An innovative sit-standing seat in urban buses: A new design to prevent falls and non-collision injuries

Abstract

BACKGROUND:

Due to the rapid growth of metropolises and the insufficiency of public transportation, nowadays, many people travel on these vehicles in a standing position. This position leads to discomfort and the risk of falling or non-collision incidents for the passengers.

OBJECTIVE:

The present study was conducted to analyze an innovative sit-standing seat to prevent falls and non-collision injuries in standing passengers.

METHODS:

A total of sixteen participated in this study. EMG signal and Borg scale were used to assess muscle activity and discomfort, respectively.

RESULTS:

The mean Borg scale score for perceived discomfort was lower in the sit-standing position than the standing position in all body organs, except for the hips. Also, in the sit-standing position compared to the standing position, the muscle activity of the soleus and medial gastrocnemius muscles was significantly lower in the constant velocity and entire phases in both legs, lower in the right leg in the acceleration phase and lower in the left leg in the deceleration phase.

CONCLUSIONS:

So, this seat can be used as an innovative idea to improve the ergonomic condition of standing passengers to prevent falls and non-collision injuries on transit buses.

Keywords

Sit-stand seat transit bus non-collision injuries electromyography discomfort

1 Introduction

Mobility is one of the most important activities of daily living. In addition to its individual aspect, mobility also has a social aspect in today’s world. Public transportation, including the subway, BRTs and buses, are among the most necessary parts of urban mobility. Today, public transport has doubled in importance, mainly due to the growing phenomenon of urbanization. According to the UN, in 2005, only 48.7% of people around the world lived in cities, but this figure is estimated to reach 60% by 2030 [1]. Iran is not an exception to this trend, as 74% of Iranians live in cities according to the latest census [2]. The increased urban population and insufficiency of facilities, especially public transportation within cities, have made many passengers travel in a standing position in public transportation. The standing position is also important among prolonged standing workers [3, 4]. Maintaining the passengers’ balance and safety in public transportation is therefore of particular importance. Many studies have examined non-collision incidents in public transportation and shown that 56% of urban public transportation passengers’ injuries are of the non-collision type [5]. A ten-year prospective study showed that 54% of injuries on transit buses are due to non-collision incidents, which shows a 24% increase over the past ten years [6]. Drivers’ behavior, poor design of public transportation and traveling while standing due to overcrowded vehicles are the major contributors to non-collision injuries in such vehicles [7]. Most non-collision injuries occur for standing passengers and during the acceleration or deceleration phases of the vehicle’s movement [8, 9]. A study by Arabian et al. Showed that the acceleration and deceleration phases of transit buses motion are the most important critical time points in the occurrence of non-collision incidents [10].

Various solutions have been implemented so far to improve the safety and comfort of the public transportation passengers’, such as improving the drivers’ performance and behavior, providing ramps to facilitate boarding on and off vehicles for those using wheelchairs, Ways to Reduce of non-collision injuries aboard buses while climbing the stairs and walking on the lower deck and the ergonomic assessment of the vehicles’ seats to verify their suitability with the anthropometric dimensions of the passengers [11 –15]. One of the solutions for passengers to maintain their balance when standing is to use handholds. A study by Schubert et al. showed that using handholds when the bus is moving helps improve balance maintenance and reduce muscle tension in the legs in older adults [16]. Studies also show that standing sideways to the direction of travel, especially during acceleration, facilitates the maintenance of balance and reduces the tension on the limbs compared to when standing in the direction or against the direction of travel [17]. Studies on improving the standing conditions for public transportation passengers have only addressed the behavior of the drivers and passengers and the passengers’ standing direction and handholds, while no practical interventions have been conducted to improve the safety and comfort of standing passengers. The findings indicate that the sit-standing position results in the least amount of fatigue in short intervals (<35 min) compared to both the sitting and the standing positions alone [18]. Since the average travel time by public transportation is about 35 minutes [19], this study was conducted to analyze an innovative sit-standing seat to prevent falls and non-collision injuries in standing passengers.

