Ranjana Mehta | Texas A&M Health Science Center (original) (raw)

Papers by Ranjana Mehta

The goal of this study was to investigate the effects of fatigue and aging on the performance of ... more The goal of this study was to investigate the effects of fatigue and aging on the performance of spatially constrained drilling tasks that are observed within the construction industry. Eight younger (18-35 years) and eight older (45-60 years) participants were selected from the local community. Participants were presented with two conditions of localized muscle fatigue in the anterior musculature of the shoulder (No Fatigue and a Fatigue condition). During each condition, participants completed a series of drilling tasks at three levels of task difficulty; as defined by the spatial arrangement of the fasteners. The dependent variables; task completion time, error rate and muscle activation patterns (shoulder APDF and coactivity indices of the upper and lower arm), were measured using observations and electromyography of the muscles of the upper extremity. The presence of localized shoulder fatigue significantly reduced task completion times for both age groups at all levels of task difficulty. Further, error rate was higher for the younger age group in the fatigue condition compared to the no fatigue condition; no such differences were seen for the older subjects. Muscle activity decreased for the anterior deltoid in the fatigue condition, and concurrent increases were observed in the coactivity indices of the upper and the lower arm musculature.

Healthcare workers have a high risk of work-related musculoskeletal disorders. This study compare... more Healthcare workers have a high risk of work-related musculoskeletal disorders. This study compared the physical demands placed on healthcare workers associated with two alternative bed design features: steering lock and bed contour. Use of a steering lock during hallway maneuvering reduced the number of adjustments required, perceived difficulty, and perceived physical effort. The contour feature reduced patient displacements after repeated bed raising/lowering, suggesting a reduction in physical demands to readjust patient position. Ergonomic evaluations can facilitate the development of hospital bed designs that reduce physical demands on healthcare workers, and contribute to a reduction in occupational injury.

Student surveys are frequently used in engineering program assessment, however, it is not clear t... more Student surveys are frequently used in engineering program assessment, however, it is not clear that established survey design and analysis strategies from the research domain are applied on a widespread basis in program assessment. This paper describes the use of a student survey as one of several important tools to assess an Industrial Engineering program. Survey development, overall survey content, data analysis methods (including factor analysis), portrayal methods for results, and insights and actions based on results, are discussed.

Workers experience combined physical and mental demands in their daily jobs, yet the contribution... more Workers experience combined physical and mental demands in their daily jobs, yet the contribution of these concurrent demands in the development of work-related musculoskeletal disorders (WMSDs) is not clearly understood. There is a need to understand how concurrent demands interact with different work parameters, such as force levels, muscles employed, and types of exertion, to influence physiological responses. Furthermore, whether muscle capacity is altered with these concurrent demands remains unclear. The current research was conducted to address these needs through three experimental studies that evaluated changes in physiological, performance, and subjective measures.

The first study investigated muscle-specific responses to concurrent physical and mental demands during intermittent static work. Mental demands adversely affected physiological responses with increasing physical demand. Furthermore, greater motor and mental performance impairment was observed at either end of the physical demand spectrum. Finally, these interactions were muscle-dependent, with postural (shoulder and torso) muscles indicating a greater propensity to interference due to concurrent demands than executive (wrist) muscles.

The aim of the second study was to evaluate differential effects of exertion type (static and dynamic) during concurrent physical and mental work. Concurrent physical and mental demands adversely affected physiological responses during static exertions compared to dynamic exertions. Furthermore, static exertions were more susceptible to decrements in muscle output and mental task performance than dynamic exertions, specifically at higher force levels.

The last study quantified the effects of concurrent physical and mental demands on muscle capacity (endurance, fatigue, and recovery) during intermittent static work. Additional mental processing was associated with shorter endurance times, greater strength decline, increased fatigability, and slower cardiovascular recovery. Concurrent demand conditions were also associated with higher levels of perceived fatigue, and rapid increases in rates of perceived exertion, time pressure, mental load, and stress.

Overall, the current research provides a comprehensive understanding of the interactive effects of physical and mental demands on physiological responses and task performance. These findings may facilitate the development of task design strategies to help reduce the risk of workplace injuries and to increase worker performance. Finally, outcomes from this research can contribute towards the revision of current ergonomic guidelines to incorporate concurrent assessment of physical and mental demands.

