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Background: Noxious acute cold stimuli cause cold shock via the sympathetic nervous system. However, no studies have investigated respiratory “heat shock” in response to noxious acute heat stimuli (( 42 C). Methods: In the present study, we examined whether short-duration whole-body immersion (for 5 min) in noxious hot water (45 C) is a sufficient stimulus to induce a respiratory acute shock response. Results and conclusion: Our results indicate that short-duration whole-body immersion in noxious 45 C water produces a significantly greater body temperature, heart rate, and perceptual and respiratory strain than immersion in innocuous warm 37 C water (p < .05). The initial first minute of hot water immersion (HWI) at 45 C (vs. immersion at 37 C) caused a cardiorespiratory shock response, which manifested as acute hyperventilation, and increased ventilatory tidal volume, respiratory exchange ratio, and heart rate (p < .05). Adjustment to this initial respiratory heat shock response within the first minute of immersion was observed as compared with remaining HWI time (1–5 min). Intriguingly, the time-course kinetics of breathing frequency, oxygen uptake, and carbon dioxide washout did not differ between whole-body immersion at 37 C and immersion at 45 C, but were higher than in control thermoneutral conditions of an empty bath (p < .05). This may be because of events initiated not only by the water temperature but also by the change in the hydrostatic pressure acting upon the body when immersed in the water bath. [ABSTRACT FROM AUTHOR]

The study aims were to investigate the effects of muscle damage induced by high-volume stretch-shortening cycle exercise on countermovement jump (CMJ) performance and vertical leg stiffness during squat and landing phases. Changes in the peak torque of knee extensor muscles, soreness, plasma CK activity, vertical leg stiffness, and CMJ characteristics were measured in recreationally active men after 50, 100, 150 and 200 drop jumps (DJs) and again 24 h later. The isometric voluntary peak torque after 50 DJs decreased by 22 ± 12% (p < 0.01). However, during the squat phase of CMJ eccentric peak power and rate of force development together with the concentric mean force during the push-off phase increased after 50 DJs (all p < 0.05). After 200 DJs, jump height and concentric peak power during push-off were decreased (p < 0.05). At 24 h after exercise, jump height, peak eccentric force, the rate of eccentric force development and the mean concentric force in CMJ and vertical leg stiffness in the squat all remained decreased (p < 0.05), while vertical leg stiffness in the landing phase was increased (p < 0.05). Muscle damaging exercise volume is associated with changes in vertical leg stiffness and CMJ performance. [ABSTRACT FROM AUTHOR]

Background: One of the most challenging environmental extremes is immersion in cold/icy water, and consequent common assumption is that even a brief exposure to cold can lead to cold-related illnesses. The increase in the concentrations of the stress hormones cortisol, epinephrine (Epi), and norepinephrine (NE) in response to acute cold stress are thought to suppress the release of proinflammatory cytokines. No previous study has explored the residual consequences of whole-body short-term cold-water immersion (CWI; 14 °C for 10 min) on the immune response in healthy non-acclimated young adult men (aged 20–30 years). Materials and methods: In the current study, we tested the hypothesis that short-term acute whole-body CWI would induce high blood levels of cortisol, NE, and Epi, which in turn would increase circulating leukocyte numbers and delay the production of proinflammatory cytokines (tumor necrosis factor α (TNF-α), interleukin 1β (IL-1β), and IL-6). Results: Short-term whole-body CWI produced a stressful physiological reaction, as manifested by hyperventilation and increased muscle shivering, metabolic heat production, and heart rate. CWI also induced the marked release of the stress hormones Epi, NE, and cortisol. The change in IL-6 concentration after CWI was delayed and TNF-α production was decreased, but IL-1β was not affected within 48 h after CWI. A delayed increase in neutrophil percentage and decrease in lymphocyte percentage occurred after CWI. Conclusion: These findings suggest that, even though CWI caused changes in stress and immune markers, the participants showed no predisposition to symptoms of the common cold within 48 h after CWI. [ABSTRACT FROM AUTHOR]

Background: Although acute thermal stress appears to be one of the most effective stressors that increase the intra- and extracellular concentrations of heat shock protein 72 (Hsp72), 17b-estradiol has been shown to inhibit heat-induced Hsp72 expression. Materials and Methods: To determine whether severe whole-body hyperthermia (increase in rectal temperature up to 39.5 °C) induced by lower-body heating is a sufficient stimulus to modulate hormonal (17b-estradiol, progesterone, prolactin, epinephrine, and norepinephrine) and extracellular Hsp72 responses, we investigated young adult women (21 ± 1 yr). Results and Conclusions: In the present study, we show that a severe whole-body hyperthermia (increase in rectal temperature of approximately 2.6 °C and heart rate of approximately 80 bpm from baseline) was sufficient to increase 17b-estradiol, progesterone, and prolactin and catecholamine norepinephrine concentration. Moreover, we show that the concentration of extracellular Hsp72 and catecholamine epinephrine were not affected by severe whole-body hyperthermia in young adult women. From the functional point of view, expression of ovarian hormones induced by passive heat stress may have therapeutic potential for young adult women in, for example, estrogen treatment and overall women's health. [ABSTRACT FROM AUTHOR]