2 Methods

2.1 Participants

Sixteen healthy men were recruited in this study (Table 1). All participants signed informed consent forms for participating in the study prior to its beginning. The participants were in good health and had no musculoskeletal problems. The classification of Body Mass Index (BMI) is divided into underweight, normal, overweight and obesity (I, II and III) [20]. In order to minimize the effect of BMI on discomfort, all participants were selected from the normal class (BMI = 18.5–24.9). The research project was approved by the Ethics Committee of Tehran University of Medical Sciences.

Table 1
Demographic profile of study participants (n = 16)

Variable Mean±SD

Age (Year) 45.81±21.10

Weight (Kg) 74.44±13.34

Height (Cm) 172.81±6.36

Variable	Mean±SD
Age (Year)	45.81±21.10
Weight (Kg)	74.44±13.34
Height (Cm)	172.81±6.36

2.2 Sit-standing seat

The participants were first asked to board a bus (Mercedes Benz 457 model) in a standing and a sit-standing position Fig. 1. The idea of using a sit-standing seat in public transportation was registered as an invention in the Intellectual Property Center of Iran under the code 97732 [21]. The seat consisted of a holding bar, 90-degree hinges, a bicycle saddle and a 100-Newton gas spring Fig. 2. After its manufacturing, the seat was mounted on the vertical bars located in the bus. In order to simulate the same position for all participants in the sit-standing position, the knee angle variable was used to adjust the height of the sit-standing seat. Before starting the experiment, the sit-standing seat was adjusted for each participant. The height the subject chose was accepted if the knee angle was at least 115° [22]. The passengers’ weight was transferred to the holding bar through their hips and then to the vertical bar in the bus. The duty of the holding bar is to fasten the sit-standing seat on the vertical bar. The 100-Newton gas spring was only used to automatic seat folding, which helped avoid occupying excessive space inside the vehicle.

Fig. 1

Participants’ position on the transit bus (Right: Standing position; Left: Sit-Standing position).

Fig. 2

The innovative sit-standing seat specialized for urban public transportation.

2.3 Driving maneuver

Studies have shown that standing sideways to the direction of travel will inflict the least tension on standing passengers [17]. Participants’ positioning in both the standing and the sit-standing positions was therefore selected sideways to the direction of travel Fig. 1. The bus moving scenario consisted of a 30-second period spent on a smooth and empty road for all participants in both positions. This period consisted of three 10-sec intervals, such that, in the first 10 seconds, the bus started moving from a still position and accelerated to a velocity of 30 km/h. In the second 10 sec, the bus continued moving at a constant velocity of 30 km/h. In the last 10 sec, the bus gradually decelerated to stop at the 30^th sec and reach the initial still phase [16]. A professional driver was employed for this study to simulate the bus movement scenario similarly for all subjects.

2.4 Objective and subjective assessment

Two ergonomic assessment techniques including objective (EMG signal) and subjective (Borg scale CR 10) were used in this study to evaluate muscle tension and perceived discomfort in transit bus passengers in standing and sit-standing positions. A surface electromyography device (DataLOG MWX8, Biometrics Ltd, UK; 1000 Hz sampling frequency) was used to measure the leg muscle activity level. Raw EMG data were adjusted with a bandpass filter of 20–490 Hz. The muscles most involved in maintaining balance and a stable state of the body in the standing position were first identified according to previous studies [16 , 23–25] and three muscles (tibialis anterior, medial gastrocnemius and soleus muscles) were ultimately selected as the target muscles for recording the EMG data. Surface Electromyography for the Non-Invasive Assessment of Muscles (SENIAM) and the ABC of EMG protocols were used to place the electromyography electrodes on the target muscles and prepare the skin for their placement [26, 27]. Before the start of the scenario, the Maximum Voluntary Contraction (MVC) was recorded for all participants by the EMG device for each target muscle using the existing protocols [27]. For measuring the MVC of the target muscles, after identifying at least three onsets and offsets of the muscular contractions for each muscle, the Root Mean Square (RMS) function in MATLAB R2014a software was used to calculate the RMS of the selected part. The EMG data were used to compare muscle tension in the standing and sit-standing positions using the RMS index. The RMS of the muscles of each participant in the standing and sit-standing positions was normalized by measuring the RMS of the MVC in the same participant.

