Load-Velocity Profiles Before and After Heated Resistance Exercise.

ABSTRACT: Sweet, DK, Qiao, J, Rosbrook, P, and Pryor, JL. Load-velocity profiles before and after heated resistance exercise. J Strength Cond Res 38(6): 1019-1024, 2024-This study examined neuromuscular performance using load-velocity (L-V) profiles in men and women before and after resistance exercise (RE) in hot (HOT; 40° C) and temperate (TEMP; 21° C) environments. Sixteen (f = 8, m = 8) resistance-trained individuals completed a single 70-minute whole-body high-volume load (6 exercises, 4 sets of 10 repetitions) RE bout in HOT and TEMP. Before and after RE, rectal temperature (TRE), muscle temperature of the vastus lateralis (TVL) and triceps brachii (TTB), and an L-V profile for the deadlift and bench press were recorded. Thermoregulatory and L-V data were analyzed using separate 2-way repeated measures analysis of variances (ANOVAs; condition [hot, temperate] and time [pre, post]) with significance level set at p ≤ 0.05. Deadlift peak velocity was reduced at 60% 1 repetition maximum (1RM) after RE in HOT but not TEMP. Peak velocity of 40% 1RM bench press was lower in TEMP vs. HOT pre-RE (p < 0.01). Peak velocity was decreased at all loads in the deadlift L-V profile after RE, regardless of condition. Despite elevated TRE (TEMP; 37.58 ± 0.35, HOT; 38.20 ± 0.39° C), TVL (TEMP; 35.24 ± 0.62, HOT; 37.92 ± 0.55° C), and TTB (TEMP; 35.05 ± 0.78, HOT; 38.00 ± 0.16° C) after RE in HOT vs. TEMP (p < 0.01), RE in HOT did not broadly affect L-V profiles. This indicates heated resistance exercise can be performed with high-volume load and high ambient temperature with minimal performance impairment.

Resistance Training in the Heat: Mechanisms of Hypertrophy and Performance Enhancement.

ABSTRACT: Pryor, JL, Sweet, D, Rosbrook, P, Qiao, J, Hess, HW, and Looney, DP. Resistance training in the heat: Mechanisms of hypertrophy and performance enhancement. J Strength Cond Res 38(7): 1350-1357, 2024-The addition of heat stress to resistance exercise or heated resistance exercise (HRE) is growing in popularity as emerging evidence indicates altered neuromuscular function and an amplification of several mechanistic targets of protein synthesis. Studies demonstrating increased protein synthesis activity have shown temperature-dependent mammalian target of rapamycin phosphorylation, supplemental calcium release, augmented heat shock protein expression, and altered immune and hormone activity. These intriguing observations have largely stemmed from myotube, isolated muscle fiber, or rodent models using passive heating alone or in combination with immobilization or injury models. A growing number of translational studies in humans show comparable results employing local tissue or whole-body heat with and without resistance exercise. While few, these translational studies are immensely valuable as they are most applicable to sport and exercise. As such, this brief narrative review aims to discuss evidence primarily from human HRE studies detailing the neuromuscular, hormonal, and molecular responses to HRE and subsequent strength and hypertrophy adaptations. Much remains unknown in this exciting new area of inquiry from both a mechanistic and functional perspective warranting continued research.

Endocrine Responses to Heated Resistance Exercise in Men and Women.

