Positive energy balance is associated with accelerated muscle atrophy and increased erythrocyte glutathione turnover during 5 wk of bed rest

Background: Physical inactivity is often associated with positive energy balance and fat gain. Objective: We aimed to assess whether energy intake in excess of requirement activates systemic inflammation and antioxidant defenses and accelerates muscle atrophy induced by inactivity. Design: Nineteen healthy male volunteers were studied before and at the end of 5 wk of bed rest. Subjects were allowed to spontaneously adapt to decreased energy requirement (study A, n = 10) or were provided with an activity-matched diet (study B, n = 9). Groups with higher (HEB) or lower (LEB) energy balance were identified according to median values of inactivity-induced changes in fat mass (\u394FM, assessed by bioelectrical impedance analysis). Results: In pooled subjects (n = 19; median \u394FM: 1.4 kg), bed rest-mediated decreases in fat-free mass (bioelectrical impedance analysis) and vastus lateralis thickness (ultrasound imaging) were significantly greater (P < 0.03) in HEBAB (-3.8 \ub1 0.4kg and -0.32 \ub1 0.04 cm, respectively) than in LEBab (-2.3 \ub1 0.5 kg and -0.09 \ub1 0.04 cm, respectively) subjects. In study A (median \u394FM: 1.8 kg), bed rest-mediated increases in plasma leptin, C-reactive protein, and myeloperoxidase were greater (P < 0.04) in HEBA than in LEBA subjects. Bed rest-mediated changes of glutathione synthesis rate in eythrocytes (L-[3,3-2H2]cysteine incorporation) were greater (P = 0.03) in HEBA (from 70 \ub1 19 to 164 \ub1 29%/d) than in LEBA (from 103 \ub1 23 to 84 \ub1 27%/d) subjects. Conclusions: Positive energy balance during inactivity is associated with greater muscle atrophy and with activation of systemic inflammation and of antioxidant defenses. Optimizing caloric intake may be a useful strategy for mitigating muscle loss during period of chronic inactivity

The effect of exercise-induced elevation in core temperature on cold-induced vasodilatation response in toes

Cold-induced vasodilatation (CIVD) has been proposed as a potential protective mechanism against cold injuries during exposure of extremities to a cold environment. The purpose of this study was to evaluate the effect of exercise and the associated elevation in core temperature on toe skin temperatures during immersion of the foot in cold (8°C) water. Subjects (N = 8) participated in two trials. In one, they conducted an incremental exercise to exhaustion (exercise) on a cycle ergometer, which was followed by immersion of the right foot in 8°C water. In the second trial (control), immersion of the foot in cold water was not preceded by exercise. Upon completion of the exercise in the exercise trial, and at the onset of the immersion of the foot in cold water, tympanic temperature was 0.6°C (P < 0.01) higher than pre-exercise levels. There was a significant increase (P < 0.05) in the number of CIVD waves, but not their amplitudes, in the exercise trial compared to the control trial. A CIVD response occurred in 57.5% of all toes in the exercise trial, and in only 27.5% in the control trial. Additionally, 50% of subjects exhibited CIVD in at least one toe in the control trial, and 87.5% during the exercise trial. It is concluded that exercise, and particularly the associated elevation in core temperature, enhances the frequency of the toe CIVD responses, and can therefore potentially act as a protective mechanism against cold injury. © Springer-Verlag 2009

Hypoxia worsens affective responses and feeling of fatigue during prolonged bed rest

Previous research, although limited, suggests that both hypoxia and bed rest influence psychological responses by exaggerating negative psychological responses and attenuating positive emotions. The present study investigated the effect of a 21-day prolonged exposure to normobaric hypoxia and bed rest on affective responses and fatigue. Eleven healthy participants underwent three 21-day interventions using a cross-over design: (1) normobaric hypoxic ambulatory confinement (HAMB), (2) normobaric hypoxic bed rest (HBR) and (3) normoxic bed rest (NBR). Affective and fatigue responses were investigated using the Activation Deactivation Adjective Check List, and the Multidimensional Fatigue Inventory, which were completed before (Pre), during (Day 7, Day 14, and Day 21) and after (Post) the interventions. The most negative psychological profile appeared during the HBR intervention. Specifically, tiredness, tension, general and physical fatigue significantly increased on days 7, 14, and 21, as well as at Post. After the HBR intervention, general and physical fatigue remained higher compared to Pre values. Additionally, a deterioration of psychological responses was also noted following HAMB and NBR. In particular, both hypoxia and BR per se induced subjective fatigue and negative affective responses. BR seems to exert a moderate negative effect on the sensation of fatigue, whereas exercise attenuates the negative effects of hypoxia as noted during the HAMB condition. In conclusion, our data suggest that the addition of hypoxia to bed rest-induced inactivity significantly worsens affective responses and feeling of fatigue. © 2018 Stavrou, Debevec, Eiken and Mekjavic