The subjects’ perceived discomfort was measured using the Borg scale CR10 for the low back, hips, thighs, legs, feet and the whole body. The Borg scale has been used in different studies for the subjective measurement of perceived discomfort [18 , 29]. The scale has a ranking between 0 (minimum perceived discomfort) and 10 (maximum perceived discomfort). The validity and reliability of the scale have been approved in many studies [30, 31].

2.5 Procedure

The participants were asked to randomly take turns in both the standing and sit-standing positions on the transit bus. Each position was repeated three times according to the scenario defined for each person and the EMG signals of the muscles were recorded each time and analyzed in MATLAB R2014a software. There was a five minutes break between each scenario repeated for each position. Also, before the start of the experiment, the subjects had enough time (five minutes) to accordance with the sit-standing seat. Therefore, after the end of the EMG signal recording for each position, the subjects’ perceived discomfort was measured only once after twenty minutes of exposure in any positions using the Borg scale CR 10. Finally, the resultant data were analyzed in SPSS at a significance level of 0.05.

3 Results

Sixteen healthy men were recruited in this study. The Borg scale CR10 of Perceived Exertion was used to assess perceived discomfort in the organs. Table 2 presents the degree of perceived discomfort in participants’ various organs and whole body for standing and sit-standing positions on a transit bus. The non-parametric Wilcoxon test was used to compare the means. There was a significant difference in perceived discomfort between the standing and sit-standing positions in all organs as well as the whole body. Table 2 shows that perceived discomfort was higher in the standing position than the sit-standing position in the whole body and in each organ, except for the hips. Therefore, the sit-standing seat had a positive effect on the perceived discomfort of the passengers in all organs except hip.

Table 2
The Borg scale results on perceived discomfort in the organs and whole body in both the standing and sit-standing positions (n = 16)

Organ Stand mean±SD Sit-stand mean±SD P-value

Low back 3.31±1.14 1.69±1.01 <0.001

Hip 0.56±0.73 3.62±1.26 <0.001

Thigh 3.31±1.70 1.50±0.82 0.001

Leg 4.94±0.99 2.44±0.81 <0.001

Foot 4.19±1.56 2.06±1.06 0.001

Whole body 4.12±0.81 1.81±0.91 <0.001

Organ	Stand mean±SD	Sit-stand mean±SD	P-value
Low back	3.31±1.14	1.69±1.01	<0.001
Hip	0.56±0.73	3.62±1.26	<0.001
Thigh	3.31±1.70	1.50±0.82	0.001
Leg	4.94±0.99	2.44±0.81	<0.001
Foot	4.19±1.56	2.06±1.06	0.001
Whole body	4.12±0.81	1.81±0.91	<0.001

The results of assessing muscle activity in the tibialis anterior, medial gastrocnemius and soleus muscles based on the acceleration, constant velocity and deceleration phases were obtained by surface EMG (% MVC) in standing and sit-standing positions Table 3. Regarding the non-normality of the EMG signal data, the Wilcoxon signed-rank test was used to compare the sEMG results between the standing and sit-standing positions. The results showed that, in the acceleration phase, the sit-standing seat reduced the soleus muscle activity significantly in both legs compared to the standing position. This reduction in muscle activity was also observed in the medial gastrocnemius muscle, but the difference was only significant in the right leg. In the acceleration phase, no significant differences were found in the tibialis anterior muscle between the two positions. According to Fig. 3, in the acceleration phase, the soleus and medial gastrocnemius muscles of the right leg were more contracted compared to the left leg. This pattern was reversed in the deceleration phase. No specific pattern was obtained for the tibialis anterior muscle. In the constant velocity phase, the EMG activity of the soleus and medial gastrocnemius muscles showed a significant improvement in the sit-standing position compared to the standing position in both legs. The significance of differences in muscle activity between the standing and sit-standing positions was similar to the deceleration and entire phases in the constant velocity phase.