Human Factors and …, Jan 1, 2009

Workplace tasks that involve multidimensional demands, such as physical and cognitive workloads, ... more Workplace tasks that involve multidimensional demands, such as physical and cognitive workloads, may increase the injury risks posed on workers. To aid in designing ergonomic guidelines for workplace safety, it is thus important to understand the interactive nature of these combined demands. The goal of this study was to investigate the effects of said multidimensional demands on the muscles of the upper extremity. Seventeen healthy participants performed isometric upper extremity exertions at five levels of physical intensities (5%, 25%, 45%, 65%, and 85% maximum voluntary contraction (MVC)) in the presence and absence of a mental task. Mean shoulder muscle activity and co-contraction indices (CCI) of the upper extremity were measured using electromyographic signals. Force fluctuations were measured using a force transducer to evaluate joint steadiness. In general, shoulder muscle activity (mean activity and CCIs) increased with increasing levels of physical exertions. A decrease in mean anterior and posterior deltoid muscle activity and CCI of the shoulder was observed in the presence of the mental task. However, these changes were more prominent at higher levels of physical workload compared to the lower levels. Force fluctuations were lowest at 25% MVC, and highest at 85% MVC. Mental workload significantly increased force fluctuations at 85% MVC, which may have been a result of decreased muscle output to maintain the loads in a steady posture. Overall, results from this study suggest that certain task demands are more susceptible to interference by mental workload than others. It will provide a better understanding of combined exposure levels in occupational settings and serve as a guideline to determine task demands for different occupational settings.

Patient handling tasks (e.g., transportation and repositioning) are important causes of musculosk... more Patient handling tasks (e.g., transportation and repositioning) are important causes of musculoskeletal disorders among healthcare workers. The purpose of this study was to evaluate, during two patient handling tasks, the physical demands resulting from alternative hospital bed design features. Twenty-four novice participants were involved in two laboratory-based studies. The effects of a steering lock and adjustable push height were evaluated during a patient transportation task using perceptual responses and measures of performance and physical demands, and the effect of a bed contour feature was determined based on patient sliding distance during repeated bed raising/lowering. Use of the steering lock reduced the number of adjustments during bed maneuvering by 28% and decreased ratings of physical demands. Use of the adjustable push height reduced shoulder moments by 30%. With the contour feature, patient sliding distance was reduced by 40% over 12 raise/lower cycles. These results suggest that the steering lock and adjustable push height features can reduce physical demands placed on healthcare workers during patient transportation tasks. Although patient sliding distance was reduced using the contour feature, assessing direct effects of this feature on physical demands (e.g., reduced need for workers to reposition patients) will require further investigation.

The purpose of this study was to quantify the effects of concurrent physical and mental demands o... more The purpose of this study was to quantify the effects of concurrent physical and mental demands on the upper extremity muscle activity during static exertions. Seventeen healthy participants performed isometric upper extremity exertions at five levels of physical intensity (5%, 25%, 45%, 65%, and 85% maximum voluntary contraction (MVC)) in the presence and absence of a mental task (Stroop color word test). Muscular responses were quantified using surface electromyography (EMG) and motor performance was measured through force fluctuations. Subjective assessments were obtained through the NASA-TLX tool and the Borg CR-10 Scale. In general, a decrease in mean anterior and posterior deltoid muscle activity and co-contraction index (CCI) of the shoulder was observed in the presence of the mental task. However, these changes were more prominent at higher physical exertion levels compared to the lower levels. Furthermore, the additional mental task resulted in decreased upper and lower arm muscle activity, specifically at the 45% MVC level. Motor performance improved at the middle exertion levels, but was adversely affected by the mental task at higher exertion levels. Decreased motor performance at higher loads may have been a result of decreased muscular effort to maintain the loads in a steady posture. Both mental and physical demand adversely affected the NASA-TLX ratings, however, ratings using the Borg CR-10 Scale were only sensitive to changes in physical demand.

The purpose of this study was to evaluate age- and gender-dependent effects of shoulder fatigue o... more The purpose of this study was to evaluate age- and gender-dependent effects of shoulder fatigue on task performance and muscular responses of a drilling task commonly observed within the construction industry. Twelve younger (18–35 years) and ten older (45–60 years) participants, balanced by gender, were recruited from the local community. Task performance (task completion times and errors made), muscle activity of the anterior deltoid (static, mean, and peak amplitude probability density function), coactivity indices of the upper and lower arm, and perceived discomfort ratings were obtained for a series of drilling tasks at three levels of task difficulty, before and after manifestation of shoulder fatigue. To induce fatigue, participants performed a sustained sub-maximal fatigue task at 40% of their maximum voluntary shoulder exertion. Fatigue decreased task completion times, irrespective of age and gender. Higher errors were observed in the fatigued condition, especially for younger participants. Females showed higher shoulder muscle activity compared to men. Additionally, fatigue resulted in lower shoulder APDF measures compared to the no-fatigue condition. Muscle recruitment patterns differed within the fatigue condition, with higher coactivity indices in the upper and lower arm muscles compensating for decreases in shoulder muscle activity. Task difficulty was not found to affect any dependent measures. Participants reported higher discomfort in the fatigued state; this effect was more prominent in females. Overall, this study demonstrated, through objective and subjective measures, that task performance and biomechanical demands are affected by fatigue, and that this effect varies with individual factors such as gender and age.