Objective: The aim of this study was to investigate the post-sauna residual consequences on brain neural network arousal, information processing and cognitive performance. Methods: Sixteen male subjects (24 ± 1 yr.) participated in the study. Whole-body hyperthermia was induced with Finnish sauna bathing. Before and 90 min after the sauna, resting electroencephalography (EEG) for spectral analysis and EEG event-related potentials (ERPs) during oddball tasks by two modalities (auditory and visual) were recorded. Results: Sauna bathing increased rectal temperature (Tre, 37.11 ± 0.33 °C to 38.84 ± 0.32 °C) and heart rate (HR, 65.63 ± 9.39 bpm to 151.0 ± 21.8 bpm). At 90 min after the sauna, Tre (37.00 ± 0.29 °C) and HR (72.1 ± 2.80 bpm) recovered to baseline levels. An increase was found in alpha power following sauna recovery. In the visual task modality, post-sauna recovery led to enhancement in the N2 amplitude with centroparietal distribution and decreases in P3 amplitude with distribution along the frontoparietal axis for executive motor-cognitive processing. In the auditory task modality, post-sauna recovery led to a decrease in P3 amplitude with a frontoparietal distribution and this change was accompanied by auditory N2 amplitude enhancement along the centroparietal distribution for non-target cognitive processing. No significant differences in task performance were found. Conclusion: Post-sauna recovery to normothermia led to enhanced resting neural network relaxation followed by increases in cognitive processing economy for the given oddball tasks. The auditory processing was not affected more by post-sauna recovery than was visual processing. Post-sauna recovery modifications in ERP components (stimulus processing) were insufficient to affect cognitive performance in both visual and auditory task modalities. [ABSTRACT FROM AUTHOR]

Purpose: The main aim of this study was to compare physiological and psychological reactions to heat stress between people who exhibited fast cooling (FC, n = 20) or slow cooling (SC; n = 20) responses to 14 °C cold water immersion. Methods: Forty healthy young men (19-25 years old) were recruited to this study based on their tolerance to cold exposure (FC versus SC). The heat stress was induced using immersion in bath water at 43-44 °C. Motor and cognitive performance, immune variables, markers of hypothalamic-pituitary-adrenal axis activity (i.e. stress hormone concentrations), and autonomic nervous system activity were monitored. Results: In the FC group, time to warm the body from a resting rectal temperature (Tre) of 37.1 ± 0.2 °C before warming to 39.5 °C was 63.7 ± 22.4 min. In the SC group, the time to warm the body from a Tre 37.1 ± 0.3 °C before warming to 39.5 °C was 67.2 ± 13.8 min ( p > 0.05 between groups). The physiological stress index (PSI) after warming was 8.0 ± 0.6 and 8.2 ± 1.0 in the FC and SC groups, respectively ( p > 0.05 between groups). During warming, the changes in subjective indicators of heat stress did not differ significantly between the FC (7.4 ± 0.5) and SC (7.1 ± 1.1) groups, respectively. Conclusion: The increase in cortisol, epinephrine, norepinephrine, and corticosterone concentrations after passive body heating did not differ between the FC and SC groups. Heat stress did not change indicators of innate and specific immunity in the FC or the SC group. An interesting finding was that heat stress did not affect motor and cognitive function in either group, although central fatigue during 1-min maximal voluntary contraction increased after heat stress in both groups. [ABSTRACT FROM AUTHOR]

Our purpose was to compare the effect of a periodized preparation consisting ofpower endurance training and high-intensity power training on the contractile properties of the quadriceps muscle and functional performances in well trained male sprinters (n= 7). After 4 weeks of high-intensity power training, 60-m splint running time improved by an average of 1.83% (SD = 0.96; p < . 05 ). This improvement was inversely related to an increase in maximal voluntary contraction torque (r = -.89, p < .05) and poorly correlated with changes in the contractile kinetics of the quadriceps muscle (r range from .36 to -.46). These findings suggest that splint performance is poorly predicted by muscle intrinsic properties and that a neural adaptation appears to explain most of the observed functional adaptations. [ABSTRACT FROM AUTHOR]

The aim of this study was to examine changes in indirect markers of muscle damage during 3 weeks of stretch-shortening exercise with a progressively increasing load and continued modulation of various key training variables. Eight healthy untrained men performed a drop-jump programme involving a progressive increase in load impact with respect to the number of jumps performed, drop (platform) height, squat depth amplitude, and addition of weights. Maximal concentric and isometric knee extensor strength were assessed immediately before and 10 min after each training session. Voluntary and 100 Hz-stimulation-evoked torque decreased acutely after each training session relative to pre-exercise values (P < 0.05) but recovered before the subsequent training session. Post-exercise plasma creatine kinase activity increased from 162.2 ± 56.2 IU · l-1 to 284.3 ± 116.3 IU · l-1 at 48 h after the first training session (P < 0.05) and remained marginally elevated throughout the training period. The present results indicate that detrimental muscle damage can be avoided with drop-jump training even with the gradual introduction of more demanding exercise induced by increasing the volume, intensity, and muscle stretch amplitude. These findings suggest that the human neuromuscular system is highly adaptable to progressively varied loading demands during stretch-shortening exercise training. [ABSTRACT FROM AUTHOR]

Healthy untrained men (N = 11) were asked to perform 10 series of 12 repetitions of knee eccentric extension (EE) at 160° per second. Quadriceps muscle torques evoked by electrical stimulation at 20 Hz (P20) and 100 Hz (P100), maximal voluntary isometric contraction torque (MVC), maximal isokinetic concentric torque (IT) at 30° per second, voluntary activation index (VA), simple reaction time (RTs), complex reaction time (RTc), and torque variability at 30% of MVC were measured before EE, immediately after EE, and 60 min and 24 hr after EE. MVC, IT, P20, P100, and VA decreased significantly after EE and remained depressed 24 hr later. Torque variability increased significantly after EE. Average RTs and RTc did not change after EE, whereas intraindividual variability in RTs and RTc increased significantly after EE. [ABSTRACT FROM AUTHOR]