Kiyoshi Onari

Decreased cortical excitability during motor imagery after disuse of an upper limb in humans

OBJECTIVE The present study investigated the effect of joint immobilization on corticomotoneuronal excitability to only intracortical input from a hierarchical level above the primary motor cortex. METHODS Motor evoked potentials (MEPs) and H-reflexes in the flexor carpi radialis muscle were elicited from 8 orthopedic patients with splints and 8 healthy volunteers. Each patient was examined on the day of splint removal (disuse stage) and 2 months after that day (recovery stage). Both potentials were recorded under 3 conditions: at rest, while imagining motor movement (during motor imagery), and during 10% of maximum voluntary contraction (10% MVC). RESULTS In the patient group, the amplitude of surface electromyography during voluntary maximum wrist flexion was lower at the disuse stage than at the recovery stage, although the supra-maximum M-wave amplitude did not change between stages. Compared to both the patient group at the recovery stage and the control group, patients at the disuse stage recorded significantly lower MEPs, but only during motor imagery. In contrast, the H-reflex amplitudes were not significantly changed under any of the 3 conditions for both patients and control. CONCLUSIONS The present results indicated a strict parallelism between motor execution (the reduction of electromyography during mvc after immobilization) and motor imagery (the reduction of MEP-amps after immobilization). This parallelism suggests that a functional reorganization or decreased excitability in the cerebral cortex area involved in executing movement likely decreases the motor capability to produce voluntary muscular output after immobilization.

Do the kinetics of peripheral muscle oxygenation reflect systemic oxygen intake

Abstract To examine whether the kinetics of local muscle oxygenation reflect systemic oxygen intake, we measured the kinetics of local muscle oxygenation and systemic oxygen consumption (V˙O2). This study included 16 healthy males who performed an exercise tolerance test on a bicycle ergometer. During the exercise test, expiratory gas analysis was performed with an expiratory gas analyzer, and the kinetics of vastus lateralis muscle oxygenation were determined by near-infrared spectroscopy (NIRS). Oxygenated hemoglobin (OxyHb) and tissue blood oxygen saturation (StO2) gradually decreased during the exercise test, while deoxygenated hemoglobin (DeoxyHb) gradually increased. We examined correlations between the mean values of these parameters, which were calculated by time-integrating the values obtained using NIRS and dividing them by the integral time, and V˙O2. There was a marked positive correlation between DeoxyHb and V˙O2 (r=0.893 − 0.986), and a marked negative correlation between StO2 and V˙O2 (r=0.859 − 0.995). There was a negative correlation between V˙O2 and OxyHb (r=0.726 − 0.978), and no correlation between TotalHb and V˙O2. These results suggest that the kinetics of peripheral muscle oxygenation reflect systemic V˙O2.

Does the coefficient of variation of the R-R intervals in diabetic patients and healthyu subjects reflect the cardiovascular response during exercise?

糖尿病患者と健常者のR-R間隔変動係数(CVR-R)と運動時における循環応答との関連を検討した。対象は2型糖尿病患者8名と,年齢をマッチさせた健常男性8名とした。対象者に自転車エルゴメータを用いた漸増負荷を行い,最大酸素摂取量(・VO2max)と換気性作業閾値(VT)を算出した。次に日を改めて,80%VTに相当する負荷強度で一定負荷運動を行わせた。その後,安静時におけるCVR-Rと,一定負荷運動における酸素摂取と心拍数の時定数を算出した。その結果,1)CVR-Rと・VO2maxはDM群で健常群と比較して低下していた。また,tau HRとtau・VO2はDM群で延長していた。2)tau・VO2とtau HRは二群共に正の相関を,CVR-Rとtau ・VO2は二群共に負の相関を認めた。2・VO2maxとtau HR,・VO2maxとtau・VO2は健常群のみ負の相関を認めた。以上の結果から,CVR-Rは運動に対する循環応答を反映する指標になる可能性が示唆された。また,先行研究において,健常者では運動開始時における循環応答特性は全身持久力を反映するものであることが示唆されているが,本研究では糖尿病患者においては関連を認めないことが明らかとなった。

Influence of mild hypoxia on cardiorespiratory responses and muscle oxygenation during incremental exercise

pressure of arterial oxygen and has an influence on ventilatory, circulatory and metabolic processes during exercise; measuring the gas exchange has been used to study cardiorespiratory response under hypoxic conditions. Recently, muscle metabolism and oxygenation, as well as arterial oxygenation and cardiorespiratory action, are seen as being limited in healthy subjects under hypoxic conditions, and also under conditions of pulmonary patient induced hypoxemia. To assess muscle metabolism, muscle biopsy during resting and phosphorus magnetic resonance spectroscopy during exercise are often used and to assess muscle Introduction oxygenation; using arterial and venous blood sampling. However, this requires invasive techniques, which limits its application to physiological and clinical measurements. Recently, measurements using near infrared spectroscopy (NIRS) have made it possible to noninvasively measure in vivo changes in tissue of both oxygenated and deoxygenated hemoglobin and myoglobin. Although several incremental exercise experiments in hypoxic conditions have been reported5-7, 9, 10, 13, 15-17) , few investigations have been done in respect to the relationship between cardiorespiratory responses and oxygenation in exercising muscle during mild hypoxia. The purpose of this study was to determine the relationships among gas exchange responses, blood lactate concentrations, and NIRS responses during Influence of mild hypoxia on cardiorespiratory responses and muscle oxygenation during incremental exercise

Discrimination of athletic characteristics based on exercise physiology and serum biochemistry

The purpose of the present study is to determine whether athletic characteristics can be discriminated by changes in serum components during exercise which are considered to reflect systemic endurance capacity muscle strength and the energy metabolism system. Thirteen male long‑distance athletes and 8 male short‑distance and field athletes performed an incremental exercise test muscle strength and endurance test. They were also observed for cha nges in serum co mponents during exercise. According to data analysis the discriminant function thus obtained was: Z = 0.8220 × peakV ・ O2 ＋ 0.0037 × AT ＋ 0.0010 × MVC ＋（－0.0276） ×6 0 deg/sec ＋ 0.2629 × MVC 50％ time ＋（－0.8715）× UN ＋ 36.1659 （peakV ・ O2: measured value of peak V ・ O2 AT: ％ peakV ・ O2 MVC: measured value of the isometric muscle strength 60 deg/sec: peak torque of the i sokinetic muscle contraction at 60 deg/sec MVC 50％ time: the time for the previously determined isometric muscle strength value to become less than 50％ UN: the increase rate of UN from the value at rest to the maximum value）. Subjects were classified into the actual group correctly while the erroneous discriminant rate was 0.73％. I n particular weighting of the discriminant coefficient of peakV ・ O2 and UN was large indicating that these are useful as parameters for discriminating athletic characteristics.