Tomohiro Kizuka

Muscular adaptations to combinations of high- and low-intensity resistance exercises.

Acute and long-term effects of resistance-training regimens with varied combinations of high- and low-intensity exercises were studied. Acute changes in the serum growth hormone (GH) concentration were initially measured after 3 types of regimens for knee extension exercise: a medium intensity (approximately 10 repetition maximum [RM]) short interset rest period (30 s) with progressively decreasing load (“hypertrophy type‘’); 5 sets of a high-intensity (90% of 1RM) and low-repetition exercise (“strength type‘’); and a single set of low-intensity and high-repetition exercise added immediately after the strength-type regimen (“combi-type‘’). Postexercise increases in serum GH concentration showed a significant regimen dependence: hypertrophy-type > combi-type > strength-type (p < 0.05, n = 8). Next, the long-term effects of periodized training protocols with the above regimens on muscular function were investigated. Male subjects (n = 16) were assigned to either hypertrophy/combi (HC) or hypertrophy/strength (HS) groups and performed leg press and extension exercises twice a week for 10 weeks. During the first 6 weeks, both groups used the hypertrophy-type regimen to gain muscular size. During the subsequent 4 weeks, HC and HS groups performed combi-type and strength-type regimens, respectively. Muscular strength, endurance, and cross sectional area (CSA) were examined after 2, 6, and 10 weeks. After the initial 6 weeks, no significant difference was seen in the percentage changes of all variables between the groups. After the subsequent 4 weeks, however, 1RM of leg press, maximal isokinetic strength, and muscular endurance of leg extension showed significantly (p < 0.05) larger increases in the HC group than in the HS group. In addition, increases in CSA after this period also tended to be larger in the HC group than in the HS group (p = 0.08). The results suggest that a combination of high- and low-intensity regimens is effective for optimizing the strength adaptation of muscle in a periodized training program.

Mental fatigue and impaired response processes: event-related brain potentials in a Go/NoGo task.

The effects of mental fatigue on the availability of cognitive resources and associated response-related processes were examined using event-related brain potentials. Subjects performed a Go/NoGo task for 60 min. Reaction time, number of errors, and mental fatigue scores all significantly increased with time spent on the task. The NoGo-P3 amplitude significantly decreased with time on task, but the Go-P3 amplitude was not modulated. The amplitude of error-related negativity (Ne/ERN) also decreased with time on task. These results indicate that mental fatigue attenuates resource allocation and error monitoring for NoGo stimuli. The Go- and NoGo-P3 latencies both increased with time on task, indicative of a delay in stimulus evaluation time due to mental fatigue. NoGo-N2 latency increased with time on task, but NoGo-N2 amplitude was not modulated. The amplitude of response-locked lateralized readiness potential (LRP) significantly decreased with time on task. Mental fatigue appears to slows down the time course of response inhibition, and impairs the intensity of response execution.

Enhancing effect of cerebral blood volume by mild exercise in healthy young men: A near-infrared spectroscopy study

A mechanism by which exercise improves brain function may be attributed to increase in cerebral blood volume (CBV) with physical activity. However, the exact exercise intensity that influences CBV is still uncertain. To clarify this issue, 10 healthy young male participants were asked to perform a graded cycling exercise to the point of exhaustion while their prefrontal cortex CBVs are being monitored using near-infrared spectroscopy. Overall responsive cerebral oxygenation showed a non-linear pattern with three distinct phases. The CBV-threshold (CBVT), an event where rapid oxygenation takes place, occurred at approximately 42% of the V O2max. The CBVT preceded the lactate threshold (LT), which was at approximately 55% of the V O2max. The V O2max was not predictive of the CBVT in among the subjects. Our results indicate that oxygenation of the prefrontal cortex increases during graded cycling even at exercise intensities below the LT, suggesting the potential role of mild exercise in enhancing CBV.

