PURPOSE:The present study examined the effects of repeated-sprint exercise in normoxia, hypoxia, and combined heat and hypoxia on the gastric emptying rate. METHODS:Eleven physically active males completed four experimental trials, consisting of a resting control (REST) and three exercise trials; three sets of 5 × 6-s maximal sprints in normoxia (NOR; 23℃, FiO2: 20.9%), hypoxia (HYP; 23℃, FiO2: 14.5%), and combined heat and hypoxia (HH; 35℃, FiO2: 14.5%) in a randomized order. Post-exercise gastric emptying rate was assessed by the 13C-sodium acetate breath test. RESULTS:The 13C excretion was significantly lower in the exercise trials (NOR, HYP, and HH) than in the REST during 10-35 min after exercise (p < 0.05). Time to peak 13C excretion was significantly delayed in all exercise trials (NOR, HYP, and HH) compared with the REST (p < 0.05), with no difference among the exercise trials. The magnitude of the gastric emptying delay was correlated with power output and blood glucose during the exercise. CONCLUSION:Repeated-sprint exercise significantly delayed gastric emptying, while additional hypoxic or heat stress did not exacerbate the delay, suggesting that hypoxic or heat stress can be applied during repeated-sprint training without negative impacts on gastric emptying.

The special issue “Physiological Aspects of Marathon Running” in “Frontiers in Physiology” aims to evoke attentions to this field. In this minireview, the two guest editors of the special issue introduce their interest in the gastrointestinal (GI) functions with endurance running and gut microbiota on marathon running. Following the introduction, the first part summarized research examining exercise-induced GI damage and methods to mitigate the damage. The latter part summarized the influence of exercise on gut microbiota, and the gut microbiota on endurance performance. From the brief overview above, this minireview synthesizes current knowledge and identifies critical topics for future studies for optimizing GI function and the gut microbiota in endurance athletes.

PURPOSE:Long-distance running performance has been reported to be associated with sprint performance in highly trained distance runners. Therefore, we hypothesized that sprint training could enhance distance running and sprint performance in long-distance runners. This study examined the effect of 6-week sprint training on long-distance running and sprint performance in highly trained distance runners. METHODS:Nineteen college runners were divided into control (n = 8) and training (n = 11) groups. Participants in the training group performed 12 sprint training sessions in 6 weeks, while those in the control group performed 12 distance training sessions. Before and after the interventions, maximal oxygen uptake (V˙O2max), O2 cost during submaximal running (290 m·min-1 and 310 m·min-1 of running velocity), and time to exhaustion (starting at 290 m·min-1 and increased 10 m·min-1 every minute) were assessed on a treadmill. Additionally, the 100-m and 400-m sprinting times and 3000-m running time were determined on an all-weather track. RESULTS:In the control group, no measurements significantly changed after the intervention. In the training group, the time to exhaustion, 100-m and 400-m sprinting times, and 3000-m running time improved significantly, while V˙O2max and O2 cost did not change. CONCLUSIONS:These results showed that 6-week sprint training improved both sprint and long-distance running performance in highly trained distance runners without a change in aerobic capacity. Improvement in the time to exhaustion without a change in V˙O2max suggests that the enhancement of long-distance running performance could be attributable to improved anaerobic capacity.

The present study examined the effects of gastric emptying rate and intestinal cell damage following a single session of endurance exercise under “hypoxic” or “normoxic” conditions at the same relative intensity. Eleven healthy males performed two trials on different days, consisting of a 60 min run on a treadmill at 70

We determined the effects of different environmental temperatures on exercise-induced gastrointestinal (GI) damage and delayed gastric emptying (GE) rate. Eleven trained males completed three trials on different days, consisting of (1) exercise in a thermoneutral environment (CON, 23 °C), (2) exercise in a hot environment (HOT, 35 °C), and (3) exercise in a cold environment (COLD, 10 °C). The subjects performed high-intensity interval-type endurance exercises in all trials. Blood intestinal fatty acid binding protein (I-FABP) levels was determine before and after exercise. We evaluated Tmax (time when the 13C-excretion/h reached a maximum level) as an indication of the GE rate during post-exercise. Rectal temperature during exercise was significantly higher (P < 0.001) in the HOT (38.7 ± 0.3 °C) trial compared with the CON (38.2 ± 0.3 °C) and COLD (38.2 ± 0.3 °C) trials, with no significant difference between the CON and COLD trials. Plasma I-FABP level after exercise (relative to the pre-exercise level) were significantly greater (P = 0.005) in the HOT trial (92.9 ± 69.6

