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Original Research

Effects of Energy Beverage Consumption on Pistol Aiming Steadiness in Law Enforcement Officers

Monaghan, Taylor P.1; Jacobson, Bert H.1; Sellers, John H.2; Estrada, Carlos A.1

Author Information
Journal of Strength and Conditioning Research: September 2017 - Volume 31 - Issue 9 - p 2557-2561
doi: 10.1519/JSC.0000000000002015
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Law enforcement officers often work long and irregular hours (31) making them susceptible to becoming excessively fatigued. To battle fatigue and weariness, many frequently turn to the use of caffeine to maintain wakefulness and alertness. Over 80% of the adult population consumes caffeine (3), making caffeine the most prevalent stimulant used throughout the world (15), and estimates suggest that next to journalists, police officers consume the greatest amount of caffeine (6). More recently, energy drinks (EDs) and energy shots (ESs) have appeared on the market and touted to provide the consumer with an enhanced performance, wakefulness, and alertness similar to cups of coffee. Since the appearance of EDs in the United States, the ED market has grown to several hundred competing brands exceeding $8 billion in sales (21). Although a generous proportion of the stimulant makeup of EDs and ESs composed of caffeine, additional active ingredients are added to beverages which may contribute to a greater concentration of stimulants. For instance, guarana, also a strong caffeine compound is typically found in EDs but excluded in the caffeine count. Other common ingredients in EDs are ginseng, vitamins, taurine, green tea extracts, Ginkgo biloba, carnitine, citric acid, sodium citrate, l-carnitine, inositol, pyridoxine hydrochloride, cyanocobalamin, and a healthy amount of 60 g sugar. In at least one instance, manufacturers seemly attempt to hide types of stimulants in the beverage identifying the mixture of active ingredients as an “Energy Blend.” For instance, one energy beverage label indicates that the amount of “Energy Blend” is 2,000 mg! Little is known about the physical effects produced by the combined or synergistic effects of these ingredients.

Relating to physical performance, previous studies have shown that caffeine may provide enhancements in both anaerobic and aerobic exercises (12,22). Also, consumption of caffeine may increase cognitive performance in sleep-deprived individuals (24) and in tactical situations, caffeine reduces friend-foe identification errors and decreases time in target detection exercises (19). However, there are some potential negative effects of caffeine consumption as well. Studies have revealed that caffeine consumption can decrease hand steadiness in motor performance activities. For instance, Jacobson et al. (16) found that consuming caffeine yielded an increase in steadiness error frequency. Similarly, in a double-blind study by Bovim et al. (4), subjects scored lower on motor steadiness after consumption of 300 mg of caffeine. Because pistol aiming and shooting is a complex task requiring target detection and steadying the pistol sights on the target, any reduction in arm and hand steadiness may impair the accuracy of the shot.

Rifle aiming point fluctuations using a laser to calculate instability have been compared with results from a live fire, concluding that the increased aiming steadiness resulted in a more successful shooting performance (5). Gillingham and associates (11) examined military reserve members on rifle marksmanship in simulated combat operations after consumption of 5 mg·kg−1 of caffeine and found an improvement in target detection and engagement speed, but no enhancement in operations requiring fine motor control and coordination. Correspondingly, another study (20) found doses of 200 and 300 mg of caffeine resulted in improvements of visual vigilance, choice reaction time, and alertness in Navy SEAL personnel but no change in fine motor coordination and steadiness. A study evaluating 3 hours of U.S. Army sentry duty with or without 200 mg caffeine concluded that caffeine had a positive effect on target detection time and no significant effect on marksmanship (18).

Research involving fine motor skill and energy beverage consumption is limited. Hence, with the importance of arm/hand steadiness on shot placement and accuracy and the dire consequences of a misplaced shot in certain circumstances, the purpose of this study was to investigate the effect of consuming a commercially available ES on pistol aiming steadiness in trained police officers.


Experimental Approach to the Problem

To determine the effect of the active ingredients in an energy beverage, full-time police officers trained in pistol marksmanship were recruited and randomly assigned to either an ES or placebo group. After pretesting, officers consumed 1 of the 2 beverages and waited 30 minutes before posttesting for aim steadiness. Arm/hand steadiness was assessed using a replicated handgun equipped with a stylus and laser. Errors in aiming were counted as the number of times the aim was off the mark during a 20-second trial. Subsequently, comparison between placebo and ES was statistically evaluated.


