Hitoshi Shimojo

Early phase adaptations of muscle use and strength to isokinetic training

The purpose of this study was to investigate the effect of short periods of isokinetic resistance training on muscle use and strength. Seven men trained the right quadriceps femoris muscles (QF) 9 d for 2 wk using 10 sets of 5 knee extensions each day. Isometric and isokinetic torques of QF were measured at six angular velocities. Cross-sectional areas (CSA) of QF were determined from axial images using magnetic resonance imaging (MRI). Transverse relaxation time (T2) and activated area of QF, which represented the area greater than the mean resting T2 + ISD in MR[pixels, were calculated at rest and immediately after repetitive isokinetic knee extensions based on T2-weighted MR images. Muscle fiber types, fiber area, and phosphofructokinase (PFK) activities were determined from biopsies of the vastus lateralis muscle. No changes were found in CSA of QF, muscle fiber types, fiber area, and PFK activities after the training. Isometric and isokinetic peak torques at 60-240 degrees x s(-1) and relative area of QF activated by knee extensions increased significantly after the training. These results suggest that muscle strength increases after short periods of isokinetic resistance training without muscle hypertrophy would be due to increased muscle contractile activity.

Collagen hybridization with poly(l-lactic acid) braid promotes ligament cell migration

Abstract The purpose of this study is to evaluate the cellular response to a poly( l -lactic acid) (PLLA)-collagen hybrid scaffold for ligament regeneration based on tissue engineering. A three-dimensional (four-axis) braid with a diameter of 2.5 mm was made from PLLA filaments. The braid was further hybridized with bovine type I collagen to prepare the PLLA-collagen hybrid braid. Cellular responses of ligament cells to the PLLA and PLLA-collagen hybrid braids were evaluated both in vitro and in vivo. More cells and more homogeneous cell distribution were observed in vitro in the hybrid braid than in the PLLA braid. More fibroblast immigration and neo-angiogenesis were detected in the hybrid braid than in the PLLA braid when implanted on ruptured medial collateral ligament (MCL). Hybridization with collagen facilitated cell seeding and spatial cell distribution, and promoted cell immigration and neo-angiogenesis. The hybrid braid would be useful for ligament tissue engineering.

Effects of different exposures of hyperbaric oxygen on ligament healing in rats

Hyperbaric oxygen (HBO) is a method of augmenting, intermittently, oxygen availability to tissues. We examined the effect of three different HBO exposures on the healing of experimentally induced ligament lacerations in the right hind limb of 44 male Wistar rats. Animals were divided into four groups after ligament injury: (a) control group, animals breathed room air at 1 ATA (atmosphere absolute) in a hyperbaric chamber for 60 min; (b) HBO treatment at 1.5 ATA for 30 min once a day, (c) HBO treatment at 2 ATA for 30 min once a day, (d) 2 ATA for 60 min once a day. At 14 days post‐ligament injury, we compared the ligaments of the four treatment groups for gross appearance, histology and expression of pro‐α(I) mRNA by northern hybridization. Our results indicate that HBO was effective in promoting ligament healing compared to control (p < 0.01). Of these three exposures, HBO at 2 ATA for 60 min was the most effective, resulting in enhanced extra‐cellular matrix deposition as measured by collagen synthesis.

Relationships between Fiber Composition and NMR Measurements in Human Skeletal Muscle

The purpose of this study was to examine the relationships between the relative contents of phosphocreatine (PCr), inorganic phosphate (Pi), β‐adenosine triphosphate (ATP), and transverse relaxation time (T2) with fiber composition, which determined histochemically in the human skeletal muscle. The vastus lateralis muscles of 28 volunteers were subjected to phosphorus nuclear magnetic resonance (31P NMR) spectroscopy, magnetic resonance imaging (MRI) and muscle biopsy. Muscle fibers were divided into type I and type II fibers using myosin ATPase stain. A wide range of fiber composition levels were observed in the subjects (27.3–74.6% type I fibers). The PCr/ATP, Pi/ATP and (PCr+Pi)/ATP ratios were positively related to the percentage of type II fibers (r=0.695, p<0.001, r=0.429, p<0.05 and r=0.773, p<0.001, respectively). There was no correlation between fiber composition and the PCr/Pi ratio (r 0.127, n.s.) or intracellular pH (r=0.305, n.s.). Moreover, no correlation was found between T2 and fiber type (r=0.144, n.s.). These results suggest that 31P NMR can detect the differences in relative content of phosphates between type I and type II fibers, thereby noninvasively evaluating fiber composition in human skeletal muscle.

