THE IMPACT OF HYDRATION STATUS DURING HEAT ACCLIMATION ON PHYSIOLOGICAL STRAIN AND EXERCISE PERFORMANCE

Heat acclimation promotes adaptations to attenuate physiological and perceptual strain associated with heat stress, and may be enhanced by promoting dehydration during acclimation. Purpose: To determine i) the effect of fluid delivery during acclimation by inducing dehydration (DEH=0.5 mL / kg / 15 min) vs. euhydration (EUH=2.0 mL / kg / 15min) following three heat acclimation bouts on heat stress factors, and ii) to determine if fluid delivery (EUH vs. DEH) affects aerobic performance in the heat. Methods: Thirteen aerobically fit males completed 90-minute heat stress test (HST) in hot conditions (40°C, 30% RH) walking at 50% VO2 max prior to and following three-days of EUH and DEH acclimation trials. Acclimation trials were in the same environment and intensity as HST, and separated by one day. Participants wore standard Wildland Firefighter (WLFF) Nomex: shirt, pants, and a cotton T-shirt. Following each HST, aerobic performance was assessed by a graded ramp protocol increasing grade 1% until 15%, and then increased 1.6km*h-1 every minute until volitional exhaustion. Peak core temperature (TC), skin temperature (Tsk), heart rate (HR), rating of perceived exertion (RPE), physiological strain index (PSI), aerobic performance, and sweat rate were collected following HST. Skin blood flow (SBF) was measured via laser doppler flowmetry at 30, 60, and 90 minutes during exercise, and a five-minute recovery period. All data was analyzed by a two-way analysis of variance (ANOVA) 2 (Trt) x 2 (Time). RESULTS: Acclimation significantly decreased peak Tc (DEH= 39.5°C± 0.10 to 39.0± 0.12, EUH=39.5°C± 0.12 to 38.9± 0.12, psk, (DEH=37.8°C± 0.19 to 37.6± 0.12, EUH=37.9°C± 0.20 to 37.5± 0.10, p=0.005), peak HR (DEH=178.1 b/min ± 3.33 to 164.1± 4.43, EUH= 179.3 b/min± 3.38 to 167.4 ± 3.72 p-1± 0.06 to 1.9 L*h-1 ± 0.09) compared to EUH (1.6 L/h± 0.06 to 1.8 L/h± 0.08) (TrtXTime: p=0.015), and blood plasma percentage increased in the DEH group as a main effect for Time (DEH= 7.1% ± 1.84, EUH= 4.1% ± 2.46, p=0.002). CONCLUSION: Short-term heat acclimation effectively attenuates heat stress, and improves aerobic performance in the heat. Fluid delivery strategies during acclimation do not affect thermal strain or performance, but may increase sweat capacity and plasma volume to additionally protect from heat stress

Skeletal muscle ferritin abundance is tightly related to plasma ferritin concentration in adults with obesity

Obesity is associated with complex perturbations to whole- body and tissue iron homeostasis. Recent evidence suggests a potentially important influence of iron storage in skeletal muscle on whole- body iron homeostasis, but this association is not clearly resolved. The primary aim of this study was to assess the relationship between whole- body and skeletal muscle iron stores by measuring the abundance of the key iron storage (ferritin) and import (transferrin receptor) proteins in skeletal muscle, as well as markers of whole- body iron homeostasis in men (n = 19) and women (n = 43) with obesity. Plasma ferritin concentration (a marker of whole- body iron stores) was highly correlated with muscle ferritin abundance (r = 0.77, P = 2 à  10- 13) and negatively associated with muscle transferrin receptor abundance (r = - 0.76, P = 1 à  10- 12). These relationships persisted when accounting for sex, age, BMI and plasma C- reactive protein concentration. In parallel with higher whole- body iron stores in our male versus female participants, men had 2.2- fold higher muscle ferritin abundance (P = 1 à  10- 4) compared with women. In accordance with lower muscle iron storage, women had 2.7- fold higher transferrin receptor abundance (P = 7 à  10- 10) compared with men. We conclude that muscle iron storage and import proteins are tightly and independently related to plasma ferritin concentration in adults with obesity, suggesting that skeletal muscle may be an underappreciated iron store.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/163407/2/eph12853_am.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/163407/1/eph12853.pd

Skeletal muscle ferritin abundance is tightly related to plasma ferritin concentration in adults with obesity

Obesity is associated with complex perturbations to whole- body and tissue iron homeostasis. Recent evidence suggests a potentially important influence of iron storage in skeletal muscle on whole- body iron homeostasis, but this association is not clearly resolved. The primary aim of this study was to assess the relationship between whole- body and skeletal muscle iron stores by measuring the abundance of the key iron storage (ferritin) and import (transferrin receptor) proteins in skeletal muscle, as well as markers of whole- body iron homeostasis in men (n = 19) and women (n = 43) with obesity. Plasma ferritin concentration (a marker of whole- body iron stores) was highly correlated with muscle ferritin abundance (r = 0.77, P = 2 à  10- 13) and negatively associated with muscle transferrin receptor abundance (r = - 0.76, P = 1 à  10- 12). These relationships persisted when accounting for sex, age, BMI and plasma C- reactive protein concentration. In parallel with higher whole- body iron stores in our male versus female participants, men had 2.2- fold higher muscle ferritin abundance (P = 1 à  10- 4) compared with women. In accordance with lower muscle iron storage, women had 2.7- fold higher transferrin receptor abundance (P = 7 à  10- 10) compared with men. We conclude that muscle iron storage and import proteins are tightly and independently related to plasma ferritin concentration in adults with obesity, suggesting that skeletal muscle may be an underappreciated iron store.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/163407/2/eph12853_am.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/163407/1/eph12853.pd

