Relationship between motor corticospinal excitability and ventilatory response during intense exercise.

PURPOSE: Effort sense has been suggested to be involved in the hyperventilatory response during intense exercise (IE). However, the mechanism by which effort sense induces an increase in ventilation during IE has not been fully elucidated. The aim of this study was to determine the relationship between effort-mediated ventilatory response and corticospinal excitability of lower limb muscle during IE. METHODS: Eight subjects performed 3 min of cycling exercise at 75-85 % of maximum workload twice (IE1st and IE2nd). IE2nd was performed after 60 min of resting recovery following 45 min of submaximal cycling exercise at the workload corresponding to ventilatory threshold. Vastus lateralis muscle response to transcranial magnetic stimulation of the motor cortex (motor evoked potentials, MEPs), effort sense of legs (ESL, Borg 0-10 scale), and ventilatory response were measured during the two IEs. RESULTS: The slope of ventilation (l/min) against CO2 output (l/min) during IE2nd (28.0 ± 5.6) was significantly greater than that (25.1 ± 5.5) during IE1st. Mean ESL during IE was significantly higher in IE2nd (5.25 ± 0.89) than in IE1st (4.67 ± 0.62). Mean MEP (normalized to maximal M-wave) during IE was significantly lower in IE2nd (66 ± 22 %) than in IE1st (77 ± 24 %). The difference in mean ESL between the two IEs was significantly (p < 0.05, r = -0.82) correlated with the difference in mean MEP between the two IEs. CONCLUSIONS: The findings suggest that effort-mediated hyperventilatory response to IE may be associated with a decrease in corticospinal excitability of exercising muscle.

Relationship between effort sense and ventilatory response to intense exercise performed with reduced muscle glycogen.

The purpose of the present study was to examine the effects of muscle glycogen reduction on surface electromyogram (EMG) activity and effort sense and ventilatory responses to intense exercise (IE). Eight subjects performed an IE test in which IE [100-105% of peak O(2) uptake ([Formula: see text]), 2 min] was repeated three times (IE(1st), IE(2nd) and IE(3rd)) at 100-120-min intervals. Each interval consisted of 20-min passive recovery, 40-min submaximal exercise at ventilatory threshold intensity (51.5 ± 2.7% of [Formula: see text]), and a further resting recovery for 40-60 min. Blood pH during IE and subsequent 20-min recovery was significantly higher in the IE(3rd) than in the IE(1st) (P < 0.05). Effort sense of legs during IE was significantly higher in the IE(3rd) than in the IE(1st) and IE(2nd). Integrated EMG (IEMG) measured in the vastus lateralis during IE was significantly lower in the IE(3rd) than in the IE(1st). In contrast, mean power frequency of the EMG was significantly higher in the IE(2nd) and the IE(3rd) than in the IE(1st). Ventilation ([Formula: see text]) in the IE(3rd) was significantly higher than that in the IE(1st) during IE and the first 60 s after the end of IE. These results suggest that ventilatory response to IE is independent of metabolic acidosis and at least partly associated with effort sense elicited by recruitment of type II fibers.

Effects of sodium bicarbonate ingestion on EMG, effort sense and ventilatory response during intense exercise and subsequent active recovery.

To determine whether post-exercise ventilation is related to decrease in blood pH and also whether post-exercise ventilation, associated or not with decreased blood pH, involves an increase in central motor command during exercise, we examined the effects of NaHCO(3) ingestion on the ventilatory response ([Formula: see text]E), integrated electromyogram (iEMG) and effort sense of legs (ESL) during intense exercise (IE) and subsequent active recovery. Subjects performed two IE tests (105-110% of maximal work rate, 2 min) after ingestion of NaHCO(3) or CaCO(3). Subjects performed light load exercise (20 W) before and after IE for 6 min and 30 min, respectively. Although there was a significant difference in blood pH between the two conditions during and after IE, [Formula: see text]E, iEMG and ESL were similar. iEMG returned to the pre-IE level immediately after the end of IE, while ESL showed slow recovery. [Formula: see text]E decreased rapidly until about 50 s after the end of IE (fast phase) and then showed a slow recovery kinetics (slow phase). The ventilatory responses during the fast phase and during the slow phase were correlated with ESL at the end of IE and from 3 min after the end of IE, respectively. Moreover, there was no significant difference in the slopes and intercepts of regression lines between [Formula: see text]E and ESL under the two conditions in both phases. These results suggest that the ventilatory response after IE is associated with effort sense indirectly-elicited by central motor command, but the effort sense-mediated response is not affected by blood pH.

Ventilatory response to moderate incremental exercise performed 24 h after resistance exercise with concentric and eccentric contractions.

In order to test our hypothesis that muscle condition has an effect on the cognition of self-motion and consequently on the ventilatory response during exercise, six healthy subjects performed a moderate incremental exercise test (IET) on a cycle ergometer under two conditions [resistance exercise condition (REC) and control condition (CC)]. In the REC, resistance exercise (30 incline leg presses) was conducted during two sessions scheduled at 48 and then 24 h prior to the IET. For the CC, the subjects were instructed to refrain from participating in strenuous exercise for a period of 2 days prior to the IET. In the IET, the workload was increased from 78 to 118 watts in steps of 8 watts every 3 min. Although the ventilatory response during the IET was significantly higher in the REC than in the CC, there were no significant differences in cognitive indexes (RPE and awareness of change in workload) between the two conditions. In addition, the magnitude of muscle soreness was significantly higher in the REC than in the CC. However, the level of soreness in the REC was very low, and there were no significant differences in blood lactate concentration and integrated EMG between the two conditions. These results suggest that a change in peripheral neural reflex is the primary cause of increased ventilatory response to moderate exercise after resistance exercise, although the role of a cognitive element cannot be absolutely excluded.

Voluntary breathing increases corticospinal excitability of lower limb muscle during isometric contraction.

The aim of the present study was to determine the effects of voluntary breathing on corticospinal excitability of a leg muscle during isometric contraction. Seven subjects performed 5-s isometric knee extension at the intensity of 10% of maximal voluntary contraction (10% MVC). During the 10% MVC, the subjects were instructed to breath normally (NORM) or to inhale (IN) or exhale (OUT) once as fast as possible. Motor-evoked potentials (MEPs) induced by transcranialmagnetic stimulation in the right vastus lateralis (VL) during the 10% MVC were recorded and compared during the three breathing tasks. MEPs in IN and OUT were significantly higher than that in NORM. Effort sense of breathing was significantly higher in IN and OUT than in NORM. There was a significant positive correlation between MEP and effort sense of breathing. These results suggest that activation of the breathing-associated cortical areas with voluntary breathing is involved in the increase in corticospinal excitability of the VL during isometric contraction.

Effects of awareness of change in load on ventilatory response during moderate exercise.

This study was designed to determine whether awareness of change in load alters ventilatory response during moderate exercise. Subjects performed two incremental exercise protocols on a cycle ergometer. The load was increased from 1.0 to 1.5kp in steps of 0.1kp every 3min. Subjects were provided true information about the load in the control protocol and untrue information that the load would remain constant in the deception protocol. Slope of ventilation against CO2 output was significantly lower in the deception protocol than control protocol. Integrated EMG (iEMG) and ratings of perceived exertion (RPE) were similar between the two protocols, but awareness of change in load was significantly attenuated by the deception protocol. However, there was no temporal coincidence between awareness and actual change in load. These results suggest that ventilatory response during moderate exercise depends not so much on RPE but mainly on awareness or attention that is closely connected to information detection.