Relationships between Morning Thirst and Later Hydration Status and Total Water Intake.

Purpose: To investigate the effects of thirst on later hydration status, total water intake (TWI-MA), and its potential sex differences. Methods: Twelve men (mean ± standard deviation; age: 21 ± 2 years; mass: 81.0 ± 15.9 kg) and twelve women (age: 22 ± 3 years; mass: 68.8 ± 15.2 kg) visited the laboratory in the morning (first thing in the morning) and afternoon (2:00-4:00 p.m.) for three consecutive days under a free-living condition. At each visit, urine osmolality (UOSM), urine specific gravity (USG), urine color (UCOL), body mass loss (BML), thirst, and plasma osmolality (POSM) were collected and analyzed. The participants recorded their food and fluid intake between the visits to determine TWI-MA. Linear regression was used to predict the effect of morning thirst on the afternoon hydration indices for all the participants, as well as for males and females separately. Results: Higher morning thirst predicted lower UOSM (r2 = 0.056, p = 0.045), USG (r2 = 0.096, p = 0.008), UCOL (r2 = 0.074, p = 0.021), and higher thirst (r2 = 0.074, p = 0.021) in the afternoon. However, morning thirst did not predict afternoon BML, POSM, or TWI-MA (p > 0.05). In males, higher morning thirst predicted lower afternoon UOSM (r2 = 0.130, p = 0.031) and USG (r2 = 0.153, p = 0.018). Additionally, higher morning thirst predicted higher TWI-MA (r2 = 0.154, p = 0.018) in females. Conclusions: Morning thirst had a negligible impact on later hydration status, specifically with afternoon urine indices. Furthermore, higher thirst sensation did not impact BML, POSM, or TWI-MA. However, thirst sensation minimally contributed to drinking behavior in females. Overall, individuals may not rely solely on thirst sensation to manipulate their drinking behavior to optimize their fluid balance during their daily lives due to the complexity of thirst mechanisms.

Eccentric muscle-damaging exercise in the heat lowers cellular stress prior to and immediately following future exertional heat exposure.

Muscle-damaging exercise (e.g., downhill running [DHR]) or heat exposure bouts potentially reduce physiological and/or cellular stress during future exertional heat exposure; however, the true extent of their combined preconditioning effects is unknown. Therefore, this study investigated the effect of muscle-damaging exercise in the heat on reducing physiological and cellular stress during future exertional heat exposure. Ten healthy males (mean ± Standard Definition; age, 23 ± 3 years; body mass, 78.7 ± 11.5 kg; height, 176.9 ± 4.7 cm) completed this study. Participants were randomly assigned into two preconditioning groups: (a) DHR in the heat (ambient temperature [Tamb], 35 °C; relative humidity [RH], 40%) and (b) DHR in thermoneutral (Tamb, 20 °C; RH, 20%). Seven days following DHR, participants performed a 45-min flat run in the heat (FlatHEAT [Tamb, 35 °C; RH, 40%]). During exercise, heart rate and rectal temperature (Trec) were recorded at baseline and every 5-min. Peripheral blood mononuclear cells were isolated to assess heat shock protein 72 (Hsp72) concentration between conditions at baseline, immediately post-DHR, and immediately pre-FlatHEAT and post-FlatHEAT. Mean Trec during FlatHEAT between hot (38.23 ± 0.38 °C) and thermoneutral DHR (38.26 ± 0.38 °C) was not significantly different (P = 0.68), with no mean heart rate differences during FlatHEAT between hot (172 ± 15 beats min-1) and thermoneutral conditions (174 ± 8 beats min-1; P = 0.58). Hsp72 concentration change from baseline to immediately pre-FlatHEAT was significantly lower in hot (-51.4%) compared to thermoneutral (+24.2%; P = 0.025) DHR, with Hsp72 change from baseline to immediately post-FlatHEAT also lower in hot (-52.6%) compared to thermoneutral conditions (+26.3%; P = 0.047). A bout of muscle-damaging exercise in the heat reduces cellular stress levels prior to and immediately following future exertional heat exposure.

The weight, urine colour and thirst Venn diagram is an accurate tool compared with urinary and blood markers for hydration assessment at morning and afternoon timepoints in euhydrated and free-living individuals.