Psychological strain: Examining the effect of hypoxic bedrest and confinement

The aim was to assess the effect of a 10-day exposure to the environmental stressors anticipated in future lunar habitats on indices of psychological strain. In addition to the reduced gravity of the Moon, future habitats on the Moon will likely maintain a hypobaric hypoxic environment. The hypobaric environment will eliminate the need for long decompression profiles prior to each extra-vehicular activity. We investigated the indices of psychological strain during three 10-day conditions, designed to assess the separate and combined effects of inactivity/unloading and normobaric hypoxia on several physiological systems. Eleven male participants underwent three 10-day campaigns in a randomised manner: 1) normobaric normoxic bed rest (NBR), 2) normobaric hypoxic bed rest (HBR) and 3) normobaric hypoxic ambulatory confinement (HAMB). The most negative psychological profile appeared on day 10 of the HBR and HAMB (hypoxic) conditions. Concomitantly, a decrease in positive emotions was observed from baseline to day 10 of the HBR and NBR conditions. Thus, confinement in a hypoxic environment seems to exert a negative effect on an individual's psychological mood. © 2014 Elsevier Inc

Hypoxia exacerbates negative emotional state during inactivity: The effect of 21 days hypoxic bed rest and confinement

Hypoxia and confinement have both been shown to influence emotional state. It is envisaged that the inhabitants of future planetary habitats will be exposed to concomitant confinement, reduced gravity and hypoxia. We examined the independent and combined effects of a 21-day inactivity/unloading and normobaric hypoxia under confined conditions on various psychological factors. Eleven healthy men participated in three 21-day experimental campaigns designed in a cross-over manner: (1) Normobaric hypoxic ambulatory confinement, (2) Normobaric hypoxic bed rest and (3) Normobaric normoxic bed rest. The Profile of Mood States, and the Positive and Negative Affect Schedule were employed to assess the participants' psychological responses before (Pre), during (Day 7, Day 14, and Day 21) and after (Post) the confinements. The most negative psychological profile appeared on days 14 and 21 of the hypoxic bed rest campaign. A significant increase in depression, tension, and confusion was noted on days 14 and 21 of the hypoxic bed rest condition. Concomitantly, a decrease, albeit not statistically significant, in positive psychological responses was observed. The psychological profile returned to the initial level at Post following all confinements. These data suggest that the combined effect of hypoxia and bed rest induced the most negative effects on an individual's mood. However, significant intra- and inter-individual differences in psychological responses were noted and should be taken into consideration. © 2018 Stavrou, Debevec, Eiken and Mekjavic

Heat acclimation does not modify autonomic responses to core cooling and the skin thermal comfort zone

Exercise heat acclimation (HA) is known to magnify the sweating response by virtue of a lower threshold as well as increased gain and maximal capacity of sweating. However, HA has been shown to potentiate the shivering response in a cold-air environment. We investigated whether HA would alter heat loss and heat production responses during water immersion. Twelve healthy male participants underwent a 10-day HA protocol comprising daily 90-min controlled-hyperthermia (target rectal temperature, Tre 38.5 °C) exercise sessions. Preceding and following HA, the participants performed a maximal exercise test in thermoneutral conditions (ambient temperature 23 °C, relative humidity 50%) and were, following exercise, immersed in 28 °C water for 60 min. Thermal comfort zone (TCZ) was also assessed with participants regulating the temperature of a water-perfused suit during heating and cooling. Baseline pre-immersion Tre was similar pre- and post-HA (pre: 38.33 ± 0.33 °C vs post: 38.12 ± 0.36 °C, p = 0.092). The Tre cooling rate was identical pre-to post-HA (−0.03 ± 0.01 °C·min−1, p = 0.31), as was the vasomotor response reflected in the forearm-fingertip temperature difference. Shivering thresholds (p = 0.43) and gains (p = 0.61) were not affected by HA. TCZ was established at similar temperatures, with the magnitude in regulated water temperature being 7.6 (16.3) °C pre-HA and 5.1 (24.7) °C post-HA (p = 0.65). The present findings suggest that heat production and heat loss responses during whole body cooling as well as the skin thermal comfort zone remained unaltered by a controlled-hyperthermia HA protocol. © 2020 Elsevier Lt

Forearm-finger skin temperature gradient as an index of cutaneous perfusion during steady-state exercise