Exercise under hot environment leads to excessive body temperature. Therefore, the use of bode cooling (e.g., whole body cryotherapy, ice bath therapy) following the exercise has been prevalent to decrease elevated body temperature. The body cooling during post-exercise has been reported to decrease rectal temperature and heart rate, enhance parasympathetic activity (AI Haddad et al., 2010). However, these procedures require specially designed equipment. In contrast, feet icing would be more applicable during post-exercise under hot environment. PURPOSE: The present study was designed to clarify the effects of post-exercise feet-icing on body temperature and autonomic nerve activity. METHODS: Six healthy males (20 ± 1 years, 177.8 ± 4.3 cm, 67.9 ± 6.0 kg) were recruited. They performed 3 conditions on different days, consisting of (1) 10 °C (20 min post-exercise feet-icing of 10 °C water), (2)20 °C (20 min post-exercise feet-icing of 20 °C water), (3)Control (without post-exercise feet-icing). Exercise (pedaling exercise at 50% of maximal oxygen uptake for 30 min) was conducted under hot environment (30 °C). Rectal temperature, skin temperature, autonomic nerve activity (HF, LF/HF) and scores of subjective feeling were monitored during exercise and 20 min post-exercise. RESULTS: During 20 min of feet icing during post-exercise, score of thermal sensation was significantly lower in 10 °C(4.1 ± 0.73) and 20 °C(4.4 ± 0.71) conditions than in Control condition (5.5 ± 1.01, P < 0.05), with no significant difference between 10 °C and 20 °C conditions. Both 10 °C(12.65 ± 0.79 °C) and 20 °C (22.05 ± 0.72 °C) conditions showed significantly lower skin temperature (immersed area) than Control (33.30 ± 0.99 °C, P < 0.05). However, rectal temperature during 20 min of feet icing did not differ significantly among conditions. Moreover, no significant difference was observed in heart rate and LF/HF (the score of autonomic nerve activity) during 20 min of feet-icing. CONCLUSIONS: Post-exercise feet-icing (10 °C and 20 °C) after exercise in hot environment significantly reduced thermal sensation. However, it did not affect rectal temperature or autonomic nerve activity.

Background:Physically active status is an important contributor to individual health. Walking is regarded as commonly accepted exercise for exercise promotion. Particularly, interval fast walking (FW), consisting of alternating between fast and slow walking speeds, has gained popularity from practical viewpoints. Although previous studies have determined the short- and long-term effects of FW programs on endurance capacity and cardiovascular variables, factors affecting these outcomes have not been clarified. In addition to physiological variables, understanding of mechanical variables and muscle activity during FW would be a help to understand characteristics of FW. In the present study, we compared the ground reaction force (GRF) and lower limb muscle activity between fast walking (FW) and running at equivalent speeds. Method:Eight healthy men performed slow walking (45% of the maximum walking speed; SW, 3.9 ± 0.2 km/h), FW (85% of the maximum walking speed, 7.4 ± 0.4 km/h), and running at equivalent speeds (Run) for 4 min each. GRF and average muscle activity (aEMG) were evaluated during the contact, braking, and propulsive phases. Muscle activities were determined for seven lower limb muscles: gluteus maximus (GM), biceps femoris (BF), rectus femoris (RF), vastus lateralis (VL), gastrocnemius medialis (MG), soleus (SOL), and tibialis anterior (TA). Results:The anteroposterior GRF was greater in FW than in Run during the propulsive phase (p < 0.001), whereas the impact load (peak and average vertical GRF) was lower in FW than in Run (p < 0.001). In the braking phase, lower leg muscle aEMGs were higher during Run than during SW and FW (p < 0.001). However, in the propulsive phase, soleus muscle activity was greater during FW than during Run (p < 0.001). aEMG of tibialis anterior was higher during FW than during SW and Run in the contact phase (p < 0.001). No significant difference between FW and Run was observed for HR and RPE. Conclusion:These results suggest that the average muscle activities of lower limbs (e.g., gluteus maximus, rectus femoris, and soleus) during the contact phase were comparable between FW and running, however, the activity patterns of lower limb muscles differed between FW and running, even at equivalent speeds. During running, muscles were mainly activated in the braking phase related to impact. In contrast, during FW, soleus muscle activity during the propulsive phase was increased. Although cardiopulmonary response was not different between FW and running, exercise using FW might be useful for health promotion among individuals who cannot exercise at high-intensity.

