Repeatability of a Checklist for Evaluating Cab Design 

Characteristics of Heavy Mobile Equipment 

Michael J. Jorgensen,1 

1Wichita State University, Industrial and Manufacturing Engineering Department, Wichita, Kansas 

N.K. Kittusamy,2,∗ 

2National Institute for Occupational Safety and Health, Spokane Research Laboratory, Spokane, 

Washington 

and Pranathi B. Aedla1 

∗Deceased 

Risk factors associated with the development of musculoskeletal discomfort and disorders during the operation of 

heavy mobile equipment include whole-body vibration and 

awkward and sustained joint postures of the shoulders, neck, 

and trunk. Cab design may influence awkward postures of the 

joints, and task duration may influence duration of exposure 

to awkward and static postures and whole-body vibration. To 

reduce exposure to risk factors related to the interface between 

cab design and task, it may be necessary for manufacturers 

to address cab design. This study assessed the repeatability of 

a cab design checklist developed to evaluate various design 

characteristics that can influence exposure to risk factors 

for musculoskeletal discomfort. The ability of the cab design 

checklist to identify posture-related deficiencies of design was 

also assessed. The checklist was used by two administrators 

across 10 pieces of heavy construction equipment. Video 

analysis was performed to quantify postures of the neck, 

shoulder, and trunk; correlation analysis was used to determine 

whether specific questions from the checklist were associated 

with the identification of awkward postures. The repeatability 

assessment resulted in kappa coefficients ranging from 0.52 

to 1.0 (good-to-excellent reproducibility) across each piece of 

equipment, and an overall kappa coefficient of 0.77 (excellent 

reproducibility) when considering all equipment together. 

Results from the correlation analysis showed that shoulder 

flexion posture was correlated with scores from the cab 

design checklist. However, results of the cab design checklist 

were not significantly correlated with shoulder abduction or 

awkward postures of the neck and trunk. Results suggest 

that the cab design checklist may be useful for identifying 

cab design characteristics that need further improvement and 

for identifying design characteristics that increase shoulder 

flexion. The strength of the repeatability assessment suggests 

that outcomes of the cab design checklist administered by 

different individuals may be consistent, independent of the type 

of equipment being assessed. 

Keywords	 awkward postures, construction, operating engineers, 

postural analysis, whole-body vibration 

The findings and conclusions in this article are those of the authors 

and do not necessarily represent the views of National Institute 

for Occupational Safety and Health (NIOSH). Mention of specific 

manufacturers does not imply endorsement by NIOSH. 

INTRODUCTION 

Kittusamy and Buchholz(1) estimated there were 540,000 operators of heavy mobile equipment in the United 

States and that 90% of these operating engineers (OEs) 

performed excavating and paving work and operated earthmoving equipment, such as scrapers, dozers, backhoes, and 

loaders; the remaining 10% were crane operators. Operators of 

earthmoving equipment historically experience elevated rates 

of musculoskeletal discomfort and disorders. Zimmerman et 

al.(2) found that OEs reported that the greatest frequency of 

symptoms, missed work, and physician visits were related 

to the low back, neck, and shoulder regions. Tola et al.(3) 

found that operators of earthmoving machinery reported higher 

magnitudes of neck and shoulder discomfort than office 

workers and carpentry construction workers. 

Two prominent work-related musculoskeletal disorder 

(WMSD) risk factors among operators of heavy earthmoving 

equipment are static sitting and whole-body vibration,(4−6) 

where long-term exposure to these risk factors has been 

associated with low back pain, disc degeneration, sciatic pain, 

and muscle fatigue.(7−9) 

Operators of earthmoving equipment are also exposed to 

awkward joint postures. Zimmerman et al.(2) indicated that 

operators self-reported job factors that were most problematic: 

bending and twisting of the back and working in the same 

position for long periods of time. Tola et al.(3) reported that 

working in twisted or bent postures increased the occurrence 

of neck and shoulder symptoms for operators of earthmoving 

machinery. Kittusamy(6) quantified the duration of time in nonneutral postures for OEs operating earthmoving equipment 

during digging-related tasks. Using videotape analysis, and 
depending on the task and equipment studied, the trunk was 

in non-neutral postures as much as 68% of the operation time, 

the shoulders were in non-neutral postures as much as 71% of 

the operation time, and the neck was in non-neutral postures 

up to 45% of the operation time. 

