Why are the wheelchairs used by Paralympic athletes in a figure eight shape?

Recently, the Paris Paralympic Games are in full swing, and the 284 athletes of the Chinese Paralympic delegation are sweating, showing their style, and winning glory for the country on the field! Friends who watch the games may find that in wheelchair tennis, wheelchair basketball, wheelchair racing and other competitions, the wheelchairs used by athletes are all in the shape of "figure eight".

Wheelchair basketball Source: Xinhua News Agency

What is the difference between an "eight-shaped" wheelchair and an ordinary wheelchair? Why are the wheelchairs used in competitions "eight-shaped"? Let's study it together~

01 The main reason for the "figure eight" wheelchair - mechanical stability

One of the main reasons why wheelchairs used in competitive sports are designed in an "eight-shaped" shape is because of their stability. We all know that large vehicles are prone to tipping over when turning, causing traffic accidents, and the same is true in wheelchair-related competitive sports. When turning, centripetal acceleration is generated, resulting in an overall non-existent, outward inertial force. The athlete's upper body will be "thrown" to the outside due to this inertial force, and the overall center of gravity will shift to the outside. Both the inertial force and the shift in the center of gravity can cause the wheelchair to tip over during a high-speed turn .

Rollover is likely to occur when turning

Image source: The Paper

The width of the wheelchair seat is determined by the human body shape. The H-shaped design of ordinary wheelchairs can reduce the space occupied and facilitate travel, but the distance between the ground fulcrums is relatively small, which will affect the stability of the wheelchair and is not suitable for use in competitive competitions. The "figure eight" wheelchair design can increase the distance between the ground fulcrums and the area enclosed by the fulcrums, making it relatively less likely to roll over .

Comparison of pivot distances Source: provided by the author

In fact, the design of competitive wheelchairs cannot be separated from relevant mechanical analysis , among which the most common is the static analysis of the wheelchair[1-3]. In addition, the dynamic analysis of the wheelchair is even more important[4]. For example, the figure below analyzes the mechanics and kinematics of the wheelchair for the sport of wheelchair curling. The relevant mechanical analysis can provide better solutions for wheelchair design and guide athlete training on the other hand .

Competitive wheelchairs cannot do without mechanical analysis. Source: Reference [4]

02 Secondary factors of the “ figure eight ” wheelchair: ergonomics

Increasing the distance between the two rear wheels can enhance the stability of the competition wheelchair. The controllable area of ​​the athlete's hands determines the "figure eight" design of the wheels, which is ergonomics [5-7]. In layman's terms, it refers to the convenience and comfort of athletes using wheelchairs as tools. The stability type requires a wider distance between the rear wheels. If an H-shaped design is adopted, athletes will always be in a posture with their arms outstretched horizontally when controlling the rear wheels. On the one hand, this posture is not conducive to the full use of arm strength and will affect the competitiveness of the sport; on the other hand, maintaining this posture for a long time can easily cause arm fatigue. The "figure eight" design can enable athletes to perform better .

Ergonomics simulation analysis source: Reference [7]

Ergonomic analysis in competitive wheelchairs is not only used to determine the distribution of the "figure eight" rear wheels, but also involves the distance between the wheelchair and the seat, the inclusiveness of the wheelchair, the athlete's posture, the working space, etc.

Ergonomic analysis of athlete posture in a racing wheelchair Source: Reference [5]

Competitive sports are never just about the competition itself. Only with the support of mechanics and ergonomics analysis can we design a competitive wheelchair with better performance; and turning the design into reality requires the support of multiple industries such as materials and manufacturing. With the strong support of the motherland, we look forward to Chinese athletes showing their best at the Paris Paralympics and making new breakthroughs.

References

[1] Qu An. Analysis and evaluation of table tennis wheelchairs[D]. Dalian Jiaotong University, 2010.

[2] Ma Xiaoling. Design and analysis of a new basketball wheelchair[D]. Dalian Jiaotong University, 2007.

[3] Fu Jiayu. Research on wheelchair frame optimization design based on behavior analysis[D]. China University of Mining and Technology, 2022. DOI:10.27623/d.cnki.gzkyu.2022.001137.

[4] Sun Dong, Zhao Liang, Huang Ying, et al. Research progress on improving sports performance of disabled people from the perspective of sports biomechanics[J]. Sports Science, 2020, 40(05): 60-72. DOI: 10.16469/j.css.202005006.

[5] Liu Jun. Research on racing wheelchair based on ergonomics[D]. Dalian Jiaotong University, 2008.

[6] Feng Yunlong. Design of basketball wheelchair based on ergonomics[D]. Tianjin University of Science and Technology, 2014.

[7] Zhang Xiuyan. Design of tennis wheelchair based on ergonomics[D]. Dalian Jiaotong University, 2007.

Author: Wang Yongjian, Associate Professor of Nanjing Agricultural University, Deputy Secretary-General of the Science Popularization Committee of Jiangsu Mechanics Society, Chief Science and Technology Communication Expert of Jiangsu Province Planner: Xiaoxiao Dandelion Editor: Xiaodingdang