suggest ways to reduce their musculoskeletal symptoms.

2. MATERIALS AND METHODS:

2.1. Subject of study:

Fifteen ambulance workers participated in this study. The workers did not have any musculoskeletal disease, record of surgical operation, or neurological disorder. They did not have any problem with their range of motion. They implemented transfer using stretchers. Every subject fully understood the purpose and methods of this study. They participated on voluntary agreement. Physical characteristics of the participants are age (25.0±1.73 years), height (172.0±4.36 cm), Weight (71.67±14.57 kg).

2.2. Measuring tools and methods:

For image recording and movement analysis, we used six infrared cameras (Motion master 100, Visol, USA) to record the movements of the participants. Each high speed camera was synchronized using LAN cables. The speed of camera was set at 100 frame/s in order to get three-dimensional spatial coordinates. For that purpose, we installed a control object (width 1m, length 1m and height 2m) in which the participant could sit down and stand up. Then we activated all six cameras and recorded them for 10 seconds before removing. The total weight that the participants lifted was 64.1 kg (6.1 kg of long spinal immobilizer and a 58 kg patient). Each participant lifted 32.5 kg and the movement analysis was conducted on the participant who lifted the stretcher standing at the patient‘s legs. To find the centroid of an asymmetric object, we hung a pendulum and drew two vertical lines. Then we found the point where the two lines met. To set the reference frame in a real space, we set the direction where a participant was looking at the stretcher as ‘Y axis’. We set the vertical direction to the ground as ‘Z axis’. Then we set the cross product from Z axis to Y axis as ‘X axis’¹².

In this study, we set three events and two phases for the experiment in order to conduct a three-dimensional image analysis of the movements that repeat sitting down and standing up with a stretcher. Event 1 is the moment when the participants are standing and are holding the stretcher. Event 2 is the moment when the participants sit down holding the stretcher and the stretcher touches the ground. Event 3 is the moment when the participants stand up with a stretcher and the stretcher is at the highest point from the ground. We regarded Events 1 and 2 as the Down Phase and Events 2 and 3 as the Up Phase. Figure 1 illustrates the distribution of events and phases.

For image analysis, we attached reflective markers with 10mm size on each constituent part of the body. The locations of the markers are indicated in Figure 2. Using VISOL‘s Kwon3D XP Software Package (Ver. 4.0), we collected and processed the raw data from the attached reflective markers. As the participants repeated sitting down and standing up with a stretcher, we analyzed the angles of their neck, back, and shoulders^13-16. To measure the muscle activity, we used Telomyo DTS (Noraxon Inc., USA) and measured electromyographic signal in upper body muscle. After sending the electro myographic analog signal to Telomyo DTS and converting it into digital signal, we conducted filtering and other signal processing using CR-XP Master program (Noraxon Inc., USA). The sampling rate of electromyographic signals was 100Hz. To remove 20-250Hz band pass filter and noise, we used a 60Hz notch filter. The collected signals went through a full wave rectification and were processed as the root mean square (RMS). To reduce skin resistance on the parts where surface electrodes were attached, we removed hairs from the skin using a shaver and scrubbed the skin with fine sandpaper. Then we rubbed using cotton with alcohol to remove the keratin layer. The interval between two attached electrodes was 2cm. For the relevant muscles and points where the electrodes were attached. See Table 1 and Figure 2

Figure 1.Distribution of events and phases

Table 1: Abbreviations of muscle names

Sternocleidomastoid	Splenius	Trapezius muscle	Backbone erector
Rt_SCM	Rt_CervicalPS	Rt_Trapezius	Rt_Erectorspinae
Lt_SCM	Lt_CervicalPS	Lt_Trapezius	Lt_Erectorspinae

Figure 2. Distribution of events and phases

The long spinal immobilizer (manufacturer: Ferno, USA) consists of a spinal immobilizer, head fixing string, head pad, and belt. Its weight is 6.1kg, size is 183 x 42 x 4.4cm, and maximum load is 275 kg. Its manufacturer is Ferno of USA. A rescue helmet for firefighting functions to protect the head and upper face of a firefighter from various risk factors generated at fields of fire and rescue. Its weight is 900g, the circumference is 64 cm, and color is green. It can be rapidly put on the head and its size is adjustable. The string is also adjustable in three directions, ensuring stability and perfect fixing^17-19. The manufacturer is Sancheong Co., Ltd. of Korea.