Participants included 10 accredited police officers (28–62 years) from a Midwest city, trained in handgun tactical marksmanship. Mean values and standard errors of the physical characteristics and average daily caffeine intake are illustrated in Table 1. After a detailed explanation of the study, those wishing to volunteer signed an Oklahoma State University institutional review board–approved consent form. All participants agreed to abstain from caffeine-containing beverages for 72 hours and food for 2 hours before testing.

Table 1.
Table 1.:
Demographic characteristics (mean ± SE) of the participants.*


Data on arm/hand steadiness were collected using a Lafayette Model 32,001 Steadiness Tester (hole/stylus type) equipped with an automatic impulse counter (Lafayette Model 1858024C). A metal stylus was attached to a nonfiring training pistol (BladesUSA Model B00CHKIMT2) with similar weight and feel as an actual firearm but incapable of live fire. For aiming purposes, the gun was fitted with a laser sight (NcSTAR Model NCS1266) and the metal plate of the steadiness tester was fitted with a target system. As the subjects retained the laser on the bulls-eye of the target, the stylus would be in the center of the metal target opening. The metal target plate was attached to a stand (Feedback Sports Model 16,020), and the height of the target was adjusted to be directly in front of the subject according to the subjects' height. The protocol was based on the arm-hand steadiness test described in the New York State Unified Courts System, Court Officer-Trainee Screening Process for Arm-Hand Steadiness (23) which measures the ability to maintain static arm-hand steadiness.

On reporting to the laboratory, participants were again briefed on the assessment protocol and were familiarized with the pistol, stylus, and laser and how these items worked with the steadiness tester. Before testing, the stand height was adjusted to the subjects' personal shooting arm and grip elevation. To standardize the officers' shooting position, the Weaver stance was used throughout the testing. In the Weaver stance, the shooter uses a two-handed grip with the feet in a “boxing” stance with the foot of the nonshooting side in front of the shooting side foot. For instance, a right-handed person will have the right foot angled outward approximately 45° and to the rear about shoulder length. It is recommended that most of the shooters weight will be on the forward foot, with the forward knee slightly flexed and the rear leg straight. The upper body should be leaning slightly forward at the hips. During testing, subjects were instructed to keep the pistol as steady as possible while aiming to avoid contact by the stylus and the edges of the 8.0-mm diameter target hole, a protocol used in the New York Court Officer Trainee Recruitment document (23). The automatic counter recorded the frequency and duration of off-target events. Pretesting consisted of 3 sets of 20-second intervals separated by a 15-second rest. Once the pretest was completed, participants were given either a 5-Hour Energy Extra Strength Berry Flavor (57 ml) or a placebo consisting of water flavored with punch and lemon juice to replicate the color and somewhat the flavor of the ES. The testing design followed a random, double-blind, counterbalanced protocol. After consumption of the beverages, participants were given a 30-minute absorption period before beginning posttesting (2) and told not to discuss or speculate on their drink or to compare taste. Posttests were conducted identically to the pretest with 3 sets of 20-second intervals of testing separated by 15-second rest. After 1 week, the officers returned to the laboratory and were given either the ED or placebo based on which beverage they had consumed at the first trial.

Statistical Analyses

Data were analyzed using a repeated-measures analysis of variance (ANOVA) for within and between group differences using SPSS 21.0. A Newman-Keuls post hoc test was used to determine the source of significant difference. An alpha (α) level of p ≤ 0.05 was considered statistically significant.


Participants complied with the instructions of abstaining from caffeine before the study. Average caffeine intake reported by the subjects was 452.62 ± 309.41 mg or 4.09 ± 3.14 mg·kg−1 body weight. This amount roughly equates to approximately 4 ½ cups of coffee based on a typical standard of 100-mg caffeine per 8 oz. cup (13,14). However, this figure may be distorted because the volume of the containers used by the officers was not indicated. With respect to body mass index (BMI), the range was between 25.84 and 36.9 with a mean of 30.91. The BMI of 25–29.9 reflects an overweight condition, whereas a BMI of 30 or greater reflects class 1 obesity. Indeed, 60% of the participants were in the class 1 category.

