Matthew John McAllister

Objective: Firefighters experience chronic stress that contributes to elevated cardiometabolic disease (CMD) risk. This study examined associations between blood and salivary biomarkers of inflammation, stress, and oxidative stress with measures of body composition, fitness, and cardiometabolic health among firefighters (n = 140). Methods: Principal components analysis was used to reduce multicollinearity among body composition, physical performance, and cardiometabolic variables, followed by multivariate regression models predicting adiponectin, C-reactive protein (CRP), and interleukin-6 (IL-6) concentrations. Results: Body mass and composition, fitness, and atherogenic dyslipidemia were associated with multiple biomarkers. Salivary IL-6 demonstrated robust associations with body composition, physical performance, and salivary CRP. Blood adiponectin and CRP were strongly associated with atherogenic dyslipidemia, insulin resistance and oxidative stress. Conclusions: Salivary inflammatory biomarkers, particularly IL-6, may provide a feasible complement to blood biomarkers for identifying CMD risk among firefighters.

Previous research supports the role of 17-β-estradiol (E2) and progesterone (P4) in altering lipid oxidation (LOx) rates during aerobic exercise, but it has yet to be determined if LOx is altered between menstrual cycle (MC) phases following strength-based resistance exercise (RE). This study examined post-exercise LOx rates in eumenorrheic females, following a bout of RE during the early-follicular, low hormone phase (LHP) and mid-luteal, high hormone phase (HHP). Twenty-two (age: 25.1±5.7 years; fat-free mass: 44.7±4.9 kg; relative strength: 1.2±0.2) well-trained females completed a repetition maximum (RM) test for the back squat, bench press, and deadlift. Participants then completed one resistance exercise session consisting of five sets of 3 repetitions at 80-85% 1RM for each exercise during the first 5 days of the participants’ MC (LHP) and once during the calculated mid-luteal phase (HHP). Metabolic testing occurred at baseline (BL) and again immediately post, 30-, 60-, and 90-min post-exercise. Despite expected hormonal differences in E2 (LHP = 1.53±0.58 pg/mL; HHP = 1.88±0.48 pg/mL) and P4 (LHP = 230.51±152.55 pg/mL; HHP = 545.22±295.72 pg/mL), there were no differences in LOx at any timepoint between MC phase (p>0.05). However, RE increased absolute LOx rates by ~49% compared to BL across the entire metabolic collection period (p<0.05), with the highest LOx rates recorded at 60-min post-exercise (0.077±0.016 g·min⁻¹, p<0.001). These findings suggest that RE acutely increases LOx rates above BL levels in well-trained, eumenorrheic females post-exercise, regardless of MC phase.

Following a comprehensive review, the International Society of Sports Nutrition (ISSN) has developed an official position on the role of dietary antioxidants in exercise and sport. Antioxidants play a complex, context-dependent role in vivo; they can facilitate recovery from exercise but may also hinder training adaptations when consumed at supraphysiological doses. While endogenous antioxidant systems can effectively maintain redox balance, dietary sources, particularly whole foods, can help mitigate excessive oxidative stress following intense/heavy training or inadequate recovery. The influence of dietary antioxidants depend on timing, dosage, type, and individual factors. The ISSN's official position encompasses the following: (1) Redox balance exists on a spectrum, with mild oxidative eustress driving beneficial physiological adaptations and excessive oxidative distress impairing health, recovery, and performance; (2) Moderate levels of exercise-induced reactive oxygen and nitrogen species (ROS/RNS) can support training adaptations but excessive levels can result in muscle damage, inflammation, and reduced physical performance and immune function; (3) Endogenous and exogenous antioxidants protect cells by neutralizing free radicals and reducing oxidative damage to biomolecules; (4) FDA labeling for "antioxidant" claims applies to nutrients with established RDIs and demonstrated antioxidant activity; this typically includes vitamins C and E, β-carotene (a source of vitamin A), selenium, zinc, copper, and manganese; (5) While dietary antioxidants show potential for both direct and indirect effects, the evidence varies, and their use should be tailored to individual performance or recovery goals; (6) Long-term exercise augments endogenous antioxidant defense and should be the primary strategy for enhancing redox capacity before considering supplementation; (7) Whole foods and beverages rich in flavonoids, polyphenols, carotenoids, vitamins, and minerals are preferred antioxidant sources; (8) Dietary supplementation is best reserved for nutrient insufficiencies or deficiencies, inadequate dietary intake, or periods of high training distress; (9) Responses to supplementation vary by individual factors, such as training status, baseline antioxidant capacity, demographics, diet, and injury risk, with some antioxidant compounds offering cognitive, behavioral, or physical-related benefits; and (10) Creatine monohydrate (i.e. 0.1 g/kg/day), omega-3 fatty acids (1000-6000 mg/day EPA+DHA for 6-12 weeks), tart cherry (480 mg powder or 60-90 mL juice/day for 7-14 days), and astaxanthin (4-12 mg/day for 4-12 weeks) rank among the top nutrients for their antioxidant effects, with moderate- to high-quality evidence supporting their use in recovery or performance without interfering with training adaptations. Most others show weak or low efficacy. This position promotes an individualized, evidence-based approach, recognizing that small to moderate exercise-induced oxidative stress aids adaptation, while excess oxidative stress causes harm; it also emphasizes food-forward and dietary supplementation strategies.

