Inami, T, Nakagawa, K, Yonezu, T, Fukano, M, Higashihara, A, Iizuka, S, Abe, T, and Narita, T. Tracking of time-dependent changes in muscle hardness after a full marathon. J Strength Cond Res 33(12): 3431-3437, 2019-We sought to identify changes in individual muscle hardness after a full marathon and to track time-dependent changes using ultrasound strain elastography (SE). Twenty-one collegiate marathon runners were recruited. Muscle hardness (i.e., strain ratio, SR) was measured using SE for the rectus femoris (RF), vastus lateralis (VL), biceps femoris (BF) long head, tibialis anterior (TA), gastrocnemius medial (GM) head, and soleus (SOL) muscles at the following time points: pre (PRE), immediately post (POST), day-1 (D1), day-3 (D3), and day-8 (D8), after a full marathon. We found that the SR decreased after the full marathon (i.e., the muscle became harder), and that the lowest SR across all measured muscles was observed on D1. Although there was no difference in the magnitude of change in SR between the muscles of the thigh, that of the MG and SOL were significantly larger than that of the TA. Muscle hardness in the vastus lateralis, biceps femoris, and SOL recovered at D8 (i.e., nonsignificant difference from PRE), whereas recovery of rectus femoris and gastrocnemius medial hardness at D8 was not observed. Thus, the degree of change in muscle hardness does not occur uniformly within the lower extremity muscles. In particular, changes in muscle hardness of the TA after a full marathon are small compared with other muscles and time-dependent changes in each muscle vary during recovery. The features of muscle hardness identified in this study will be useful for coaches when mentoring runners on proper forms and for training advisers and therapists who seek to address deficiencies in running.

The relative-salience hypothesis has been proposed as a possible explanation for the stability of bimanual coordination. This explanation proceeds from a psychological viewpoint and is based on the following tenets: (1) cyclic joint motions involving two movements are conceived of as a unified event, (2) if a “single” point in each movement is seen as the most salient, the salient points of the two movements prefer to go together, and (3) in other cases, a unified event will be constrained by movement direction. In this investigation, we examined whether the relative-salience hypothesis could predict the type of constraint (i.e., action coupling vs movement direction) for various bimanual coordination movements. Participants performed six different joint movements in synchrony with metronome beats. Both index finger flexion/extension and forearm pronation/supination had a “single” salient point (JMsingleSP), the others had “two” salient points (JMtwoSP). Then, we applied the relative-salience hypothesis to four bimanual coordinations. The coupling of simultaneous forearm pronation was more stable than alternate pronation. Similarly, the coupling of finger flexion and forearm pronation was more stable than that of finger flexion and forearm supination. For the coordination of radial flexion/ulnar flexion and index finger flexion/extension as well as forearm pronation/supination and radial flexion/ulnar flexion, symmetric movements were more stable than asymmetric movements. The results indicated that the stability of bimanual coordination was predominantly constrained by coupling of salient points when using two JMsingleSP and it was predominantly constrained by movement direction when coordinating JMsingleSP and JMtwoSP. Thus, the relative-salience hypothesis was supported.

The effects of motor imagery on spinal reflexes such as the H-reflex are unclear. One reason for this is that the muscles that can be used to record spinal reflexes are limited to traditional evoking methods Recently, transcutaneous spinal cord stimulation has been used for inducing spinal reflexes from multiple muscles and we aimed to examine the effect of motor imagery on spinal reflexes from multiple muscles. Spinal reflexes evoked by transcutaneous spinal cord stimulation were recorded from six muscles from lower limbs during motor imagery of right wrist extension and ankle plantarflexion with maximum isometric contraction. During both imaginary tasks, facilitation of spinal reflexes was detected in the ankle ipsilateral plantarflexor and dorsiflexor muscles, but not in thigh, toe or contralateral lower limb muscles. These results suggest that motor imagery of isometric contraction facilitates spinal reflex excitability in muscles of the ipsilateral lower leg and the facilitation does not correspond to the imaginary involved muscles.