ABSTRACT: Pryor, JL, Sweet, DK, Rosbrook, P, Qiao, J, Looney, DP, Mahmood, S, and Rideout, T. Endocrine responses to heated resistance exercise in men and women. J Strength Cond Res 38(7): 1248-1255, 2024-We examined the endocrine responses of 16 (female = 8) resistance trained volunteers to a single bout of whole-body high-volume load resistance exercise in hot (HOT; 40° C) and temperate (TEMP; 20° C) environmental conditions. Thermoregulatory and heart rate (HR) data were recorded, and venous blood was acquired before and after resistance exercise to assess serum anabolic and catabolic hormones. In men, testosterone increased after resistance exercise in HOT and TEMP ( p < 0.01), but postexercise testosterone was not different between condition ( p = 0.51). In women, human growth hormone was different between condition at pre-exercise ( p = 0.02) and postexercise ( p = 0.03). After controlling for pre-exercise values, the between-condition postexercise difference was abolished ( p = 0.16). There were no differences in insulin-like growth factor-1 for either sex ( p ≥ 0.06). In women, cortisol increased from pre-exercise to postexercise in HOT ( p = 0.04) but not TEMP ( p = 0.19), generating a between-condition difference at postexercise ( p < 0.01). In men, cortisol increased from pre-exercise to postexercise in HOT only ( p < 0.01). Rectal temperature increased to a greater extent in HOT compared with TEMP in both men ( p = 0.01) and women ( p = 0.02). Heart rate increased after exercise under both conditions in men and women ( p = 0.01), but only women experience greater postexercise HR in HOT vs. TEMP ( p = 0.04). The addition of heat stress to resistance exercise session did not overtly shift the endocrine response toward an anabolic or catabolic response. When acute program variables are prescribed to increase postresistance exercise anabolic hormones, adding heat stress is not synergistic but does increase physiologic strain (i.e., elevated HR and rectal temperature).

Movement Technique During Jump-Landing Differs Between Sex Among Athletic Playing Surfaces.

ABSTRACT: Pryor, JL, Burbulys, ER, Root, HJ, and Pryor, RR. Movement technique during jump-landing differs between sex among athletic playing surfaces. J Strength Cond Res 36(3): 661-666, 2022-Whether athletic surface type affects movement technique, a causal factor for lower extremity injury, is unclear. This study evaluated the influence of 4 common athletic surfaces on movement technique using the Landing Error Scoring System (LESS). Secondarily, we aimed to evaluate differences in movement technique between men and women among surfaces. Recreationally active men and women (n = 38) completed jump-landing tests on 4 common athletic surfaces in a quasi-randomized crossover fashion. Vertical jump height, perceptual fatigue, and muscle soreness were evaluated before jump-landing movement analyses and were similar across testing sessions (p > 0.05). Men achieved higher LESS scores on hardwood and artificial pellet turf compared with women (p ≤ 0.037). Women exhibited lower LESS scores on grass and artificial turf vs. concrete (p ≤ 0.048). Data indicate differential lower extremity movement technique and therefore injury risk across athletic surface types and sex, challenging the generalizability of the LESS construct. Athletic playing surface should be considered during movement technique assessment and implementation of injury prevention programs.

Verification of Maximal Oxygen Uptake in Active Military Personnel During Treadmill Running.

ABSTRACT: Figueiredo, PS, Looney, DP, Pryor, JL, Doughty, EM, McClung, HL, Vangala, SV, Santee, WR, Beidleman, BA, and Potter, AW. Verification of maximal oxygen uptake in active military personnel during treadmill running. J Strength Cond Res 36(4): 1053-1058, 2022-It is unclear whether verification tests are required to confirm "true" maximal oxygen uptake (V̇o2max) in modern warfighter populations. Our study investigated the prevalence of V̇o2max attainment in U.S. Army soldiers performing a traditional incremental running test. In addition, we examined the utility of supramaximal verification testing as well as repeated trials for familiarization for accurate V̇o2max assessment. Sixteen U.S. Army soldiers (1 woman, 15 men; age, 21 ± 2 years; height, 1.73 ± 0.06 m; body mass, 71.6 ± 10.1 kg) completed 2 laboratory visits, each with an incremental running test (modified Astrand protocol) and a verification test (110% maximal incremental test speed) on a motorized treadmill. We evaluated V̇o2max attainment during incremental testing by testing for the definitive V̇O2 plateau using a linear least-squares regression approach. Peak oxygen uptake (V̇o2peak) was considered statistically equivalent between tests if the 90% confidence interval around the mean difference was within ±2.1 ml·kg-1·min-1. Oxygen uptake plateaus were identified in 14 of 16 volunteers for visit 1 (87.5%) and all 16 volunteers for visit 2 (100%). Peak oxygen uptake was not statistically equivalent, apparent from the mean difference in V̇o2peak measures between the incremental test and verification test on visit 1 (2.3 ml·kg-1·min-1, [1.3-3.2]) or visit 2 (1.1 ml·kg-1·min-1 [0.2-2.1]). Interestingly, V̇o2peak was equivalent, apparent from the mean difference in V̇o2peak measures between visits for the incremental tests (0.0 ml·kg-1·min-1 [-0.8 to 0.9]) but not the verification tests (-1.2 ml·kg-1·min-1 [-2.2 to -0.2]). Modern U.S. Army soldiers can attain V̇o2max by performing a modified Astrand treadmill running test. Additional familiarization and verification tests for confirming V̇o2max in healthy active military personnel may be unnecessary.