The weight, urine colour and thirst (WUT) Venn diagram is a practical hydration assessment tool; however, it has only been investigated during first-morning. This study investigated accuracy of the WUT Venn diagram at morning and afternoon timepoints compared with blood and urine markers. Twelve men (21 ± 2 years; 81·0 ± 15·9 kg) and twelve women (22 ± 3 years; 68·8 ± 15·2 kg) completed the study. Body mass, urine colour, urine specific gravity (USG), urine osmolality (UOSM), thirst and plasma osmolality (POSM) were collected at first-morning and afternoon for 3 consecutive days in free-living (FL) and euhydrated states. Number of markers indicating dehydration levels were categorised into either 3, 2, 1 or 0 WUT markers. Receiver operating characteristics analysis calculated the sensitivity and specificity of 1, 2 or 3 hydration markers in detecting dehydration or euhydration. Specificity values across morning and afternoon exhibited high diagnostic accuracy for USG (0·890-1·000), UOSM (0·869-1·000) and POSM (0·787-0·990) when 2 and 3 WUT markers were met. Sensitivity values across both timepoints exhibited high diagnostic accuracy for USG (0·826-0·941) and UOSM (0·826-0·941), but not POSM in the afternoon (0·324) when 0 and 1 WUT markers were met. The WUT Venn diagram is accurate in detecting dehydration for WUT2 and WUT3 based off USG, UOSM and POSM during first-morning and afternoon. Applied medical, sport and occupational practitioners can use this tool in field settings for hydration assessment not only at various timepoints throughout the day but also in FL individuals.

Ginger Supplementation Attenuated Mitochondrial Fusion and Improved Skeletal Muscle Size in Type 2 Diabetic Rats.

BACKGROUND/AIM: Oxidative stress, regulated by SOD2 and mitochondrial dynamics, contributes to muscle atrophy in diabetes. Ginger root extract (GRE) reduces oxidative stress. However, its effect on oxidative stress, mitochondrial dynamics, and muscle atrophy is not known in the diabetic muscle. This study examined the effect of GRE on intramuscular oxidative stress, mitochondrial dynamics, and muscle size in diabetic rats. MATERIALS AND METHODS: Twenty-six male Sprague-Dawley rats were randomly divided into control diet (CON; n=10), high-fat diet with one dose of 35 mg/kg streptozotocin (HFD; n=9), and high-fat diet with one dose of 35 mg/kg streptozotocin and 0.75% w/w GRE (GRE; n=7) fed for seven weeks. Subsequently, the muscle was analyzed for cross-sectional area (CSA), H2O2 concentration, and DRP-1, MFN2, Parkin, PINK1, SOD2 mRNA. Additionally, the protein levels of SOD2, DRP-1, DRP-1ser616, LC3AB, MFN2, OPA1, Parkin, and PINK1 were analyzed. CSA, H2O2 concentration, and gene and protein expression levels were analyzed using a one-way ANOVA. Correlations among intramuscular H2O2, CSA, and SOD2 protein were assessed using Pearson's bivariate correlation test. RESULTS: In the soleus, the GRE group had a greater CSA and lower intramuscular H2O2 concentration compared to the HFD group. Compared to the HFD group, the GRE group had higher SOD2 and DRP-1 mRNA levels and lower MFN2 and total OPA1 protein levels. H2O2 concentration was negatively correlated with CSA and positively correlated with SOD2. CONCLUSION: GRE attenuated intramuscular H2O2, mitochondrial fusion, and muscle size loss. These findings suggest that GRE supplementation in diabetic rats reduces oxidative stress, which may contribute to muscle size preservation.

Effect of Neuromuscular Electrical Stimulation Training on Control of Involuntary Muscular Torque and Stimulation Intensity in Older Adults.

The purpose of this study was to examine the effects of a 4-week neuromuscular electrical stimulation (NMES) training regimen on involuntary torque output and electrical stimulation intensity in older adults. Twelve older adults (ages: 68.4 ± 6.5 years; men: n = 6, women: n = 6; weight: 158.6 ± 27.3 lbs; height: 65.2 ± 2.1 in) received submaximal intensity NMES to the quadriceps for 4 weeks to determine training-related changes in stimulation intensity and involuntary control of muscular torque during the NMES protocol. Two-way repeated measures ANOVAs were used to compare torque parameters and stimulation intensity between days and across protocol time bins. After training, stimulation intensity and torque increased over the course of the NMES protocol, while torque decreased during the protocol pre-training. These results suggest that muscular endurance of involuntary muscle contraction is increased with NMES training, and that stimulation intensity should be increased throughout the course of training to augment muscular torque output.

