New study: Grip strength and shooting performance

Researchers recommend agencies examine the adoption of pistols with lower trigger pull weights to mitigate grip strength-related shooting issues


Originally published on the Force Science Institute websiteRepublished here with permission.

By Lewis “Von” Kliem, MCJ, JD, LLM

A new study led by Ph.D. student Andrew Brown [1] examined the effects of grip strength and gender on shooting performance. [2]

Brown and fellow researchers sought to verify independent studies showing that grip strength was directly related to a person’s ability to manage aim, recoil and trigger pull. These skills are widely recognized as some of the key components of superior shooting performance.

This latest study was designed to replicate previous research relative to grip strength and to identify what range of strength might be required to achieve shooting test standards. The resulting data was used to examine the relationship between grip strength, gender and shooting scores.

Shaking Hands

According to the researchers, a standard-issue 9 mm pistol might have between 4lbs-6lbs of trigger pull weight. A double-action-only pistol might be closer to 9lbs-12lbs. Still, trigger pull weight can depend on the type of gun, the hammer mechanism (e.g., single-action vs. double action), and whether mechanical adjustments have been made. As a rule of thumb, the amount of pressure required to pull a trigger and fire a round (“trigger pull weight”) is roughly equivalent to a firm handshake.

Researchers explained the influence of trigger pull weight: “Trigger pull weight appears to impact shooting performance as triggers that are too heavy [for the individual shooter] seem to activate additional muscles in the hand.” They continued: “If the trigger pull of a firearm exceeds the force of a handshake, isolation of the index finger becomes difficult, causing the hand to engage in the use of additional muscles to complete the task of pulling the trigger. The overcompensation of unnecessary muscles, in turn, negatively affects shooting performance through involuntary hand movements.”

The questions remained, how much strength is needed to avoid these grip-related issues and pass a standard police pistol course, and will an officer’s gender predict negative shooting performance related to grip strength?

The Study

Researchers had 118 active police officers, ranging in age from 22-62, conduct a standardized police pistol qualification using a double-action-only pistol with a trigger pull weight of between 8lbs-12lbs.

Before attempting to qualify, the participants completed a demographic questionnaire to document their age, rank, gender and years of police service. Researchers then measured and recorded the participants’ dominant hand maximum grip strength.

After their grip strength was measured, participants performed the police pistol qualification with stationary targets between 10 and 82 feet. The results of the tests were analyzed and compared to the grip strength measurements and officer demographics.

The Results

Male officers in this study had, on average, higher qualification scores than the female officers: 21.9 % of the female officers in this study failed the qualification compared to 8.1% of the male officers. Researchers theorized that insufficient grip strength would negatively impact shooting performance, and that female officers would, on average, have lower grip strength than male officers. Both theories were supported by the research results.

First, researchers determined that grip strength in the range of 80lbs and 125lbs was needed to score approximately 85% and 90% on the pistol qualification test. The average grip strength for the female officers in the study was 77.5lbs, while the average for the men was 121.5lbs.

Seventy-eight percent of the females and 92% of the males passed the qualification test (22% and 8% failed respectively). Researchers observed that, for every pound below the average grip strength required to score between 85% and 90%, the odds of an officer failing the pistol qualification increased by 2%.

Discussion

Shooting performance is influenced by a variety of factors, and it appears that grip strength is certainly one of them. Andrew Brown provided the following observations: “In our study, higher rates of failure appeared to be correlated with lower grip strength. Agencies should consider minimum grip requirements based on the issued duty pistol trigger weight. Although grip strength issues might disproportionately impact female officers, strength training may help to mitigate grip-related deficiencies regardless of the officer’s gender.”

A recent article reported that NYPD is moving toward lighter trigger pull weights for their recruits. This move is consistent with Brown’s recommendation that agencies “examine the adoption of pistols with lower trigger pull weights to mitigate grip strength-related shooting issues.”

Dr. Bill Lewinski, executive director of the Force Science Institute, supports Brown’s recommendations and was encouraged by the NYPD’s move to a lighter trigger pull weight: “We often hear that higher trigger pull weights can provide increased decision-making time for officers. The research does not support that position. Even the heavier triggers can have a travel time as quick as 6/100 to 8/100 of a second. If the decision to pull the trigger has already been made, the travel time of the trigger isn’t going to result in sufficient time to change your mind and stop that action.”

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Mitigating Unintended Discharges

Dr. Lewinski addressed another concern that often accompanies lower trigger pull weights: “Agencies are always looking for ways to reduce the number of unintentional discharges, and trigger pull weights should always be a part of that discussion.”

Lewinski cautioned, “Researchers have observed officers unintentionally and non-consciously touch the trigger of their firearm while they were engaged in vigorous physical movements during a simulated high-threat robbery scenario. About 6% of those officers unintentionally applied sufficient pressure to pull a 12 lbs. trigger weight. More importantly, nearly 20% unintentionally applied enough pressure to fire a gun with a 5 lbs. trigger pull weight.” [3]

Dr. Lewinski reiterated what remains the most important consideration for avoiding unintended discharges, “In our research, we saw that around 31% of the unintended discharges involved striker-fired weapons. Of those, well over half of the unintended discharges were the result of intentionally pulling the trigger before clearing the chamber during disassembly [i.e., field stripping the weapon]. To mitigate unintentional trigger pulls and subsequent discharges, including cases that involve muscle co-activation, startle response, or routine weapon handling, keeping the finger outside of the trigger well is a critical safety protocol regardless of the trigger pull weight.”      

NEXT: Why firearms standardization puts police officers at risk

References

1. Andrew Brown is a Ph.D. student in Psychology at Carleton University, Ottawa, Ontario, Canada, He has a B.A. and M.A. in Psychology.

2. Andrew Brown was joined by fellow researchers and Ph.D. candidates Simon Baldwin and Brittany Blaskovits, as well as Dr. Craig Bennell, Ph.D. in Psychology. 

3. See Heim C, Schmidtbleicher D, Niebergall E. (2006a). The risk of involuntary firearms discharge. Human Factors, 48(3), 413-421.


About the author

With nearly 30 years in the criminal justice profession, Lewis “Von” Kliem, MCJ, JD, LLM, worked as a civilian police officer, attorney, educator and author. Von is the executive editor of Force Science News and co-owner of Von Kliem Consulting, LLC, where he trains and consults on constitutional policing, use of force analysis, crisis communications and trauma-informed interviewing.  

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