Table 3

Results of Wilcoxon signed-rank test on EMG (% MVC). S indicates “stand”, SS indicates “sit-stand”

Acceleration phase (time interval: 0–10 seconds)
Muscles	TAR_S	TAR_SS	MGR_S	MGR_SS	SR_S	SR_SS	TAL_S	TAL_SS	MGL_S	MGL_SS	SL_S	SL_SS
Mean±Sd	4.24±3.18	4.26±4.91	11.44±5.19	6.14±3.99	27.63±12.54	11.91±6.65	6.22±6.44	5.07±3.59	5.95±3.20	4.68±3.27	15.12±6.20	6.85±3.79
p-value	0.717		0.007		<001		0.796		0.163		0.001
Constant velocity phase (time interval: 10–20 seconds)
Muscles	TAR_S	TAR_SS	MGR_S	MGR_SS	SR_S	SR_SS	TAL_S	TAL_SS	MGL_S	MGL_SS	SL_S	SL_SS
Mean±Sd	1.71±1.05	2.24±2.84	5.74±2.65	3.28±2.40	18.79±10.92	6.76±4.38	1.94±1.73	1.51±0.95	5.58±3.32	3.47±2.74	16.39±7.73	5.69±3.08
p-value	0.352		0.004		<0.001		0.255		0.001		<0.001
Deceleration phase (time interval: 20-30 seconds)
Muscles	TAR_S	TAR_SS	MGR_S	MGR_SS	SR_S	SR_SS	TAL_S	TAL_SS	MGL_S	MGL_SS	SL_S	SL_SS
Mean±Sd	3.68±3.37	4.78±4.77	5.27±3.06	3.13±2.38	15.20±9.23	5.36±3.67	2.75±2.26	3.16±3.50	14.17±11.17	5.84±4.25	23.98±9.79	11.18±8.38
p-value	0.438		0.039		0.001		0.717		<0.001		<0.001
Total phases (time interval: 0–30 seconds)
Muscles	TAR_S	TAR_SS	MGR_S	MGR_SS	SR_S	SR_SS	TAL_S	TAL_SS	MGL_S	MGL_SS	SL_S	SL_SS
Mean±Sd	3.69±2.60	4.26±4.04	8.10±4.57	4.19±2.61	20.19±10.24	8.57±4.87	4.07±3.92	3.65±2.33	9.58±7.07	4.82±3.33	19.06±7.79	8.73±5.14
p-value	0.679		0.013		<0.001		0.756		0.001		<0.001

Note: TAR = tibialis anterior (right), MGR = medial gastrocnemius (right), SR = soleus (right), TAL = tibialis anterior (left), MGL = medial gastrocnemius (left), SL = soleus (left).

Fig. 3

The EMG signal sample of the soleus, medial gastrocnemius and tibialis anterior muscles of both legs during the bus movement scenario for the standing and sit-standing positions.

Due to the fact that in this study only the leg muscles activity were evaluated, the relationship between the mean % MVC of leg muscles and legs discomfort was assessed by the standardized regression coefficients Table 4. Discomfort was related to the mean % MVC of the right soleus muscle (beta = 0.51, p < 0.01) and the left soleus muscle (beta = 0.51, p < 0.01) in standing position. High muscle activity of the right and left soleus muscles corresponded with more legs discomfort in standing position.

Table 4

Standardized regression coefficients (beta) of the relationship between EMG. (% MVC) and perceived discomfort (Leg)

Dependent variable	EMG measurement	Beta	P-value
Perceived discomfort (Leg)	Stand
	TAR	0.09	n.s.
	MGR	0.16	n.s.
	SR	0.51	<0.01
	TAL	0.15	n.s.
	MGL	0.33	n.s.
	SL	0.51	<0.01
	Sit-stand
	TAR	0.21	n.s.
	MGR	0.35	n.s.
	SR	0.54	n.s.
	TAL	0.17	n.s.
	MGL	–0.21	n.s.
	SL	0.03	n.s.

Note: TAR = tibialis anterior (right), MGR = medial gastrocnemius (right), SR = soleus (right), TAL = tibialis anterior (left), MGL = medial gastrocnemius (left), SL = soleus (left).

