Max Le Moine
Industrial Design Student
Ergonomic Analysis
March 2023
I wrote this research paper during my Human Factors / Ergonomics in Design course. It goes over the ergonomic implications of the interaction between the Easy Stroll Connector Between a wheelchair and a baby carriage and the Maxi Cosi Lara Ultracompact Stroller.
Executive Summary
The Easy Stroll Connector (“Stroller & Wheelchair Connector That Enables Independent Parenthood,” n.d.) and Maxi Cosi Lara Ultracompact Stroller (“Maxi Cosi Lara Ultracompact Stroller,” n.d.) will be used to examine how a wheelchair can be attached to a stroller. This allows a user in a wheelchair to push a child in a stroller. As a system, the products can create hazards to the pusher and the child. Hence, design features will be proposed in this paper to improve the safety of this system.
Introduction
Many studies and media have been published to view persons with disabilities in a variety of contexts; however, parenting with a disability is one area of this world that requires more attention. This paper will focus on parenting with a disability by looking at The Easy Stroll Connector (“Stroller & Wheelchair Connector That Enables Independent Parenthood,” n.d.) designed by Jonathon Bar-Or Industrial Design Ltd. as it is supposed to connect a stroller and wheelchair to help a person in a wheelchair push a stroller. This can be a great product to increase independence; however, there are many ergonomic factors that may cause concern in respect to this system (see section 1.2) that will be explored throughout the paper. Data has been collected and displayed in the "Anthropometrics" section on users with Spinal Cord Injuries, CNS disorders, Orthopedic Injuries or Disorders, Cerebral Vascular Disease, Respiratory or Cardiovascular Disorders, and other disabilities (Paquet & Feathers, 2004) which will be used to see if the system is actually usable for its intended users.
The Stroller
Even though Jonathon Bar-Or Industrial Design Ltd. has not specified what type of stroller is recommended for the system, the Maxi Cosi Lara Ultracompact Stroller (“Maxi Cosi Lara Ultracompact Stroller,” n.d.) will be used as a reference. The product is 64.2 cm in height, 25.4 cm in length, 51.4 cm in width, and weighs 9.1 kg (“Maxi Cosi Lara Ultracompact Stroller,” n.d.). It is important to compare the previously mentioned data to the anthropometric data in the "Anthropometric" section to see if the system fits the user’s needs.
Definitions
System The combination of a wheelchair, connector, and stroller.
Pusher The user that is controlling the movement of the stroller.
Child The user who is being pushed in the stroller.
Context of Use
The Easy Stroll Connector (“Stroller & Wheelchair Connector That Enables Independent Parenthood,” n.d.) attaches a baby stroller to a pusher’s wheelchair. This is done with an arm that is permanently attached to the stroller which hooks onto a mount on the wheelchair. In order to attach the two entities, the pusher must lift the stroller onto/off of the mount. It is important to note that the stroller’s back (fixed) wheels are lifted to allow the system to use the wheelchair’s turning radius. In addition, the pusher is situated much further back from the stroller and lower from the ground than a pusher in a standing posture. Cognitive loads of using this system is increased from just pushing a stroller while walking. The pusher has to think about controlling the wheelchair and stroller. Therefore, this product creates a unique interaction between the pusher and the stroller.
Hazards
Most hazards come from the fact that the user needs to lift the stroller in order to connect it to the wheelchair. The Maxi Cosi Lara Ultracompact Stroller weighs 9.1 kg (“Maxi Cosi Lara Ultracompact Stroller,” n.d.) and can carry up to 28.6 kg (Dorel Juvenile Group, Inc., 2021). This can cause stress on the pusher’s arms as this lifting is done in an awkward posture – and this is to assume the pusher has the capability to lift the stroller in the first place. Not only is this hazardous for the pusher but can cause harm to the child due to potential ataxic lifting motions. Hence, the lifting requirements of this interaction can cause hazards.
