Taku Hamada

Moderate physical exercise increases cardiac autonomic nervous system activity in children with low heart rate variability

ObjectOur objective was to investigate the effect of a long-term moderate exercise program on cardiac autonomic nervous system (ANS) activity in healthy children.MethodsThree hundred and five children aged 6–11xa0years participated in a 12-month school-based exercise training program (130–140xa0bpm, 20xa0min/day, 5xa0days/week). Cardiac ANS activities were measured using heart rate variability (HRV) power spectral analysis in resting conditions. Following the first measurement, 100 children from the lowest total power (TP) HRV were chosen as experimental samples and the same number of age-, height-, and weight-matched controls (CG) was randomly selected from the remaining children.ResultsIn the low group (LG), all the frequency components of the HRV were significantly increased after the training period, whereas only low-frequency power was augmented in the control group (CG).ConclusionOur data suggest that the 12-month moderate exercise training has a positive effect on cardiac ANS activity in the children who initially had low HRV.

Increase in reaction time for the peripheral visual field during exercise above the ventilatory threshold.

The purpose of the present study was to determine whether reaction time (RT) for the peripheral visual field increases at exercise intensity above the ventilatory threshold (VT) during incremental exercise and to examine the relationship between aerobic capacity and the extent of increase in the RT. Nine healthy subjects performed a simple manual RT task for the peripheral visual field at rest, during exercise on a cycle ergometer, and immediately after exercise. After warm-up exercise, the subjects cycled at 40xa0W for 3xa0min, increasing by 40xa0W every 3xa0min until 240xa0W in a step-wise manner. During incremental exercise, RT measurements were performed 1xa0min and 30xa0s after the start of every increase in workload. The RT for the peripheral visual field significantly increased at exercise intensity above VT, as compared with at rest. The increase in the RT, which was calculated by subtracting the RT at rest from the RT at 240xa0W, negatively correlated with maximal oxygen uptake

Mechanomyographic responses in human biceps brachii and soleus during sustained isometric contraction

left( {dot V{text{O}_{2 max}}} right)

Electrical stimulation of human lower extremities enhances energy consumption, carbohydrate oxidation, and whole body glucose uptake.

for each subject (r=−0.73, P<0.05). It is likely that high aerobic capacity attenuates the increase in the RT for the peripheral visual field during exhaustive exercise.

High-fat diet impairs the effects of a single bout of endurance exercise on glucose transport and insulin sensitivity in rat skeletal muscle

The present study examined, whether or not mechanomyogram (MMG) amplitude and frequency component could reflect the contractile properties of the triceps surae muscles, composed of relatively slow soleus (SOL) and fast medial gastrocnemius (MG), during experimentally induced hypothermia condition. In eight male subjects, lying in prone position, supramaximal single twitch and repetitive electrical stimulations at 10 Hz were applied at the intramuscular temperatures of control (34 degrees C), 15, 20, and 25 degrees C, respectively. The hypothermia induced substantial reduction in muscle contractile properties, e.g. prolonged twitch contraction and half relaxation times, resulted in a highly significant reduction in the fluctuation of force signal during the repetitive stimulations. These changes were almost mirrored by the similar and significant reductions in the MMG amplitude in both SOL and MG. Power spectrum analysis revealed that peak frequency components of MMG and fluctuation of force were almost matched with the applied stimulation frequencies, independent of the temperature condition. These results strongly suggest that MMG analysis could be employed to study muscle contractile properties varying across different physiological conditions.

α2 Isoform–specific activation of 5′adenosine monophosphate–activated protein kinase by 5-aminoimidazole-4-carboxamide-1-β-d-ribonucleoside at a physiological level activates glucose transport and increases glucose transporter 4 in mouse skeletal muscle

The purpose of this study was to elucidate the responses of the mechanomyogram (MMG) from two apparently different muscles (biceps brachii and soleus) during a sustained voluntary contraction at 50% maximum voluntary contraction. The MMG and surface electromyogram (EMG) were recorded from human biceps brachii and soleus during sustained elbow flexion and plantar flexion, respectively. Results indicated that the slope coefficient of rise in EMG amplitude as a function of time for the biceps was significantly greater than that for the soleus (P<0.001). On the contrary, the MMG amplitude of the biceps showed a significant increase during the initial phase of sustained contraction (P<0.05); however, when exhaustion was approached the amplitude declined significantly (P<0.05). In the soleus muscle the decrease in MMG amplitude toward exhaustion occurred to a much lesser extent than that observed in the biceps. This difference could be attributed to the nature of the fusion state of the underlying muscle fibers. That is, the great extent of fusion observed in the biceps may be as a result of a greater quantity of fatigable motor units. In addition, the absence of MMG reduction in the soleus would indicate the absence of fatigue-induced slowing of contractile machinery and/or the lack of full activation (tetanus) of muscle fibers even at the exhaustion phase of plantar flexion.