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Biomedical subjects

Keisho Katayama

Publications and source records attributed to Keisho Katayama.

23 records · Page 2Linked to original sources
PubMed2002

Enhanced chemosensitivity after intermittent hypoxic exposure does not affect exercise ventilation at sea level.

The purpose of the present study was to test the hypothesis that the ventilatory response to exercise at sea level may increase after intermittent hypoxic exposure for 1 week, accompanied by an increase in hypoxic or hypercapnic ventilatory chemosensitivity. One group of eight subjects (hypoxic group) were decompressed in a chamber to 432 torr (where 1 torr=1.0 mmHg, simulating an altitude of 4,500 m) over a period of 30 min and maintained at that pressure for 1 h daily for 7 days. Oxygen uptake and pulmonary ventilation (V(E)) were determined at 40%, 70%, and 100% of maximal oxygen uptake at sea level before (Pre) and after (Post) 1 week of daily exposures to hypoxia. The hypoxic ventilatory response (HVR) was determined using the isocapnic progressive hypoxic method as an index of ventilatory chemosensitivity to hypoxia, and the hypercapnic ventilatory response (HCVRSB) was measured by means of the single-breath carbon dioxide method as an index of peripheral ventilatory chemosensitivity to hypercapnia. The same parameters were measured in another group of six subjects (control group). In the hypoxic group, resting HVR increased significantly ( P<0.05) after intermittent hypoxia and HCVRSB increased at Post, but the change was not statistically significant ( P=0.07). In contrast, no changes in HVR and HCVRSB were found in the control group. There were no changes in either V(E) or the ventilatory equivalent for oxygen during maximal and submaximal exercise at sea level throughout the experimental period in either group. These results suggest that the changes in resting hypoxic and peripheral hypercapnic chemosensitivities following short-term intermittent hypoxia have little effect on exercise ventilation at sea level.

Adaptation, Physiological↗
PubMed2002

Cross education of muscular strength during unilateral resistance training and detraining.

The purpose of the present study was to examine the changes in maximum voluntary isometric contraction (MVC) in the contralateral untrained limb during unilateral resistance training and detraining, and to examine the factors inducing these changes by means of electrophysiological techniques. Nine healthy males trained their plantar flexor muscles unilaterally 4 day-s x week(-1) for 6 weeks using 3 sets of 10-12 repetitions at 70-75% of one-repetition maximum a day, and detrained for 6 weeks. Progressive unilateral resistance training significantly (P < 0.05) increased MVC, integrated electromyogram (iEMG), and voluntary activation in the trained and contralateral untrained limbs. The changes in MVC after training were significantly correlated with the changes in iEMG in both limbs. No significant changes occurred in MVC, voluntary activation, and iEMG in the contralateral limb after detraining. The changes in MVC after detraining did not correlate with the changes in voluntary activation or iEMG in either limb. Training and detraining did not alter twitch and tetanic peak torques in either limb. These results suggest that the mechanisms underlying cross education of muscular strength may be explained by central neural factors during training, but not solely so during detraining.

Adult↗
PubMed2002

Changes in blood volume and oxygenation level in a working muscle during a crank cycle.

PURPOSE: This study examined circulatory and metabolic changes in a working muscle during a crank cycle in a pedaling exercise with near-infrared spectroscopy (NIRS). METHODS: NIRS measurements sampled under stable metabolic and cadence conditions during incremental pedaling exercise were reordered according to the crank angles whose signals were obtained in eight male subjects. RESULTS: The reordered changes in muscle blood volume during a crank cycle demonstrated a pattern change that corresponded to changes in pedal force and electrical muscle activity for pedal thrust. The top and bottom peaks for muscle blood volume change at work intensities of 180 W and 220 W always preceded (88 +/- 32 and 92 +/- 23 ms, respectively) those for muscle oxygenation changes. Significant differences in the level of NIRS parameters (muscle blood volume and oxygenation level) among work intensities were noted with a common shape in curve changes related to pedal force. In addition, a temporary increase in muscle blood volume following a pedal thrust was detected at work intensities higher than moderate. This temporary increase in muscle blood volume might reflect muscle blood flow restriction caused by pedal thrusts. CONCLUSION: The results suggest that circulatory and metabolic conditions of a working muscle can be easily affected during pedaling exercise by work intensity. The present method, reordering of NIRS parameters against crank angle, serves as a useful measure in providing additional findings of circulatory dynamics and metabolic changes in a working muscle during pedaling exercise.

Adult↗
PubMed2002

Effect of cycling experience and pedal cadence on the near-infrared spectroscopy parameters.

PURPOSE: Previously we demonstrated that the method to reorder near-infrared spectroscopy (NIRS) parameters against crank angle could serve as a useful measure in providing circulatory dynamics and metabolic changes in a working muscle during pedaling exercise. To examine further applicability of this method, we investigated the effects of cycling experience and pedal cadence on the NIRS parameters. METHODS: Noncyclists (NON), triathletes (TRI), and cyclists (CYC) performed pedaling exercises at a work intensity of 75% VO2max while changing pedal cadence (50, 75, 85, and 95 rpm). Physiological and biomechanical responses and NIRS parameters were measured. RESULTS: NIRS measurements determined with the reordered NIRS change demonstrated significant differences depending on the factors. The bottom peak of reordered NIRS changes in muscle blood volume and oxygenation level shifted upward with an increase in pedal cadence in NON but remained unchanged in CYC. The reordered NIRS change demonstrated a temporary increase at the crank angle corresponding to the relaxation phase of the working muscle. This temporary increase was observed even in the highest pedal cadence in CYC. The difference in levels between the peak of the temporary increase and the bottom peak of reordered NIRS change (LPB-diff) for CYC at 85 rpm was significantly larger than that for NON. The results with NIRS parameters corresponded to changes in pedal force and myoelectric activity during pedal thrust. CONCLUSIONS: The bottom peak level of the reordered NIRS changes and LPB-diff determined for blood volume are available to detect noninvasively the differences in circulatory dynamics and metabolic change during pedaling exercises performed at different pedal cadences and also to estimate the difference of physiological and technical developments for endurance cycling in athletes.

Adaptation, Physiological↗