Date of Award

Summer 2022

Document Type

Open Access Dissertation


Exercise Science

First Advisor

Shawn M. Arent


Military and law enforcement personnel are required to possess sufficient physical and cognitive fitness to perform their official duties. Tactical athletes must have fast reaction times (RT), high levels of various aspects of muscular performance, including power, strength, and endurance, as well as high anaerobic and aerobic capacities. The purpose of this dissertation was to investigate acute sports nutrition and chronic strength and conditioning strategies to improve health and human performance in tactical athletes, including law enforcement officers, active-duty military service members, and Reserve Officers’ Training Corps (ROTC) cadets and midshipmen.

The first study tested the effects of a combination of caffeine, methylliberine, and theacrine compared to caffeine alone and placebo on RT and marksmanship following a sustained vigilance task along with hemodynamic responses using a doubleblind, randomized, placebo-controlled design. Male law enforcement officers, military service members, and ROTC cadets and midshipmen (N=49) were randomized into one of three groups: 1) a combination of 150 mg caffeine, 100 mg methylliberine, and 50 mg theacrine, 2) 300 mg caffeine alone, or 3) placebo. They then participated in a 150-min protocol consisting of two rounds. Each round began with leisurely reading followed by a 30-min vigilance task before beginning two trials of movement and marksmanship tasks. The results showed the combination of 150 mg caffeine, 100 mg methylliberine, and 50 mg theacrine as well as the 300 mg caffeine alone improved vigilance RT over the 150-min protocol while placebo did not, and there were no differences in marksmanship performance between groups. However, caffeine alone resulted in large increases in diastolic blood pressure above placebo while the combination did not.

The second study tested the effects of six weeks of minimal-equipment resistance exercise training (RET) with and without blood flow restriction (BFR) on the military-relevant performance tasks of the Army Combat Fitness Test (ACFT) along with laboratory-based performance and body composition measures compared to traditional-equipment RET using a randomized, parallel-group, between-subjects design. Male and female ROTC cadets and midshipmen (N=54, 40.7%) were randomized into one of three groups: 1) traditional-equipment RET, 2) minimal-equipment RET, or 3) minimal-equipment RET with BFR. Performance and body composition changes were assessed from pre- to post-training, and measures of intensity and overall workload were evaluated throughout the study. The results showed RET with minimal equipment improves multiple aspects of human performance and body composition over six weeks, though traditional-equipment RET showed greater improvements in muscular strength. Further, the addition of BFR did not augment changes performance or body composition following minimal-equipment RET, though this finding may be sex-specific as males improved strength to a greater extent with BFR. Subjective and objective workload measures were higher for both minimal-equipment RET groups compared to traditionalequipment RET.

The results of these studies show the efficacy of sports nutrition and strength and conditioning interventions for improving health and human performance outcomes in law enforcement officers and military personnel. Tactical athletes can use the supplementation strategy of combined caffeine, methylliberine, and theacrine prior to periods of overwatch to maintain vigilance without experiencing substantial adverse hemodynamic responses induced by higher-dosed caffeine alone. Further, military personnel can expect similar improvements in ACFT score, muscular power, muscular endurance, anaerobic and aerobic capacity, and body composition, albeit an attenuation in muscular strength, during periods of limited access to traditional RET equipment. Both strategies tested in this dissertation can be used concomitantly as caffeine and caffeine-like supplements improve health and human performance outcomes acutely and the strength and conditioning intervention tested confers chronic benefits on these measures.

Available for download on Wednesday, April 05, 2023