Acute work rate adjustments during high-intensity interval training in a hot and temperate environment.

Heart rate drifts upward over time during interval exercise and during exercise in hot conditions. As such, work rate must be lowered to maintain target heart rate. The purpose was to characterize acute work rate adjustments during high-intensity interval training based on target heart rate. Seven humans (three females) completed five study visits: a graded exercise test on a cycle ergometer to measure maximal heart rate (HRmax) in ∼22 °C and four trials performed in ∼22 °C (TEMP) or ∼35 °C (HOT), consisting of an 8 min warm-up at 70% HRmax followed by one (15TEMP and 15HOT) or five (43TEMP and 43HOT) rounds of high-intensity interval training (one round = 4 min work at 90% HRmax and 3 min recovery at 70% HRmax) totaling 15 min or 43 min of exercise, respectively. Work rate was lowered 33 ± 20 W (p = 0.005) in 43TEMP and 56 ± 30 W (p = 0.003) in 43HOT between the first and fifth work intervals. Thermal strain (0.2 °C higher rectal temperature, p = 0.01) and cardiovascular strain (6 beats·min-1 larger increase in heart rate from first to fifth recovery interval, p = 0.01) were greater in 43HOT versus 43TEMP. Using target heart rate during high-intensity interval training may reduce the training stimulus, especially in hot environments, but it may also limit thermal strain and enable participants to complete the prescribed workout despite the heat.

Effect of Work-to-Rest Cycles on Cardiovascular Strain and Maximal Oxygen Uptake during Heat Stress.

Cardiovascular drift-a progressive increase in heart rate (HR) and decrease in stroke volume (SV) during prolonged exercise-is exacerbated by heat stress and thermal strain, and often accompanied by a decrease in work capacity (indexed as maximal oxygen uptake [V.O2max]). To attenuate physiological strain during work in the heat, use of work:rest ratios is recommended by the National Institute for Occupational Safety and Health. The purpose of this study was to test the hypothesis that during moderate work in hot conditions, utilizing the recommended 45:15 min work:rest ratio would result in cardiovascular drift 'accumulating' over consecutive work:rest cycles and accompanying decrements in V.O2max. Eight people (5 women; (mean ± SD) age = 25 ± 5 y; body mass = 74.8 ± 11.6 kg; V.O2max = 42.9 ± 5.6 mL·kg-1·min-1) performed 120 min of simulated moderate work (201-300 kcal·h-1) in hot conditions (indoor wet-bulb globe temperature = 29.0 ± 0.6 °C). Participants completed two 45:15 min work:rest cycles. Cardiovascular drift was evaluated at 15 and 45 min of each work bout; V.O2max was measured after 120 min. On a separate day, V.O2max was measured after 15 min under identical conditions for comparison before and after cardiovascular drift occurred. HR increased 16.7% (18 ± 9 beats·min-1, p = 0.004) and SV decreased 16.9% (-12.3 ± 5.9 mL, p = 0.003) between 15 and 105 min, but V.O2max was unaffected after 120 min (p = 0.14). Core body temperature increased 0.5 ± 0.2 °C (p = 0.006) over 2 h. Recommended work:rest ratios preserved work capacity but did not prevent the accumulation of cardiovascular and thermal strain.

Effect of Ice Slurry Beverages on Voluntary Fluid Intake and Exercise Performance.

ABSTRACT: Ng, J and Wingo, JE. Effect of ice slurry beverages on voluntary fluid intake and exercise performance. J Strength Cond Res 37(6): e376-e383, 2023-Voluntary intake of cold fluid is greater than warm fluid as a result of more favorable palatability, resulting in better maintenance of hydration status and improved exercise performance. It remains unclear whether voluntary ingestion of ice slurry beverages compared with cold fluid during exercise yields superior results. Eight recreationally active subjects (mean ± SD ; age = 24 ± 4 years, height = 175.2 ± 7.8 cm, mass = 79.6 ± 11.2 kg, body fat = 13.0 ± 5.2%) completed a pretest in 22° C to determine maximal workload (W max ). Then, in 2, separate, counterbalanced trials, they cycled for 60 minutes at 50%W max in 35° C and 40% relative humidity with either ad libitum ice slurry (-1.3 ± 0.3° C) or cold fluid (11.1 ± 2.4° C) ingestion. This was immediately followed by a 15-minute cycling time trial. Subjects avoided 2% body mass loss in both conditions but ingested twice as much cold fluid as ice slurry (fluid: 1,074.7 ± 442.1 g, ice slurry: 526.9 ± 214.1 g; p = 0.001). Nonetheless, neither 15-minute performances (cold fluid: 119.5 ± 34.8 kJ, ice slurry: 114.6 ± 20.9 kJ; p = 0.59) nor whole-body sweat rates (fluid: 1,370 ± 311 ml·h -1 , ice slurry: 1,242 ± 191 ml·h -1 ; p = 0.20) were different between the conditions. Despite ingesting half as much ice slurry as cold fluid, subjects experienced similar physiological responses and thus had similar performances under heat stress while avoiding excessive hypohydration. Under the conditions of this study, ice slurry ingestion was an effective alternative form of exercise hydration.

