Short answer

When designing grasping mechanisms, especially for prosthetic hands, focus on enabling robust finger spreading and closing (abduction/adduction) as a primary function, as this has a greater impact on general daily activities than individual finger bending.

Field: Human Factors
Source: Scientific Reports (2016)
Method: Experimental study using custom orthoses to restrict finger movement.
Evidence: Moderate effect

The ability to spread and bring fingers together (abduction/adduction) is more critical for grasping activities of daily living than the ability to bend and straighten individual fingers (flexion/extension), provided an opposable thumb is present. This human factors research insight is drawn from a 2016 study published in Scientific Reports. Using Experimental study using custom orthoses to restrict finger movement., researchers explored how this design variable affects real-world outcomes. The key design takeaway: When designing grasping mechanisms, especially for prosthetic hands, focus on enabling robust finger spreading and closing (abduction/adduction) as a primary function, as this has a greater impact on general daily activities than individual finger bending.

Study

Human FactorsHigh ImpactModerate effect

Independent finger flexion/extension is secondary to abduction/adduction for grasping with an opposable thumb.

Scientific Reports · 2016

Key Findings

01Independent long fingers provide a measurable advantage in activities of daily living only when precision grasps are involved, given an opposable thumb.
02The grasping skills of the human hand rely more on the independent abduction/adduction of the fingers than on their independent flexion/extension.

Application

Design takeaway

How to apply

When developing a prosthetic hand or a robotic gripper, consider a design that allows for significant finger splaying and closing, potentially simplifying the individual finger bending mechanisms.

Project actions

01Consider how your design allows for finger separation and convergence.
02If designing a prosthetic, think about the most common grasping actions users need.

Method & Evidence

AimTo determine the relative importance of independent finger flexion/extension versus abduction/adduction for grasping activities of daily living when an opposable thumb is present.

MethodExperimental study using custom orthoses to restrict finger movement.

ProcedureParticipants performed activities of daily living with custom-made orthoses that either allowed or restricted independent finger flexion/extension, while maintaining thumb opposition. Performance was evaluated based on task completion and efficiency.

ContextDesign of prosthetic hands, exoskeletons, and other assistive devices for grasping.

Variables

IVType of finger movement restriction (independent flexion/extension vs. abduction/adduction).

DVPerformance in activities of daily living (e.g., task completion time, success rate).

CVPresence of an opposable thumb, types of objects to be grasped, specific activities performed.

Strengths & Limitations

Strengths

+Directly addresses a key question in prosthetic design.
+Uses custom orthoses to isolate specific biomechanical functions.

Limitations

The custom orthoses might not perfectly simulate natural hand movement, and the range of 'activities of daily living' tested might be limited.

Reliability & validity

The use of custom orthoses to isolate variables enhances internal validity. Reliability would depend on the consistency of task performance and measurement.

Think critically

If independent finger flexion/extension is less important for general grasping, what specific types of tasks would still necessitate this capability, and how could a design accommodate both priorities?

Design Principles

"Prioritize gross motor control (abduction/adduction) over fine motor control (independent flexion/extension) for general grasping tasks when an opposable thumb is present."

This insight challenges conventional assumptions in the design of assistive devices and prosthetics. By prioritizing abduction/adduction over independent flexion/extension, designers can potentially create more functional and less complex artificial hands, improving user capabilities in everyday tasks.

What This Means for Your Design

For artificial hands, being able to spread your fingers wide and then close them together is more important for picking things up than being able to bend each finger separately, as long as there's a thumb to oppose them.

How to use in your project

1.This research can be used to justify design choices for prosthetic hands or grippers, explaining why certain movements were prioritized over others based on user needs.

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Quick Cite

Paragraph starter

Research indicates that for grasping activities of daily living, the independent abduction and adduction of fingers are more critical than independent flexion and extension, particularly when an opposable thumb is present. This suggests that design efforts for prosthetic hands and assistive devices should prioritize mechanisms enabling finger spreading and closing to enhance functionality.

Source

Scientific Reports

Independent Long Fingers are not Essential for a Grasping Hand

journal · 2016

View source

Questions About This Research

What does the research say about independent finger flexion/extension is secondary to abduction/adduction for grasping with an opposable thumb?: When designing grasping mechanisms, especially for prosthetic hands, focus on enabling robust finger spreading and closing (abduction/adduction) as a primary function, as this has a greater impact on general daily activities than individual finger bending. Evidence: Scientific Reports (2016).
Why does "Independent finger flexion/extension is secondary to abduction/adduction for grasping with an opposable thumb." matter for design?: This insight challenges conventional assumptions in the design of assistive devices and prosthetics. By prioritizing abduction/adduction over independent flexion/extension, designers can potentially create more functional and less complex artificial hands, improving user capabilities in everyday tasks.
How can designers apply this research?: When designing grasping mechanisms, especially for prosthetic hands, focus on enabling robust finger spreading and closing (abduction/adduction) as a primary function, as this has a greater impact on general daily activities than individual finger bending.
What were the main findings?: Independent long fingers provide a measurable advantage in activities of daily living only when precision grasps are involved, given an opposable thumb.. The grasping skills of the human hand rely more on the independent abduction/adduction of the fingers than on their independent flexion/extension.
What research method was used?: Experimental study using custom orthoses to restrict finger movement..
How strong is the evidence?: Evidence strength is rated Moderate effect, based on a 2016 journal from Scientific Reports.
What should I do differently in my next project?: When developing a prosthetic hand or a robotic gripper, consider a design that allows for significant finger splaying and closing, potentially simplifying the individual finger bending mechanisms.
What are the limitations?: The study used custom orthoses, which may not perfectly replicate natural hand biomechanics. The definition of 'activities of daily living' and 'precision grasps' could be further refined.