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Understanding the relationship between nurses’ perceived subjective effort and objective neuromuscular effort of prefilled syringes with varying injection variables

¹ Ph.D. Student, Mechanical Engineering, Texas A&M University; ² Device Development & Technology, Merck, Rahway, NJ

Tiash Rana Mukherjee¹, Alicia Douglas², Esther Foo², Daniel Bonanno²

• Current mechanical testing of syringes (e.g., break loose and extrusion forces) are evaluated against a constant force
• This is a notable gap since users vary widely in their physical capabilities and no single force can accurately represent the intended end-user population—users aren't machines
• The aim of this research is to investigate the relationship between the perception of subjective effort and objective force and neuromuscular outcomes when interacting with pre-filled syringes of different viscosities, volumes, and injection locations.

Objective

1 cP ↔ 70 cP

1 mL ↔ 2.1 mL

Abdomen or Thigh

With or without

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12 injections

n = 60

registered nurses

1. How can we capture “total user effort ”?

3. Is there a relationship between “total user effort” and the “total muscular demands”?

Since users are not machines, user behavior, such as duration and force input, adapts based on system feedback. Area Under the Curve as a metric captures this.

Subjective force ratings and the calculated area under the curve show moderate to strong correlations.

• Area under the curve captures relevant information representing “user effort” that can be missed if only looking at force or duration
• Users can tell the difference when interacting with PFS requiring different levels of effort
• Muscular demands seem to be closely related with user efforts, however conclusions on impact of PFS design variables on muscles cannot be determined without knowing “how exactly users were physically holding and interacting” with the PFS.

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• Muscular demands of all muscle groups increase with increase in area under the curve (effort). However, the trends differ between muscle groups.

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• Muscular effort is affected by both viscosity and volume. However, viscosity dominates. ​

Approach

Objective force measurements through sensors ​

Subjective perceptual responses through questionnaires ​

Physiological measurements through electromyography

2. Do users feel the difference when they apply different effort?

Key Takeaways

Acknowledgement: This study was performed through a project with Mauro Usability Science