Physical demands and physiological strain of American football referees while officiating.

OBJECTIVES: Certain occupations are associated with greater risk of triggering a sudden cardiac event because of high levels of physical exertion and extreme thermal environments in which they occur. The extent to which sports officials--particularly high school (HS) American football referees--experience these conditions is unknown. Forty-six male HS officials (72% White/Caucasian; age = 48 ± 12 years, body mass index = 31.7 ± 6.6 kg·m-2) were studied to quantify the physiological strain and physical demands of officiating. METHODS: Referee demographics (e.g., experience, habitual exercise), pre-game urine specific gravity (USG), thermal (peak core temperature [Tcore]) and cardiovascular (average heart rate [HR]) strain, kinematic activity (e.g., total distance, speed, mechanical intensity), and environmental conditions were measured during 10 regular season varsity HS football games (≈2.5 h each) in the Southeastern United States (average wet bulb globe temperature and relative humidity: 18.9 ± 6.0 °C and 78.2% ± 12.1%). Analyses included descriptive statistics, bivariate correlations, and linear regression. RESULTS: Referees covered 5.2 ± 1.2 km per game, eliciting average HR and peak Tcore of 71.5% ± 8.0% HRmax and 38.3 ± 0.5 °C, respectively; 38% began games dehydrated (USG = 1.026 ± 0.004). Multiple regression analyses revealed that obesity (ß = 0.34), not participating in regular exercise (ß = -0.36), and officiating at lower mechanical intensity (ß = -0.33) predicted greater cardiovascular strain (all p ≤ 0.03). White/Caucasian race/ethnicity (ß = 0.59), younger age (ß = -0.46), and obesity (ß = 0.28) predicted greater thermal strain (all p ≤ 0.01). CONCLUSION: HS football referees experienced elevated levels of physiological strain while officiating, with individual factors modulating the magnitude of strain. Strategies aimed at reducing obesity, increasing exercise participation, and improving cardiovascular health should be emphasized to mitigate strain and prevent cardiac events.

Roundtable on Preseason Heat Safety in Secondary School Athletics: Heat Acclimatization.

OBJECTIVE: To provide best-practice recommendations for developing and implementing heat-acclimatization strategies in secondary school athletics. DATA SOURCES: An extensive literature review on topics related to heat acclimatization and heat acclimation was conducted by a group of content experts. Using the Delphi method, action-oriented recommendations were developed. CONCLUSIONS: A period of heat acclimatization consisting of ≥14 consecutive days should be implemented at the start of fall preseason training or practices for all secondary school athletes to mitigate the risk of exertional heat illness. The heat-acclimatization guidelines should outline specific actions for secondary school athletics personnel to use, including the duration of training, the number of training sessions permitted per day, and adequate rest periods in a cool environment. Further, these guidelines should include sport-specific and athlete-specific recommendations, such as phasing in protective equipment and reintroducing heat acclimatization after periods of inactivity. Heat-acclimatization guidelines should be clearly detailed in the secondary school's policy and procedures manual and disseminated to all stakeholders. Heat-acclimatization guidelines, when used in conjunction with current best practices surrounding the prevention, management, and care of secondary school student-athletes with exertional heat stroke, will optimize their health and safety.

Menstrual cycle effects on cardiovascular drift and maximal oxygen uptake during exercise heat stress.