Storing urine samples with moisture preserves urine hydration marker stability up to 21 days.

INTRODUCTION: To assess hydration status, hydration markers [urine color, osmolality, and urine-specific gravity (USG)] are used. Urine color, osmolality, and USG have shown to be stable for 7, 7, and 3 days, respectively, at 4 °C. However, refrigeration could produce a dry environment which enhances evaporation and potentially affects urine hydration markers. PURPOSE: To examine the effect of duration and moisture on urine markers with refrigeration. METHODS: 24 participants provided urine samples between 9 and 10 AM. Urine color, osmolality, and USG were analyzed within 2 h (baseline). Then, each urine sample was divided into two urine cups and placed in a storage container with (moisture condition) and without (no moisture condition) water bath at 3 °C. Hydration markers were analyzed at day 1(D1), D2, D7, D10, D14, and D21. A two-way ANOVA (time x condition) and repeated-measures ANOVA on time were performed to examine differences. RESULTS: No significant (p > 0.05) condition x time effect was observed for urine color (p = 0.363), urine osmolality (p = 0.358), and USG (p = 0.248). When urine samples were stored in moisture condition, urine color (p = 0.126) and osmolality (p = 0.053) were stable until D21, while USG was stable until D2 (p = 0.394). CONCLUSION: When assessing hydration status, it appears that the urine color and osmolality were stable for 21 days, while USG was stable for 2 days when stored with moisture at 3 °C. Our results provide guidelines for practitioners regarding urine storage duration and conditions when urine cannot be analyzed immediately.

Trunk and shoulder kinematics of rowing displayed by Olympic athletes.

The purpose of this study was to assess the effects of stroke rate and sex on trunk and shoulder kinematics of Olympic athletes during rowing on an ergometer. Fifty-eight participants (31 females and 27 males) from the Chinese National Rowing Team were recruited. Trunk (i.e., the pelvis, lumbar and thoracic spine) and shoulder kinematics were measured using an inertial measurement unit system for three stroke rates (18, 26, and 32 strokes/min). Range of motion and angles at the catch and finish were assessed using mixed model ANOVA and correlation analyses with rowing power. Range of motion increased significantly at higher rates for both female and male athletes. This may be a strategy used by athletes when dealing with higher demand for power during training, because a greater range of motion with a longer stroke length could reduce the demand for force generation and possibly delay fatigue. Female rowers exhibited greater range of motion in the lumbar spine, thorax and shoulders than males due to more extended positions at the finish. The sex-related kinematic differences may be attributed to differences in body size, muscle strength and endurance. Practitioners are recommended to consider these factors when developing rowing techniques and providing training suggestions.

Geranylgeraniol Supplementation Mitigates Soleus Muscle Atrophy via Changes in Mitochondrial Quality in Diabetic Rats.

BACKGROUND/AIM: With diabetes, skeletal muscle mitochondrial quality (fusion, fission & mitophagy) and muscle mass are compromised. Geranylgeraniol (GGOH) can prevent mitochondrial damage, inflammation, and improve muscle health; however, the effect of GGOH on a diabetic model is not known. This study aimed to determine the effect of GGOH on mitochondrial quality and muscle mass in diabetic rats. MATERIALS AND METHODS: Sprague-Dawley rats were divided into three groups: regular diet (CON; n=7), high-fat-diet with 35 mg/kg body weight of streptozotocin (STZ) (HFD; n=7), and HFD/STZ with 800 mg/kg of GGOH (GG; n=7) for a total of 8 weeks. At the end of the study, soleus and gastrocnemius muscles were collected and analyzed for gene and protein expression of OPA1, MFN2, DRP1, p-DRP, LC3AB, PINK1, Parkin, SOD2, NF-[Formula: see text]B, IL-6, TNF-α, and IL-1ß. Additionally, the cross-sectional area (CSA) of soleus muscles was analyzed. RESULTS: In soleus, HFD group had significantly higher IL-1ß and lower LC3A, MFN2, DRP1, and SOD2 mRNA expression compared to CON group. The GG group had higher PINK1 mRNA expression than the HFD group. Additionally, the GG group had lower LC3B and DRP1 protein than the HFD group and lower LC3A and MFN2 protein than the HFD and CON groups. Lastly, HFD and GG groups had a smaller CSA than CON group, whereas GG had a greater CSA than HFD. CONCLUSION: GGOH supplementation could prevent mitochondrial fragmentation and potentially decrease the demand for mitochondrial fusion. Additionally, autophagosome degradation occurred at a greater rate than formation, indicating increased clearance of damaged organelles. Improved mitochondrial quality could potentially rescue muscle CSA in diabetic rats with GGOH supplementation.

