Atsuo Maruyama

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.

Effect of acute sodium bicarbonate ingestion on excess C02 output during incremental exercise

SummaryThe effect of bicarbonate ingestion on total excess volume of CO2 Output (CO2 excess), due to bicaronate buffering of lactic acid in exercise, was studied in eight healthy male volunteers during incremental exercise on a cycle ergometer performed after ingestion (0.3 g · kg−1 body mass) of CaCO3 (control) and NaHCO3 (alkalosis). The resting arterialized venous blood pH (P<0.05) and bicarbonate concentration ([HCO3−]b;P<0.01) were significantly higher in acute metabolic alkalosis [AMA; pH, 7.44 (SD 0.03); [HCO3−]b; 29.4 (SD 1.5) mmol·1-1] than in the control [pH, 7.39 (SD 0.03); [HCO3−]b, 25.5 (SD 1.0) mmol·1−1]. The blood lactate concentrations ([la−]b) during exercise below the anaerobic threshold (AT) were not affected by AMA, while significantly higher [la−]b at exhaustion [12.29 (SD 1.87) vs 9.57 (SD 2.14) mmol·1−1,P < 0.05] and at 3 min after exercise [14.41 (SD 1.75) vs 12.26 (SD 1.40) mmol · l−1,P < 0.05] were found in AMA compared with the control. The CO2 excess increased significantly from the control [3177 (SD 506) ml] to AMA [3897 (SD 381) ml;P < 0.05]. The CO2 excess per body mass was found to be significantly correlated with both the increase of [la−]b from rest to 3 min after exercise (Δ [la−]b;r=0.926,P < 0.001) and with the decrease of [HCO3−]b from rest to 3 min after exercise (Δ [HCO3−]b;r=0.872,P<0.001), indicating that CO2 excess per body mass increased linearly with both Δ [la−b and Δ [HCO3−]b. As a consequence, CO2 excess per body mass per unit increase of [la−]b (CO2 excess·mass−1·Δ [la−]b) was similar for the two conditions. The present results would suggest that the relationship between CO2 excess and blood lactate accumulation was unaffected by acute metabolic alkalosis, because the relative contribution of bicarbonate buffering of lactic acid was the same as in the control.

Unilateral grip fatigue reduces short interval intracortical inhibition in ipsilateral primary motor cortex

OBJECTIVE This study was designed to examine whether exhaustive grip exercise of the left hand affected intracortical excitability in ipsilateral motor cortex. METHODS Ten healthy male subjects (aged 21-24 years) participated in experiment 1 in which paired-pulse transcranial magnetic stimulation (TMS) was used to test corticospinal and corticocortical excitability in right (relaxed) first dorsal interosseous (FDI) muscle during the recovery period after exhaustive forceful grip exercise of the left hand. Seven of the same subjects participated in experiment 2, in which the intensity of the test stimulus was adjusted so that the amplitude of motor evoked potential (MEP(TEST)) was kept constant throughout the measurement. RESULTS In experiment 1, MEP(TEST) was slightly reduced from 5 to 15min after exercise whilst short interval intracortical inhibition (SICI) at interstimulus interval (ISI) of 2 and 3ms became less effective. Intracortical facilitation (ICF) was unchanged. In experiment 2 when the MEP(TEST) was maintained at a constant size there was again no change in ICF, and the reduction in SICI was still present at the same intervals. CONCLUSIONS We conclude that unilateral exhaustive grip exercise reduced the excitability of the corticospinal output of the ipsilateral motor cortex whilst simultaneously reducing the excitability of SICI. These results would be compatible with the idea that fatigue increases the tonic level of interhemispheric inhibition from the fatigued to the non-fatigued cortex. SIGNIFICANCE Muscle fatigue to the point of exhaustion has lasting effects on the excitability of intracortical circuits in the non-exercised hemisphere, perhaps via changes in the tonic levels of activity in transcallosal pathways.