AIM: Compared to other modulators of physiological strain associated with exercise heat stress, hyperthermia results in the greatest magnitude of cardiovascular (CV) drift and associated decrements in maximal oxygen uptake ([Formula: see text]). PURPOSE: To determine if elevated core temperature in the luteal phase (LP) of the menstrual cycle results in greater CV drift and reductions in [Formula: see text] versus the follicular phase (FP). METHODS: Seven women performed 15- and 45-min cycling bouts on separate occasions (60% [Formula: see text], 35 °C) followed by a [Formula: see text] test during the FP and LP. CV drift was measured between 15 and 45 min during the 45-min bout, and the 15-min bout was for measuring [Formula: see text] over the same time interval that CV drift occurred. RESULTS: Core temperature during LP was ~ 0.3 °C higher than FP (P < 0.05), but changes from rest during exercise were similar between phases (all P > 0.05). Heart rate increased significantly over time but was not different between phases (P = 0.78). Stroke volume decreased more over time during LP compared to FP (P = 0.02), but the values were similar at the end of exercise between phases (both time points P > 0.05). [Formula: see text] decrements for FP (13%) and LP (16%) were also comparable (P = 0.97). CONCLUSIONS: The LP-FP difference in core temperature in this study was not sufficient to amplify CV strain and decrements in [Formula: see text]. Greater differences in core temperature may be required to independently modulate CV drift and accompanying decrements in [Formula: see text] during prolonged exercise heat stress.

Cardiovascular Drift and Maximal Oxygen Uptake during Running and Cycling in the Heat.

INTRODUCTION: Greater cardiovascular (CV) drift occurs during cycling compared to running in temperate conditions. CV drift also corresponds to proportional reductions in maximal oxygen uptake (V˙O2max) during heat stress. Whether exercise mode differentially affects CV drift-and accompanying declines in V˙O2max-during heat stress is uncertain. The purpose of this study was to test the hypothesis that a greater magnitude of CV drift, accompanied by a greater decrement in V˙O2max, occurs during cycling compared to running in hot conditions. METHODS: 7 active men (mean ± SD; age = 25 ± 6 yr, percent body fat = 11.9% ± 2.4%) completed a control graded exercise test (GXT) on a cycle ergometer and treadmill. Then on separate, counterbalanced occasions they completed 15 or 45 min of cycling or running at 60% V˙O2max in 35°C, immediately followed by a GXT to measure V˙O2max (4 trials total). The separate 15- and 45-min trials were designed to measure CV drift and V˙O2max over the same time interval. RESULTS: Heart rate increased 19% and 17% and stroke volume decreased 20% and 15% between 15 and 45 min during running and cycling, respectively, but modes were not different (all P > 0.05). Despite a 1.8°C larger core-to-skin thermal gradient during running, decrements in V˙O2peak were not different between exercise modes (95% CI for difference in change scores between 15 and 45 min: -0.2, 0.3). CONCLUSIONS: CV strain (indexed as CV drift) during prolonged exercise in the heat corresponds to reduced V˙O2max, irrespective of exercise mode or the thermal gradient. As such, the upward drift in heart rate associated with CV drift reflects increased relative metabolic intensity (%V˙O2max) during prolonged cycling or running in the heat.

Fan cooling after cardiovascular drift does not reverse decrements in maximal oxygen uptake during heat stress.

Cardiovascular (CV) drift, the progressive increase in heart rate (HR) and decrease in stroke volume (SV) during constant rate, moderate intensity exercise, is related to reduced maximal oxygen uptake (V̇O2max) during heat stress. Once it has already occurred, it is unknown whether the detrimental effects of CV drift on V̇O2max can be reversed. This study tested the hypothesis that fan cooling after CV drift has occurred attenuates decrements in V̇O2max associated with CV drift. Eight men completed a control graded exercise test (GXT) in 22°C to measure V̇O2max. Then on separate, counterbalanced occasions, they completed one 15-min (15MIN) and two 45-min bouts (45NF and 45FAN) of cycling in 35°C, 40% RH at 60% V̇O2max, each immediately followed by a GXT to measure V̇O2max. For one of the 45-min trials (45FAN), fan airflow (4.5 m/s) was directed at participants beginning ~5 min before the GXT and continuing throughout the remainder of exercise. The purpose of the separate 15- and 45-min trials was to measure V̇O2max during the same time interval that CV drift occurred. HR increased (13.8% and 11.4%) and SV decreased (14.4% and 14.1%) for 45NF and 45FAN, respectively; trials were not different (all P > 0.05). Despite a decrease in mean skin temperature of ~1°C with fan use, V̇O2max decreased similarly between conditions (17% vs. 15% for 45NF and 45FAN, P = 0.54). Fan cooling after CV drift was insufficient to reverse the negative consequences of CV drift on V̇O2max after prolonged exercise in a hot environment. Abbreviations: 15MIN: 15-min trial; 45FAN: 45-min, fan trial; 45NF: 45-min, no fan trial; ANOVA: Analysis of variance; CV: Cardiovascular; GXT: Graded exercise test; HR: Heart rate; SV: Stroke volume; T̅b: Mean body temperature; Tre: Rectal temperature; T̅sk: Mean skin temperature; V̇O2max: Maximal oxygen uptake.

