Daisuke Takeshita

Mechanism of quadriceps femoris muscle weakness in patients with anterior cruciate ligament reconstruction

The purpose of this study was to investigate gamma loop function in the quadriceps femoris muscle in patients who with less than 6 month‐history of anterior cruciate ligament (ACL) reconstruction. For this purpose, we compared the response to vibration stimulation in 10 patients with ACL repair and 12 normal healthy subjects, by measuring the maximal voluntary isometric contraction (MVC) and integrated electromyograms (I‐EMG) of the quadriceps muscles. Pre‐vibration data were obtained from each subject by measuring the MVC of the knee extension and the I‐EMG from the vastus medialis, vastus lateralis, and rectus femoris muscles. Vibration stimulation was applied to the infrapatellar tendons, followed immediately by repeating the MVC and I‐EMG recording. Prolonged vibration resulted in a significant decrease of both MVC and I‐EMG in the control group. In contrast, the same stimulus failed to elicit changes in ACL‐repair group. Our results suggest the presence of abnormal gamma loop function in the quadriceps femoris muscle of patients with ACL repair, which may explain the muscle weakness often described in such patients.

Length Change of Human Gastrocnemius Aponeurosis and Tendon during Passive Joint Motion

The extent of elongation and slackness of aponeurosis and tendon, and muscle fiber length of human medial gastrocnemius muscle are determined in vivo using ultrasonography. The ankle joint is passively moved at 5°/s within the joint range of –36 to 7° (0° = neutral anatomic position; positive values for dorsiflexion) by a dynamometer while the length change of the aponeurosis and tendon is determined using ultrasonography (n = 8 men). Strain is calculated as the length change relative to the reference length of aponeurosis and tendon when the passive joint moment is 0. Elongation (positive strain values) of aponeurosis and tendon at 7° are 2.1 ± 1.1 and 2.4 ± 1.0%, respectively. The extent of slackness (negative strain values) of aponeurosis and tendon at –36° are –1.8 ± 1.1 and –3.5 ± 1.6%, respectively, and there is a significant difference between them (p < 0.05). This may be related to the existence of muscle fibers that attach to the aponeurosis over its whole length and do not allow it to fold. The results indicate that the length change of aponeurosis and tendon of medial gastrocnemius muscle occurs over the range of ankle joint positions even during passive joint motions.

A comparison of the mechanical effect of arm swing and countermovement on the lower extremities in vertical jumping.

The purposes of this study were to quantify and compare how arm swing and countermovement affect lower extremity torque and work during vertical jumping and to gain insight into the mechanisms that enable the arm swing and countermovement to increase jump height. Five participants maximally performed two types of vertical squat jumps with (SJA) and without (SJ) an arm swing and two types of countermovement vertical jumps with (CJA) and without (CJ) an arm swing. The participants jumped from a force platform and all performances were videotaped with a high-speed video camera (200 Hz). Jump heights, joint torques and work were calculated by combining kinematic and kinetic data. It was found that of the four jumping conditions, the participants jumped highest when they used an arm swing with countermovement (i.e., CJA). The increase of the countermovement jump height with an arm swing is the result of the increase of the lower extremity work. In the hip joint, the increase in torque caused by the countermovement predominantly occurred at the beginning of the propulsion phase, while the increase in torque caused by the arm swing occurred in the rest of the propulsion phase. A key finding of our study is that arm swing and countermovement have independent effects on lower extremity work, and their effects are additive in CJA to produce greater jump height.

Imaging cortical electrical stimulation in vivo : fast intrinsic optical signal versus voltage-sensitive dyes

We applied high-temporal-resolution optical imaging utilizing both the fast intrinsic optical signal (fIOS) and voltage-sensitive dyes (VSDs) to observe the spatiotemporal characteristics of rat somatosensory cortex during electrical stimulation. We find that changes in both the fIOS and VSD signals occur rapidly (<30 ms) after the stimulus is applied, suggesting that both membrane depolarization and transmembrane ion movement occur shortly after the stimulus, preceding the more gradual physiological changes in oxygen consumption revealed by the slower component of the intrinsic optical signal. We find that the VSD signal spreads through a much larger area of cortex than the fIOS.

In vivo Mechanical Properties of Proximal and Distal Aponeuroses in Human Tibialis Anterior Muscle

Load-strain characteristics of distal (deep) and proximal (superficial) aponeuroses were determined in vivo for human tibialis anterior muscle (TA). Seven male subjects exerted isometric dorsiflexion torque from relaxation to voluntary maximum while elongation of both aponeuroses of TA was determined by ultrasonography. Two positions (end of the muscle belly and a proximal part) and one position (distal part) were scanned for the deep and superficial aponeuroses, respectively, and tendinous movements of the respective positions were determined. Based on the tendinous movements, elongation of each aponeurosis was determined. Both aponeuroses were elongated significantly, and there was no significant difference in strain between the deep (3.3 ± 0.8%) and superficial (3.0 ± 0.5%) aponeuroses. In addition, there was a significant linear relationship between strain of deep and superficial aponeuroses. It was suggested that both aponeuroses similarly act as an elastic component in pennate muscles.

Synchronization analysis of voltage-sensitive dye imaging during focal seizures in the rat neocortex

Seizures are often assumed to result from an excess of synchronized neural activity. However, various recent studies have suggested that this is not necessarily the case. We investigate synchronization during focal neocortical seizures induced by injection of 4-aminopyridine (4AP) in the rat neocortex in vivo. Neocortical activity is monitored by field potential recording and by the fluorescence of the voltage-sensitive dye RH-1691. After removal of artifacts, the voltage-sensitive dye (VSD) signal is analyzed using the nonlinear dynamics-based technique of stochastic phase synchronization in order to determine the degree of synchronization within the neocortex during the development and spread of each seizure event. Results show a large, statistically significant increase in synchronization during seizure activity. Synchrony is typically greater between closer pixel pairs during a seizure event; the entire seizure region is synchronized almost exactly in phase. This study represents, to our knowledge, the first application of synchronization analysis methods to mammalian VSD imaging in vivo. Our observations indicate a clear increase in synchronization in this model of focal neocortical seizures across a large area of the neocortex; a sharp increase in synchronization during seizure events was observed in all 37 seizures imaged. The results are consistent with a recent computational study which simulates the effect of 4AP in a neocortical neuron model.

Higher order approximation of isochrons

Phase reduction is a commonly used techinque for analysing stable oscillators, particularly in studies concerning synchronization and phase lock of a network of oscillators. In a widely used numerical approach for obtaining phase reduction of a single oscillator, one needs to obtain the gradient of the phase function, which essentially provides a linear approximation of the local isochrons. In this paper, we extend the method for obtaining partial derivatives of the phase function to arbitrary order, providing higher order approximations of the local isochrons. In particular, our method in order 2 can be applied to the study of dynamics of a stable oscillator subjected to stochastic perturbations, a topic that will be discussed in a future paper. We use the Stuart–Landau oscillator to illustrate the method in order 2.

Analyzing spike trains with circular statistics

In neuroscience, specifically electrophysiology, it is common to replace a measured sequence of action potentials or spike trains with delta functions prior to analysis. We apply a method called circular statistics to a time series of delta functions and show that the method is equivalent to the power spectrum. This technique allows us to easily visualize the idea of the power spectrum of spike trains and easily reveals oscillatory and stochastic behavior. We provide several illustrations of the method and an example suitable for students, and suggest that the method might be useful for courses in introductory biophysics and neuroscience.