The effect of wrist angle and finger grip on maximum trigger pull force

Area of Science:

• Forensic Science
• Biomechanics
• Human Factors Engineering

Background:

• Forensic investigations of handgun discharge require understanding shooter biomechanics.
• Previous research indicates grip force is influenced by arm posture, wrist angle, and finger grip type.

Purpose of the Study:

• To quantify the impact of wrist angle and finger grip on maximum index finger trigger pull force.
• To provide data relevant to forensic analysis of handgun use.

Main Methods:

• Participants performed maximum voluntary index finger contractions to pull a trigger under varying wrist angles (flexion, neutral, extension).
• Two grip types were tested: finger pad grip and finger hook grip.
• Trigger pull force was measured in Newtons (N) and pounds (lb).

Main Results:

• Trigger pull force decreased significantly with wrist flexion, especially beyond 60°.
• Male subjects experienced a 50% drop in force with significant wrist flexion, while female subjects saw a 38% drop.
• A finger hook grip yielded higher forces than a finger pad grip.
• In scenarios with poor grip and awkward posture, forces could fall below the trigger weight of many handguns.

Conclusions:

• Wrist posture and grip type are critical determinants of the force a person can exert on a handgun trigger.
• These findings have implications for forensic investigations, particularly in determining the likelihood of accidental or deliberate discharge.
• Understanding these biomechanical factors is essential for accurate interpretation of firearm evidence.