It has been suggested that exposure to WMSD risk factors 

stems from the interface between the design of the equipment 

and cab interior (e.g., location of controls, windows, and 

mirrors)(1,2) and characteristics of the task (e.g., duration 

of the task, location of the task that dictates the viewing 

angle).(2,6) Thus, the design of the cab interior may influence awkward postures of the joints, whereas the long 

duration of the task may influence the static exposure to 

awkward postures as well as long-term exposure to whole-body 

vibration. 

To reduce long-term exposure to the WMSD risk factors 

related to the interface between cab design and task, it may be 

necessary for manufacturers to address the design of the cab.(2) 

Feedback from equipment evaluations and user comments 

to the manufacturers are necessary for successful redesign, 

suggesting there is a need for a reproducible evaluation tool to 

assess the design of the cab of the equipment. 

Kittusamy(10) developed a checklist to evaluate the cab design of mobile construction equipment (Table I). The checklist 

is a general assessment tool for identifying characteristics of 

the cab that may affect operator performance and suggest 

need for improvement. The checklist was drafted on the 

basis of a literature review and discussion with operators of 

construction equipment. Subsequently, the draft checklist was 

pilot tested with input from trainers, operating engineers, and 

apprentices.(10) 

TABLE I. Cab Design Checklist Questions 

Questions Yes No N/A Comments 

1 

2 

3 

4 

5 

6 

7 

8 

9 

10 

11 

12 

13 

14 

15 

16 

17 

18 

19 

20 

21 

22 

23 

24 

25 

26 

27 

28 

29 

30 

31 

Is the seat height adjustable? 

Can the seat be adjusted horizontally? 

Is the seat set at proper height? 

Does the seat have a back support? 

Does the seat have a lumbar support? 

Are there armrests available? 

Are the armrests adjustable? 

Are the armrests set at proper height? 

Do you feel any vibration from the equipment through the seat? 

Do you feel any vibration from the equipment through the floor? 

Do you feel any vibration from the equipment through the controls? 

Is the seat firmly mounted to the floor of the cab? 

Can the seat be tilted backward? 

Can the seat swivel? 

Is the location of the controls or levers adjustable? 

Can you easily reach the levers or controls? 

Can you easily operate the levers or controls? 

Can you easily reach the pedals? 

Can you easily operate the pedals? 

Is the cab area large enough (e.g., uncramped area) for you? 

Do you have sufficient upward visibility? 

Is your view of the operation obstructed (e.g., cab guards, pipes/hoses, etc.)? 

Do you feel the cab is noisy? 

Can you control the temperature of the cab? 

Does the equipment have steps? 

Does the equipment have handrails? 

Can you easily open/close the cab doors? 

Does the equipment have proper means for entering the cab? 

Does the equipment have proper means for exiting the cab? 

Do you have a good general view of the ground? 

Are the cab windows free from distracting reflections? 

Note: Questions are from article by Kittusamy. 

 

This checklist was designed to be used as an interactive 

tool between the operator of the equipment and the individual 

administering the checklist. Approximately half the questions 
 

ask the operator’s opinion (yes/no) on cab design issues such 

as vibration from the equipment, reaching, and operating 

the controls, visibility of the task, and the cab area. The 

remaining questions address cab design characteristics that 

are more structural in nature, such as seat characteristics (e.g., 

back and lumbar support, adjustable, tilt capability), armrest 

characteristics (e.g., are they present, adjustable, etc.), and 

egress means. 

Although the intent of this checklist is to provide manufacturers with feedback on cab design issues that may 

need to be improved, the checklist has not been assessed 

for repeatability of responses. In addition, because previous 

research suggests that cab design may influence postural 

contributions to musculoskeletal discomfort, it is of interest to 

determine whether specific sets of questions of this checklist 

are associated with awkward postures during operation. 

The objective of this study was to assess the repeatability of 

the cab design checklist from the observations of the administrators and responses of the operators to the checklist questions. 

Also investigated were the potential associations between 

specific sets of questions of the cab design characteristics and 

resulting awkward postures of the neck, shoulder, and trunk. 