Aspartate supplementation has been reported to improve endurance performance by facilitating the tricarboxylic acid cycle flux. The present study was performed to investigate the effects of aspartate supplementation on repeated-sprint performance and blood pH. Following an overnight fast, fourteen healthy males completed three sets of 10 × 6 s maximal sprints after consuming sodium L-aspartate (ASP) or placebo (PLA), in a double-blind manner. Both supplements were taken twice on each test day (2 × 4.5 g). Exercise performance (e.g., cadence and power output) and blood variables (e.g., pH and plasma amino acid levels) were measured. The ASP trial evidenced significantly higher plasma aspartate concentration during the first (ASP, 45.3 ± 9.2 μM; PLA, 6.1 ± 0.8 μM) and the second exercise sets (ASP, 24.2 ± 4.5 μM; PLA, 6.6 ± 0.9 μM) and peak cadence during the second set (ASP, 153 ± 3 rpm; PLA, 152 ± 3 rpm) compared with the PLA trial (all p < 0.05). The peak power output during the second exercise set (ASP, 743 ± 32 W; PLA, 734 ± 31 W; p = 0.060) and the blood pH immediately before (ASP, 7.280 ± 0.020; PLA, 7.248 ± 0.016; p = 0.087) and after the third exercise set (ASP, 7.274 ± 0.019; PLA, 7.242 ± 0.018; p = 0.093) tended to be higher in the ASP than in the PLA trial. In conclusion, ASP supplementation partially improved repeated-sprint performance (peak cadence during the second exercise set). However, it did not affect the mean power output.

To determine the effects of heat acclimation on gastrointestinal (GI) damage and the gastric emptying (GE) rate following endurance exercise in a hot environment. Fifteen healthy men were divided into two groups: endurance training in hot (HOT, 35 °C, n = 8) or cool (COOL, 18 °C, n = 7) environment. All subjects completed 10 days of endurance training (eight sessions of 60 min continuous exercise at 50% of the maximal oxygen uptake (V·O2max). Subjects completed a heat stress exercise tests (HST, 60 min exercise at 60% V·O2max) to evaluate the plasma intestinal fatty acid-binding protein (I-FABP) level and the GE rate following endurance exercise in a hot environment (35 °C) before (pre-HST) and after (post-HST) the training period. We assessed the GE rate using the 13C-sodium acetate breath test. The core temperature during post-HST exercise decreased significantly in the HOT group compared to the pre-HST (p = 0.004) but not in the COOL group. Both the HOT and COOL groups showed exercise-induced plasma I-FABP elevations in the pre-HST (p = 0.002). Both groups had significantly attenuated exercise-induced I-FABP elevation in the post-HST. However, the reduction of exercise-induced I-FABP elevation was not different significantly between both groups. GE rate following HST did not change between pre- and post-HST in both groups, with no significant difference between two groups in the post-HST. Ten days of endurance training in a hot environment improved thermoregulation, whereas exercise-induced GI damage and delay of GE rate were not further attenuated compared with training in a cool environment.