Sex-specific mitochondrial dynamics and mitophagy response to muscle damage.

Muscle damage imposes stress on mitochondria resulting in mitochondrial fusion, fission, and mitophagy. Testosterone is a regulator of these processes. However, no study has examined the effect of sex-specific resistance exercise (RE)-induced hormonal response on mitochondrial dynamics and mitophagy after muscle damage in untrained men and women. Untrained men and women performed two sessions of 80 unilateral maximal eccentric knee extensions (ECC) followed by upper-body RE (ECC+RE) aimed to induce hormonal changes and maintain a similar lower body demands between conditions or 20 min seated rest (ECC+REST). Vastus lateralis samples were analyzed for gene and protein expression of OPA1, MFN1, DRP1, PINK1, and Parkin at baseline (BL), 12 and 24 h. Testosterone area under the curve was greater for ECC+RE than ECC+REST in men and was greater in men than women for both conditions. A significant time × sex × condition effect was found for Parkin protein expression. At 12 and 24 h, Parkin was lower for ECC + REST than ECC + RE for men; whereas, Parkin was increased at 24 h for women regardless of condition. A significant time effect was found for OPA1 protein expression increasing at 12 and 24 h. A significant time × sex × condition effects were found for MFN1, DRP1, and PINK1 gene expression with increases at 12 h in men for ECC + RE. A significant time × sex effect was found for OPA1 gene expression with a decrease at 12 h in men, and 12 h expression in men was lower than women. RE-induced hormonal changes promoted expression of fission, fusion, and mitophagy markers in men. With muscle damage, regardless of condition, expression of inner mitochondrial membrane fusion markers are promoted in both sexes; whereas, those for mitophagy were promoted in women but reduced in men.

Differential Autophagy Response in Men and Women After Muscle Damage.

Following muscle damage, autophagy is crucial for muscle regeneration. Hormones (e.g., testosterone, cortisol) regulate this process and sex differences in autophagic flux exist in the basal state. However, to date, no study has examined the effect of a transient hormonal response following eccentric exercise-induced muscle damage (EE) between untrained young men and women. Untrained men (n = 8, 22 ± 3 years) and women (n = 8, 19 ± 1 year) completed two sessions of 80 unilateral maximal eccentric knee extensions followed by either upper body resistance exercise (RE; designed to induce a hormonal response; EE + RE) or a time-matched rest period (20 min; EE + REST). Vastus lateralis biopsy samples were collected before (BL), and 12 h, and 24 h after RE/REST. Gene and protein expression levels of selective markers for autophagic initiation signaling, phagophore initiation, and elongation/sequestration were determined. Basal markers of autophagy were not different between sexes. For EE + RE, although initiation signaling (FOXO3) and autophagy-promoting (BECN1) genes were greater (p < 0.0001; 12.4-fold, p = 0.0010; 10.5-fold, respectively) for women than men, autophagic flux (LC3-II/LC3-I protein ratio) did not change for women and was lower (p < 0.0001 3.0-fold) than men. Furthermore, regardless of hormonal changes, LC3-I and LC3-II protein content decreased (p = 0.0090; 0.547-fold, p = 0.0410; 0.307-fold, respectively) for men suggesting increased LC3-I lipidation and autophagosome degradation whereas LC3-I protein content increased (p = 0.0360; 1.485-fold) for women suggesting decreased LC3-I lipidation. Collectively, our findings demonstrated basal autophagy was not different between men and women, did not change after EE alone, and was promoted with the acute hormonal increase after RE only in men but not in women. Thus, the autophagy response to moderate muscle damage is promoted by RE-induced hormonal changes in men only.