Agreement between supine and standing bioimpedance spectroscopy devices and dual-energy X-ray absorptiometry for body composition determination.

BACKGROUND: Research comparing bioimpedance spectroscopy (BIS) to dual-energy X-ray absorptiometry (DXA) is limited, especially with newer BIS devices that take measures in a standing position instead of the traditional supine position. PURPOSE: The purpose of this study was to compare a standing BIS device (BISSTA ) and a supine BIS device (BISSUP ) to DXA for measuring body fat percentage (BF%), fat mass (FM) and fat-free mass (FFM) in a cohort of male and female subjects displaying a wide range of ages and BMI levels. METHODS: Ninety-five subjects (30 ± 15 years, 170 ± 8·0 cm, 72·6 ± 14·8 kg) participated in the study. Body composition measures were taken from BISSTA , BISSUP and DXA during a single visit to the laboratory following an 8- to 12-h fast in a euhydration state. RESULTS: Supine BIS device and BISSTA produced r-values >0·91 and low SEE values for all measurements compared to DXA. Effect sizes were 'trivial' for FFM comparing both BISSUP and BISSTA to DXA (<0·1) and 'small' for FM and BF% (<0·39). Compared to DXA, BISSTA resulted in lower total (TE) and constant errors/mean differences (CE) (TE < 3·6 kg, CE < -1·82 kg) versus BISSUP (TE < 4·35 kg, CE < -3·10 kg) for FFM. CONCLUSION: Fat-free mass values for BISSTA resulted in the most comparable measurements to DXA with no mean differences and the lowest total error and effect size. However, the findings indicated both BIS devices may be acceptable alternatives to DXA for BF%, FM and FFM in clinical practice.

Effect of Ice Slurry Ingestion on Cardiovascular Drift and V˙O2max during Heat Stress.

External body cooling by fan airflow mitigates the decrease in maximal oxygen uptake (V˙O2max) associated with cardiovascular (CV) drift during cycling in hot conditions. It remains unknown whether internal body cooling via ice slurry ingestion elicits a similar response. PURPOSE: This study aimed to test the hypothesis that ice slurry ingestion attenuates the magnitude of CV drift and accompanying decrement in V˙O2max during heat stress. METHODS: Eight men completed a graded exercise test on a cycle ergometer in 22°C to measure V˙O2max. Then on three separate occasions (in randomly assigned counterbalanced treatment orders), they cycled at 60% V˙O2max in hot conditions (35°C, 40% RH) for 15 min, 45 min with tepid (23°C) fluid ingestion (45FL), or 45 min with ice (-1°C) slurry ingestion (45ICE), followed immediately by measurement of V˙O2max. The purpose of the separate 15- and 45-min trials was to measure CV drift and V˙O2max over the same time interval. RESULTS: The increase in heart rate between 15 and 45 min was twice as large in 45FL (8.6%) compared with 45ICE (4.6%; P = 0.02). Stroke volume declined by 6.2% in 45FL but was maintained with 45ICE (P = 0.02). V˙O2peak decreased from 15 to 45 min by 8.6% and 9.0% in 45FL and 45ICE, respectively, but was not different between conditions (P = 0.79). CONCLUSION: Although ice slurry ingestion attenuated CV drift more than fluid ingestion, it did not mitigate the decline in V˙O2max. Contrary to previous findings, when ice slurry is ingested, changes in heart rate may not reflect changes in relative metabolic intensity during prolonged exercise in the heat.

An Evaluation of Select Physical Activity Exercise Classes on Bone Metabolism.