Endurance exercise has been known to be a potent procedure to avoid obesity and useful for preventing cardiovascular diseases and hyperglycemia. Several types of exercise modalities (e.g., walking, running, swimming) are currently utilized, but walking is highly accessible. Although general walking is performed around 4-5 km/h, walking at a faster speed (i.e., fast walking, brisk walking) has been increasing attention. In previous study, five months of fast walking (FW) increased maximal oxygen uptake and lowered blood pressure (Nemoto et al., 2007). However, endocrine responses following a single session of fast walking have not been elucidated so far. PURPOSE: To compare endocrine response between FW and running at the equivalent speed. METHODS:Nine males (age; 24 ± 2 yr, height; 168.2 ± 4.0 cm, bodyweight; 62.7 ± 8.0 kg,) participated in the present study. All subjects performed FW trial and running trial (Run) on different days. FW consisted of 8 repetitions (8 × 5 min walking) of 2 min of slow walking (at 40 % of the maximum walking speed) and 3 min of FW (at 80-95 % of the maximum walking speed). In Run, the subjects performed 40 min running at the equivalent speed utilized during FW phase. During each trial, metabolic variables (energy expenditure (EE), carbohydrate (CHO) oxidation, fat oxidation), blood variables (blood lactate, glucose, growth hormone (GH), glycerol, myoglobin (Mb), haptoglobin), heart rate (HR) and rating of perceived exertion (RPE) were evaluated. RESULTS:Energy Expenditure during exercise did not differ significantly between the two trials. FW trial presented significant higher CHO oxidation compared to Run (FW; 1.20 ± 0.42 vs. Run; 0.83 ± 0.26 g/min, p < 0.05). In contrast, fat oxidation was significantly lower in FW (0.32 ± 0.10 g/min) than in Run (0.42 ± 0.11 g/min, p < 0.05). Post-exercise blood lactate was significantly higher in FW (2.8 ± 1.3 mmol/L) than in Run (1.4 ± 0.2 mmol/L, p < 0.05). Exercise-induced serum GH elevation was significantly smaller in FW (3.4 ± 3.4 ng/mL) than in Run (8.2 ± 6.8 ng/mL, p < 0.05). Furthermore, the exercise-induced relative change in serum Mb was significantly higher in Run (139 ± 24 %) than in FW (161 ± 42 %, p < 0.05). CONCLUSIONS:These results suggest that FW caused smaller muscle damage and facilitated CHO metabolism compared to running at equivalent speed.

We hypothesized that the trained distance runners, who have a relatively high respiratory muscle endurance, but not high respiratory muscle strength, have lower dyspneic sensations during submaximal running. Twenty-one male collegiate distance runners participated. Incremental respiratory endurance tests (IRET) and maximal inspiratory mouth pressure (PImax) measurements were performed under resting conditions. A submaximal exercise test was also performed on a treadmill at two different speeds (16 and 18 km/h) for 4 min each, and the subjects reported the rate of dyspnea (range: 0-10). The time to endpoint during the IRET, an index of respiratory muscle endurance, ranged from 9.4 to 18.8 min, and PImax, as an index of inspiratory muscle strength, ranged from 74.1 to 137.0 cmH2O. The dyspnea rating during running at 16 and 18 km/h ranged from 1 to 6 and from 4 to 8, respectively. The relative exercise intensity was approximately 80 % of peak oxygen uptake (VO2peak) at 16 km/h and 90 %VO2peak at 18 km/h. The time to endpoint during the IRET was significantly negatively correlated with dyspnea during running at 18 km/h (r = -0.459, P = 0.040), but not at 16 km/h (r = -0.161, P = 0.470). There was no significant correlation between PImax and dyspnea during running at 16 km/h (r = -0.003, P = 0.989) or 18 km/h (r = 0.070, P = 0.755). These results suggest that dyspneic sensations during high-intensity running are related to respiratory muscle endurance, but not inspiratory muscle strength, in trained distance runners.