Effects of hyperbaric oxygen therapy on exercise-induced muscle damage.

Purpose: To perform a literature review on hyperbaric oxygen (HBO2) therapy as a treatment for exercise-induced muscle damage (EIMD). Methods: PubMed, Web of Science and Google Scholar were searched for articles related to HBO2 therapy as a treatment for exercise-induced muscle damage. Inclusion criteria included HBO2 therapy as the primary intervention to treat EIMD. Articles used in this review ranged from 1995-2021. Conclusion: Current literature on the effectiveness of HBO2 therapy to treat EIMD is mixed. Early and frequent treatments seem to be important factors when it comes to the success of HBO2 therapy. Additional research is needed to determine if HBO2 therapy has potential to treat more severe forms of EIMD and the role HBO2 therapy has on inflammation and satellite cell function after EIMD.

Exercise during hot-water immersion in divers habituated to hot-dry and hot-wet conditions.

Purpose: Diving in warm water increases thermal risk during exercise compared to thermoneutral waters. The purpose of this study was to evaluate exercise endurance in warm- and hot-water conditions in divers habituated to wet or dry heat. Methods: Nineteen male divers completed this study at the Navy Experimental Diving Unit. Subjects were assigned DRY or WET heat habituation groups. The DRY group (n=9) cycled at 125-150W for one hour in a non-immersed condition (34.4˚C, 50%RH), while the WET group (n=10) cycled at 50W for one hour while immersed in 34.4˚C water. Exercise time to exhaustion was tested on an underwater cycle ergometer in 35.8˚C (WARM) and 37.2˚C (HOT) water at 50W. Core temperature (Tc) was continuously recorded and for all dives. Results: Time to exhaustion was reduced in HOT compared to WARM water (p ≺0.01) in both DRY (92.7 ± 41.6 minutes in 35.8°C vs. 43.4 ± 17.5 minutes in 37.2°C) and WET (95.9 ± 39.2 minutes in 35.8°C vs. 53.4 ± 27.5 minutes in 37.2°C) groups, but did not differ between groups (p=0.62). Rate of Tc rise was greater with higher water temperature (p ≺0.01), but was not different between groups (p=0.68). Maximum Tc (p=0.94 and p=0.95) and Tc change from baseline (p=0.38 and p=0.34) was not different between water temperatures or habituation group, respectively. Conclusion: Endurance decreased with increased water temperature but was not different between WET and DRY. Divers became exhausted at a similar core temperature during WARM- and HOT-water exercise. Mechanisms and applications of heat acclimation for warm-water diving should be further explored.

Pacing Strategy of a Full Ironman Overall Female Winner on a Course With Major Elevation Changes.

Pryor, JL, Adams, WM, Huggins, RA, Belval, LN, Pryor, RR, and Casa, DJ. Pacing strategy of a full Ironman overall female winner on a course with major elevation changes. J Strength Cond Res 32(11): 3080-3087, 2018-The purpose of this study was to use a mixed-methods design to describe the pacing strategy of the overall female winner of a 226.3-km Ironman triathlon. During the race, the triathlete wore a global positioning system and heart rate (HR)-enabled watch and rode a bike outfitted with a power and cadence meter. High-frequency (every km) analyses of mean values, mean absolute percent error (MAPE), and normalized graded running pace and power (accounting for changes in elevation) were calculated. During the bike, velocity, power, cadence, and HR averaged 35.6 km·h, 199 W, 84 rpm, and 155 b·min, respectively, with minimal variation except for velocity (measurement unit variation [MAPE]: 7.4 km·h [20.3%], 11.8 W [7.0%], 3.6 rpm [4.6%], 3 b·min [2.3%], respectively). During the run, velocity and HR averaged 13.8 km·h and 154 b·min, respectively, with velocity varying four-fold more than HR (MAPE: 4.8% vs. 1.2%). Accounting for elevation changes, power and running pace were less variable (raw [MAPE] vs. normalized [MAPE]: 199 [7.0%] vs. 204 W [2.7%]; 4:29 [4.8%] vs. 4:24 min·km [3.6%], respectively). Consistent with her planned pre-race pacing strategy, the triathlete minimized fluctuations in HR and watts during the bike and run, whereas velocity varied with changes in elevation. This case report provides observational evidence supporting the utility of a pacing strategy that allows for an oscillating velocity that sustains a consistent physiological effort in full Ironman races.