4 Discussion

The results showed that, in all parts of the body, except for the hips, perceived discomfort was significantly lower in the sit-standing position. A study by Nicoletti and Läubli compared the comfort of three positions including standing, sitting and sit-standing [22]. This comparison was performed in a work environment and after five minutes of being in each position. The results showed that the sit-standing position was more comfortable than the standing position, which is in agreement with the results of the present study. A study by Chester et al. was conducted with the aim of comparing comfort between standing, sitting and sit-standing positions showed that sit-standing position increases lower limb comfort compared to standing posture [18]. In this study, no significant difference was observed in terms of perceived comfort in the low back in both standing and sit-standing positions. Also, in the study by Sartika and Dawal, perceived discomfort in the low back did not show a significant difference between the two positions [4]. As the results of this study showed, unlike previous studies, the sit-standing seat significantly reduced perceived discomfort in the low back compared to the standing position. According to Fig. 1, the vertical bars inside the bus act as a support for the low back, which can be a major factor in relieving discomfort, but they need to be covered by a suitable backrest. Although many studies show an improvement in lower limbs discomfort when using a sit-standing seat [4 , 32], which is consistent with the results of the present study, the study by Vink et al. did not report a significant difference in lower limbs between the two positions [33]. Review studies have reported that sit-standing seats may improve discomfort and it has not been definitively confirmed [34, 35]. It has been suggested that more studies should be done in this area. According to the findings, using the sit-standing seat reduced participants’ perceived discomfort significantly in various organs, and perceived discomfort was only higher in the sit-standing position than the standing position in the hips. Previous studies have reported discomfort in the hips in the sit-standing position compared to the standing position [4 , 32]. One of the important factors that increased perceived discomfort in the hips was not to use the handhold. Therefore, the use of the handhold can reduce the force of subjects’ upper trunk weight applied to the hips and reduces perceived discomfort. Also, another factor that increased perceived discomfort in the hips was the upper half of the passengers’ body weight, which is transferred to the sit-standing seat by the hips.

Table 3 shows the tibialis anterior, medial gastrocnemius and soleus muscle activities in both standing and sit-standing positions. The results show that, throughout all phases (0–30 seconds), the tension on the soleus and medial gastrocnemius muscles of both the left and right legs was significantly lower in the sit-standing position. Also, in the constant velocity phase, the tension on the soleus and medial gastrocnemius muscles of both legs was significantly different between the two positions. No reports were found on the effects of using sit-standing seats for controlling leg muscle tension in passengers standing on public transportation. Nonetheless, several studies have been conducted on the use of the sit-standing seat for improving work conditions in work environments [34 , 37–41]. The effects of the sit-standing seat showed that gastrocnemius and soleus muscle activities decreased in the sit-standing position compared to the standing position which is in agreement with the results of the present study [4].