Weight-bearing physical activity can optimize bone mass early in life and prevent the development of osteoporosis. However, less is known about the potential benefits of non-weight-bearing activities. The purpose of this study was to assess the efficacy of structured physical activity classes on bone metabolism. Twenty-eight premenopausal women, aged 18-35 years who were either enrolled in a yoga class (n=14) or cardio-kickboxing class (n=14) voluntarily consented to participate. Both classes were introductory classes meeting twice per week for 50 min per session for 12 weeks. Anteroposterior spine (L1-L4), hip (dual femur), and total body bone mineral density (BMD) was measured in both groups pre and post intervention using dual-energy X-ray absorptiometry (DXA). Pre and post blood samples were drawn for measurement of serum osteocalcin (OC) by enzyme-linked immunosorbent assay (ELISA) in each group. Baseline subject characteristics including age, height, weight, body fat percentage, and lean body mass did not differ between groups. BMD levels did not increase but were held stable over the course of the intervention. Yoga increased OC by 68% (P < 0.001) and cardio-kickboxing increased OC by 67% (P < 0.001) over the course of the 12-week classes. While 12 weeks of yoga and cardio-kickboxing were insufficient to induce BMD changes, OC levels reflect the bone formation process was initiated, but not yet complete. Increased OC levels suggest the selected physical activity classes provided enough of a stimulus to precipitate a future response of bone growth, assuming exercise training remains constant.

Ice Slurry Ingestion and Physiological Strain During Exercise in Non-Compensable Heat Stress.

INTRODUCTION: Precooling with ice slurry ingestion attenuates the increase in rectal temperature (Tre) during subsequent running and cycling. It remains unclear how this cooling method affects physiological strain during work while wearing protective garments. This study investigated the effect of ice slurry ingestion on physiological strain during work in hot conditions while wearing firefighter protective clothing. METHODS: In three counterbalanced trials, eight men (mean ± SD; age = 21 ± 2 yr, height = 179.5 ± 3.5 cm, mass = 79.1 ± 4.1 kg, body fat = 11.4 ± 3.7%) wore firefighter protective clothing and walked (4 km · h-1, 12% incline, ∼7 METs) for 30 min in hot conditions (35°C, 40% RH). Every 2.5 min, subjects ingested 1.25 g · kg-1 (relative total: 15 g · kg-1, absolute total: 1186.7 ± 61.3 g) of a tepid (22.4 ± 1.7°C), cold (7.1 ± 1.5°C), or ice slurry (-1.3 ± 0.2°C) beverage. RESULTS: Heart rates (HR) were lower with ice slurry ingestion compared to both fluid trials starting 5 min into exercise (tepid = 158 ± 14, cold = 157 ± 11, ice slurry = 146 ± 13 bpm) and persisting for the remainder of the bout (min 30: tepid = 196 ± 10, cold = 192 ± 10, ice slurry = 181 ± 13 bpm). Tre was lower with ice slurry ingestion compared to cold and tepid trials (min 5: tepid = 37.17 ± 0.38, cold = 37.17 ± 0.39, ice slurry = 37.05 ± 0.43°C; min 30: tepid = 38.15 ± 0.29, cold = 38.31 ± 0.36, ice slurry = 37.95 ± 0.32°C). The physiological strain index (PSI) was lower with ice slurry ingestion compared to fluid trials starting at min 5 (tepid = 3.8 ± 0.7, cold = 3.8 ± 0.6, ice slurry = 3.0 ± 0.5) and remained lower throughout exercise (min 30: tepid = 8.2 ± 0.6, cold = 8.3 ± 0.9, ice slurry = 6.9 ± 1.2). DISCUSSION: A large quantity of ice slurry ingested under non-compensable heat stress conditions mitigated physiological strain during exercise by blunting the rise in heart rate and rectal temperature.Ng J, Wingo JE, Bishop PA, Casey JC, Aldrich EK. Ice slurry ingestion and physiological strain during exercise in non-compensable heat stress. Aerosp Med Hum Perform. 2018; 89(5):434-441.

Effect of Magnesium Carbonate Use on Repeated Open-Handed and Pinch Grip Weight-Assisted Pull-Ups.

The purpose was to determine if pull-up performance was affected by the use of chalk (100% magnesium carbonate) during open-handed and pinch grip weight-assisted pull-ups (WAPU) in recreationally-trained rock climbers. Furthermore, the reliability of open-handed and pinch grip WAPU was also investigated. Recreationally-active volunteers (n = 9) completed six counterbalanced trials. Participants used chalk during four trials to determine the reliability (test-retest) of the open-handed and pinch grips. While two of the six trials were used to determine if open-handed and pinch grip WAPU performance was affected without using chalk. Three of the six trials included one set of open-handed WAPU, while the remaining trails included one set of pinch grip WAPU. Sets were performed until failure and consisted of either the open-handed or pinch grip pull-ups assisted by a 50% reduction of body weight. Heart rate, ratings of perceived exertion, perceived recovery scale and session-RPE were not significantly different (p > 0.05) among trials. Intraclass correlations (ICC's) for test-retest of the open-handed (R = 0.99) and pinch grip (R = 0.96) WAPU evidenced reliable values. When compared to the non-chalked trials, chalk improved both openhanded (mean = 22.8 ± 4.53 vs. mean no chalk = 19.7 ± 4.39 reps; p = 0.006,) and pinch grip (mean = 14.4 ± 4.47 vs. mean no chalk = 9.1 ± 4.83 reps; p = 0.007) WAPU. ICC's indicated a reliable measurement, while chalk improved performance for both open-handed and pinch grip WAPU when compared to no chalk trials.