METHODS 

Approach 

The methodology used for this study consisted of videotaping OEs while they operated different types of heavy 

mobile equipment, quantification of joint postures through 

observational techniques, and administration of the cab design 

checklist by two individuals to assess the repeatability of the 

checklist. 

Subjects 

Four OEs volunteered to answer questions from the cab 

design checklist. The mean age of the OEs was 47 years 

(standard deviation [SD], 6.4 years) and they had a mean 

experience of 25 years (SD, 7.1 years). 

Study Site 

The cab design checklist data were collected over 2 days at 

the International Union of Operating Engineers training center 

in Ellensburg, Wash. Weather and soil conditions were dry 

during data collection days. Cabs of 10 different types of heavy 

mobile equipment such as excavators, dozers, tower cranes, 

graders, scrapers, loaders, and dump trucks were assessed 

(Table II); the operators were videotaped. 

TABLE II. Equipment Characteristics 

Type of 

Equipment Manufacturer Model 

Skidsteer Bobcat 763 

Tower Crane Liebherr 132HC 

Excavator Hitachi EX 220 

Loader John Deere 744H 

Dozer 1 John Deere 650H 

Dump Truck John Deere BELL25C 

Scraper International Harvester 431B 

Grader John Deere 772CH 

Dozer 2 Caterpillar (CAT) D8R 

Backhoe/Loader Caterpillar (CAT) 416C 

Experimental Procedure 

Prior to data collection, the four participating OEs were 

briefed about the study and provided their informed consent. All data collection was performed by researchers from 

the National Institute for Occupational Safety and Health– 

Spokane Research Laboratory, with support from the International Union of Operating Engineers. Detailed data 

analysis was performed by researchers at Wichita State 

University. 

The cab design checklist was administered by two individuals: one administrator with 2 years’ experience in 

ergonomics, the other with approximately 20 years’ experience 

in ergonomics. One of the administrators read the checklist questions to the equipment operator and then recorded 

the operator’s responses. After answering all the questions, 

the operator then performed construction tasks that were 

videotaped for approximately 30 min. After videotaping 

was completed, the operator returned to the data collection location. The other administrator then read checklist 

questions to the operator and recorded the responses. The 

order in which the administrators collected this data was 

randomized. 

Two unsynchronized video cameras were installed in the 

cabs to capture left and right side views of the OEs. The 

cameras were turned on as close to simultaneously as possible, 

and video was collected for approximately 30 min in each 

piece of equipment. Camera angles were chosen so that 

joints of interest (i.e., the neck, trunk, and shoulders) were 

clearly visible. After videotaping, a posture analysis was 

performed on all subjects for all joints of interest, on all pieces 

of construction equipment. Then the video analysis process 

was repeated once more to verify consistency with the first 

analysis. 

To analyze the recorded postures, video analysis software (Multimedia Video Task Analysis [MVTA], NexGen 

Ergonomics, Montreal) was used. Events (e.g., posture) were 

discretely and interactively identified by using break points in 

the video record (identifying the start and end of an event). 

MVTA produces time study reports that included the duration 

of each defined event. 

Three different joints and their corresponding categories 

of posture (i.e., high and low exposure) were predefined in 

the software. While the video played, the analyst pressed the 

appropriate predefined key, and the software automatically 

recorded the duration of cycle time and saved it under 

the corresponding category. During the video analysis, the 
 

analysts had the option of stopping or slowing down the 

video. 

Postural Categories 

Range of motion of the joints was divided into predetermined postural categories (Figure 1), which were based on 

the categories identified in the WMSD exposure assessment 

literature.(6,11−15) Lowe(16) indicated that fewer postural categories resulted in fewer posture exposure misclassifications, 

increasing the accuracy of the exposure assessment. Thus, 

two postural categories were used for each joint and plane 

of interest for the postural assessment. 