Objective: Law enforcement officers (LEOs) face numerous stressors that exacerbate cardiometabolic disease (CMD) risk. The current study examined novel and classic risk factors among a cohort of LEOs to better understand relationships between biomarkers of stress, oxidative stress, inflammation, and CMD risk. Methods: Associations between measures of cardiorespiratory and muscular fitness, body composition, and cardiometabolic health with novel/classic CMD risk factors were assessed among 66 male LEOs. Results: Muscular fitness and cardiorespiratory fitness were significantly associated with reduced insulin resistance. Moreover, higher fat mass and body fat percentages were significantly associated with increased markers of inflammation and insulin resistance. Conclusions: Maintaining high cardiorespiratory and muscular fitness levels and improving body composition profiles can ameliorate cardiometabolic health.

Objective: The present study examined novel and classic cardiovascular disease (CVD) risk factors among career firefighters to understand better the associations between physiological stress, oxidative stress, inflammation biomarkers, and CVD risk. Methods: Associations between muscular and cardiorespiratory fitness (CRF) measures, body composition, physiological stress, and novel/classic CVD risk factors were assessed among 97 career male firefighters. Results: Muscular fitness/CRF, adiposity, body composition, and blood lipids were associated with CVD risk as measured by biomarkers for insulin resistance, inflammation, and oxidative stress. No associations between physiological stress biomarkers and CVD risk factors were found. Conclusions: Firefighters should improve their muscular fitness/CRF and body composition to reduce CVD risk.

Tactical occupations regularly encounter life-threatening situations while on duty. Although these occupations are often trained to utilize slow breathing (SB) during intense stress, there is no evidence supporting the effects on markers of stress in response to a virtual reality active shooter training drill (VR-ASD). The purpose of the study was to determine the impact of acute SB on biomarkers of stress in response to a VR-ASD. Seventy-nine (n = 79) subjects performed either slow breathing method 1 (SB1), slow breathing method 2 (SB2), or normal breathing (control) for five minutes, both pre- and post-VR-ASD. Saliva samples were analyzed for stress markers, including α-amylase (sAA) and secretory immunoglobulin-A (SIgA). Both methods of SB resulted in significantly lower sAA concentrations at 5 (p < 0.001) and 30 min post-VR-ASD (SB1: p = 0.008; SB2: p < 0.001) compared to the control. In the control condition, the sAA concentrations were significantly elevated 5 min post-VR-ASD (p < 0.001) but did not change across time in SB1 or SB2 (p > 0.05). Thus, both SB1 and SB2 reduced the sAA response and resulted in lower concentrations post-VR-ASD. This study was pre-registered as a clinical trial (“Impact of Breathing Interventions on Stress Markers”; NCT05825846).

Strenuous exercise involving eccentric muscle actions induces skeletal muscle damage resulting in delayed onset muscle soreness (DOMS). Antioxidant supplementation, such as astaxanthin (AX), may alleviate muscle injury following intense exercise. The purpose of this study was to investigate the effect of a four-week course of AX supplementation at 12 mg/day⁻¹ on subjective markers of DOMS, recovery, and performance after a bout of muscle damaging eccentric exercise. Nineteen resistance-trained men (mean ± SD: age, 22.6 ± 2.2 y) completed a between-group design with a four-week supplementation period of 12 mg/day⁻¹ of either AX or a placebo. Subjects completed four trials, with trials One and Three designed to induce muscle damage, consisting of a one repetition maximum test (1RM) for leg-press, followed by five sets of ten repetitions at 65% of 1RM. Trials Two and Four were performance trials, conducted 48 h later and consisting of repetitions to failure at 65%, 70%, and 75% of 1RM. Subjective markers of DOMS and recovery were collected at multiple timepoints post-trial for trials One and Three. Although performance was not affected (p > 0.05), AX supplementation significantly decreased subjective markers of DOMS (p = 0.01) compared to the placebo. The results demonstrated that AX may enhance recovery by reducing DOMS without detriment to performance in resistance-trained men.