Since the participants were standing sideways to the direction of travel (i.e. Newton’s first law), they were inclined toward the right leg in the acceleration phase and toward the left leg in the deceleration phase. The results show that, in the acceleration phase, the activity of the soleus and medial gastrocnemius muscles in both the standing and sit-standing positions were higher in the right leg compared to the left. Meanwhile, in the deceleration phase, the soleus and medial gastrocnemius muscles had more activity in the left leg Fig. 3. No defined pattern was obtained for the tibialis anterior muscle in either the acceleration or deceleration phases. The most important function of the tibialis anterior muscle is dorsiflexion in the ankle. Because the participants were standing sideways to the direction of travel, very little force is exerted in the direction of dorsiflexion during the bus motion, and this is likely to be the main cause of the tibialis anterior muscle results. However, further studies are suggested to examine the leg muscles activity during bus motion. According to Newton’s first law passengers standing sideways to the direction of travel are inclined toward the right leg in the acceleration phase and toward the left leg in the deceleration phase. This effect creates a different muscle activity pattern during the acceleration vs. the deceleration phases in both the standing and sit-standing positions. The patterns obtained for each of the three muscles in the acceleration and deceleration phases were consistent with the biomechanical requirements of the passengers in the standing condition [16]. Several studies have shown the effect of acceleration and deceleration on the loss of balance, falling and non-collision incidents [8–10 , 42]. The acceleration limit tolerated by the human body in the standing position with no external support for helping maintain balance is less than the actual velocity of transit buses [43]. Therefore, standing passengers will never be able to maintain their balance without external support in public transportation. Many studies have reported the advantages of using handholds and their positive effects on standing passengers’ conditions in public transportation [16, 17]. The innovative sit-standing seat was able to maintain balance the standing passengers in the worst-case conditions (without the use of the handholds) on the transit bus. This seat improved the safety of standing passengers by reduced bus acceleration in the tolerated range of the human body by creating sit-stand support. This improvement of safety is particularly important in the acceleration and deceleration phases. Table 3 shows that, in the acceleration phase, the sit-standing seat significantly decreased the soleus and medial gastrocnemius muscle activity in the right leg compared to the standing position. Also, in the deceleration phase, this innovative seat reduced the soleus and medial gastrocnemius muscle activity in the left leg significantly compared to the standing position. This reduction in muscle activity has been achieved in the acceleration and deceleration phases without using handholds. Also, it is proven, the seat belt helps to prevent falls and injuries due to the acceleration or deceleration phases of the vehicle’s movement [6]. Therefore, the use of a seat belt along with the sit-standing seat may improve the safe position for standing passengers. Determining the effect of using the handhold and seat belt along with the sit-standing seat are suggested in future studies. On the other hand, due to the convenience of using the sit-standing seat, can stand up from the seat and use it again in the shortest possible time, and this feature causes the least disturbance for wheeled mobility users. Of course, if the bus is full of passengers, the use of this sit-stand seat may create restrictions for other standing passengers.

The relationship between legs muscle activity (% MVC) and legs discomfort assessed by the standardized regression coefficients and showed that only muscle activity of the right and left soleus muscles are associated with legs discomfort in standing position. Therefore, it is not clear how muscle activity is associated with perceived discomfort. A review article confirms this result [44]. A study was conducted to investigate the relationship between objective and subjective measurements of discomfort in hand tools. In this study, it was concluded that EMG measurement could not be used as an objective measurement method to determine discomfort experience [45].

This study has some limitations. First, this study was performed on only 16 males and the results of the EMG signal and perceived discomfort may not be representative of all public transport passengers. Therefore, a study on more samples in different age groups and both genders is recommended. Second, given that this study was performed without the use of handholds, and seat belt, using them are expected to improve the safety and perceived discomfort of standing passengers. Hence, the use of a handhold and seat belt along with this innovative sit-standing seat should be considered in future studies.

5 Conclusion

This study was conducted to analyze an innovative sit-standing seat to prevent falls and non-collision injuries in standing passengers. The results obtained by the Borg scale showed that using this seat reduces perceived discomfort significantly in various organs of the body, except for the hips. Also, the EMG signals of the muscles implied that the sit-standing seat reduces the muscle activity of the soleus and medial gastrocnemius muscles in the sit-standing position compared to the standing position in the entire phase, especially in acceleration and deceleration phases. These results were achieved without using handholds. In addition to the noted items, the seat provided good support for standing passengers. The innovative sit-standing seat was examined in this study and is therefore recommended as a useful tool to decrease discomfort and reduce muscle tension in the standing passengers’ legs on public transport.

Conflict of interest

The authors declare no competing interests for this research.

Funding

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Footnotes

Acknowledgments

The authors thank all participants for their kind corporation in this study.

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An innovative sit-standing seat in urban buses: A new design to prevent falls and non-collision injuries

Abstract

BACKGROUND:

OBJECTIVE:

METHODS:

RESULTS:

CONCLUSIONS:

Keywords

1 Introduction

2 Methods

2.1 Participants

Table 1 Demographic profile of study participants (n = 16) Variable Mean±SD Age (Year) 45.81±21.10 Weight (Kg) 74.44±13.34 Height (Cm) 172.81±6.36

2.4 Objective and subjective assessment

2.5 Procedure

3 Results

5 Conclusion

Conflict of interest

Funding

Footnotes

Acknowledgments

References

Table 1
Demographic profile of study participants (n = 16)

Variable Mean±SD

Age (Year) 45.81±21.10

Weight (Kg) 74.44±13.34

Height (Cm) 172.81±6.36