FIGURE 1. Posture categories used to classify neck, trunk, and shoulder postures 

Exposure categories for neck flexion were 0◦–45◦ (low) and 

>45◦ (high), and 0◦–20◦ (low) and >20◦ (high) for lateral 

neck bending and neck twisting.(13,14) Postural categories 

for trunk flexion were 0◦–30◦ (low) and >30◦ (high), 0◦– 

20◦ (low) and >20◦ (high) for lateral trunk bending and 

trunk twisting.(12,15) Shoulder flexion and abduction postural categories were defined as 0◦–60◦ (low) and >60◦ 

(high).(17) 
 

Data Analysis 

The overall cab design checklist score was determined by 

using all 31 questions of the cab design checklist. Questions 9, 

10, 11, 22, and 23 were negatively phrased so that an affirmative 

answer meant the same as the other questions in the checklist (a positive response). The percentage of the affirmative 

answers to all 31 questions was determined. The closer this 

value was to 100%, the better the design (or acceptability) of 

the cab. This measure assumes equal weighting for each of the 

questions, and each question measures a different characteristic 

that might impact the ergonomics of the cab design. 

Joint-specific checklist scores were determined using specific questions about cab design features that could contribute 

to awkward postures of the neck, trunk, and shoulders. 

Questions that addressed cab design characteristics that could 

impact awkward postures of a specific joint were grouped. Ten 

questions from the cab design checklist were used for the neck 

postures (Questions 1, 2, 3, 14, 16, 17, 21, 22, 30, and 31). 

These included questions about seat height and adjustability, 

which could affect neck posture to see controls or see the work 

location, and location of controls that may necessitate awkward 

postures to see the levers. 

Fourteen questions were used for the trunk postures (Questions 1, 2, 3, 4, 5, 13, 14, 15, 16, 17, 21, 22, 30, and 31), 

which included questions about seat height, adjustability, tilt, 

lumbar support, and lever locations that may result in reaching, 

bending of the trunk, and view of the work outside the cab. 

Seven questions were used for the shoulder postures (Questions 

1, 2, 3, 14, 15, 16, and 17), which included questions about seat 

adjustability and lever locations that may result in reaching to 

operate. 

Again, the closer the joint specific cab design checklist score 

was to 100%, the better the design (or acceptability) of the 

cab for the specific joint of interest. For assessment purposes, 

a checklist score at or above 80% was arbitrarily chosen to 

suggest adequate design or acceptability. 

Statistical Analysis 

Due to the intended interactive nature for the administration 

of the cab design checklist, the repeatability assessment is 

a combination of repeatability: (a) for the questions about 

equipment operation, and (b) of the interaction between the 

administrator and operator in addressing questions regarding 

cab characteristics that were more structural in nature. Checklist repeatability was assessed by using the kappa coefficient, 

which was computed using the data collected by two different 

administrators for all 31 questions, assessing each of the 

10 pieces of equipment separately. In addition, the overall 

repeatability of the cab design checklist was determined by 

calculating the kappa coefficient for the combination of the 10 

pieces of equipment. The kappa values were interpreted using 

the guidelines by Landis and Koch(18) and a one-tailed test was 

employed to test the hypothesis H0: κ = 0 vs. H1: κ > 0 setting 

α = 0.05.(19) 

To determine whether specific groups of questions of 

the cab design checklist were capable of identifying cab 

design features that may be associated with awkward joint 

postures, the Pearson product moment correlation coefficient 

was calculated between the duration of each joint in the low 

postural category and the joint-specific cab design checklist 

score (i.e., neck, shoulder, trunk) from the 10 pieces of 

equipment combined. Only the checklist scores from the more 

experienced administrator were used for this analysis. 

RESULTS 

Overall Cab Design Checklist Scores 

The results of the overall cab design checklist scores for 

each of the 10 pieces of equipment are shown in Table III. 

Six of the 10 pieces of equipment had scores greater than 

80%, indicating that for 6 pieces of equipment, more than 

80% of the 31 checklist questions were answered with an 

affirmative (or positive) response. The grader had the highest 

score (90%) and the skidsteer the lowest score (56%), suggesting the grader had a better overall cab design than the 

skidsteer. 

TABLE III. Overall Cab Design Checklist Scores 

Equipment Overall Score (%) 

Skidsteer 56 

Tower crane 86 

Excavator 81 

Loader 74 

Dozer 1 76 

Dump truck 87 

Scraper 61 

Grader 90 

Dozer 2 81 

Backhoe/loader 81 

Note: Percentages of affirmative answers as a function of each piece of 

equipment. 