We recently reported that wearing unstable rocker shoes (Masai Barefoot Technology: MBT) may enhance recovery from marathon race-induced fatigue. However, this earlier study only utilized a questionnaire. In this study, we evaluated MBT utilizing objective physiological measures of recovery from marathon-induced muscle damages. Twenty-five university student novice runners were divided into two groups. After running a full marathon, one group wore MBT shoes (MBT group), and the control group (CON) wore ordinary shoes daily for 1 week following the race. We measured maximal isometric joint torque, muscle hardness (real time tissue elastography of the strain ratio) in the lower limb muscles before, immediately after, and 1, 3, and 8 days following the marathon. We calculated the magnitude of recovery by observing the difference in each value between the first measurement and the latter measurements. Results showed that isometric torques in knee flexion recovered at the first day after the race in the MBT group while it did not recover even at the eighth day in the CON group. Muscle hardness in the gastrocnemius and vastus lateralis showed enhanced recovery in the MBT group in comparison with the CON group. Also for muscle hardness in the tibialis anterior and biceps femoris, the timing of recovery was delayed in the CON group. In conclusion, wearing MBT shoes enhanced recovery in lower leg and thigh muscles from muscle damage induced by marathon running.

The object of this study was to clarify the effects of foot muscle relaxation on activity in the primary motor cortex (M1) of the hand area. Subjects were asked to volitionally relax the right foot from sustained contraction of either the dorsiflexor (tibialis anterior
TA relaxation) or plantarflexor (soleus
SOL relaxation) in response to an auditory stimulus. Single- and paired-pulse transcranial magnetic stimulation (TMS) was delivered to the hand area of the left M1 at different time intervals before and after the onset of TA or SOL relaxation. Motor evoked potentials (MEPs) were recorded from the right extensor carpi radialis (ECR) and flexor carpi radialis (FCR). MEP amplitudes of ECR and FCR caused by single-pulse TMS temporarily decreased after TA and SOL relaxation onset, respectively, d as compared with those of the resting control. Furthermore, short-interval intracortical inhibition (SICI) of ECR evaluated with paired-pulse TMS temporarily increased after TA relaxation onset. Our findings indicate that muscle relaxation of the dorsiflexor reduced corticospinal excitability of the ipsilateral hand muscles. This is most likely caused by an increase in intracortical inhibition.

&nbsp;&nbsp;The aim of this study was to clarify the relationship between maximal running speed, step frequency, step frequency index, step length, step length index, foot contact time, and aerial time during sprinting in elementary school children. The participants were 335 girls and 352 boys (age: 6 to 12 years) who ran a 50-m sprint race as part of their school fitness test in 2013. Their maximal running speed, step frequency, and step length were calculated from images captured by video cameras (60 frames/second) located at the sides of the lanes. Contact time and aerial time over the distance from 20 m to 30 m were calculated from images captured by high-speed video cameras (300 frames/second) located at the side of the 25-m mark for the lanes. Two-way ANOVA with the Games-Howell procedure was used to test differences among all grades. Two-way ANCOVA was used to test interaction and the main effect of gender and grade on maximal running speed. The Pearson product-moment correlation coefficient (r) and partial correlation coefficient (pr) were calculated to analyze the relationship between maximal running speed, step frequency, stride length, foot contact time, and aerial time. Step length (which was strongly correlated with maximal running speed) showed a strong partial correlation (controlled for age) with maximal running speed. Therefore, it is suggested that step length contributes to not only the increase in running speed with growth, but also individual differences in running speed among the children at the same age. There were slight tendencies for step frequency and foot contact time to increase with growth. However, these factors showed a significant partial correlation (controlled for age) with running speed. Therefore, it was suggested that these factors contribute to individual differences in running speed. The absence of a negative impact of a shorter foot contact time on stride length suggests that the running performance of school children could be improved by decreasing their foot contact time. In order to establish effective methods for augmenting the development of running ability in children, it will be necessary to consider foot contact time and aerial time in addition to step frequency and step length.<br>

We investigated how corticospinal excitability of the resting digit muscles was modulated by the digit movement in the ipsilateral limb. Subjects performed cyclical extension-flexion movements of either the right toes or fingers. To determine whether corticospinal excitability of the resting digit muscles was modulated on the basis of movement direction or action coupling between ipsilateral digits, the right forearm was maintained in either the pronated or supinated position. During the movement, the motor evoked potential (MEP) elicited by transcranial magnetic stimulation (TMS) was measured from either the resting right finger extensor and flexor, or toe extensor and flexor. For both finger and toe muscles, independent of forearm position. MEP amplitude of the flexor was greater during ipsilateral digit flexion as compared to extension, and MEP amplitude of the extensor was greater during ipsilateral digit extension as compared to flexion. An exception was that MEP amplitude of the toe flexor with the supinated forearm did not differ between during finger extension and flexion. These findings suggest that digit movement modulates corticospinal excitability of the digits of the ipsilateral limb such that the same action is preferred. Our results provide evidence for a better understanding of neural interactions between ipsilateral limbs, and may thus contribute to neurorehabilitation after a stroke or incomplete spinal cord injury.

