Biomedical subjects

Keiji Hayashi

Publications and source records attributed to Keiji Hayashi.

6 recordsLinked to original sources

PubMed2006

Metabolic response during intermittent graded sprint running in moderate hypobaric hypoxia in competitive middle-distance runners.

The purpose of this study was to determine whether the metabolic response and running performance during intermittent graded sprint running were affected by moderate hypobaric hypoxia (H; 2,500 m above sea level) in competitive middle-distance runners. Nine male runners performed intermittent graded sprint running until exhaustion, to evaluate the metabolic response and running performance in H and normobaric normoxia (N). The test constructed of incremental (25 m min(-1)) 20 s running bouts (4 degrees inclination) interspaced with 100 s recovery periods. Maximal running speed was not different between conditions [453 (7) m min(-1) vs. 458 (4) m min(-1) in N vs. H]. V(O2) at each speed was lower in H than N (ANOVA; P < 0.05). Although, oxygen deficit (D(O2)) at each speed was not different between N and H (ANOVA; P = 0.1), total accumulated D(O2) in all bouts was significantly higher in H than N [165 (10) ml kg(-1) in N and 173 (10) ml kg(-1) in H]. The ratio of D(O2).V(O2)(-1) was similar in all bouts, but higher in H than N. These results suggest that intermittent graded sprint running performance is not affected by moderate hypobaria despite a reduction in the energy supplied by aerobic metabolism due to a compensatory increase in the energy supplied by the anaerobic metabolism in competitive middle-distance runners.

Adult↗

PubMed2005

Relationship between ventilatory response and body temperature during prolonged submaximal exercise.

We examined whether an increase in skin temperature or the rate of increase in core body temperature influences the relationship between minute ventilation (Ve) and core temperature during prolonged exercise in the heat. Thirteen subjects exercised for 60 min on a cycle ergometer at 50% of peak oxygen uptake while wearing a suit perfused with water at 10 degrees C (T10), 35 degrees C (T35), or 45 degrees C (T45). During the exercise, esophageal temperature (Tes), skin temperature, heart rate (HR), Ve, tidal volume, respiratory frequency (f), respiratory gases, blood pressure (BP), and blood lactate were all measured. We found that oxygen uptake, carbon dioxide output, BP, and blood lactate did not differ among the sessions. Tes, HR, Ve, and f remained nearly constant from minute 10 onward in the T10 session, but all of these parameters progressively increased in the T35 and T45 sessions, and significantly higher levels were seen in the T45 than the T35 session. For all but two subjects in the T35 and T45 sessions, plotting Ve as a function of Tes revealed no threshold for hyperventilation; instead, increases in Ve were linearly related to Tes, and there were no significant differences in the slopes or intercepts between the T35 and T45 sessions. Thus, during prolonged submaximal exercise in the heat, Ve increases with core temperature, and the influences of skin temperature and the rate of increase in Tes on the relationship between Ve and Tes are apparently small.

Adult↗

PubMed2005

Intermittent short-term graded running performance in middle-distance runners in hypobaric hypoxia.

This study investigated whether in trained middle-distance runners, intermittent short-term graded running performance is affected by a hypobaric hypoxic environment (simulated 2,500 m) (H). Seven male middle-distance runners performed an aerobic performance test and an intermittent short-term graded anaerobic running-performance test (MART) both in H and in a normobaric normoxic environment (N). VO(2max) and OBLA were markedly lower (by 18.1% and 8.7%, respectively) in H than in N. In MART, neither maximal running velocity (V(max)) nor exhaustion-time was different between N and H (454 (7) m min(-1) vs. 451 (6) m min(-1), respectively, and 208.7 (5.2) s vs. 205.7 (4.2) s, respectively). The blood lactate concentration at sub-maximal running speed (425 m min(-1)) was significantly greater in H than in N (paired t-test: P<0.05). These results suggest that, in trained middle-distance runners, intermittent short-term graded running performance is not affected by H, despite a considerable decrease in aerobic power in H during the aerobic performance test.

Adult↗

PubMed2004

Effects of brief leg cooling after moderate exercise on cardiorespiratory responses to subsequent exercise in the heat.