Precooling and Warm-Up Effects on Time Trial Cycling During Heat Stress.

BACKGROUND: Heat stress limits endurance exercise performance. Combining precooling and warm-up prior to endurance exercise in the heat may exploit the benefits of both strategies while avoiding the potential negative consequences of each. This study tested the hypothesis that precooling combined with warm-up improves time trial cycling performance in the heat relative to either treatment alone. METHODS: Nine healthy men completed three 16.1-km time trials in 33°C after: 1) precooling (ice slurry and ice vest) alone (PREC); 2) warm-up alone (WU); or 3) PREC plus WU (COMBO). RESULTS: Tre was lower after PREC compared to WU throughout exercise and lower than COMBO for the first 12 km; COMBO was lower than WU for the first 4 km. Tsk during PREC was lower than COMBO and WU for the first 8 km, and lower in COMBO than WU for the first 4 km. PREC lowered pre-exercise heart rate relative to COMBO and WU (68 ± 10, 106 ± 12, 101 ± 13 bpm, respectively), but it increased similarly during exercise. Local sweat rate (SR) was lower in PREC (0.1 ± 0.1 mg · cm-2 · min-1) than COMBO (0.5 ± 0.2 mg · cm-2 · min-1) and WU (0.6 ± 0.2 mg · cm-2 · min-1) for the first 4 km. Treatments did not differentially affect performance (PREC = 31.9 ± 1.9 min, COMBO = 32.6 ± 2.7 min, WU = 33.1 ± 2.9 min). DISCUSSION: We conclude precooling alone or with warm-up mitigated thermal strain during exercise, but did not significantly improve 16.1-km cycling time trial performance.Al-horani RA, Wingo JE, Ng J, Bishop P, Richardson M. Precooling and warm-up effects on time trial cycling during heat stress. Aerosp Med Hum Perform. 2018; 89(2):87-93.

Comparison of Bioelectrical Impedance Analysis and Dual-Energy X-Ray Absorptiometry for Estimating Bone Mineral Content.

The purpose of this study was to validate single-frequency hand-to-foot bioelectrical impedance analysis (HFBIA) for estimating bone mineral content (BMC) using dual-energy X-ray absorptiometry as the criterion measure in healthy men and women aged 18-40 years. A total of 80 men and women participated in this study. BMC was estimated on the same day using HFBIA and dual-energy X-ray absorptiometry. The HFBIA device provided higher mean BMC values in men and the entire sample, but not in women. A smaller standard error of estimate was observed in women (0.20, corresponding to 8% of the mean reference BMC values) compared with men (0.39, corresponding to 12% of the mean reference BMC values) and the combined sample (0.31). HFBIA provided a smaller constant error and individual estimation error indicated by the 95% limits of agreement in women (-0.05 ± 0.39) compared with men (-0.16 ± 0.78) and the entire sample (-0.10 ± 0.63). In conclusion, although BMC values were found to be more accurate in women, HFBIA overestimated BMC compared with dual-energy X-ray absorptiometry, especially in individuals with lower values. Given these results, using HFBIA to measure BMC would be inappropriate for diagnostic purposes.

Impact of upper body precooling during warm-up on subsequent time trial paced cycling in the heat.