The goal of this study was to investigate the effects of fatigue and aging on the performance of ... more The goal of this study was to investigate the effects of fatigue and aging on the performance of spatially constrained drilling tasks that are observed within the construction industry. Eight younger (18-35 years) and eight older (45-60 years) participants were selected from the local community. Participants were presented with two conditions of localized muscle fatigue in the anterior musculature of the shoulder (No Fatigue and a Fatigue condition). During each condition, participants completed a series of drilling tasks at three levels of task difficulty; as defined by the spatial arrangement of the fasteners. The dependent variables; task completion time, error rate and muscle activation patterns (shoulder APDF and coactivity indices of the upper and lower arm), were measured using observations and electromyography of the muscles of the upper extremity. The presence of localized shoulder fatigue significantly reduced task completion times for both age groups at all levels of task difficulty. Further, error rate was higher for the younger age group in the fatigue condition compared to the no fatigue condition; no such differences were seen for the older subjects. Muscle activity decreased for the anterior deltoid in the fatigue condition, and concurrent increases were observed in the coactivity indices of the upper and the lower arm musculature.

Healthcare workers have a high risk of work-related musculoskeletal disorders. This study compare... more Healthcare workers have a high risk of work-related musculoskeletal disorders. This study compared the physical demands placed on healthcare workers associated with two alternative bed design features: steering lock and bed contour. Use of a steering lock during hallway maneuvering reduced the number of adjustments required, perceived difficulty, and perceived physical effort. The contour feature reduced patient displacements after repeated bed raising/lowering, suggesting a reduction in physical demands to readjust patient position. Ergonomic evaluations can facilitate the development of hospital bed designs that reduce physical demands on healthcare workers, and contribute to a reduction in occupational injury.

Student surveys are frequently used in engineering program assessment, however, it is not clear t... more Student surveys are frequently used in engineering program assessment, however, it is not clear that established survey design and analysis strategies from the research domain are applied on a widespread basis in program assessment. This paper describes the use of a student survey as one of several important tools to assess an Industrial Engineering program. Survey development, overall survey content, data analysis methods (including factor analysis), portrayal methods for results, and insights and actions based on results, are discussed.

Workers experience combined physical and mental demands in their daily jobs, yet the contribution... more Workers experience combined physical and mental demands in their daily jobs, yet the contribution of these concurrent demands in the development of work-related musculoskeletal disorders (WMSDs) is not clearly understood. There is a need to understand how concurrent demands interact with different work parameters, such as force levels, muscles employed, and types of exertion, to influence physiological responses. Furthermore, whether muscle capacity is altered with these concurrent demands remains unclear. The current research was conducted to address these needs through three experimental studies that evaluated changes in physiological, performance, and subjective measures.

The first study investigated muscle-specific responses to concurrent physical and mental demands during intermittent static work. Mental demands adversely affected physiological responses with increasing physical demand. Furthermore, greater motor and mental performance impairment was observed at either end of the physical demand spectrum. Finally, these interactions were muscle-dependent, with postural (shoulder and torso) muscles indicating a greater propensity to interference due to concurrent demands than executive (wrist) muscles.

The aim of the second study was to evaluate differential effects of exertion type (static and dynamic) during concurrent physical and mental work. Concurrent physical and mental demands adversely affected physiological responses during static exertions compared to dynamic exertions. Furthermore, static exertions were more susceptible to decrements in muscle output and mental task performance than dynamic exertions, specifically at higher force levels.

The last study quantified the effects of concurrent physical and mental demands on muscle capacity (endurance, fatigue, and recovery) during intermittent static work. Additional mental processing was associated with shorter endurance times, greater strength decline, increased fatigability, and slower cardiovascular recovery. Concurrent demand conditions were also associated with higher levels of perceived fatigue, and rapid increases in rates of perceived exertion, time pressure, mental load, and stress.

Overall, the current research provides a comprehensive understanding of the interactive effects of physical and mental demands on physiological responses and task performance. These findings may facilitate the development of task design strategies to help reduce the risk of workplace injuries and to increase worker performance. Finally, outcomes from this research can contribute towards the revision of current ergonomic guidelines to incorporate concurrent assessment of physical and mental demands.