Effects of heat acclimation on hand cooling efficacy following exercise in the heat.

This study examined the separate and combined effects of heat acclimation and hand cooling on post-exercise cooling rates following bouts of exercise in the heat. Seventeen non-heat acclimated (NHA) males (mean ± SE; age, 23 ± 1 y; mass, 75.30 ± 2.27 kg; maximal oxygen consumption [VO2 max], 54.1 ± 1.3 ml·kg-1·min-1) completed 2 heat stress tests (HST) when NHA, then 10 days of heat acclimation, then 2 HST once heat acclimated (HA) in an environmental chamber (40°C; 40%RH). HSTs were 2 60-min bouts of treadmill exercise (45% VO2 max; 2% grade) each followed by 10 min of hand cooling (C) or no cooling (NC). Heat acclimation sessions were 90-240 min of treadmill or stationary bike exercise (60-80% VO2 max). Repeated measures ANOVA with Fishers LSD post hoc (α < 0.05) identified differences. When NHA, C (0.020 ± 0.003°C·min-1) had a greater cooling rate than NC (0.013 ± 0.003°C·min-1) (mean difference [95%CI]; 0.007°C [0.001,0.013], P = 0.035). Once HA, C (0.021 ± 0.002°C·min-1) was similar to NC (0.025 ± 0.002°C·min-1) (0.004°C [-0.003,0.011], P = 0.216). Hand cooling when HA (0.021 ± 0.002°C·min-1) was similar to when NHA (0.020 ± 0.003°C·min-1) (P = 0.77). In conclusion, when NHA, C provided greater cooling rates than NC. Once HA, C and NC provided similar cooling rates.

The addition of beta-hydroxy-beta-methylbutyrate and isomaltulose to whey protein improves recovery from highly demanding resistance exercise.

OBJECTIVE: This study evaluated whether a combination of whey protein (WP), calcium beta-hydroxy-beta-methylbutyrate (HMB), and carbohydrate exert additive effects on recovery from highly demanding resistance exercise. METHODS: Thirteen resistance-trained men (age: 22.6 ± 3.9 years; height: 175.3 ± 12.2 cm; weight: 86.2 ± 9.8 kg) completed a double-blinded, counterbalanced, within-group study. Subjects ingested EAS Recovery Protein (RP; EAS Sports Nutrition/Abbott Laboratories, Columbus, OH) or WP twice daily for 2 weeks prior to, during, and for 2 days following 3 consecutive days of intense resistance exercise. The workout sequence included heavy resistance exercise (day 1) and metabolic resistance exercise (days 2 and 3). The subjects performed no physical activity during day 4 (+24 hours) and day 5 (+48 hours), where recovery testing was performed. Before, during, and following the 3 workouts, treatment outcomes were evaluated using blood-based muscle damage markers and hormones, perceptual measures of muscle soreness, and countermovement jump performance. RESULTS: Creatine kinase was lower for the RP treatment on day 2 (RP: 166.9 ± 56.4 vs WP: 307.1 ± 125.2 IU · L(-1), p ≤ 0.05), day 4 (RP: 232.5 ± 67.4 vs WP: 432.6 ± 223.3 IU · L(-1), p ≤ 0.05), and day 5 (RP: 176.1 ± 38.7 vs 264.5 ± 120.9 IU · L(-1), p ≤ 0.05). Interleukin-6 was lower for the RP treatment on day 4 (RP: 1.2 ± 0.2 vs WP: 1.6 ± 0.6 pg · ml(-1), p ≤ 0.05) and day 5 (RP: 1.1 ± 0.2 vs WP: 1.6 ± 0.4 pg · ml(-1), p ≤ 0.05). Muscle soreness was lower for RP treatment on day 4 (RP: 2.0 ± 0.7 vs WP: 2.8 ± 1.1 cm, p ≤ 0.05). Vertical jump power was higher for the RP treatment on day 4 (RP: 5983.2 ± 624 vs WP 5303.9 ± 641.7 W, p ≤ 0.05) and day 5 (RP: 5792.5 ± 595.4 vs WP: 5200.4 ± 501 W, p ≤ 0.05). CONCLUSIONS: Our findings suggest that during times of intense conditioning, the recovery benefits of WP are enhanced with the addition of HMB and a slow-release carbohydrate. We observed reductions in markers of muscle damage and improved athletic performance.