OBJECTIVES: The purpose of this study was to test the hypothesis that cooling the upper body during a warm-up enhances performance during a subsequent 16.1-km simulated cycling time trial in a hot environment. DESIGN: Counterbalanced, repeated measures design. METHODS: Eight trained, male cyclists (peak oxygen uptake=57.8±5.0mLkg-1min-1) completed two simulated 16.1-km time trials in a hot environment (35.0±0.5°C, 43.8±2.0% relative humidity) each separated by 72h. Treatments were counterbalanced; participants warmed up for 20min while either wearing head and neck ice wraps and an ice vest (COOLING) or no cooling apparatus (CONTROL). RESULTS: Following the warm-up mean skin temperature (T¯sk), mean body temperature (T¯b) and rating of thermal comfort were significantly lower than baseline following the COOLING trial (all P<0.05); however, rectal temperature was unaffected (P=0.35). Because the effects of precooling on T¯sk and T¯b were not sustained during exercise, values for COOLING and CONTROL were not different throughout the time trial (P=0.38). Nonetheless, time to completion was significantly faster following the COOLING intervention when compared to the CONTROL (29.3±3.6min, vs. 30.3±3.1min; P=0.04). CONCLUSIONS: These data suggest that in short distance time trials in hot conditions cyclists may benefit from utilizing a cooling modality during the warm-up.

Heart Rate Variability and Training Load Among National Collegiate Athletic Association Division 1 College Football Players Throughout Spring Camp.

Flatt, AA, Esco, MR, Allen, JR, Robinson, JB, Earley, RL, Fedewa, MV, Bragg, A, Keith, CM, and Wingo, JE. Heart rate variability and training load among National Collegiate Athletic Association Division 1 college football players throughout spring camp. J Strength Cond Res 32(11): 3127-3134, 2018-The purpose of this study was to determine whether recovery of cardiac-autonomic activity to baseline occurs between consecutive-day training sessions among positional groups of a collegiate football team during Spring camp. A secondary aim was to evaluate relationships between chronic (i.e., 4-week) heart rate variability (HRV) and training load parameters. Baseline HRV (lnRMSSD_BL) was compared with HRV after ∼20 hours of recovery before next-day training (lnRMSSDpost20) among positional groups composed of SKILL (n = 11), MID-SKILL (n = 9), and LINEMEN (n = 5) with a linear mixed model and effect sizes (ES). Pearson and partial correlations were used to quantify relationships between chronic mean and coefficient of variation (CV) of lnRMSSD (lnRMSSD_chronic and lnRMSSDcv, respectively) with the mean and CV of PlayerLoad (PL_chronic and PL_cv, respectively). A position × time interaction was observed for lnRMSSD (p = 0.01). lnRMSSD_BL was higher than lnRMSSDpost20 for LINEMEN (p < 0.01; ES = large), whereas differences for SKILL and MID-SKILL were not statistically different (p > 0.05). Players with greater body mass experienced larger reductions in lnRMSSD (r = -0.62, p < 0.01). Longitudinally, lnRMSSDcv was significantly related to body mass (r = 0.48) and PL_chronic (r = -0.60). After adjusting for body mass, lnRMSSDcv and PL_chronic remained significantly related (r = -0.43). The ∼20-hour recovery time between training sessions on consecutive days may not be adequate for restoration of cardiac-parasympathetic activity to baseline among LINEMEN. Players with a lower chronic training load throughout camp experienced greater fluctuation in lnRMSSD (i.e., lnRMSSDcv) and vice versa. Thus, a capacity for greater chronic workloads may be protective against perturbations in cardiac-autonomic homeostasis among American college football players.

Impact of Measured vs. Predicted Residual Lung Volume on Body Fat Percentage Using Underwater Weighing and 4-Compartment Model.

Nickerson, BS, Esco, MR, Bishop, PA, Schumacker, RE, Richardson, MT, Fedewa, MV, Wingo, JE, and Welborn, BA. Impact of measured vs. predicted residual lung volume on body fat percentage using underwater weighing and 4-compartment model. J Strength Cond Res 31(9): 2519-2527, 2017-The purpose of this study was to compare underwater weighing (UWW) and 4-compartment (4C) model body fat percentage (BF%) for predicted vs. simultaneously measured residual lung volume (RLV). Forty-seven women and 33 men (age = 22 ± 5 years) had UWW and 4C model BF% determined using Boren et al. (RLVBOREN), Goldman and Becklake (RLVGB), and Miller et al. (RLVMILLER) RLV prediction equations. Criterion UWW BF% included body density (BD) values with simultaneous RLV. Criterion 4C model BF% included BD through UWW with simultaneous RLV, total body water through bioimpedance spectroscopy, and bone mineral content through dual-energy x-ray absorptiometry. The standard error of estimate (SEE) for UWW and 4C model BF% determined through RLV prediction equations varied from 2.0 to 2.6% and from 1.3 to 1.5%, respectively. The constant error (CE) was significantly different for UWW BF% when using RLVBOREN, RLVGB, and RLVMILLER (all p < 0.016; CE = 0.7, -2.0, 1.0%, respectively). However, the CEs for RLVBOREN and RLVMILLER were not significant in the 4C model (p = 0.73 and 0.11; CE = 0.1 and 0.2%, respectively), whereas RLVGB remained significantly different (p < 0.001; CE = -1.5%). The 95% limits of agreement were less than ±5.2% for UWW BF% and less than ±3.1% for the 4C model when using the 3 RLV equations. When used in a 4C model, the RLV equations yielded a smaller CE, SEE, and 95% limits of agreement than UWW BF% results. However, because of the range of individual error shown in the current study, caution should be employed when using the 4C model as a criterion method with predicted RLV.