Kinesthetic illusory feeling induced by a finger movement movie effects on corticomotor excitability

The present study aimed to clarify whether a kinesthetic illusion arises in our experimental condition (visual stimulus) and whether corticomotor excitability changes in parallel with the kinesthetic illusion. The visual stimulus was a movie in which someone elses limb was being moved. The computer screen showing the movie was installed at an appropriate portion of the subjects forearm, so that the performers hand appeared as if it were the subjects hand (illusion). The experience of kinesthetic illusion under this condition was verified by interview using a visual analog scale. Healthy male subjects participated in this experiment. Transcranial magnetic stimulation was applied to induce motor-evoked potential (MEP) from the first dorsal interosseous and abductor digiti minimi muscle. Each subject was instructed to watch the same computer display shown as in the illusion, with his own stationary hand in full view (non-illusion) and to watch a display of non-biological movement (moving text) (sham) as the control conditions. The present results showed significant facilitation of MEP under the illusion compared with the control conditions for the index finger abducting in the movie, although not for adducting. MEP in the abductor digiti minimi showed no change during either abduction or adduction of the little finger. The present study demonstrated that an illusion of self-motion can be created by a video of a moving abstract index finger, and inputs to the corticomotor pathways during the self-motion illusion facilitated the corticomotor excitability. The excitatory effect of the illusion depended on the movement direction of the index finger.

Differences in EMG Activity in Scapular Plane Abduction under Variable Arm Positions and Loading Conditions

PURPOSE The present study was performed to investigate the activities of four shoulder muscles-the supraspinatus, the middle deltoid, the infraspinatus, and the upper trapezius-in scapular plane abduction in various exercise conditions. METHODS Eight male subjects (mean +/- SD: 23.4 +/- 1.3 yr) with an asymptomatic nondominant left shoulder participated in this study. Each subject performed scapular plane abduction with humeral external rotation (full can position) and with humeral internal rotation (empty can position), producing constant target torques of 4 and 12 N.m, respectively. In addition, the subjects performed each exercise in the supine position with the limb supported by straps. Electromyogram (EMG) was recorded with intramuscular electrodes at the supraspinatus and infraspinatus, and with surface electrodes placed at the middle deltoid and upper trapezius. The EMG activity (RMS) of each muscle was normalized according to the highest EMG activity (100% MVC) during a maximum manual muscle test for the corresponding muscle (% MVC). RESULTS EMG activity of the supraspinatus was significantly greater than those of the other shoulder muscles in the full can position from 10-20 degrees to 50-60 degrees arcs with a target torque of 4 N.m (P < 0.05). In contrast, the supraspinatus and middle deltoid showed similar EMG activities under other exercise conditions. CONCLUSIONS These results suggest that there is an exercise condition that induces greater activity of the supraspinatus in scapular plane abduction.

A comparison of stimulus synchronous activity in the primary motor cortices of athletes and non-athletes.

In this study, we measured primary motor cortex (MI) activity during a reaction time task to examine the appearance of MI activity that synchronized with the stimulus presentation (stimulus synchronous MI activity, SSMA). Because brain activity was expected to be enhanced by the repetitive/extensive activation, we hypothesized that the SSMA would be more clearly observable in athletes who were trained to perform reactive movements than in non-athletes. MI activity was measured in ten athletes and ten non-athletes by magnetoencephalography. The tasks were a simple reaction task and a Go/Nogo reaction task in which the subjects were asked to abduct their right index fingers in response to a visual stimulus. The Go/Nogo reaction time task was adopted to confirm the presence of the SSMA, because the MI activity in response to a Nogo stimulus did not overlap with the MI activity that was synchronous with the execution of the movement. The results show that the SSMA was clearly apparent in the athlete group (9/10). In the non-athlete group, however, only three subjects showed the SSMA (3/10). Moreover, the MI activity of the athletes tended to be larger than that of the non-athletes, even though the athletes did not specifically practice these index finger movements during their daily training. We concluded that long-term physical training promotes MI activity and the effects of reactive task repetition were more clearly apparent in the MI activity of the athletes.

Automatic and imperative motor activations in stimulus-response compatibility: magnetoencephalographic analysis of upper and lower limbs.