Rhythmic two-limb coordinated movements in the sagittal plane are variable and inaccurate when the movements are in the opposite direction as compared with those in the same direction (directional constraint). The magnitude of directional constraint depends on the particular limb combination. It is prominent in ipsilateral hand-foot coordination, but minimal in bimanual hand coordination. The reason for such differences remains unclear. In this study, we investigated the possible mechanisms underlying the production of the difference that depend on limb combination. Subjects performed two-limb rhythmic coordinated movements either in the same or in the opposite direction for three separate limb combinations (bilateral hands, contralateral hand and foot, and ipsilateral hand and foot). For each combination two different tasks were performed. In the first condition, subjects actively moved two limbs (active condition). Second, subjects actively moved one limb in coordination with a passively moved limb (passive condition). In the active condition, the directional constraint was dependent upon the limb combination, as reported in previous studies
the directional constraint was quite prominent in ipsilateral combinations, intermediate in contralateral combinations, and minimal for bilateral combination. However, differences in the directional constraint did not depend on limb combination for any combination in the passive conditions which apparently utilized closed-loop control. In other word, the difference depending on limb combination disappeared when control strategies become uniformly closed-loop. Thus, we speculate that the control strategy utilized depends on limb combination in the active condition. Additionally, different mechanisms other than closed-loop control also would have influence depending on the particular limb combination. This may result in differences in performance depending upon the limb combination.

In performing simultaneous rhythmic movements of the ipsilateral hand and foot, there are differences in the level of stability between same directional (stable) and opposite directional (unstable) movements. This is the directional constraint. In this study, we investigated three factors (“interaction in efferent process,” “interaction of afferent signals,” and “error correction”) proposed to underlie for the directional constraint. We compared the performance of three tasks: (1) coordination of actively moved ipsilateral hand and foot, (2) active hand movement in coordination with passively moved foot, (3) active hand movement not coordinated with a passively moved foot. In each task, both same and opposite directional movements were executed. There was no difference between performance estimated with success rate for the first and second task. The directional constraint appeared in both tasks. Thus, the interaction in efferent processes, which was shown to be responsible for the directional constraint in bimanual coordination, was not involved with the directional constraint of ipsilateral hand–foot coordination. The directional constraint did not appear in the third task, which suggested that “interaction of afferent signals” also had no contribution. These results indicated that “error correction” must be the most critical of these factors for mediating the directional constraint in ipsilateral hand–foot coordinated movements.

Our previous studies showed that corticospinal excitability during imagery of squeezing a foam ball was enhanced by somatosensory input generated by passively holding the ball. In the present study, using the same experimental model, we investigated whether corticospinal excitability was influenced by holding the object with the hand opposite to the imagined hand. Corticospinal excitability was assessed by monitoring motor evoked potentials (MEPs) in the first dorsal interosseous muscle following transcranial magnetic stimulation over the motor cortex during motor imagery. Subjects were asked to imagine squeezing a foam ball with the right hand (experiment 1) or the left hand (experiment 2), while either holding nothing (Null condition), a ball in the right hand (Right condition) or a ball in the left hand (Left condition). The MEPs amplitude during motor imagery was increased, only when the holding hand and the imagined hand were on the same side. These results suggest that performance improvement and rehabilitation exercises will be more effective when somatosensory stimulation and motor imagery are done on the same side. (C) 2012 Elsevier Ireland Ltd. All rights reserved.

We investigated whether corticospinal excitability during motor imagery of actions (the power or the pincer grip) with objects was influenced by actually touching objects (tactile input) and by the congruency of posture with the imagined action (proprioceptive input). Corticospinal excitability was assessed by monitoring motor evoked potentials (MEPs) in the first dorsal interosseous following transcranial magnetic stimulation over the motor cortex. MEPs were recorded during imagery of the power grip of a larger-sized ball (7 cm) or the pincer grip of a smaller-sized ball (3 cm) with or without passively holding the larger-sized ball with the holding posture or the smaller-sized ball with the pinching posture. During imagery of the power grip, MEPs amplitude was increased only while the actual posture was the same as the imagined action (the holding posture). On the other hand, during imagery of the pincer grip while touching the ball, MEPs amplitude was enhanced in both postures. To examine the pure effect of touching (tactile input), we recorded MEPs during imagery of the power and pincer grip while touching various areas of an open palm with a flat foam pad. The MEPs amplitude was not affected by the palmer touching. These findings suggest that corticospinal excitability during imagery with an object is modulated by actually touching an object through the combination of tactile and proprioceptive inputs.