2.3. Data processing and analysis method:

To collect the data, 15 ambulance workers who participated in this study performed lifting and lowering a stretcher before and after wearing helmets. At the same time, we compared the upper body muscles including Rt_SCM, Lt_SCM, Rt_CervicalPS, Lt_CervicalPS, Rt_Trapezius, Lt_TrapeziusRt_Erectorspinae, and Lt_Erectorspinae. Using SPSS ver. 21.0, we performed descriptive statistics for each situation in each part. To verify the difference before and after wearing helmets, we used a paired t-test method.

3. RESULTS AND DISCUSSION:

Table 2 and Figure 3 indicate the muscle activity of upper body when lowering the stretcher before and after wearing helmets. The muscle activity was the highest in trapezius muscle, followed, in the descending order, by erector spinae muscle, splenius capitis and sternocleidomastoid muscle. In the right sternocleidomastoid muscle, it was 13.52±2.47μV without a helmet and 19.15±5.22μV with a helmet (p<.005). In the right splenius capitis, it was 25.56±4.80μV without a helmet and 46.07±19.44 (p<.001) and with a helmet. In the left splenius capitis, it was 26.11±4.51μV without a helmet and 34.00±11.41μV with a helmet (p<.05). In the right trapezius muscle, it was 107.50±22.94μV without a helmet and 144.13±61.04μV with a helmet (p<.05). In the left erector spinae, it was 84.96±15.37μV without a helmet and 99.31±18.97μV with a helmet (p<.005). The difference between them was statistically significant.

Table 2: Comparison of muscle activity of upper body muscle during lowering a stretcher with a helmet

(Unit : μV)
P1	No Helmet	Helmet	t	p
P1	Mean±SD		t	p
Rt_SCM	13.52±2.47	19.15±5.22	-3.513	.003**
Lt_SCM	15.09±4.83	16.59±5.17	-1.379	.189
Rt_CercicalPS	25.56±4.80	46.07±19.44	-4.413	.001***
Lt_CercicalPS	26.11±4.51	34.00±11.41	-2.438	.029*
Rt_Trapezius	107.50±22.94	144.13±61.04	-2.573	.022*
Lt_Trapezius	117.62±65.33	119.05±45.64	-.090	.930
Rt_Erectorspinae	96.28±14.22	96.38±28.02	-.016	.988
Lt_Erectorspinae	84.96±15.37	99.31±18.97	-3.446	.004**

Figure 3.Comparison of Muscle Activity of Upper Body Muscle during Lowering Stretcher with Helmet

Table 3 and Figure 4 indicate the muscle activity of upper body when lifting a stretcher before and after wearing helmets. The muscle activity was the highest in the erector spinae muscle, followed, in the descending order, by trapezius muscle, splenius capitis, and sternocleidomastoid muscle. In the left splenius capitis, it was 28.22±7.86μV without a helmet and 40.16±13.76μV with a helmet (p<.001). In the left trapezius muscle, it was 42.22±14.46μV without a helmet and 84.14±51.59μV with a helmet (p<.05). In the right erector spinae, it was 121.83±12.71μV without a helmet and 120.76±28.83μV with a helmet (p<.001). The difference between them was statistically significant.

Table 3: Comparison of muscle activity of upper body muscle while the worker was lifting the stretcher with helmet

(Unit : μV)
P1	No Helmet	Helmet	t	p
P1	Mean±SD		t	p
Rt_SCM	13.16±1.31	13.37±3.47	-.270	.791
Lt_SCM	13.39±2.03	13.71±3.12	-.283	.781
Rt_CercicalPS	26.53±7.58	34.61±11.95	-1.978	.068
Lt_CercicalPS	28.22±7.86	40.16±13.76	-3.646	.003**
Rt_Trapezius	71.94±22.45	94.69±34.55	-1.952	.071
Lt_Trapezius	42.22±14.46	84.14±51.59	-2.806	.014*
Rt_Erectorspinae	121.83±12.71	153.38±11.41	-8.645	.000***
Lt_Erectorspinae	127.59±22.31	120.76±28.83	.970	.349

The incidence rate of musculoskeletal disease at workplace has remarkably increased. Since musculoskeletal disease occurred in all types of occupations these days, it is very important to have an appropriate posture at work to remove the risk of musculoskeletal disease. Among work-related musculoskeletal diseases, backaches are particularly frequent among nurses and ambulance workers. The symptoms are benign in the initial stage and are not regarded as serious problems. However, they get worse later, often to the degree when they considerably complicate the sufferer’s everyday life. Backaches easily recur and can become chronic. Therefore, it is crucial to have appropriate posture at work. Ambulance workers need to repeat movements with a great deal of stress. Although more and more ambulance workers suffer from musculo skeletal disease, there is a lack of scientific research on this issue and its prevention. In this study, we analyzed the upper body angle and muscle activity of 15 ambulance workers when they were carrying a patient on a stretcher with or without helmets.