Joint-Specific Cab Design Checklist Scores 

Joint-specific cab design checklist scores are shown in 

Table IV. For the neck and trunk, the majority of the equipment 

had scores ≥80% (e.g., affirmative answers on the jointspecific questions), whereas only half the equipment had 

shoulder joint-specific scores ≥80%. The skidsteer and the 

scraper had joint-specific scores less than 80% for all three 

joints, suggesting that the design of the cab may influence awkward postures of multiple joints of the operators. Conversely, 

the excavator, grader, and backhoe/loader had joint-specific 

checklist scores ≥80% for all three joints, suggesting that cab 

design characteristics may result in what may be considered 

nonawkward postures of the neck, trunk, and shoulders. 

Joint-Specific Posture Analysis 

The type of equipment used by the operators along with 

the duration (percentage of time) in the low postural category 
 

TABLE IV. Joint-Specific Cab Design Checklist 

Scores 

Joint 

Equipment Neck (%) Trunk (%) Shoulder (%) 

Skidsteer 60 54 60 

Tower crane 82 69 80 

Excavator 82 81 80 

Loader 73 80 70 

Dozer 1 80 87 70 

Dump truck 73 88 80 

Scraper 73 75 50 

Grader 82 82 90 

Dozer 2 82 82 70 

Backhoe/loader 91 82 80 

Note: Percentages of affirmative answers as a function of individual equipment 

and body joints. 

for neck, trunk, and shoulder joints obtained from postural 

analysis are shown in Table V. Operators spent at least 90% 

of the observed operation time in the low postural category 

for all 10 pieces of equipment for neck flexion, lateral neck 

bending, trunk flexion and lateral bending, left shoulder flexion 

(except for the scraper), right shoulder flexion, and left and 

right shoulder abduction. 

Neck twisting and trunk twisting were more prevalent as 

far as percentage of time spent away from the low postural 

category. For neck twisting, only the skidsteer resulted in 

duration above 90% in the low postural category, with a mean 

across all equipment of 77.1%. Twisting of the trunk was also 

less prevalent in the low postural category, where the excavator, 

loader, both dozers, scraper, and grader had durations in the 

low postural category of less than 90%, with a mean across all 

equipment of 88.5%. 

Cab Design Checklist Repeatability 

The kappa coefficients ranged from 0.52 to 1.0 across 

each piece of equipment, which represents good-to-perfect 

repeatability of the checklist (Table VI), and all kappa coefficients were significantly greater than zero (p < 0.001). 

The skidsteer, the scraper, and one of the dozers had excellent 

repeatability; the excavator had perfect agreement; and the rest 

of the equipment had good repeatability. When considering all 

10 pieces of equipment together, the kappa coefficient was 

0.77, which indicates excellent repeatability for the cab design 

checklist across multiple equipment types. 

Matching answers to the checklist questions given to 

both administrators are presented in Table VII. Twenty of 

the 31 questions (64.5%) had either no mismatches or one 

mismatched response across the 10 pieces of equipment; 9 

of the 31 questions (29%) had two mismatched answers. The 

questions that had the largest number of mismatched responses 

were Question 13: Can the backrest be tilted backward? (three 

mismatched answers) and Question 22: Is your view of the 

operation obstructed? (four mismatched answers). 

Cab Design and Joint Posture Correlation 

The correlation assessment between the joint-specific cab 

design checklist scores (across all 10 pieces of equipment) 

and the duration of time in the low postural category resulted 

in no significant correlations (Table VIII). All 10 pieces of 

construction equipment were large machinery except for the 

skidsteer, where the cabin was much more cramped than the 

rest of the equipment. Thus, the correlation between the jointspecific cab design checklist scores and the duration of time in 

the low postural category were assessed for mobile equipment 

of similar size (i.e., excluding the skidsteer), which can be 

found in Table VIII. 

Left shoulder flexion was significantly correlated with the 

joint-specific cab design checklist score for the shoulder (r = 

0.73; p = 0.025), whereas right shoulder flexion approached 

significance (r = 0.59; p = 0.095). No other postures were 

significantly correlated with the joint-specific cab design 

checklist scores. 

DISCUSSION 

The operation of mobile construction equipment results in 

exposure to several risk factors for WMSDs, including 

whole-body vibration and long duration of sitting that result 

in static loading on the spine.(1) In addition, the location of the 

controls, combined with the necessity to be able to see outside 

the cab in nearly all directions, can result in sustained and 

repeated awkward postures of the neck, shoulder, and torso. 