Misuse
Easy Stroll displays mostly pushers in manual wheelchairs using this system (“Stroller & Wheelchair Connector That Enables Independent Parenthood,” n.d.) that have a limited power output. Even though this is good for marketing, problems may come when users are in more powerful mobility devices. For example, Daymak’s Boomerbeast 2D has two 500W watt motors that can go up to 50 km/h – yes, this is advertised as a “Mobility Scooter” (Boomerbeast 2D User Manual, n.d., p. 4). This intentional error can easily occur as the manufacturer does not specify what additional devices they recommend for this system. Using devices that are more powerful can interfere with the structural integrity of the system making it unsafe.
Anthropometrics
Using an attachment mechanism such as the Easy Stroll Connector (“Stroller & Wheelchair Connector That Enables Independent Parenthood,” n.d.) will mean that the stroller attached to a wheelchair such as the Maxi Cosi Lara Ultracompact Stroller (“Maxi Cosi Lara Ultracompact Stroller,” n.d.) will have to meet the anthropometric needs of the wheelchair user. This is different than traditional stroller design considerations as the user is in a seated posture rather than an upright posture. Therefore, this section will be focused on wheelchair anthropometric data and how it can restrict the design of the stroller.
Eye Height
Eye Hight from “An Anthropometric Study of Manual and Powered Wheelchair Users” by Paquet and Feathers is summarized in table 01. This is different from data in “Bodyspace: Anthropometry, Ergonomics, and the Design of Work” (Pheasant & Haslegrave, 2006) as the user is in a seated position. The most significant measurement from this set is the 5th percentile for female eye height, right which equals 103.0 cm (Paquet & Feathers, 2004); most users will be able to see above this measurement. Stroller dimensions that might be affected by this include the height of the handle and the canopy as they may restrict visibility.
Horizontal Arc of Grasp
In their book, Pheasant and Haslegrave describe the horizontal restrictions for the seated working area. This is crucial to look at for tasks such as reaching the child in the stroller for wheelchair users as they have limited trunk movement. To accommodate the 5th percentile of persons, the maximum horizontal reach should be 65.0 cm referenced in figure 4.6 of “Bodyspace: Anthropometry, Ergonomics, and the Design of Work” (Pheasant & Haslegrave, 2006). This can restrict the width of a stroller to ensure the pusher can reach across it.
Wrist Hight
Wrist height is another anthropometric dimension that is altered between a standing posture to a sitting posture refenced in data collected by Pheasant & Haslegrave, 2006. This can be defined as the “Vertical distance from the floor plane to the radial styloid.” (Paquet & Feathers, 2004, p. 194). The recommended measurement to use is the averages of the 50th percentile values which equals 77.6 cm to accommodate for persons above and below the measurement. This can help the vertical positioning of the stroller’s handle to ensure it is not reached in an awkward posture.
Thigh Breadth
The width of a stroller’s handle supports will be restricted by the space between the pusher’s outer thighs. This is more important for pushers in wheelchairs as their legs are situated between the stroller’s handle and body in a seated posture. Thigh breadth can be measured “…between parallel vertical planes that cross the left and right lateral-most point landmarks,” (Paquet & Feathers, 2004, p. 194). The recommended measurement to use in stroller design would be the 95th percentile male measurement equaling 62.5 cm to fit the widest person.
Buttock-Knee Length
Again, the anthropometric data for below the waist is more important for stroller pushers in wheelchairs as that portion of the body will be between the handle and rest of the stroller’s components. The distance between the handle and main stroller (e.g., seat) can be controlled by the Buttock-Knee Length. This can be described as the “Shortest perpendicular distance from seat back plane to knee point…” (Paquet & Feathers, 2004, p. 194). It is recommended that this should be dimensioned as 76.0 cm (95th percentile female) to accommodate the longest person. Foot length should be added to this measurement which is 28.5 cm for 95th percentile males (Pheasant & Haslegrave, 2006).
Product Improvements
Stroller Back Wheels
As said in the "Hazard" section, the fact that the stroller needs to be lifted to attach it to the stroller is a major hazard. With traditional stroller design, this is needed to lift the back fixed wheels off the ground so that the system’s center of its turning radius is at the wheelchair’s fixed wheels. One way to help meet this requirement safely is to add a mechanical lifting mechanism to the Easy Stroll Connector (“Stroller & Wheelchair Connector That Enables Independent Parenthood,” n.d.). This would have to be designed to aid the pusher in lifting the wheelchair in a gentle manner. A spring-loaded arm could work as an engineering control. However, the best solution for this would be to change the back wheels of the stroller from a fixed to a swivel design. This allows the pusher to turn the system freely with all wheels on the ground. Therefore, it would be safer as this eliminates the need to lift the stroller.