We investigated the effects of brief leg cooling after moderate exercise on the cardiorespiratory responses to subsequent exercise in the heat. Following 40 min of ergometer cycling [65% peak oxygen uptake (VO(2peak))] at 35 degrees C (Ex. 1), seven male subjects [21.9 (1.1) years of age; 170.9 (1.9) cm height; 66.0 (2.0) kg body mass; 46.7 (2.0) ml kg(-1) min(-1) VO(2peak)] immersed their legs in 35 degrees C (control condition, CONT) or 20 degrees C (cooling condition, COOL) water for 5 min and then repeated the cycling (as before, but for 10 min) (Ex. 2). Just before Ex. 2, esophageal temperature ( T(es)) was lower in COOL than in CONT [36.9 (0.2) vs 37.5 (0.1) degrees C] ( P<0.01), as also were both mean skin temperature [33.9 (0.2) vs 35.2 (0.2) degrees C] ( P<0.01), and heart rate (HR) [93.2 (6.0) vs 102.7 (4.9) beats min(-1)] ( P<0.05). During Ex. 2, no differences between CONT and COOL were observed in oxygen uptake, arterial blood pressure, blood lactate concentration, or ratings of perceived exertion; however, T(es), skin temperature, and HR were lower in COOL than in CONT. Further, during the first 5 min of Ex. 2, minute ventilation was significantly lower in COOL than in CONT [50.3 (2.0) vs 53.4 (2.6) l min(-1)] ( P<0.01). These results suggest that brief leg cooling during the recovery period may be effective at reducing thermal and cardiorespiratory strain during subsequent exercise in the heat.

Adult↗

PubMed2004

Modulation of arterial baroreflex dynamic response during mild orthostatic stress in humans.

We tested the hypothesis that in humans, carotid-baroreflex dynamic responses (evaluated by examining the time course of the carotid-baroreflex-induced alterations in muscle sympathetic nerve activity (MSNA), mean arterial blood pressure (MAP) and heart rate (HR)) would be altered during mild orthostatic stress in ways that serve to limit orthostatic hypotension. In 12 healthy subjects (10 male, 2 female), 5-s periods of neck pressure (NP) (50 mmHg) and neck suction (NS) (-60 mmHg) were used to evaluate carotid baroreflex function at rest (CON) and during lower body negative pressure (LBNP) (-15 mmHg). During LBNP (as compared with CON) (a) the augmentations in MSNA and MAP elicited by NP were greater, (b) the NS-induced period of MSNA suppression was, if anything, shorter, (c) the peak decrement in MAP elicited by NS, although not different in amplitude, occurred earlier and recovered to its initial level more quickly after NS, and (d) the HR responses to NP and NS were greater. These results suggest that during mild orthostatic stress, carotid-baroreflex dynamic responses are modulated in ways that should help maintain blood pressure and limit orthostatic hypotension.

Adult↗

PubMed2004

Modulation of control of muscle sympathetic nerve activity during orthostatic stress in humans.

We tested the hypothesis that orthostatic stress would modulate the arterial baroreflex (ABR)-mediated beat-by-beat control of muscle sympathetic nerve activity (MSNA) in humans. In 12 healthy subjects, ABR control of MSNA (burst incidence, burst strength, and total activity) was evaluated by analysis of the relation between beat-by-beat spontaneous variations in diastolic blood pressure (DAP) and MSNA during supine rest (CON) and at two levels of lower body negative pressure (LBNP: -15 and -35 mmHg). At -15 mmHg LBNP, the relation between burst incidence (bursts per 100 heartbeats) and DAP showed an upward shift from that observed during CON, but the further shift seen at -35 mmHg LBNP was only marginal. The relation between burst strength and DAP was shifted upward at -15 mmHg LBNP (vs. CON) and further shifted upward at -35 mmHg LBNP. At -15 mmHg LBNP, the relation between total activity and DAP was shifted upward from that obtained during CON and further shifted upward at -35 mmHg LBNP. These results suggest that ABR control of MSNA is modulated during orthostatic stress and that the modulation is different between a mild (nonhypotensive) and a moderate (hypotensive) level of orthostatic stress.

Adult↗