Thus, the design of the cab and the interface with the job 

requirements influences the exposure to WMSD risk factors. 

Intervention strategies to reduce the WMSD risk include 

decreasing the magnitude and duration of exposure to risk 

factors, such as vibration and unsupported static sitting. 

However, to address the awkward postures that can result due 

to the design of the cab and location of controls, it may be 

necessary to identify these limitations early in the design stage. 

Thus, the cab design checklist was developed in an attempt to 

identify design deficiencies with respect to WMSD risk factors. 

It is anticipated that the cab design checklist will be used by 

multiple administrators as a tool to evaluate multiple pieces of 

mobile equipment. Because it is likely that different individuals 

will administer a checklist such as this one, it is important that 

the checklist produce repeatable results regardless of who is 

performing the evaluation. 

Thus, the major objective of this study was to assess 

the repeatability of the cab design checklist. Using two 

checklist administrators, one with many years of experience 

in ergonomics and heavy construction and one relatively new 

to the field, the results indicated that the repeatability of the 

cab design checklist ranged from good to perfect across all 

10 pieces of equipment, with an overall kappa coefficient of 

0.77 across all the equipment (i.e., excellent agreement). This 
TABLE V. Joint-Specific Duration of Time (%) in Low Exposure Category 

Trunk Left Left Right Right 

Neck Neck Neck Trunk Lateral Trunk Shoulder Shoulder Shoulder Shoulder 

Flexion Bending Twist Flexion Bending Twist Flexion Abduction Flexion Abduction Mean 

Equipment (<45◦) (<20◦) (<20◦) (<30◦) (<20◦) (<20◦) (<60◦) (<60◦) (<60◦) (<60◦) (SD) 

Skidsteer 100 100 93 100 100 99 100 100 100 100 99.2 

(2.2) 

Tower crane 99 100 82 100 100 100 100 100 100 91 97.2 

(6.0) 

Excavator 99 99 84 97 98 79 92 100 100 100 94.8 

(7.5) 

Loader 98 100 82 98 99 88 100 100 99 100 96.4 

(6.2) 

Dozer 1 99 100 88 97 98 88 91 99 100 100 96.0 

(5.0) 

Dump truck 97 95 69 99 99 91 100 99 98 99 94.6 

(9.4) 

Scraper 95 100 60 99 92 76 65 100 97 100 88.4 

(15.5) 

Grader 99 99 66 97 95 74 100 100 100 100 93.0 

(12.4) 

Dozer 2 93 90 68 98 94 92 100 99 100 98 93.2 

(9.5) 

Backhoe/loader 100 99 79 100 100 98 100 100 100 100 97.6 

(6.6) 

Mean 97.9 98.2 77.1 98.5 97.5 88.5 94.8 99.7 99.4 98.8 

(SD) (2.3) (3.3) (10.7) (1.3) (2.8) (9.5) (11.1) (0.5) (1.1) (2.8) 

TABLE VI. Kappa Coefficients for the Repeatability 

of the Cab Design Checklist 

Equipment 

Kappa 

Coefficient p-value Agreement 

Skidsteer 

Tower crane 

Excavator 

Loader 

Dozer 1 

Dump truck 

Scraper 

Grader 

Dozer 2 

Backhoe/loader 

All equipment 

0.77 

0.70 

1.00 

0.69 

0.74 

0.52 

0.87 

0.53 

0.90 

0.71 

0.77 

<0.001 

<0.001 

<0.001 

<0.001 

<0.001 

<0.001 

<0.001 

<0.001 

<0.001 

<0.001 

<0.001 

Excellent 

Good 

Perfect 

Good 

Good 

Good 

Excellent 

Good 

Excellent 

Good 

Excellent 

Note: Coefficients as a function of each piece of construction equipment. 

checklist thus has the potential to produce reproducible results 

no matter who is administering the checklist. 

The majority of the checklist questions (29 of 31) were 

consistently answered for both administrators across 80% 

of the equipment assessed. Question 22 (Is your view of 

the operation obstructed?) was inconsistently answered for 

four pieces of equipment. It is possible that the inconsistent 

response may be related to the tasks that were performed 

between the time of the first and second administration of 

the checklist. Question 13 (Can the seat be tilted backward?) 

was inconsistently answered for three pieces of equipment. 