Figure 1: Difference between fixed (with 1 axis of rotation) and swivel (with 2 axes of rotation) wheels.
Visibility
As mentioned in the "Eye Height" subsection, sight is a major concern for this system as it is significantly lower when persons are using a wheelchair. Studies have shown that the minimum measurement for eye height is 103.0 cm as shown in Figure 2 (Paquet & Feathers, 2004). This can limit the stroller's height of its vertical extremities (e.g., canopy) in order to ensure the pusher can see over the stroller.
Figure 2: Propper height for a stroller to accommodate a wheelchair.
Handle Position
In order to ensure the pusher can hold the handle in a neutral posture, it is important to position the handle in an appropriate location. Relevant anthropometric data to consider include wrist height and buttock-knee length; relevant data of these measurements are 77.6 cm and 76.0 cm respectively as shown in Figure 3 (Paquet & Feathers, 2004). These measurements should restrict the positioning of the handle from the ground (vertically) and stroller body (horizontally) to ensure the handle is reached in a neutral posture.
Figure 3: Appropriate handle position for a stroller to accommodate a pusher in a wheelchair.
Summary and Reflection
combination of the Easy Stroll Connector (“Stroller & Wheelchair Connector That Enables Independent Parenthood,” n.d.) and Maxi Cosi Lara Ultracompact Stroller (“Maxi Cosi Lara Ultracompact Stroller,” n.d.) creates a unique system that can help a pusher in a wheelchair control a stroller. The indicated is a unique system which works to provide a person with disabilities more independence when caring for a child. On the other hand, many ergonomic and human factors have to be taken into consideration to see if the system is actually safe and easily usable.
Some safety concerns have been mentioned that are important to note. First of all, the Easy Stroll Connector (“Stroller & Wheelchair Connector That Enables Independent Parenthood,” n.d.) requires the user to lift the back wheels of the stroller which can cause harm to the pusher and child. Elimination and engineering design controls must be taken into consideration in order to deal with this concern. In addition, the product range that can be used in the system is too wide making it easy to be misused. The universal use of the connector is attractive from a marketing standpoint but must be altered with engineering or administrative controls to ensure safety. Last but not least, anthropometric data of wheelchair users including Eye Height, Horizontal Arc of Grasp, Wrist Height, Thigh Breadth, and Buttock-Knee Length (Paquet & Feathers, 2004; Pheasant & Haslegrave, 2006) must be taken into consideration. In reference to stroller dimensions in section 1.1, wheelchair users will not fit traditional stroller design. It is crucial to take these factors into consideration to ensure the user can control the system in neutral postures. These design considerations must be implemented to ensure safety as the system will be used in medical and childhood applications.
Jonathon Bar-Or Industrial Design Ltd’s product is an exciting way to give persons with disabilities more independence. On the contrary, ergonomic and human factors displayed above can show the negative impacts of the system it creates. Many design features must be altered in this product to make it more usable and safer.
References (APA 7)
Boomerbeast 2D User Manual. (n.d.). Daymak. https://daymak.com/manuals/mobility/daymak-boomerbeast-2-
manual.pdf
Maxi Cosi Lara Ultracompact Stroller. (n.d.). Babies R Us Canada. https://www.babiesrus.ca/en/Maxi-Cosi-
Lara-Ultracompact-Stroller/14F6CBBC.html
Paquet, V., & Feathers, D. (2004). An Anthropometric Study of Manual and Powered Wheelchair Users.
International Journal of Industrial Ergonomics, 33(3), 191–204. https://doi.org/10.1016/j.ergon.2003.10.003
Pheasant, S., & Haslegrave, C. (2006). Bodyspace: Anthropometry, Ergonomics, and the Design of Work
(Third). Taylor & Frances Group.
Stroller & Wheelchair Connector That Enables Independent Parenthood. (n.d.). Jonathon Bar-Or Industrial
Design Ltd. https://www.jbdesign.co.il/en/portfolio/easystroll-2/