Mitsuharu Inaki

Control of the rate of phosphocreatine resynthesis after exercise in trained and untrained human quadriceps muscles.

We examined the effect of differences in exercise intensity on the time constant (tc) of phosphocreatine (PCr) resynthesis after exercise and the relationships betweentc and maximal oxygen uptake (VO2max) in endurance-trained runners (n = 5) and untrained controls (n = 7) (average VO2max = 66.2 and 52.0 ml · min−1 · kg−1, respectively). To measure the metabolism of the quadriceps muscle using phosphorus nuclear magnetic resonance spectroscopy, we developed a device which allowed knee extension exercise inside a magnet. All the subjects performed four types of exercise: light, moderate, severe and exhausting. The end-exercise PCr: [PCr + inorganic phosphate (Pi)] ratio decreased significantly with the increase in the exercise intensity (P < 0.01). Although there was little difference in the end-exercise pH, adenosine diphosphate concentration ([ADP]) and the lowest intracellular pH during recovery between light and moderate exercise, significant changes were found at the two higher intensities (P < 0.01). These changes for runners were smaller than those for the controls (P < 0.05). Thec remained constant after light and moderate exercise and then lengthened in proportion to the increase in intensity (P < 0.05). The runners had a lowertc at the same PCr and pH than the controls, particularly at the higher intensity (P < 0.05). There was a significant correlation betweentc and [ADP] in light exercise and betweentc and both end-exercise PCr and pH in severe and exhausting exercise (P < 0.05). The threshold of changes in pH andtc was a PCr: (PCr + Pi) ratio of 0.5. There was a significant negative correlation between the VO2max andtc after all levels of exercise (P<0.05).However, in the controls a significant correlation was found in only light and moderate exercise (P < 0.05). These findings suggest the validity of the use oftc at an end-exercise PCr:(PCr + Pi) ratio of more than 0.5 as a stable index of muscle oxidative capacity and the correlation between local and general aerobic capacity. Moreover, endurance-trained runners are characterized by the faster PCr resynthesis at the same PCr and intracellular pH.

Changes in magnetic resonance images in human skeletal muscle after eccentric exercise

To investigate the time-course of changes in transverse relaxation time (T2) and cross-sectional area (CSA) of the quadriceps muscle after a single session of eccentric exercise, magnetic resonance imaging was performed on six healthy male volunteers before and at 0, 7, 15, 20, 30 and 60 min and 12, 24, 36, 48, 72 and 168 h after exercise. Although there was almost no muscle soreness immediately after exercise, it started to increase 1 day after, peaking 1–2 days after the exercise (P<0.01). Immediately after exercise, T2 increased significantly in the rectus femoris, vastus lateralis and intermedius muscles (P<0.05) and decreased quickly continuing until 60 min after exercise. At and after the 12th h, a significant increase was perceived again in the T2 values of the vastus lateralis and intermedius muscles (P<0.01) [maximum 9.3 (SEM 2.8)% and 10.9 (SEM 2.2)%, respectively]. The maximal values were exhibited at 24–36 h after exercise. In contrast, the rectus femoris muscle showed no delayed-stage increase. Also, in CSA, an increase after 12 h was observed in addition to the one immediately after exercise in the vastus lateralis, intermedius and medialis and quadriceps muscles as a whole (P < 0.01), reaching the maximal values at 12–24 h after exercise. The plasma creative kinase activity remained unchanged up to 24 h after and then increased significantly 48 h after exercise (P < 0.05). Beginning 12 h after exercise, the subjects whose T2 and CSA increased less than the others displayed a faster decrease in muscle soreness. These results suggested that T2 and CSA displayed bimodal responses after eccentric exercise and the time-courses of changes in them were similar to those in muscle soreness.

Effect of endurance training on excessive CO2 expiration due to lactate production in exercise

SummaryWe attempted to determine the change in total excess volume of CO2 Output (CO2 excess) due to bicarbonate buffering of lactic acid produced in exercise due to endurance training for approximately 2 months and to assess the relationship between the changes of CO2 excess and distance-running performance. Six male endurance runners, aged 19–22 years, were subjects. Maximal oxygen uptake (VO2max), oxygen uptake (VO2) at anaerobic threshold (AT), CO2 excess and blood lactate concentration were measured during incremental exercise on a cycle ergometer and 12-min exhausting running performance (12-min ERP) was also measured on the track before and after endurance training. The absolute magnitudes in the improvement due to training for C02 excess per unit of body mass per unit of blood lactate accumulation (Ala−) in exercise (CO2 excess·mass−1·Δla−), 12-min ERP, VO2 at AT (AT-VO2) and VO2max on average were 0.8 ml·kg−1·l−1·mmol−1, 97.8m, 4.4 ml·kg−1· min−1 and 7.3 ml·kg−1·min−1, respectively. The percentage change in CO2 excess·mass−1·Δla− (15.7%) was almost same as those of VO2max (13.7%) and AT-VO2 (13.2%). It was found to be a high correlation between the absolute amount of change in CO2 excess·mass−1·Δla− and the absolute amount of change in AT-VO2 (r=0.94, P<0.01). Furthermore, the absolute amount of change in C02 excess·mass−1·Δla−, as well as that in AT-VO2 (r=0.92, P<0.01), was significantly related to the absolute amount of change in 12-min ERP (r=0.81, P<0.05). It was concluded that a large CO2 excess·mass−1·Δla−1 of endurance runners could be an important factor for success in performance related to comparatively intense endurance exercise such as 3000–4000 m races.

Muscle energetics in short-term training during hypoxia in elite combination skiers

AbstractFour well-trained combination skiers were studied through pre- and post-training for the effects of short-term intermittent training during hypoxia on muscle energetics during submaximal exercise as measured by Phosphorus-31 nuclear magnetic resonance and maximal aerobic power (

Effects of Sprint Cycle Training on Architectural Characteristics Torque-velocity Relationships and Power output in Human Skeletal Muscles

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STUDIES ON THE EFFECT OF NaHCO3 INTAKE ON INTRACELLULAR pH AND PCr CONCENTRATION DURING EXERCISE BY 31P NMR

O2max). The hypoxia and training in the cold was conducted in a hypobaric chamber and comprised 60-min aerobic exercise (at an intensity equivalent to the blood lactate threshold), using a cycle ergometer or a treadmill twice a day for 4, consecutive days at 5°C, in conditions equivalent to an altitude of 2000 m (593 mm Hg). No change in

2P-P-14 Duration of effects by aerobic exercise on cerebral nerve function(The Proceedings of the 16th Annual Meetings of Japan Society of Exercise and Sports Physiology August 2-3, (Nara))

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