Hydration Status and Sodium Balance of Endurance Runners Consuming Postexercise Supplements of Varying Nutrient Content.

Postexercise protein and sodium supplementation may aid recovery and rehydration. Preserved beef provides protein and contains high quantities of sodium that may alter performance related variables in runners. The purpose of this study was to determine the effects of consuming a commercial beef product postexercise on sodium and water balance. A secondary objective was to characterize effects of the supplementation protocols on hydration, blood pressure, body mass, and running economy. Eight trained males (age = 22 ± 3 y, VO2max = 66.4 ± 4.2 ml·kg-1·min-1) completed three identical weeks of run training (6 run·wk-1, 45 ± 6 min·run-1, 74 ± 5% HRR). After exercise, subjects consumed either, a beef nutritional supplement (beef jerky; [B]), a standard recovery drink (SRD), or SRD+B in a randomized counterbalanced design. Hydration status was assessed via urinary biomarkers and body mass. No main effects of treatment were observed for 24 hr urine volume (SRD, 1.7 ± 0.5; B, 1.8 ± 0.6; SRD+B, 1.4 ± 0.4 L·d-1), urine specific gravity (1.016 ± 0.005, 1.018 ± 0.006, 1.017 ± 0.006) or body mass (68.4 ± 8.2, 68.3 ± 7.7, 68.2 ± 8.1 kg). No main effect of treatment existed for sodium intake-loss (-713 ± 1486; -973 ± 1123; -980 ± 1220 mg·d-1). Mean arterial pressure (81.0 ± 4.6, 81.1 ± 7.3, 83.8 ± 5.4 mm Hg) and average exercise running economy (VO2: SRD, 47.9 ± 3.2; B, 47.2 ± 2.6; SRD+B, 46.2 ± 3.4 ml·kg-1·min-1) was not affected. Urinary sodium excretion accounted for the daily sodium intake due to the beef nutritional supplement. Findings suggest the commercial beef snack is a viable recovery supplement following endurance exercise without concern for hydration status, performance decrements, or cardiovascular consequences.

Habitual exercise may maintain endothelium-dependent dilation in overweight postmenopausal women.

Compared with their physically active peers, overweight sedentary postmenopausal women demonstrate impaired vascular endothelial function (VEF), substantially increasing the risk for cardiovascular disease (CVD). Habitual exercise is associated with improved VEF and reduced CVD risk. The purpose of this study was to compare brachial artery flow mediated dilation (FMD), a measure of VEF, in overweight, postmenopausal women who were physically active (EX: n = 17, BMI: 29.3 ± 3.11 kg/m2) or sedentary (CON: n = 8, BMI: 30.3 ± 3.6 kg/m2). Anthropomorphic measures were similar in both groups (P > .05). FMD was significantly greater in EX (10.24 ± 2.36%) versus CON (6.60 ± 2.18%) (P < .002). FMD was not significantly correlated with estimated VO2max (EX: r = .17, P = .52; CON: r = .20, P = .60) but was negatively associated with percent body fat in EX group (EX: r = -.48, P = .05; CON: r = .41, P = .31). These results are consistent with the positive effects of habitual exercise on VEF in overweight postmenopausal women.