The purpose of this study was to examine whether the forearm-finger skin temperature gradient (Tforearm-finger), an index of vasomotor tone during resting conditions, can also be used during steady-state exercise. Twelve healthy men performed three cycling trials at an intensity of ~60% of their maximal oxygen uptake for 75 min separated by at least 48 h. During exercise, forearm skin blood flow (BFF) was measured with a laser-Doppler flowmeter, and finger skin blood flow (PPG) was recorded from the left index fingertip using a pulse plethysmogram. Tforearm-finger of the left arm was calculated from the values derived by two thermistors placed on the radial side of the forearm and on the tip of the middle finger. During exercise, PPG and BFF increased (P<0·001), and Tforearm-finger decreased (P<0·001) from their resting values, indicating a peripheral vasodilatation. There was a significant correlation between Tforearm-finger and both PPG (r = -0·68; P<0·001) and BFF (r = -0·50; P<0·001). It is concluded that Tforearm-finger is a valid qualitative index of cutaneous vasomotor tone during steady-state exercise. © 2013 Scandinavian Society of Clinical Physiology and Nuclear Medicine. Published by John Wiley & Sons Ltd

No ergogenic effects of a 10-day combined heat and hypoxic acclimation on aerobic performance in normoxic thermoneutral or hot conditions

Purpose: Hypoxic acclimation enhances convective oxygen delivery to the muscles. Heat acclimation-elicited thermoregulatory benefits have been suggested not to be negated by adding daily exposure to hypoxia. Whether concomitant acclimation to both heat and hypoxia offers a synergistic enhancement of aerobic performance in thermoneutral or hot conditions remains unresolved. Methods: Eight young males (V˙ O 2 max: 51.6 ± 4.6 mL min−1 kg−1) underwent a 10-day normobaric hypoxic confinement (FiO2 = 0.14) interspersed with daily 90-min normoxic controlled hyperthermia (target rectal temperature: 38.5 °C) exercise sessions. Prior to, and following the confinement, the participants conducted a 30-min steady-state exercise followed by incremental exercise to exhaustion on a cycle ergometer in thermoneutral normoxic (NOR), thermoneutral hypoxic (FiO2 = 0.14; HYP) and hot (35 °C, 50% relative humidity; HE) conditions in a randomized and counterbalanced order. The steady-state exercise was performed at 40% NOR peak power output (Wpeak) to evaluate thermoregulatory function. Blood samples were obtained from an antecubital vein before, on days 1 and 10, and the first day post-acclimation. Results: V˙ O 2 max and ventilatory thresholds were not modified in any environment following acclimation. Wpeak increased by 6.3 ± 3.4% in NOR and 4.0 ± 4.9% in HE, respectively. The magnitude and gain of the forehead sweating response were augmented in HE post-acclimation. EPO increased from baseline (17.8 ± 7.0 mIU mL−1) by 10.7 ± 8.8 mIU mL−1 on day 1 but returned to baseline levels by day 10 (15.7 ± 5.9 mIU mL−1). Discussion: A 10-day combined heat and hypoxic acclimation conferred only minor benefits in aerobic performance and thermoregulation in thermoneutral or hot conditions. Thus, adoption of such a protocol does not seem warranted. © 2019, Springer-Verlag GmbH Germany, part of Springer Nature

The trainability and contralateral response of cold-induced vasodilatation in the fingers following repeated cold exposure

Cold-induced vasodilatation (CIVD) is proposed to be a protective response to prevent cold injuries in the extremities during cold exposure, but the laboratory-based trainability of CIVD responses in the hand remains equivocal. Therefore, we investigated the thermal response across the fingers with repeated local cold exposure of the whole hand, along with the transferability of acclimation to the fingers of the contralateral hand. Nine healthy subjects immersed their right hand up to the styloid process in 8°C water for 30 min daily for 13 days. The left hand was immersed on days 1 and 13. Skin temperature was recorded on the pads of the five fingertips and the dorsal surface of the hand. The presence of CIVD, defined as an increase in finger skin temperature of 0.5°C at any time during cooling, occurred in 98.5% of the 585 (9 subjects × 5 sites × 13 trials) measurements. Seven distinct patterns of thermal responses were evident, including plateaus in finger temperature and superimposed waves. The number (N) of CIVD waves decreased in all digits of the right hand over the acclimation period (P = 0.02), from average (SD) values ranging from 2.7 (1.7) to 3 (1.4) in different digits on day 1, to 1.9 (0.9) and 2.2 (0.7) on day 13. Average (SD) finger skin temperature (Tavg) ranged from 11.8 (1.4)°C in finger 5 to 12.7 (2.8)°C in finger 3 on day 1, and then decreased significantly (P < 0.001) over the course of the training immersions, attaining values ranging from 10.8 (0.9)°C in finger 4 to 10.9 (0.9)°C in finger 2 on day 13. In the contralateral hand, N was reduced from 2.5 to 1.5 (P < 0.01) and Tavg by ∼2°C (P < 0.01). No changes were observed in thermal sensation or comfort of the hand over the acclimation. We conclude that, under conditions of whole-hand immersion in cold water, CIVD is not trainable and may lead to systemic attenuation of thermal responses to local cooling. © Springer-Verlag 2008