Hongsun Song

Effect of increased excursion of the ankle on the severity of acute eccentric contraction-induced strain injury in the gastrocnemius: an in vivo rat study.

Background Although muscle strain injury models are frequently employed, highly invasive procedures, including surgical intervention, are typically used to produce these models. In this study, a minimally invasive model of acute strain injury was produced with a single eccentric contraction. Hypothesis The authors tested whether the severity of strain injury in the in vivo gastrocnemius depends on the excursion of the ankle. Study Design Controlled laboratory study. Methods Animals were randomly assigned to 2 groups: a small range of motion group (90°-105°, n = 10) and a large range of motion group (90°-125°, n = 10). Tetanically activated gastrocnemius muscles with percutaneous electrical stimulation were simultaneously elongated by forced dorsiflexion of the ankle joint. Results Isometric tetanic force of the large range of motion group was significantly lower than the pretreatment control 1, 2, and 3 days after treatment. Such reduction was not observed in the small range of motion group. Apparent pathologic damage was observed in the large range of motion group throughout the study period of 10 days. Conclusions A larger range of motion causes more damage in eccentric contraction by using the in vivo model. Clinical Relevance This in vivo model is useful to elucidate mechanisms of prevention and recovery of strain injury.

Aging effects on passive resistive torque in the rat ankle joint after lengthening contractions

BackgroundThe aim of this study was to evaluate whether aging affects (1) the sensation of joint stiffness after lengthening contractions (LCs); (2) passive resistive torque (PRT) of the ankle joint; (3) and the connectin (titin) isoform composition in the medial gastrocnemius (MG) muscle.MethodsAnesthetized young (9 weeks) and adult (35 weeks) Wistar rats (n = 6 per group) were used in the present study. A single bout of LCs was performed on the MG muscle with a combination of electrically induced tetanic contractions via a skin electrode and simultaneous forced dorsiflexion of the ankle joint (angular velocity 15°/s, 0°–45°). Static PRT of the ankle joint (at 30° and 45°) was measured to evaluate joint stiffness. These parameters were measured until 10 days after treatment. The connectin isoform was measured as muscle extensibility employing low-porosity 2% polyacrylamide gel electrophoresis.ResultsThe averaged static PRT was significantly higher in adult rats than in young rats. Connectin isoform analysis revealed that the adult group contained larger amounts of β-connectin than did the young rats. After the LCs, static PRT of the ankle joint gradually increased until day 4 in the young group, whereas the adult group did not show a significant change during the experimental period.ConclusionsWe concluded that (1) joint stiffness of adult rats is greater than in young rats, similar to human studies; (2) the increased joint stiffness may be due to connectin isoform composition; and (3) joint stiffness after MG muscle LCs is more apparent in young rats.

Characteristics of myogenic response and ankle torque recovery after lengthening contraction-induced rat gastrocnemius injury

BackgroundAlthough muscle dysfunction caused by unfamiliar lengthening contraction is one of most important issues in sports medicine, there is little known about the molecular events on regeneration process. The purpose of this study was to investigate the temporal and spatial expression patterns of myogenin, myoD, pax7, and myostatin after acute lengthening contraction (LC)-induced injury in the rat hindlimb.MethodsWe employed our originally developed device with LC in rat gastrocnemius muscle (n = 24). Male Wistar rats were anesthetized with isoflurane (aspiration rate, 450 ml/min, concentration, 2.0%). The triceps surae muscle of the right hindlimb was then electrically stimulated with forced isokinetic dorsi-flexion (180°/sec and from 0 to 45°). Tissue contents of myoD, myogenin, pax7, myostatin were measured by western blotting and localizations of myoD and pax7 was measured by immunohistochemistry. After measuring isometric tetanic torque, a single bout of LC was performed in vivo.ResultsThe torque was significantly decreased on days 2 and 5 as compared to the pre-treatment value, and recovered by day 7. The content of myoD and pax7 showed significant increases on day 2. Myogenin showed an increase from day 2 to 5. Myostatin on days 5 and 7 were significantly increased. Immunohistochemical analysis showed that myoD-positive/pax7-positive cells increased on day 2, suggesting that activated satellite cells play a role in the destruction and the early recovery phases.ConclusionWe, thus, conclude that myogenic events associate with torque recovery after LC-induced injury.