A profile of a National Football League team.

The purpose of this study was to document the physical profiles of players on the 2011 New York Giants (NYG) team and to make comparisons with the historical literature on previous National Football League (NFL) player profiles. In this study, height, body mass (BM), body fat percentage (BF%) using skinfold measurements, and several predicted 1 repetition maximal strength and power measures in 30 returning players from the 2011 NYG team, who recently won the Super Bowl, were collected. Players were grouped by position: running back, quarterback (QB), wide receiver (WR), tight end, offensive lineman (OL), defensive lineman (DL), linebacker (LB), and defensive back (DB). Pooled and weighted mean differences (NYG - NFL) and effect sizes were used to evaluate height, BM, and BF% comparisons of NYG to previous NFL studies from 1998 to 2009. The characteristics of the players as a group were: age, height, BM, BF%: 26 ± 2 years, 183.8 ± 9.0 cm, 144.9 ± 20.8 kg, 14.3 ± 5.5%, respectively. Comparisons highlight distinct position-specific dissimilarity in strength measures, BM, and BF%, which reflect current strength training, conditioning, and team play strategy. As expected, NYG positional differences were found for height (p ≤ 0.05), BM (p ≤ 0.037), BF% (p ≤ 0.048), bench press (p ≤ 0.048), inclined bench press (p ≤ 0.013), and squat (p ≤ 0.026). Anthropometrics profiles did not significantly differ from previously published trends in NFL players indicating equity in physical characteristics over the past 13 years. However, NYG LBs, DLs, OLs, QBs, and WRs trended toward less BF% but generally similar BM compared with NFL players, suggesting greater lean BM in these positions. This study adds new players' data to prototypical position-specific databases that may be used as templates for comparison of players for draft selection or physical training.

Repetitive box lifting performance is impaired in a hot environment: implications for altered work-rest cycles.

This study investigated the effects of environmental temperature on repetitive box lifting (RBL) performance, associated stress hormone and creatine kinase (CK) responses. Ten healthy males performed two experimental trials in a random crossover design. The trials consisted of three 40 min (10 min sitting, 20 min standing, and 10 min RBL) circuits performed in either 23 °C or 38 °C followed by a 180 min seated recovery period in 23 °C. RBL performance (i.e., number of boxes lifted) was reduced (p ≤ 0.05) in 38 °C compared to the 23 °C trial. Physiological Strain Index was significantly different between trials (38 °C: 8.5 ± 1.1 versus 23 °C: 7.2 ± 0.7; p ≤ 0.01). Plasma testosterone was elevated (p ≤ 0.05) across both trials and then decreased at 60 min recovery, compared to pre-exercise (PRE) measures, but was higher (p ≤ 0.05) during the 38 °C trial. Plasma cortisol increased (p ≤ 0.05) at 60 min during both trials and remained elevated until 120 min in 23 °C, and until 60 min recovery in 38 °C. Serum CK was greater through 48 hr post compared to PRE values in both trials. Thus, 10 min RBL performance was reduced in 38 °C despite the 30-min rest periods between RBL intervals. Plasma testosterone and cortisol were generally higher during the 38 °C trial, suggesting a greater stress response. Additional research is needed to determine optimal work:rest cycles for maximizing work performance in thermally oppressive environments.

Plateau in Core Temperature during Shorter but Not Longer Work/Rest Cycles in Heat.

This study compared physiological responses to two work/rest cycles of a 2:1 work-to-rest ratio in a hot environment. In a randomized crossover design, fourteen participants completed 120 min of walking and rest in the heat (36.3 ± 0.6 °C, 30.2 ± 4.0% relative humidity). Work/rest cycles were (1) 40 min work/20 min rest [40/20], or (2) 20 min work/10 min rest [20/10], both completing identical work. Core temperature (Tc), skin temperature (Tsk), heart rate (HR), nude body mass, and perception of work were collected. Comparisons were made between trials at equal durations of work using three-way mixed model ANOVA. Tc plateaued in [20/10] during the second hour of work (p = 0.93), while Tc increased in [40/20] (p < 0.01). There was no difference in maximum Tc ([40/20]: 38.08 ± 0.35 °C, [20/10]: 37.99 ± 0.27 °C, p = 0.22) or end-of-work Tsk ([40/20]: 36.1 ± 0.8 °C, [20/10]: 36.0 ± 0.7 °C, p = 0.45). End-of-work HR was greater in [40/20] (145 ± 25 b·min-1) compared to [20/10] (141 ± 27 b·min-1, p = 0.04). Shorter work/rest cycles caused a plateau in Tc while longer work/rest cycles resulted in a continued increase in Tc throughout the work, indicating that either work structure could be used during shorter work tasks, while work greater than 2 h in duration may benefit from shorter work/rest cycles to mitigate hyperthermia.