Data were analyzed through an IBM SPSS 23 statistical software package. Analysis consisted of a repeated-measures ANOVA and any specific location(s) of significance were further determined by ad hoc analysis. Results of the repeated-measures ANOVA yielded an F value of 3.89 (p = 0.012) specifying a significant difference between/among groups (pre vs. posttest, ES vs. placebo) existed. A Newman-Keuls post hoc test determined that there was no significant (p > 0.05) pretest difference between treatment and placebo and that there was no significant within group pre-to-posttest difference in the arm-hand aim steadiness in the placebo group. However, the ES group demonstrated significant (p ≤ 0.05) within group pre-to-posttest detrimental effect in the arm-hand aim steadiness after consumption of the ES. In addition, the ES group was significantly less stable in the arm-hand aim steadiness than the placebo group after ES consumption (Figure 1), illustrating the detrimental effect on steadiness resulting from ED consumption.

Figure 1.
Figure 1.:
Mean ± SE of pistol hand-arm aim steadiness before and 30 minutes after energy shot and placebo consumption.


Caffeine is absorbed orally, then quickly released from the stomach, and is almost completely absorbed from the gastrointestinal tract (1). Caffeine directly affects vagal, medullary, and vasomotor centers (28) and modifies neurotransmitter formation and release (8). Furthermore, caffeine affects calcium release and uptake in the muscle which can alter muscular contraction. Similar to other stimulants, a tolerance to caffeine will develop with chronic daily consumption (7) and symptoms of withdrawal such as lethargy and headaches can occur in heavy chronic users (31).

Consumption of the commercial ES containing an array of ingredients labeled as an “Energy Blend” resulted in a detriment to pistol the arm-hand steadiness in trained police officers. These results were consistent with previous caffeine-related findings; in that, caffeine has the potential to decrease hand steadiness (4,16). Further support for the current results comes from Tikuisis et al (29) after a study which investigated the effect of caffeine consumption on restoring shooting speed and precision in sleep-deprived military members. Findings showed a restoration of shots fired and target engagement but not in shooting precision. However, the current study is contradicted by others who suggest that caffeine has no effect on marksmanship (10,19,20,26). It is possible that the additional active ingredients in energy beverages, along with caffeine, may have resulted in an additive or synergistic effect on pistol hand-arm unsteadiness. For instance, tobacco usage combined with caffeine usage has been reported to have an even greater detrimental effect on decision time and motor time scores on choice reaction-time assessments than caffeine alone (27).

A survey conducted by the US Department of Agriculture found on average caffeine consumers' intake was 193 mg·d−1 (9). In our previous study, it was found that in the workplace, average coffee intake was estimated to be 350 mg·d−1 (14) which was attributed to the work environment such as stress, boredom, social breaks, etc. One survey of over 10,000 professional indicated that 85% consume at least 3 cups per day (estimated at 300 mg) and that police officers were second only to journalists in consumption of coffee (25). The results of the current study found a mean caffeine intake of 413 mg which is considerably more than the aforementioned suggested averages. It should be noted that the SD was rather large indicating a broad range of consumption (60–1,000 mg) which opens the possibility that some officers were rather tolerant to the effects of caffeine, whereas others were not.

Consumption of caffeine-containing energy beverages may not be of serious consequences in the average workplace, unless these beverages are consumed in excess. However, when the task at hand requires extraordinary hand steadiness in tasks performed by certain professions such as surgeons, dentists, or jewelers, energy beverage consumption may become a liability to the accuracy of their work. This, of course, is of concern with respect to certain law enforcement duties because of the negative effects on the arm-hand steadiness produced by the ES. It is axiomatic that the lack of steady aim may result in tragic consequences in some scenarios of law enforcement. Along with negative results in steadiness, consumption of large amounts of caffeine daily may have harmful effects in and of itself (13,17). For instance, for the FDA reported that since 2004, 34 deaths have been linked to EDs and 22 deaths have been attributed to ESs (30).

Practical Applications

This investigation sought to determine the effect of a single dose of an energy beverage on the arm-hand steadiness during the aiming process of a handgun by trained police officers (32).

In the line of duty, police officers may on occasion be forced to draw, aim, and discharge their firearms in a life-or-death situation. Interference with firearm aim could, therefore, have grave consequences because the threat may not have been neutralized with the shot.


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caffeine; marksmanship; police; stimulant; shooting performance; tactical

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