The stimulus–response (S–R) compatibility effect refers to the difference in performance due to the spatial S–R relationship in choice reaction time. We investigated the mechanism of neural activities in S–R compatibility at the level of the primary motor cortices for upper and lower limbs responses using magnetoencephalography (MEG). In the S–R compatible task, subjects were required to respond on the same side of the stimulus light using either an upper or lower limb. In the incompatible task, subjects were required to respond in the reverse manner. Premotor times of upper and lower limbs were faster for the compatible response than for the incompatible response. The neuromagnetic brain activities related to response execution were estimated using a multi-dipole model. Stimulus-locked MEG indicated that the current moments of motor dipoles for both effectors occurred bilaterally and reached the first peak at a constant delay irrespective of whether the task was compatible or incompatible. This indicates that the neural activation of the primary motor cortex is automatically synchronized with the stimulus onset. Response-locked MEG showed that the peak current moment of the motor dipole contralateral to the response was stronger for the compatible task than for the incompatible one regardless of whether the responses were made using the upper or lower limbs. The MEG results suggest that automatic motor activation facilitates imperative motor activation for a compatible response, whereas it is not sufficient to prime imperative motor activation for an incompatible response.

Increased c-fos gene expression in alpha motoneurons in rat loaded hindlimb muscles with inclined locomotion.

The potential usefulness of c-fos gene expression as an indicator of the activity level of spinal alpha motoneurons was examined in loaded locomotive rats. The motor pools of the plantaris (PL) and soleus muscles (SOL), mainly composed respectively of fast- and slow-twitch muscle fibers, were investigated in rats under locomotion at 25 m/min on a 20% incline. We first labeled motoneurons with a retrograde tracer, Nuclear Yellow (NY), and then quantified the c-fos mRNA expression level in the NY-labeled alpha motoneurons by means of in situ hybridization. Electromyographic (EMG) activities were also recorded. The c-fos expression level per alpha motoneuron showed a greater increase in the PL (75%) than in the SOL motor pool (38%). EMG activities also showed a greater increase in the PL (159%) than in the SOL (43%). Taken together, these results suggest that c-fos expression levels in alpha motoneurons are associated with the activity levels of their corresponding muscle. This cytochemical method for identifying the c-fos expression level has potential for use as a tool for estimating the activity level of large populations of alpha motoneurons in unrestricted animals.

Bilateral cerebral activity for unilateral foot movement revealed by whole-head magnetoencephalography

The primary motor cortices controlling foot movement are located on opposite sides of the longitudinal fissure. As a separation of closely located activity sources is not successful, the possibility of bilateral activation for lower limb movement remains undetermined. We therefore examined cerebral activity during unilateral foot movement to investigate the possibility of bilateral activation of primary foot motor cortices. Self-paced foot movement and finger movement (for comparison) were performed on ten subjects. Brain magnetic fields were recorded using a 64-channel whole-cortex magnetoencephalography (MEG) system. Brain activities were identified using 1- to 3-dipole models. Results evaluating finger movement were similar to previous reports. Equivalent current dipoles (ECDs) for foot movements were estimated in the primary foot motor and sensory regions. Sensory activity was always localized to the contralateral hemisphere. Motor activity was estimated by one ECD, but the laterality differed between subjects. Additional activity was discovered together with the primary motor activity, localized around the precentral sulcus. In contrast to consistent results of primary sensory activity, the variation of laterality of the foot primary motor ECD can be explained with a cancellation model, in which the magnetic fields generated from two closely spaced ECDs overlap to cancel each other out. Consequently, activation of the primary foot motor cortices was determined to be bilateral. Furthermore, it was estimated that additional activity may occur in the premotor area. This work suggests not only the bilateral activation of the primary foot motor cortices but also the possibility of a contribution of the premotor area.

Stimulus–Response Compatibility and Response Preparation: Effects on Motor Component of Information Processing for Upper and Lower Limb Responses

The effects of stimulus-response compatibility and response preparation on the motor component of the information processing system were investigated by analyzing the fractionated reaction time for the upper and lower limbs. The reaction time was divided into two periods with respect to the onset of electromyographic activity, premotor and motor times. The response preparation was manipulated by the probability that the locations of the precue and subsequent imperative stimulus corresponded. On a stimulus-response compatible task, subjects were required to release a key on the same side as an imperative stimulus, irrespective of the precued side. On an incompatible task, subjects were required to act in the reverse manner. The upper and lower limb responses were measured during both tasks. A repeated-measures design was used with 12 male university students. Analysis of the reaction and premotor times indicated that the stimulus-response compatibility effect became larger as response preparation decreased. The analysis of motor time yielded significant interactions between stimulus-response compatibility and limb and between response preparation and limb. These findings indicated that the motor component of information processing for the lower limb response is affected by both stimulus-response compatibility and response preparation.