PURPOSE:The present study compared energy metabolism between walking and running at equivalent speeds during two incremental exercise tests.METHODS:Thirty four university students (18 males, 16 females) were recruited. Each participant completed two trials, consisting of walking (Walk) and running (Run) trials on different days, with 2-3 days apart. Exercise on a treadmill was started from initial stage of 3 min (3.0 k/m in Walk trial, 5.0 km/h in Run trial), and the speed for walking and running was progressively every minute by 0.5 km/h. The changes in metabolic variables, heart rate (HR), and rating of perceived exertion (RPE) during exercise were compared between the trials.RESULTS:Energy expenditure (EE) increased with speed in each trial. However, the Walk trial had a significantly higher EE than the Run trial at speeds exceeding 92 ± 2 % of the maximal walking speed (MWS, p < 0.01). Similarly, carbohydrate (CHO) oxidation was significantly higher in the Walk trial than in the Run trial at above 92 ± 2 %MWS in males (p < 0.001) and above 93 ± 1 %MWS in females (p < 0.05).CONCLUSION:These findings suggest that EE and CHO oxidation during walking increase non-linearly with speed, and walking at a fast speed causes greater metabolic responses than running at the equivalent speed in young participants.

We sought to determine the effects of heat acclimation on endurance exercise-induced hepcidin elevation under hot conditions. Fifteen healthy men were divided into two groups: endurance training under hot conditions (HOT, 35 °C, n = 8) and endurance training under cool conditions (CON, 18 °C, n = 7). All subjects completed 10 days of endurance training (8 sessions in total), consisting of 60 min of continuous exercise at 50% of maximal oxygen uptake ( $$\dot{V}{\text{O}}_{2\max }$$ ) under their assigned environment condition. Subjects completed a heat stress exercise test (HST, 60 min exercise at 60% $$\dot{V}{\text{O}}_{2\max }$$ ) to evaluate the exercise-induced thermoregulatory and hepcidin responses under hot conditions (35 °C) before (pre-HST) and after (post-HST) the training period. Core temperature during exercise in the post-HST decreased significantly in the HOT group compared to pre-HST (P = 0.004), but not in the CON group. The HOT and CON groups showed augmented exercise-induced plasma interleukin-6 (IL-6) elevation in the pre-HST (P = 0.002). Both groups had significantly attenuated increases in exercise-induced IL-6 in the post-HST; however, the reduction of exercise-induced IL-6 elevation was not different significantly between both groups. Serum hepcidin concentrations increased significantly in the pre-HST and post-HST in both groups (P = 0.001), no significant difference was observed between both groups during each test or over the study period. 10 days of endurance training period under hot conditions improved thermoregulation, whereas exercise-induced hepcidin elevation under hot conditions was not attenuated following the training.

Purpose The purpose of this study was to determine the effects of 3 consecutive days of endurance training in hypoxia on hepcidin responses. Method Nine active healthy males completed two trials, consisting of 3 consecutive days of endurance training in either hypoxia [fraction of inspired oxygen (F i O 2 ): 14.5

The purpose of the present study was to determine muscle blood flow and muscle oxygenation during repeated-sprint exercise under combined hot and hypoxic conditions. In a single-blind, cross-over research design, 11 active males performed three sets of 5 × 6-s maximal sprints with 30-s active recovery on a cycling ergometer under control (CON; 23 °C, 50% rH, 20.9% FiO2), normobaric hypoxic (HYP; 23 °C, 50% rH, 14.5% FiO2), or hot + normobaric hypoxic (HH; 35 °C, 50% rH, 14.5% FiO2) conditions. The vastus lateralis muscle blood flow after each set and muscle oxygenation during each sprint were evaluated using near-infrared spectroscopy methods. Despite similar repeated-sprint performance among the three conditions (peak and mean power outputs, percent decrement score), HH was associated with significantly higher muscle blood flow compared with CON after the first set (CON: 0.61 ± 0.10 mL/min/100 g; HYP: 0.81 ± 0.13 mL/min/100 g; HH: 0.99 ± 0.16 mL/min/100 g; P < 0.05). The tissue saturation index was significantly lower in HYP than in CON during the latter phase of the exercise (P < 0.05), but it did not differ between HH and CON. These findings suggest that a combination of normobaric hypoxia and heat stress partially facilitated the exercise-induced increase in local blood flow, but it did not enhance tissue desaturation.