Effect of short-interval intracortical inhibition in motor cortex during pre-set on rebound drop jumping performance

This study aimed to assess the effect of short-interval intracortical inhibition (SICI) before a jump off a platform (pre-set) on drop jump (DJ); the purpose was to investigate the relationship between this activity and performance, and the different effects of SICI on agonist and antagonist muscles during pre-set for jump athletes. Jump athletes (Jumper group, n=13) and Other athletes (Other group, n=9) performed DJ from drop heights of 0.30, 0.45, and 0.60 m). DJ performance was evaluated with DJ-index which was calculated from contact time and jump height. SICI was calculated from motor evoked potentials (MEP) recorded using paired-pulse transcranial magnetic stimulation for the medial gastrocnemius (MG) and tibialis anterior (TA) muscles in 7 jump athletes. Significantly higher DJ performance was observed for the Jumper group at all drop heights, and the Jumper group exhibited greater performance for the highest drop height than the Other groups. Significant decreases in SICI for MG were observed for the Jumper groups, and this decrease in inhibition was more prominent for the highest drop height during pre-set. Furthermore, the correlation between SICI for MG and DJ-index was stronger for increased drop heights, and a significantly positive correlation between these variables was observed at a height of 0.60 m. However, the SICI during the pre-set for TA exhibited no significant change under any of the conditions. The results of the present study suggest the importance of selective disinhibition of brain areas associated with the agonistic muscles during preset for higher DJ performance. Jpn J Phys Fitness Sports Med, 65(4): 401-413 (2016)

P3-18 Facilitation of F-waves by cortical and cervical magnetic stimulation

Objective: We reported previously that motor imagery executed with cutaneous input by cutaneous input tape (CIT) facilitated corticospinal tract excitability. However, the amount of influence induced by the cutaneous input has not been clarified. The purpose of the present study was to clarify the influence of the CIT on motor neuron pool excitability. Methods: Healthy subjects participated in this experiment. There were four test conditions, the rest condition: Rest, the cutaneous input-rest condition: CI-Rest, the motor imagery condition: MI, and the cutaneous input-motor imagery condition: CI-MI. H-reflex was recorded from the right soleus muscle for each condition. CIT was applied from the right sole to the gastrocnemius muscle. The motor imagery was executed, so that the ankle plantar flexion was imaged in the brain. H-reflex test stimulus intensity was defined as the level at which half amplitude of the maximum H-reflex amplitude could be evoked. Results: The mean value of H-reflex amplitude increased in the order of Rest, MI, CI-Rest, and CI-MI, and there was a significant main effect on the condition. A post hoc test revealed that the H-reflex amplitude increased more significantly in CI-MI than in Rest or MI. The increasing ratio of H-reflex amplitude during motor imagery was significantly larger than that recorded without CIT. Conclusions: The results of this study suggested that CIT affects the motor neuron pool excitability at the spinal level during motor imagery. One possible explanation is that two independent facilitatory effects of CIT and the motor imagery were finally detected after those independent interventions were combined. Another possible explanation is purposive utilization. A facilitatory effect of gain modification induced by taping was shown during motor imagery, but this effect did not occur during the rest condition, when no motor imagery was invoked.

PF4.1 Facilitation of F-waves by Transcranial Magnetic Stimulation

Seiji Etoh1 *, Ryoji Nakanishi2, Kyohei Takahashi3, Fumitomo Iwanaga2, Shuji Matsumoto1, Megumi Shimodozono1, Atsuo Maruyama3, Kazumi Kawahira1, John C. Rothwell4 1Dept. of Rehabilitation and Physical Medicine, Faculty of Medicine, Kagoshima University, Japan, 2Dept. of Neurology, Kumamoto Kinoh Hospital, Japan, 3Dept. of Physical Education, Faculty of Education, Kagoshima University, Japan, 4Sobell Dept. of Motor Neuroscience and Movements Disorders, Institute of Neurology, University College London, UK E-mail address: etohs@m2.kufm.kagoshima-u.ac.jp

6. Effect of muscle fatigue due to grip task on ipsilateral intracortical inhibition

the somatosensory, visual and vestibular components of postural balance. The patients had normal nerve conduction velocities, no visual impairments and no clinical signs of vestibular disorders. Composite equilibrium score (mathematic average of 6 test conditions of SOT) was significantly lower in PD compared with controls. Low scores for conditions 4 (eyes open and platform sway), 5 (eyes closed and platform sway) and 6 (eyes open and platform and visual sway) suggested poor use of somatosensory, visual and vestibular references, respectively. Over-reliance on visual cues even when sensory information is inaccurate was not different between PD and control groups. Basal ganglia that neutrally project into motor areas are mainly involved in the integration of somatosensory, visual and vestibular inputs. We propose that postural instability in PD may be due to dysfunction in central integration of somatosensory, visual and vestibular inputs, rather than conduction failure of these inputs from the periphery.