Heat stress increases carbohydrate oxidation rates and oxygen uptake during prolonged load carriage exercise.

Military missions are conducted in a multitude of environments including heat and may involve walking under load following severe exertion, the metabolic demands of which may have nutritional implications for fueling and recovery planning. Ten males equipped a military pack loaded to 30% of their body mass and walked in 20°C/40% relative humidity (RH) (TEMP) or 37°C/20% RH (HOT) either continuously (CW) for 90 min at the first ventilatory threshold or mixed walking (MW) with unloaded running intervals above the second ventilatory threshold between min 35 and 55 of the 90 min bout. Pulmonary gas, thermoregulatory, and cardiovascular variables were analyzed following running intervals. Final rectal temperature (MW: p < 0.001, g = 3.81, CW: p < 0.001, g = 4.04), oxygen uptake, cardiovascular strain, and energy expenditure were higher during HOT trials (p ≤ 0.05) regardless of exercise type. Both HOT trials elicited higher final carbohydrate oxidation (CHOox) than TEMP CW at min 90 (HOT MW: p < 0.001, g = 1.45, HOT CW: p = 0.009, g = 0.67) and HOT MW CHOox exceeded TEMP MW at min 80 and 90 (p = 0.049, g = 0.60 and p = 0.024, g = 0.73, respectively). There were no within-environment differences in substrate oxidation indicating that severe exertion work cycles did not produce a carryover effect during subsequent loaded walking. The rate of CHOox during 90 minutes of load carriage in the heat appears to be primarily affected by accumulated thermal load.

Metabolic Costs of Walking with Weighted Vests.

INTRODUCTION: The US Army Load Carriage Decision Aid (LCDA) metabolic model is used by militaries across the globe and is intended to predict physiological responses, specifically metabolic costs, in a wide range of dismounted warfighter operations. However, the LCDA has yet to be adapted for vest-borne load carriage, which is commonplace in tactical populations, and differs in energetic costs to backpacking and other forms of load carriage. PURPOSE: The purpose of this study is to develop and validate a metabolic model term that accurately estimates the effect of weighted vest loads on standing and walking metabolic rate for military mission-planning and general applications. METHODS: Twenty healthy, physically active military-age adults (4 women, 16 men; age, 26 ± 8 yr old; height, 1.74 ± 0.09 m; body mass, 81 ± 16 kg) walked for 6 to 21 min with four levels of weighted vest loading (0 to 66% body mass) at up to 11 treadmill speeds (0.45 to 1.97 m·s -1 ). Using indirect calorimetry measurements, we derived a new model term for estimating metabolic rate when carrying vest-borne loads. Model estimates were evaluated internally by k -fold cross-validation and externally against 12 reference datasets (264 total participants). We tested if the 90% confidence interval of the mean paired difference was within equivalence limits equal to 10% of the measured walking metabolic rate. Estimation accuracy, precision, and level of agreement were also evaluated by the bias, standard deviation of paired differences, and concordance correlation coefficient (CCC), respectively. RESULTS: Metabolic rate estimates using the new weighted vest term were statistically equivalent ( P < 0.01) to measured values in the current study (bias, -0.01 ± 0.54 W·kg -1 ; CCC, 0.973) as well as from the 12 reference datasets (bias, -0.16 ± 0.59 W·kg -1 ; CCC, 0.963). CONCLUSIONS: The updated LCDA metabolic model calculates accurate predictions of metabolic rate when carrying heavy backpack and vest-borne loads. Tactical populations and recreational athletes that train with weighted vests can confidently use the simplified LCDA metabolic calculator provided as Supplemental Digital Content to estimate metabolic rates for work/rest guidance, training periodization, and nutritional interventions.