Although it is unknown why this was responded to differently 

three times, it is possible that the operators did not, in fact, 

know the true ability of the seat, or confused it with another seat 

function. 

Overall, however, the cab design checklist proved to be repeatable, with the majority of the questions eliciting consistent 

responses. The checklist may have the potential to be used to 

assess different types of large mobile equipment to provide 

feedback to manufacturers for improvement in the interface 

between the task and interior cabin design, with the ultimate 

goal of reducing exposure to risk factors to WMSDs for the 

operators of the equipment. 

The postural assessment during operation of the various 

pieces of equipment suggests that twisting of the neck and of 

the torso are the most frequent awkward postures assumed. 

This is consistent with findings from previous studies by 

Zimmerman et al.(2) and Tola et al.(3) Zimmerman et al. 

reported that OEs felt that working in the same position 

and bending and twisting the back in an awkward way 

were the two highest rated job factors perceived as most 
 

TABLE VII. Correct Matches Between the Two Administrators 

Questions Yes No N/A Comments 

Correct 

Matches 

1 Is the seat height adjustable? 

2 Can the seat be adjusted horizontally? 

3 Is the seat set at proper height? 

4 Does the seat have a back support? 

5 Does the seat have a lumbar support? 

6 Are there armrests available? 

7 Are the armrests adjustable? 

8 Are the armrests set at proper height? 

9 Do you feel any vibration from the equipment through the seat? 

10 Do you feel any vibration from the equipment through the floor? 

11 Do you feel any vibration from the equipment through the controls? 

12 Is the seat firmly mounted to the floor of the cab? 

13 Can the seat be tilted backward? 

14 Can the seat swivel? 

15 Is the location of the controls or levers adjustable? 

16 Can you easily reach the levers or controls? 

17 Can you easily operate the levers or controls? 

18 Can you easily reach the pedals? 

19 Can you easily operate the pedals? 

20 Is the cab area large enough (e.g., uncramped area) for you? 

21 Do you have sufficient upward visibility? 

22 Is your view of the operation obstructed (e.g., cab guards, pipes/hoses, etc.)? 

23 Do you feel the cab is noisy? 

24 Can you control the temperature of the cab? 

25 Does the equipment have steps? 

26 Does the equipment have handrails? 

27 Can you easily open/close the cab doors? 

28 Does the equipment have proper means for entering the cab? 

29 Does the equipment have proper means for exiting the cab? 

30 Do you have a good general view of the ground? 

31 Are the cab windows free from distracting reflections? 

10/10 

8/10 

10/10 

10/10 

8/10 

10/10 

8/10 

8/10 

8/10 

8/10 

9/10 

10/10 

7/10 

10/10 

9/10 

9/10 

10/10 

10/10 

10/10 

8/10 

10/10 

6/10 

8/10 

9/10 

9/10 

10/10 

8/10 

10/10 

10/10 

9/10 

10/10 

Note: Correct matches across the 10 pieces of equipment. 

problematic. Tola et al. reported that working in twisted or 

bent postures (e.g., neck and shoulders) were predictors of 

neck and shoulder symptoms of operators of earthmoving 

machinery. 

All other postures were in the low postural category for 

more than 90% of the observation time (mean of all 10 pieces 

of equipment), suggesting adequate posture for the individuals 

observed. The scraper was the piece of equipment that resulted 

in the lowest percentage of time for postures in the low 

postural category collectively across all equipment, which was 

dictated by longer durations in the high awkward postural 

category for neck twisting, trunk twisting, and left shoulder 

flexion. 

The durations of time in the low postural categories in 

this study were higher than those reported by Kittusamy,(6) 

However, Kittusamy quantified posture of the trunk, neck, and 

shoulders for dynamic digging tasks, which may have required 

more awkward postures of the joints to see the work location. In 

addition, the video cameras for Kittusamy were placed outside 

the cab, which may have resulted in obstructions in the video, 

whereas the cameras in the present study were placed inside 

the cab. 

The correlation analysis performed between the jointspecific cab design checklist scores and the low exposure 

posture category values suggested a potential relationship between design characteristics of the cab (e.g., lever and control 

placement, seat height, and adjustability) and shoulder flexion. 