Figure 4.Comparison of Muscle Activity of Upper Body Muscle while raising a stretcher with and without a helmet

We calculated the upper body muscle activity when lowering a stretcher. It was high in the right sternocleidomastoid muscle (p<.005), right splenius capitis (p<.001), left splenius capitis (p<.05), right trapezius muscle (p<.05), and left erector spinae muscle (p<.005) when the ambulance worker was wearing a helmet. The difference between them was statistically significant. In the variation of neck angle, there was more hyperextension in P1 with a helmet. The study by Lee indicated that the muscle activity and muscle fatigue of sternocleidomastoid muscle and splenius capitis were higher when the participants extended their necks to look upward¹¹.

We calculated the upper body muscle activity when lifting a stretcher. It was high in the left splenius capitis (p<.001), left trapezius muscle (p<.05), and right erector spinae muscle (p<.001). The difference between them was statistically significant. According to the movement analysis of lifting a stretcher, the angle of the neck, back, and shoulders was considerable with a helmet. We estimate that the muscle activity became bigger in the muscles that influence the movements of the neck and back, as the angles became bigger. Weon reported that the trapezius muscle is activated as the posture of head and neck changes²⁰. Janda stated that the sterno cleidomastoid muscle, splenius capitis, and trapezius muscle are constricted in order to handle the weight of the head, as the head is far off the midline in the forward head posture²¹. This indicates that the muscle activity of the neck and shoulder muscles becomes bigger as the weight increases. This corresponds with the results of our study. In the study by Kim the muscle fatigue of the erector spinae muscle in the case of patient lifting was 14.6~23.1% in women and 18.3~32.8% in men, as compared to the maximum strength. Since the figures exceed 20%, we assess that the muscle fatigue at work is high²². In the present study, the muscle activity of the erector spinae muscle varied according to the presence/absence of a helmet. Therefore, we estimate that there is a possibility that stretcher transportation can cause musculoskeletal disease in the lumbar part.

This study has several limitations. First of all, the participants were only 15, so it is difficult to generalize the results. Second, we assumed an experimental situation instead of a real situation. Finally, in our research focus, we were limited to the upper body angle and muscle activity. Therefore, further research on the overall body targeting more ambulance workers would be needed in the future.

4. CONCLUSION:

After experimenting upper body angle and muscle activity with or without helmets, we reached the following conclusion. In our results, our muscle activity during transportation using a stretcher with a helmet in P1, the muscle activity was statistically significant in the right sternocleidomastoid muscle, left and right splenius capitis, right trapezius muscle, and left erector spinae muscle. In P2, the muscle activity was statistically significant in the left splenius capitis and the right erector spinae muscle. In our results, our upper body angle and muscle activity, wearing a helmet changed the angle of the body and seemed to be able to cause stress in movement. Also, the muscle activity was high in the muscles that influence the movements of the neck and head. Therefore, there is a strong possibility that stretcher transportation wearing a helmet can cause musculoskeletal disease of the cervical and lumbar vertebrae. In developing new helmets, a reduction of their weight should be considered so that to reduce stress and muscle fatigue in the neck and back. This could be a measure to prevent musculoskeletal disease.

5. ACKNOWLEDGMENT:

This study was supported by the Research Program funded by the Korea National University of Transportation in 2017. This research was supported by the Fire Fighting Safety & 119 Rescue Technology Research and Development Program funded by the Ministry of Public Safety and Security(“MPSS-fire safety-2015-83”).

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Received on 12.12.2017 Modified on 24.12.2017

Research J. Pharm. and Tech. 2018; 11(1): 170-174

DOI: 10.5958/0974-360X.2018.00031.8

Analysis of Muscle Activity of Ambulance Workers carrying a patient on a stretcher with or without Helmets

Figure 1.Distribution of events and phases

Table 1: Abbreviations of muscle names

Table 2: Comparison of muscle activity of upper body muscle during lowering a stretcher with a helmet

Table 3: Comparison of muscle activity of upper body muscle while the worker was lifting the stretcher with helmet