Biomechanics Analysis of the Firefighters' Thorax Movement on Personal Protective Equipment during Lifting Task Using Inertial Measurement Unit Motion Capture

Back injury is a common musculoskeletal injury reported among firefighters (FFs) due to their nature of work and personal protective equipment (PPE). The nature of the work associated with heavy lifting tasks increases FFs' risk of back injury. This study aimed to assess the biomechanics movement of FFs on personal protective equipment during a lifting task. A set of questionnaires was used to identify the prevalence of musculoskeletal pain experienced by FFs. Inertial measurement unit (IMU) motion capture was used in this study to record the body angle deviation and angular acceleration of FFs' thorax extension. The descriptive analysis was used to analyze the relationship between the FFs' age and body mass index with the FFs' thorax movement during the lifting task with PPE and without PPE. Sixty-three percent of FFs reported lower back pain during work, based on the musculoskeletal pain questionnaire. The biomechanics analysis of thorax angle deviation and angular acceleration has shown that using FFs PPE significantly causes restricted movement and limited mobility for the FFs. As regards human factors, the FFs' age influences the angle deviation while wearing PPE and FFs' BMI influences the angular acceleration without wearing PPE during the lifting activity.

Implementation of Kinetic and Kinematic Variables in Ergonomic Risk Assessment Using Motion Capture Simulation: A Review

Work-related musculoskeletal disorders (WMSDs) are among the most common disorders in any work sector and industry. Ergonomic risk assessment can reduce the risk of WMSDs. Motion capture that can provide accurate and real-time quantitative data has been widely used as a tool for ergonomic risk assessment. However, most ergonomic risk assessments that use motion capture still depend on the traditional ergonomic risk assessment method, focusing on qualitative data. Therefore, this article aims to provide a view on the ergonomic risk assessment and apply current motion capture technology to understand classical mechanics of physics that include velocity, acceleration, force, and momentum in ergonomic risk assessment. This review suggests that using motion capture technologies with kinetic and kinematic variables, such as velocity, acceleration, and force, can help avoid inconsistency and develop more reliable results in ergonomic risk assessment. Most studies related to the physical measurement conducted with motion capture prefer to use non-optical motion capture because it is a low-cost system and simple experimental setup. However, the present review reveals that optical motion capture can provide more accurate data.

Proprioceptive afferents differentially contribute to effortful perception of object heaviness and length

When humans handle a tool, such as a tennis racket or hammer, for the first time, they often wield it to determine its inertial properties. The mechanisms that contribute to perception of inertial properties are not fully understood. The present study's goal was to investigate how proprioceptive afferents contribute to effortful perception of heaviness and length of a manually wielded object in the absence of vision. Blindfolded participants manually wielded specially designed objects with different mass, the static moment, and the moment of inertia at different wrist angles and angular kinematics. These manipulations elicited different tonic and rhythmic activity levels in the muscle spindles of the wrist, allowing us to relate differences in muscle activity to perceptual judgments of heaviness and length. Perception of heaviness and length depended on an object's static moment and the moment of inertia, respectively. Manipulations of wrist angle and angular kinematics affected perceived heaviness and length in distinct ways. Ulnar deviation resulted in an object being perceived heavier but shorter. Compared to static holding, wielding the object resulted in it being perceived heavier but wielding did not affect perceived length. These results suggest that proprioceptive afferents differentially contribute to effortful perception of object heaviness and length. Critically, the role of afferent is specific to the mechanical variable used to derive a given object property. These findings open a new possibility of studies on the link between physiology, and different mechanical variables picked up by the perceptual system.

Does Attention Modify Contributions to Heaviness Perception?

Purpose: The current study investigated the effect of attention on heaviness perception and its physiological and kinematic contributions. Method: Participants lifted objects that varied in mass and volume while their muscle activity and movement were recorded. Participants were instructed to pay attention to their arm (internal) or the object (external). Results: While heaviness perception did not change as a function of attention, whether muscle activity and movement combined for perception differed across attention conditions. Specifically, muscle activity and movement combined to significantly predict heaviness perception in the external condition, but not the internal condition. Additionally, movement was more salient for perception in both conditions compared to previous research investigating the contribution of muscle activity and movement to heaviness perception. Conclusion: It is suggested that these results support the constrained action hypothesis, which suggests that adopting an external focus of attention benefits motor task performance and learning, and should be further explored in the context of a theory of haptic perception that suggests that the medium for haptic perception is the multifractal tensegrity structure of the body.