Human Factors and …, Jan 1, 2009

Workplace tasks that involve multidimensional demands, such as physical and cognitive workloads, ... more Workplace tasks that involve multidimensional demands, such as physical and cognitive workloads, may increase the injury risks posed on workers. To aid in designing ergonomic guidelines for workplace safety, it is thus important to understand the interactive nature of these combined demands. The goal of this study was to investigate the effects of said multidimensional demands on the muscles of the upper extremity. Seventeen healthy participants performed isometric upper extremity exertions at five levels of physical intensities (5%, 25%, 45%, 65%, and 85% maximum voluntary contraction (MVC)) in the presence and absence of a mental task. Mean shoulder muscle activity and co-contraction indices (CCI) of the upper extremity were measured using electromyographic signals. Force fluctuations were measured using a force transducer to evaluate joint steadiness. In general, shoulder muscle activity (mean activity and CCIs) increased with increasing levels of physical exertions. A decrease in mean anterior and posterior deltoid muscle activity and CCI of the shoulder was observed in the presence of the mental task. However, these changes were more prominent at higher levels of physical workload compared to the lower levels. Force fluctuations were lowest at 25% MVC, and highest at 85% MVC. Mental workload significantly increased force fluctuations at 85% MVC, which may have been a result of decreased muscle output to maintain the loads in a steady posture. Overall, results from this study suggest that certain task demands are more susceptible to interference by mental workload than others. It will provide a better understanding of combined exposure levels in occupational settings and serve as a guideline to determine task demands for different occupational settings.

Patient handling tasks (e.g., transportation and repositioning) are important causes of musculosk... more Patient handling tasks (e.g., transportation and repositioning) are important causes of musculoskeletal disorders among healthcare workers. The purpose of this study was to evaluate, during two patient handling tasks, the physical demands resulting from alternative hospital bed design features. Twenty-four novice participants were involved in two laboratory-based studies. The effects of a steering lock and adjustable push height were evaluated during a patient transportation task using perceptual responses and measures of performance and physical demands, and the effect of a bed contour feature was determined based on patient sliding distance during repeated bed raising/lowering. Use of the steering lock reduced the number of adjustments during bed maneuvering by 28% and decreased ratings of physical demands. Use of the adjustable push height reduced shoulder moments by 30%. With the contour feature, patient sliding distance was reduced by 40% over 12 raise/lower cycles. These results suggest that the steering lock and adjustable push height features can reduce physical demands placed on healthcare workers during patient transportation tasks. Although patient sliding distance was reduced using the contour feature, assessing direct effects of this feature on physical demands (e.g., reduced need for workers to reposition patients) will require further investigation.

The purpose of this study was to quantify the effects of concurrent physical and mental demands o... more The purpose of this study was to quantify the effects of concurrent physical and mental demands on the upper extremity muscle activity during static exertions. Seventeen healthy participants performed isometric upper extremity exertions at five levels of physical intensity (5%, 25%, 45%, 65%, and 85% maximum voluntary contraction (MVC)) in the presence and absence of a mental task (Stroop color word test). Muscular responses were quantified using surface electromyography (EMG) and motor performance was measured through force fluctuations. Subjective assessments were obtained through the NASA-TLX tool and the Borg CR-10 Scale. In general, a decrease in mean anterior and posterior deltoid muscle activity and co-contraction index (CCI) of the shoulder was observed in the presence of the mental task. However, these changes were more prominent at higher physical exertion levels compared to the lower levels. Furthermore, the additional mental task resulted in decreased upper and lower arm muscle activity, specifically at the 45% MVC level. Motor performance improved at the middle exertion levels, but was adversely affected by the mental task at higher exertion levels. Decreased motor performance at higher loads may have been a result of decreased muscular effort to maintain the loads in a steady posture. Both mental and physical demand adversely affected the NASA-TLX ratings, however, ratings using the Borg CR-10 Scale were only sensitive to changes in physical demand.

The purpose of this study was to evaluate age- and gender-dependent effects of shoulder fatigue o... more The purpose of this study was to evaluate age- and gender-dependent effects of shoulder fatigue on task performance and muscular responses of a drilling task commonly observed within the construction industry. Twelve younger (18–35 years) and ten older (45–60 years) participants, balanced by gender, were recruited from the local community. Task performance (task completion times and errors made), muscle activity of the anterior deltoid (static, mean, and peak amplitude probability density function), coactivity indices of the upper and lower arm, and perceived discomfort ratings were obtained for a series of drilling tasks at three levels of task difficulty, before and after manifestation of shoulder fatigue. To induce fatigue, participants performed a sustained sub-maximal fatigue task at 40% of their maximum voluntary shoulder exertion. Fatigue decreased task completion times, irrespective of age and gender. Higher errors were observed in the fatigued condition, especially for younger participants. Females showed higher shoulder muscle activity compared to men. Additionally, fatigue resulted in lower shoulder APDF measures compared to the no-fatigue condition. Muscle recruitment patterns differed within the fatigue condition, with higher coactivity indices in the upper and lower arm muscles compensating for decreases in shoulder muscle activity. Task difficulty was not found to affect any dependent measures. Participants reported higher discomfort in the fatigued state; this effect was more prominent in females. Overall, this study demonstrated, through objective and subjective measures, that task performance and biomechanical demands are affected by fatigue, and that this effect varies with individual factors such as gender and age.