Diver Underwater Cycling Endurance After Short-Term Warm and Hot Water Acclimation.

INTRODUCTION: It is unclear whether immersion heat acclimation benefits exercise in warm water conditions. This study examined the effects of heat acclimation strategies on heart rate (HR), core temperature, and time to exhaustion (TTE) during cycling exercise in varying warm water conditions. METHODS: Twenty male divers completed this study at the Navy Experimental Diving Unit. Subjects were randomly assigned to one of two 9-day heat acclimation groups. The first group (WARM; n = 10) cycled for 2 hours at 50 W in 34.4 °C water, while the second group (HOT; n = 10) cycled for 1 hour against minimal resistance in 36.7 °C water. Following acclimation, TTE was tested by underwater cycling (30 W) in 35.8 °C, 37.2 °C, and 38.6 °C water. RESULTS: Throughout acclimation, the rate of core temperature rise in the first 30 minutes of exercise increased (P = .02), but the maximum core temperature reached was not different for either group. Time to exhaustion (TTE) was reduced, and the rate of core temperature rise during performance testing increased (both P < .001) with increasing water temperature but was not different between groups. Core temperature and HR increased throughout performance testing in each water condition and were lower in the HOT compared to the WARM acclimation group (all P < .05) with the exception of core temperature in the 37.2 °C condition. CONCLUSIONS: Underwater exercise performance did not differ between the two acclimation strategies. This study suggests that passive acclimation to a higher water temperature may improve thermoregulatory and cardiovascular responses to exercise in warm water. Hot water immersion adaptations are dependent on exercise intensity and water temperature.

Verification Phase Confirms V̇O 2max in a Hot Environment in Sedentary Untrained Males.

PURPOSE: This study aimed to assess the V̇O 2 uptake obtained during a GXT and subsequent verification phase in untrained participants in a hot environment. METHODS: Twelve sedentary males completed a GXT followed by a biphasic supramaximal-load verification phase in a hot environment (39°C, 32% relative humidity). Rest between tests occurred in a temperate chamber and lasted until gastrointestinal temperature returned to baseline. RESULTS: Mean verification phase V̇O 2max (37.8 ± 4.3 mL·kg -1 ·min -1 ) was lower than GXT (39.8 ± 4.1 mL·kg -1 ·min -1 ; P = 0.03) and not statistically equivalent. Using an individualized analysis approach, only 17% (2/12) of participants achieved a V̇O 2 plateau during the GXT. Verification phase confirmed GXT V̇O 2max in 100% of participants, whereas the traditional and the new age-dependent secondary V̇O 2max criteria indicated GXT V̇O 2max achievement at much lower rates (8/12 [67%] vs 7/12 [58%], respectively). Correlational indices between GXT and verification phase V̇O 2max were strong (intraclass correlation coefficient = 0.95, r = 0.86), and Bland-Altman analysis revealed a low mean bias of -2.1 ± 1.9 mL·kg -1 ·min -1 and 95% limits of agreement (-5.8 to 1.7 mL·kg -1 ·min -1 ). CONCLUSIONS: Very few untrained males achieved a V̇O 2 plateau during GXT in the heat. When conducting GXT in a hot condition, the verification phase remains a valuable addition to confirm V̇O 2max in untrained males.

Persistent Knowledge Gaps Regarding Exertional Heat Stroke Treatment.

Individualized patient care is ideal for treating and rehabilitating patients with athletic illnesses and injuries. Exertional heat stroke (EHS) treatment best-practice recommendations state that all patients should undergo identical cold-water immersion (CWI) treatment for ideal outcomes. It is unknown, however, whether CWI can be optimized with individualized treatment plans, encouraging personalized medicine. To accomplish this task, clinicians and researchers need to better understand the factors affecting CWI effectiveness. In this short report, we will provide an update to the American College of Sports Medicine Roundtable on Exertional Heat Stroke, review research regarding EHS treatment, and identify knowledge gaps in EHS treatment.