Endurance exercise in hypoxia resulted in similar hepcidin elevation compared with exercise in normoxia (Govus et al. 2014; Goto et al. 2017). However, how consecutive days of endurance training in hypoxia affects hepcidin elevation remains unclear. PURPOSE: The purpose of the present study was to determine the effect of three consecutive days of endurance training in hypoxia on hepcidin response. METHODS: Nine active healthy males completed two trials on different days, consisting of either three consecutive days of endurance training in hypoxia (FiO2: 14.5%) or normoxia (FiO2: 20.9%). They performed 90-min sessions of endurance training consisting of high-intensity endurance interval exercise (10 × 4 min pedaling at 80% of VO2max with 2 min of active rest at 30% of VO2max) followed by 30 min continuous pedaling at 60% of VO2max during three consecutive days (days 1-3). Venous blood samples were collected after an overnight fast during experimental periods (days 1-4) to determine the serum hepcidin, iron, ferritin and haptoglobin concentrations. RESULTS: Pedaling workload during endurance training were significantly lower in the HYP (interval exercise: 166 ± 4.3 W) than in the NOR (194 ± 7.6 W, P < 0.0001). Serum iron (P < 0.0001) and ferritin (P = 0.005) concentrations on days 2-4 significantly increased in both trials, whereas there was no significant difference between the two trials. Serum haptoglobin concentrations did not significantly change throughout the experimental periods in either trial. Moreover, NOR showed significantly greater serum hepcidin elevation on the days 2-4 compared with day 1 (day1: 13.9 ± 8.6 ng/mL, day2: 30.4 ± 9.9 ng/mL, P = 0.004). However, no significant difference was observed in serum hepcidin concentrations between the NOR and HYP. CONCLUSION: Three consecutive days of endurance training in hypoxia did not affect further hepcidin elevation compared with endurance training in normoxia.

PURPOSE:The present study investigated the effect of endurance exercise with blood flow restriction (BFR) performed at either 25% maximal oxygen uptake (V˙O2 max) or 40% V˙O2 max) on muscle oxygenation, energy metabolism, and endocrine responses.METHODS:Ten males were recruited in the present study. The subjects performed three trials: (1) endurance exercise at 40% V˙O2 max without BFR (NBFR40), (2) endurance exercise at 25% V˙O2 max with BFR (BFR25), and (3) endurance exercise at 40% V˙O2 max with BFR (BFR40). The exercises were performed for 15 min during which the pedaling frequency was set at 70 rpm. In BFR25 and BFR40, 2 min of pressure phase (equivalent to 160 mmHg) followed by 1 min of release phase were repeated five times (5 × 3 min) throughout 15 minutes of exercise. During exercise, muscle oxygenation and concentration of respiratory gases were measured. The blood samples were collected before exercise, immediately after 15 min of exercise, and at 15, 30, and 60 minutes after completion of exercise.RESULTS:Deoxygenated hemoglobin (deoxy-Hb) level during exercise was significantly higher with BFR25 and BFR40 than that with NBFR40. BFR40 showed significantly higher total-hemoglobin (total-Hb) than NBFR40 during 2 min of pressure phase. Moreover, exercise-induced lactate elevation and pH reduction were significantly augmented in BFR40, with concomitant increase in serum cortisol concentration after exercise. Carbohydrate (CHO) oxidation was significantly higher with BFR40 than that with NBFR40 and BFR25, whereas fat oxidation was lower with BFR40.CONCLUSION:Deoxy-Hb and total Hb levels were significantly increased during 15 min of pedaling exercise in BFR25 and BFR40, indicating augmented local hypoxia and blood volume (blood perfusion) in the muscle. Moreover, low-and moderate-intensity exercise with BFR facilitated CHO oxidation.

Endurance exercise in hypoxia promotes carbohydrate (CHO) metabolism. However, detailed CHO metabolism remains unclear. The purpose of this study was to evaluate the effects of endurance exercise in moderate hypoxia on exogenous glucose oxidation at the same energy expenditure or relative exercise intensity.