Exercise training decreases whole- body and tissue iron storage in adults with obesity

The regulation of iron storage is crucial to human health, because both excess and deficient iron storage have adverse consequences. Recent studies suggest altered iron storage in adults with obesity, with increased iron accumulation in their liver and skeletal muscle. Exercise training increases iron use for processes such as red blood cell production and can lower whole- body iron stores in humans. However, the effects of exercise training on liver and muscle iron stores in adults with obesity have not been assessed. The aim of this study was to determine the effects of 12 weeks of exercise training on whole- body iron stores, liver iron content and the abundance of ferritin (the key iron storage protein) in skeletal muscle in adults with obesity. Twenty- two inactive adults (11 women and 11 men; age, 31 ± 6 years; body mass index, 33 ± 3 kg/m2) completed 12 weeks (four sessions/week) of either moderate- intensity continuous training (MICT; 45 min at 70% of maximal heart rate; n = 11) or high- intensity interval training (HIIT; 10 à  1 min at 90% of maximal heart rate, interspersed with 1 min active recovery; n = 11). Whole- body iron stores were lower after training, as indicated by decreased plasma concentrations of ferritin (P = 3 à  10- 5) and hepcidin (P = 0.02), without any change in C- reactive protein. Hepatic R2*, an index of liver iron content, was 6% lower after training (P = 0.06). Training reduced the skeletal muscle abundance of ferritin by 10% (P = 0.03), suggesting lower muscle iron storage. Interestingly, these adaptations were similar in MICT and HIIT groups. Our findings indicate that exercise training decreased iron storage in adults with obesity, which might have important implications for obese individuals with dysregulated iron homeostasis.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/167108/1/eph12950_am.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/167108/2/eph12950.pd

Exercise training remodels subcutaneous adipose tissue in adults with obesity even without weight loss

Excessive adipose tissue mass underlies much of the metabolic health complications in obesity. Although exercise training is known to improve metabolic health in individuals with obesity, the effects of exercise training without weight loss on adipose tissue structure and metabolic function remain unclear. Thirty-six adults with obesity (body mass index = 33 ± 3 kg · m–2) were assigned to 12 weeks (4 days week–1) of either moderate-intensity continuous training (MICT; 70% maximal heart rate, 45 min; n = 17) or high-intensity interval training (HIIT; 90% maximal heart rate, 10 × 1 min; n = 19), maintaining their body weight throughout. Abdominal subcutaneous adipose tissue (aSAT) biopsy samples were collected once before and twice after training (1 day after last exercise and again 4 days later). Exercise training modified aSAT morphology (i.e. reduced fat cell size, increased collagen type 5a3, both P ≤ 0.05, increased capillary density, P = 0.05) and altered protein abundance of factors that regulate aSAT remodelling (i.e. reduced matrix metallopeptidase 9; P = 0.02; increased angiopoietin-2; P < 0.01). Exercise training also increased protein abundance of factors that regulate lipid metabolism (e.g. hormone sensitive lipase and fatty acid translocase; P ≤ 0.03) and key proteins involved in the mitogen-activated protein kinase pathway when measured the day after the last exercise session. However, most of these exercise-mediated changes were no longer significant 4 days after exercise. Importantly, MICT and HIIT induced remarkably similar adaptations in aSAT. Collectively, even in the absence of weight loss, 12 weeks of exercise training induced changes in aSAT structure, as well as factors that regulate metabolism and the inflammatory signal pathway in adults with obesity.Key pointsExercise training is well-known to improve metabolic health in obesity, although how exercise modifies the structure and metabolic function of adipose tissue, in the absence of weight loss, remains unclear.We report that both 12 weeks of moderate-intensity continuous training (MICT) and 12 weeks of high-intensity interval training (HIIT) induced modifications in adipose tissue structure and factors that regulate adipose tissue remodelling, metabolism and the inflammatory signal pathway in adults with obesity, even without weight loss (with no meaningful differences between MICT and HIIT).The modest modifications in adipose tissue structure in response to 12 weeks of MICT or HIIT did not lead to changes in the rate of fatty acid release from adipose tissue.These results expand our understanding about the effects of two commonly used exercise training prescriptions (MICT and HIIT) on adipose tissue remodelling that may lead to advanced strategies for improving metabolic health outcomes in adults with obesity.Abstract figure legend. Three months of moderate-intensity continuous training (MICT) or high-intensity interval training (HIIT) without weight loss induced similar structural and metabolic adaptations in subcutaneous adipose tissue in adults with obesity.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/172245/1/tjp15006_am.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/172245/2/tjp15006-sup-0002-PeerReview.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/172245/3/tjp15006.pd