Ryotaro Kime

Discrepancy between cardiorespiratory system and skeletal muscle in elite cyclists after hypoxic training

BackgroundThe purpose of this study was to determine the effects of hypoxic training on the cardiorespiratory system and skeletal muscle among well-trained endurance athletes in a randomized cross-over design.MethodsEight junior national level competitive cyclists were separated into two groups; Group A trained under normoxic condition (21% O2) for 2 hours/day, 3 days/week for 3 weeks while Group B used the same training protocol under hypoxic condition (15% O2). After 3 weeks of each initial training condition, five weeks of self-training under usual field conditions intervened before the training condition was switched from NT to HT in Group A, from HT to NT in Group B. The subjects were tested at sea level before and after each training period. O2 uptake (O2), blood samples, and muscle deoxygenation were measured during bicycle exercise test.Results and DiscussionNo changes in maximal workload, arterial O2 content, O2 at lactate threshold and O2max were observed before or after each training period. In contrast, deoxygenation change during submaximal exercise in the vastus lateralis was significantly higher at HT than NT (p < 0.01). In addition, half time of oxygenation recovery was significantly faster after HT (13.2 ± 2.6 sec) than NT (18.8 ± 2.7 sec) (p < 0.001).ConclusionsThree weeks of HT may not give an additional performance benefit at sea level for elite competitive cyclists, even though HT may induce some physiological adaptations on muscle tissue level.

A novel method to measure regional muscle blood flow continuously using NIRS kinetics information

BackgroundThis article introduces a novel method to continuously monitor regional muscle blood flow by using Near Infrared Spectroscopy (NIRS). We demonstrate the feasibility of the new method in two ways: (1) by applying this new method of determining blood flow to experimental NIRS data during exercise and ischemia; and, (2) by simulating muscle oxygenation and blood flow values using these newly developed equations during recovery from exercise and ischemia.MethodsDeoxy (Hb) and oxyhemoglobin (HbO2), located in the blood ofthe skeletal muscle, carry two internal relationships between blood flow and oxygen consumption. One is a mass transfer principle and the other describes a relationship between oxygen consumption and Hb kinetics in a two-compartment model. To monitor blood flow continuously, we transfer these two relationships into two equations and calculate the blood flow with the differential information of HbO2 and Hb. In addition, these equations are used to simulate the relationship between blood flow and reoxygenation kinetics after cuff ischemia and a light exercise. Nine healthy subjects volunteered for the cuff ischemia, light arm exercise and arm exercise with cuff ischemia for the experimental study.ResultsAnalysis of experimental data of both cuff ischemia and light exercise using the new equations show greater blood flow (four to six times more than resting values) during recovery, agreeing with previous findings. Further, the simulation and experimental studies of cuff ischemia and light exercise agree with each other.ConclusionWe demonstrate the accuracy of this new method by showing that the blood flow obtained from the method agrees with previous data as well as with simulated data. We conclude that this novel continuous blood flow monitoring method can provide blood flow information non-invasively with NIRS.

Modeling of Oxygen Diffusion and Metabolism from Capillary to Muscle

In the bioengineering and sports training field, there are interests in obtaining information on oxygen transport and metabolism during muscle exercise. The goal of our study was to develop a time-dependent model which can simulate the changes in oxygen diffusion and metabolism in muscle tissue, especially from capillary to mitochondria. We postulate that oxygen diffuses into the tissue at a rate proportional to the oxygen concentration in plasma when applied to a steady state condition. As we know, any build up of oxygen in the tissue is directly related to oxygen leaving the capillary into the tissue and the consumption of oxygen by the mitochondria, or the metabolic demand. We designed a model which consisted of four compartments: (1) capillary; (2) interstitial space between capillary and myofibril tissue cell; (3) parenchymal cell through myofibril to mitochondria in muscle tissue; (4) at mitochondria. Oxygen comes from arteriole to capillary, then diffuses to mitochondria through interstitial space and myofibril. Oxygen is reduced to water in mitochondria, and ATP is generated through proton transport. Our model simulates the measured oxygen uptake during rest and muscle exercise as the input oxygen uptake represented as H2O formation.