Maintenance of myoglobin concentration in human skeletal muscle after heavy resistance training

Abstract The aim of this study was to determine the effects of 8 weeks of resistance training (RT) on the myoglobin concentration ([Mb]) in human skeletal muscle, and to compare the change in the [Mb] in two different RT protocols. The two types of protocol used were interval RT (IRT) of moderate to low intensity with a high number of repetitions and a short recovery time, and repetition RT (RRT) of high intensity with a low number of repetitions and a long recovery time. A group of 11 healthy male adults voluntarily participated in this study and were divided into IRT (n = 6) and RRT (n = 5) groups. Both training protocols were carried out twice a week for 8 weeks. At the completion of the training period, the one-repetition maximal force values and isometric force were increased significantly in all the subjects, by about 38.8% and 26.0%, respectively (P < 0.01). The muscle fibre composition was unchanged by the 8 weeks of training. The muscle fibre cross-sectional areas were increased significantly by both types of training in all fibre types (I, IIa and IIb, mean +16.1%, P < 0.05). The [Mb] showed no significant changes at the completion of the training [IRT from 4.63 (SD 0.63) to 4.48 (SD 0.72), RRT from 4.47 (SD 0.75) to 4.24 (SD 0.80) mg · g−1 wet tissue] despite a significant decrease in citrate synthase activity [IRT from 5.27 (SD 1.45) to 4.49 (SD 1.48), RRT from 5.33 (SD 2.09) to 4.85 (SD 1.87) μmol · min−1 · g−1 wet tissue; P < 0.05] observed after both protocols. These results suggested that myoglobin and mitochondria enzymes were regulated by different mechanisms in response to either type of RT. Moreover, the maintained [Mb] in hypertrophied muscle should preserve oxygen transport from capillaries to mitochondria even when diffusion distance is increased.

Mechanical stretch in anterior cruciate ligament derived cells regulates type I collagen and decorin expression through extracellular signal-regulated kinase 1/2 pathway

Abstract Anterior cruciate ligament (ACL) is continuously exposed to tensile load, which is generally recognized to be an essential factor in maintaining the physiological homeostasis of the ACL fibers during daily activities. Although this kind of mechanical stimulation is clearly known to play an important role in quickening repair of ACL injury, responses of ACL cells to mechanical stimulation still remain unclear. We have investigated whether extracellular signal-regulated kinase 1/2 (ERK1/2) in human ruptured ACL-derived cells are phosphorylated and involved in type I collagen (Col I) and decorin gene expression by mechanical stimulation. Mechanical stretch stimulates time-dependent phosphorylation of ERK1/2 in human ruptured ACL-derived cells. While Col I gene expression levels were increased in 48-h continuous mechanical stretch, decorin gene expression levels were decreased for 24-h continuous stimulation. Decorin gene expression levels were increased, however, in mechanical stretch+PD98059, which is an inhibitor of ERK pathway, treated cells as compared with control cells at 24 h. Our results show that ERK pathway is stimulated by mechanical stretch, and may be involved in regulation of Col I and decorin gene expression in ACL-derived cells.

Dynamic viscoelasticity of the healing ligament treated by in vivo intermittent oxygen exposure in rats

Abstract The effects of intermittent exposure to hyperbaric oxygen (HBO) on experimentally induced ligament tear were studied in the right hind limb of 10 male Wistar rats. Ten rats were divided into the following two groups of five: Group A, merely exposed to normobaric room air (control group); Group B, treated with HBO at 2 ATA 100% O2×60 min×once/day (HBO group). The dynamic stiffness and tanδ of the injured patellar ligament were measured 4 weeks after infliction with the original viscoelastic spectrometer. From our results, the stiffness of injured ligament did not recover from the average of control site at 4 weeks after injury, whether or not HBO was used (p This study suggests, from the point of elasticity, that the ligament of accelerated collagen synthesis with HBO were still fragile at the time of 4 weeks after wounding. However, dynamic viscoelasticity was found to be not influenced enough by in vivo intermittent oxygen supply.