In the present thesis, the association of anthropometric and range of motion ROM with the comfortable riding posture (CRP) and comfortable riding position (RP) have been described by establishing the roles of these riders’ attributes. Previous studies were unable to establish the effect of rider’s physical attributes in the context of CRP and optimal riding positions.
However, few two-wheeler (bicycle) studies (Grainger et al., 2017; Hsiao et al., 2015) established the relationship between the (cyclist) riders’ physical attributes (anthropometry), CRP and seating/ saddle positions. The present thesis shows the method to increase the degree of comfort using riders’ physical attributes via anthropometrics as well as ROM measurements.
The present chapter explains the key findings or outcomes of the whole research described in different chapters.
6.1.1 Key findings of the present thesis
The salient findings of the present thesis obtained from the experimental studies described in different chapters are listed below.
Eighteen (18) key dimensions were measured from each of the 23 motorcycles (standard motorcycles of different make and models which are popularly available in India) using the new (in-house fabricated) instruments. This measurement helped to find the dimensional difference across the standard motorcycles under study. It was intended to understand the standard or traditional dimensions, which are practiced for three interface parts (handlebar, seat, and footrest) in a motorcycle. It was found that 12 out of 18 key dimensions had a marginal deviation from the mean value. For instance, standard deviation (SD) of seat dimensions (i.e. front width (SS), narrowest width (SXL), distance between the front width and narrowest width (S2S)) were found between 1.3 cm and 2cm. The fuel tank’s dimensions (i.e. tank length, minimum and maximum fuel tank breadths) varied with a SD ranging from 3.1cm to 5.3cm. The SD of footrest dimensions (i.e. distance between the footrests (F)) SD were also found as 2cm. Although there were some variations of the dimensions across the motorcycles but the SD values were very less or marginal for most of the cases. Moreover, the measured dimensions were in line with the existing Japanese standards, namely JASO T003:2009, 2009, and JASO T102-84, 1975. Dimensional data regarding the 3 interface points (handlebar, seat and footrest) gathered from the 23 standard motorcycles helped to develop the test-rig or static-simulator for studying the comfort/discomfort posture of the motorcyclists.
In the present research, 29 anthropometric dimensions, and 20 ROM measurements were taken from 120 male adult (aged 19–44 years) Indian motorcycle riders following standard measurement protocol. Conducting PCA analysis, a total of 14 out of 29 anthropometric variables (i.e., crotch height, stature, buttock extension, sitting shoulder height, sitting cervical height, lower-leg length, knee height, elbow–hand length, shoulder–elbow length, buttock–popliteal length, buttock–knee-length, acromion grip length, hand length, and ball- of-foot length) and six out of 20 ROM variables (i.e., wrist extension, wrist flexion, elbow flexion, knee extension, shoulder extension, and shoulder abduction) were identified as the key variables defining the physical characteristics of Indian male motorcyclists.
Although higher dimensional differences were evident while comparing with general Indian population data, the anthropometry of Indian drivers was more or less similar to Indian motorcyclists (present study). Overall, the results showed that there was profound difference in most of the anthropometric dimensions between the non-Indian and Indian motorcyclist populations. While the ROM data from the present study were compared with general Indian population data, prominent variations were noticed. The angular difference of lower limbs among Indian motorcyclists was smaller than the general population, whereas it was higher in the case of upper limbs. It is evident from the present study that the existing anthropometry and ROM databases of Indian general population are either inadequate in terms of relevant information or not representative of the whole Indian motorcycle rider population. As there is no other anthropometric and ROM database for the Indian motorcyclist population, the physical measurements acquired in present research could be used for the ergonomic design of motorcycles for Indian users unless a larger database is generated.
Following the experiment on static motorcycle test-rig, CRP and RP was identified based on the perceived discomfort/comfort of the joint angles. The mean comfort joint angles (CRP) for the ten joints were observed as Neck (θW1) 18°, Shoulder (θW2) 33°, Elbow (θW3) 110°, Lower back (θW4) 120°, hip (θW5) 81°, Knee (θW6) 62°, Ankle (θW7) 85°, Wrist (θW8) 129°, Shoulder abduction/adduction (θW9) 40°, and Hip abduction/adduction (θW10) 33°.
Similarly, dimensions of rider-motorcycle interface points (handlebar, seat and footrest) were measured by adjusting different adjustable features of the motorcycle test-rig to identify the comfortable riding position (RP). Finally, the optimal riding position was defined based on the ten (10) dimensional variables which included the vertical distance between the F-point and D-point (R1) 48 cm, the vertical distance between the F-point and G’-point (R2) 65 cm, the horizontal distance between the F-point and D-point (R3) 34 cm, the horizontal distance between the F-point and G’-point (R4) 17 cm, the distance between the G’-points on the right and left handlebar/grips (G) 78 cm, the distance between the G- points on the right and left handlebar/grips (T) 72 cm and the distance between the F-points on the right and left footrest (O) 59 cm, D -point from the ground (H) 81 cm, the vertical distance between the H-point and the ground (MR1) 91 cm and horizontal distance between the H-point and the F-point (MR2) 26 cm.
PCA analysis revealed that comfort hip joint angles, comfort joint angles of upper limbs, and comfort joint angles of lower limbs are the principal components that explain the most variance in CRP (joint angles). Similarly, following PCA analysis of RP variables, principal components like vertical dimensions at sagittal plane, dimensions at transverse plane, horizontal dimensions at sagittal plane, and footrest dimensions at transverse plane were able to explain the most variance in the RP. Considering the principal components of anthropometrics and ROM as independent variable, and CRP as dependent variable, stepwise multiple linear regression (SMLR) analysis was conducted. Significant association of CRP were found with the anthropometric and ROM variables of the motorcyclists. Likewise, SMLR analysis showed significant association of RP with the physical characteristics (anthropometry and ROM) of the motorcyclists.