Validity of Selected Bioimpedance Equations for Estimating Body Composition in Men and Women: A Four-Compartment Model Comparison.

Nickerson, BS, Esco, MR, Bishop, PA, Schumacker, RE, Richardson, MT, Fedewa, MV, Wingo, JE, and Welborn, BA. Validity of selected bioimpedance equations for estimating body composition in men and women: a four-compartment model comparison. J Strength Cond Res 31(7): 1963-1972, 2017-The purpose of this study was to compare body fat percentage (BF%) and fat-free mass (FFM) values from bioelectrical impedance analysis (BIA) equations to values determined from a 4-compartment (4C) model. Eighty-two adults (42 men and 40 women) volunteered to participate (age = 23 ± 5 years). Body fat percentage and FFM were estimated from previously developed BIA equations by Chumlea et al. (BIACH), Deurenberg et al. (BIADE), Kyle et al. (BIAKYLE), and Sun et al. (BIASUN). Four-compartment model body composition was derived from underwater weighing for body density, dual-energy X-ray absorptiometry for bone mineral content, and bioimpedance spectroscopy for total body water. The standard error of estimate (SEE) for group BF% and FFM ranged from 3.0 to 3.8% and 2.1 to 2.7 kg, respectively. The constant error (CE) was significantly higher and lower for BF% and FFM (p < 0.001), respectively, for 3 BIA equations (BIACH, CE = 3.1% and -2.2 kg; BIADE, CE = 3.7% and -2.9 kg; BIAKYLE, CE = 2.3% and -1.9 kg), but was not significant for BF% (p = 0.702) and FFM (p = 0.677) for BIASUN (CE = -0.1% and 0.1 kg). The 95% limits of agreement were narrowest for BIACH (±5.9%; ±4.2 kg) and largest for BIADE (±7.4%; ±6.2 kg). The significant CE yielded by BIACH, BIADE, and BIAKYLE indicates these equations tend to overpredict group BF% and underestimate group FFM. However, all BIA equations produced low SEEs and fairly narrow limits of agreement. When the use of a 4C model is not available, practitioners might consider using one of the selected BIA equations, but should consider the associated CE.

Combined facial heating and inhalation of hot air do not alter thermoeffector responses in humans.

The influence of thermoreceptors in human facial skin on thermoeffector responses is equivocal; furthermore, the presence of thermoreceptors in the respiratory tract and their involvement in thermal homeostasis has not been elucidated. This study tested the hypothesis that hot air directed on the face and inhaled during whole body passive heat stress elicits an earlier onset and greater sensitivity of cutaneous vasodilation and sweating than that directed on an equal skin surface area away from the face. Six men and two women completed two trials separated by ∼1 wk. Participants were passively heated (water-perfused suit; core temperature increase ∼0.9°C) while hot air was directed on either the face or on the lower leg (counterbalanced). Skin blood flux (laser-Doppler flowmetry) and local sweat rate (capacitance hygrometry) were measured at the chest and one forearm. During hot-air heating, local temperatures of the cheek and leg were 38.4 ± 0.8°C and 38.8 ± 0.6°C, respectively (P = 0.18). Breathing hot air combined with facial heating did not affect mean body temperature onsets (P = 0.97 and 0.27 for arm and chest sites, respectively) or slopes of cutaneous vasodilation (P = 0.49 and 0.43 for arm and chest sites, respectively), or the onsets (P = 0.89 and 0.94 for arm and chest sites, respectively), or slopes of sweating (P = 0.48 and 0.65 for arm and chest sites, respectively). Based on these findings, respiratory tract thermoreceptors, if present in humans, and selective facial skin heating do not modulate thermoeffector responses during passive heat stress.