Twisting of the arms and shoulders and bending have been 

noted in studies assessing musculoskeletal discomfort,(2,3) 

which were related to location of controls. The correlations 

between the cab design checklist questions related to shoulder 

posture and duration of shoulder flexion were not significant 
 

TABLE VIII. Correlation Between Joint-Specific Cab Design Checklist Scores and Duration of Time in Low 

Exposure Category 

All Equipment All Equipment Except Cab Design (N = 10) Skidsteer (N = 9) Checklist 

Joint Posture Correlation (r) p-value Correlation (r) p-value 

Neck Neck flexion 0.08 0.80 0.23 0.51 

Neck lateral bending −0.22 0.50 −0.17 0.64 

Neck twisting −0.31 0.32 −0.16 0.66 

Trunk Trunk flexion −0.28 0.43 −0.14 0.72 

Trunk lateral bending 0.02 0.95 0.19 0.63 

Trunk twisting −0.19 0.60 −0.01 0.98 

Shoulder Shoulder flexion (right) 0.35 0.32 0.59 0.095 

Shoulder flexion (left) 0.52 0.12 0.73 0.025 

Shoulder abduction (right) 0.00 1.00 0.11 0.78 

Shoulder abduction (left) 0.05 0.89 0.23 0.55 

when the skidsteer was included in the analysis, whereas these 

correlations became and approached significance when it was 

excluded. 

It may be that the compact design of the skidsteer, and 

placement of the video camera that showed a view of the 

operator, was unlike the operators of other larger equipment 

that had larger cabs. Overall, for larger mobile construction 

equipment, questions from the cab design checklist related to 

seat height and adjustability, and the location of controls in 

relation to ease of operation, may have the potential to identify 

cab design characteristics that are consistent with awkward 

postures of the shoulder, specifically, shoulder flexion. 

The results of this study should be considered in light 

of methodological limitations. First, although the postural 

categories were based on previous studies and epidemiologic 

research, the duration in the different joints in the low postural 

category should be interpreted with caution, as some joints 

included a large range in the low postural category (e.g., 

shoulder flexion and abduction from 0◦ to 60◦), and shoulder 

musculoskeletal problems may arise at shoulder flexion and 

abduction angles less than 60◦ . 

Also, it is likely that operators reduced the loading on the 

shoulders at large angles of flexion by resting their arms on 

the steering wheel at times; however, the confined space in 

the cabs did not allow a camera field of view large enough to 

consistently determine this. Second, the categorical postural 

quantification was based on one observer where the reliability 

of the postural assessment is not known. 

Third, only the responses from one of the checklist administrator’s was used for correlation analysis between the 

postural categories and specific checklist sets of questions 

related to posture of the neck, shoulder, and trunk. Because the 

repeatability was good to excellent across the responses of both 

administrators, this was considered to be a minor limitation. 

Finally, the accuracy of the off-plane postures such as twist 

and lateral bending is not known and may be questioned due 

to the postures not being in the oblique field of view of the video 

camera. This may be why only the sagittal plane postures of the 

shoulders resulted in higher correlations with posture specific 

cab design checklist questions. 

CONCLUSION 

Operating engineers experience musculoskeletal discomfort at elevated rates to the low back, neck, and shoulders. 

The risk factors that increase the risk of musculoskeletal 

discomfort and disorders are related to the design of the 

task and the design characteristics of the cab of mobile 

construction equipment. The cab design checklist developed 

by Kittusamy(10) contains excellent repeatability when used 

across multiple types of mobile construction equipment. 

Compared with videotaping and analysis, this checklist is a 

quick and less costly method to identify potential problems 

in the cab design. Finally, use of this checklist can provide 

information that can be used by the operator, supervisor, and 

equipment manufacturer of mobile equipment to modify cab 

characteristics that can enhance the overall safety and health 

of the operators. 

ACKNOWLEDGMENTS 

This study was funded by the National Institute for 

Occupational Safety and Health, Spokane Research 

Lab (NIOSH-SRL). The authors are grateful for the participation of the members of International Union of Operating Engineers (IUOE) Training Center at Ellensburg, 

Washington. 

The authors would also like to thank researchers from 

NIOSH-SRL: Richard E. Miller, Grant W. King, and 

Muthukaruppan Viswanathan (contractor) for collecting field 

data for this study. The authors appreciate the support of IUOE 

Headquarters in performing this study. 
 

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