Showing papers by "Gordon L. Warren published in 2003"
TL;DR: Data suggest that satellite cell proliferation is required for approximately half of the force recovery after eccentric contraction-induced injury, and torque production of irradiated injured animals did not recover fully and was 25% less than that of injured nonirradiated mice 35 days postinjury.
Abstract: The purpose of this study was to determine if the elimination of satellite cell proliferation using γ-irradiation would inhibit normal force recovery after eccentric contraction-induced muscle inju...
72 citations
TL;DR: It is suggested that chemokines, such as monocyte chemoattractant protein-1 (MCP-1), associated with monocyte/macrophage influx and activation, are abundantly expressed in postinjured muscle, and they might play a role in traumatic muscle injury/recovery processes.
Abstract: Traumatic skeletal muscle injury causes a specific sequence of cellular events consisting of degeneration, inflammation, regeneration, and fibrosis. The role of early posttraumatic mechanisms, including acute inflammatory response, in muscle repair is not well understood. In the present study, oligonucleotide microarray analyses were used to examine the candidate genes that are involved in these early events of the muscle injury/repair process. cDNA was prepared from the injured and control tibialis anterior (TA) muscle of mice 24 h postinjury and labeled with the fluorescent dye Cy5 or Cy3 prior to hybridization to a DNA microarray. The microarray analysis, including 732 genes, was conducted in triplicate, and we describe only genes modulated by the injury showing a differential expression (both increased and decreased) 1.7-fold or greater (p < 0.05) from control uninjured TA muscle. Selected expression patterns were confirmed by other gene expression detection methods, including real-time reverse transcription-polymerase chain reaction (RT-PCR) and RNase protection assay (RPA) or immunohistochemistry detection methods. The upregulated genes (2.8%) were mainly associated with inflammation, oxidative stress, and cell proliferation, whereas the downregulated genes (3.2%) were related to metabolic and cell signaling pathways. In addition, the study suggested that chemokines, such as monocyte chemoattractant protein-1 (MCP-1), associated with monocyte/macrophage influx and activation, are abundantly expressed in postinjured muscle, and they might play a role in traumatic muscle injury/recovery processes.
69 citations
TL;DR: The results indicate that the QF muscle may not necessarily fatigue more than the TA muscle, and suggest that VFTs augment the force of fatigued, human skeletal muscle irrespective of fiber type.
Abstract: Background and Purpose. The quadriceps femoris (QF) and tibialis anterior (TA) muscles are often activated through the use of electrical stimulation by physical therapists. These 2 muscles are fundamentally different in regard to their fiber-type composition. Whether protocols developed using a given muscle can be applied to another muscle has seldom been questioned, even if they differ in fiber type. The purpose of this study was to test the hypothesis that torque augmentation during variable-frequency train (VFT) stimulation as compared with constant-frequency train (CFT) stimulation in the fatigued state would not differ between these muscles, even though the TA muscle has 50% relatively more slow fibers than the QF muscle relative to each muscle's overall composition. Subjects. Ten recreationally active men with no history of lower-extremity pathology participated in the study (mean age=25 years, SD=4, range=19–31; mean height=179 cm, SD=5, range=170–188; mean body mass=80 kg, SD=15, range=63–111). Methods. The subjects' TA and QF muscles were stimulated with CFTs (six 200-microsecond square waves separated by 70 milliseconds) or VFTs (first interpulse interval=5 milliseconds) that evoked an isometric contraction. Results. After potentiation, the torque-time integral and peak torque were not different for the VFT and CFT stimulation. Rise time was longer for the TA muscle than for the QF muscle and for CFT stimulation versus VFT stimulation (both approximately 40%). After 180 CFTs (50% duty cycle), peak torque decreased 56% overall, with no differences between muscles. Enhancement of the torque-time integral (25%) by VFT stimulation was not different between fatigued QF and TA muscles. Torque augmentation was due to the VFT stimulation evoking 27% greater peak torque and less slowing of rise time than the CFT stimulation (15% versus 30%). Discussion and Conclusion. The results indicate that the QF muscle may not necessarily fatigue more than the TA muscle. The results suggest that VFTs augment the force of fatigued, human skeletal muscle irrespective of fiber type.
39 citations
TL;DR: These responses show that the torque-time integral can be enhanced at both moderate and high stimulation amplitudes, and it is suggested that neither recruitment nor preferential activation of fast muscle is responsible for the "catch-like" property that can be demonstrated in fatigued human skeletal muscle.
Abstract: Aim: Variable frequency trains have been reported to enhance force of fatigued human skeletal muscle. More rapid calcium turnover and/or enhanced stiffness may be responsible for the augmented torque–time integral during surface stimulation at moderate amplitude. In contrast, it has recently been suggested that variable frequency train enhancement occurs only at low forces as a result of preferential stimulation of fast fibres and/or altered motor unit recruitment. If correct, this would limit the practical benefit of variable frequency trains. Accordingly, we tested the hypothesis that torque augmentation by variable frequency trains in fatigued skeletal muscle was independent of stimulation amplitude. Methods: The m. quadriceps femoris of six males was stimulated with constant frequency trains (six 200-ls square waves separated by 70 ms) or variable frequency trains (first interpulse interval 5 ms) at an amplitude that initially evoked � 25 or � 50% of maximal voluntary isometric torque. Results: After 180 constant frequency trains (50% duty cycle), isometric peak torque decreased � 63%. In fatigued muscle, variable frequency trains enhanced the torque–time integral by � 23% over that for constant frequency trains and this effect was independent of stimulation amplitude. This was due to greater peak torque and less slowing of rise time. Conclusion: These responses show that the torque–time integral can be enhanced at both moderate and high stimulation amplitudes. As such, it is suggested that neither recruitment nor preferential activation of fast muscle is
32 citations