Percussive Massage Increases Capillary Density in Type I and II Skeletal Muscle Fibers

Capillaries play a critical role in delivering oxygen and nutrients to cells. Skeletal muscle adapts to increased demand by increasing capillary density through a process known as angiogenesis. The effects of alternative therapies such as massage on angiogenic adaptation in skeletal muscle are inconclusive, particularly for newer techniques such as percussive massage. PURPOSE: To investigate the effect of 6 weeks of percussive massage on skeletal muscle myofiber area and angiogenesis. METHODS: 11 healthy young (22±4 yr.) men (n=5) and women (n=6) received 18 sessions of 30-min-percussive massage on their right thigh over the course of 6 weeks. Muscle samples were collected one week before the start of massage sessions and 48 h after the last session from the participant’s treated thigh. Sections from the biopsies were stained with CD31 for capillary analysis and type I myosin heavy chain for fiber type analysis. Capillary per fiber, capillary density, fiber area and fiber type were analyzed before and after massage treatment. RESULTS: The mean cross-sectional area of type I fibers did not change after massage treatment, but type II fiber area decreased by 7.5% (p=0.04). The number of capillaries per fiber increased only for type I fibers (p=0.01) and did not change in type II fibers. Massage increased overall capillary density (capillary per fiber/area) of both type I (p=0.04) and II muscle fibers (p=0.03). CONCLUSION: Although capillary density increased for both muscle fiber types; massage likely affected the two fiber types differently. Whereas increased capillary density of type I fibers was the likely result of angiogenesis, the increase in capillary density for type II fibers was driven largely by a reduction in type II fiber area

Pericyte NF-κB Activation Enhances Endothelial Cell Proliferation and Proangiogenic Cytokine Secretion

Pericytes are skeletal muscle resident, multipotent stem cells that are localized to capillaries. They respond to damage through activation of nuclear-factor kappa-B (NF-κB), a transcription factor that regulates many cellular processes including inflammation. Research has shown that pericyte NF-κB activation positively affects myoblast proliferation. It is unknown how pericyte NF-κB affects signaling and proliferation of endothelial cells, an important component of muscle tissue microcirculation. PURPOSE: To determine the effects of altered pericyte NF-κB activity on endothelial cell proliferation and identify inflammatory factors involved in this cell-cell signaling. METHODS: Human primary pericytes were transfected with vectors designed to increase or decrease NF-κB activity (or empty vector control). Transfected pericytes were co-cultured with human microvascular endothelial cells (HMVECs) using transwell inserts. HMVEC proliferation was assessed via cell counting at 24 and 48 hr. Secreted cytokines in cell culture supernatants were screened using a Luminex multiplex assay. RESULTS: HMVEC proliferation was greater in the increased pericyte NF-κB activity condition compared to the decreased NF-κB condition at 24 and 48 hr (1.3 fold, p=0.002). At 24 hr, cytokine secretion was greater in the increased NF-κB condition compared to control and decreased NF-κB conditions for 14 cytokines, including interleukin-8 (IL-8; 6.4 fold, p CONCLUSION: NF-κB activation in pericytes caused increased HMVEC proliferation, which may have been mediated by proinflammatory and proangiogenic cytokines known to be under the transcriptional regulation of NF-κB

The Role of T Lymphocytes in Skeletal Muscle Repair From Traumatic and Contraction-Induced Injury

Skeletal muscle is prone to damage from a range of stimuli, and initiates a robust repair process that requires the participation of immune cells. Among the more well characterized immune cells involved in muscle repair are those of the myeloid lineage, including neutrophils, macrophages, monocytes, and eosinophils. More recently, studies have begun to elucidate the role of the lymphoid-derived immune cells, most notably T lymphocytes (T-cells), in the complex processes of muscle repair. Though T-cells have been traditionally been associated with pathological degeneration of skeletal muscle in disease, recent studies show that T-cells are instrumental in the repair/regeneration process following severe muscle damage in mice. Furthermore, a few studies using basic immunohistochemical assays have shown that T-cells accumulate in human skeletal muscle in the days following contraction-induced muscle damage. The functional significance of T-cells in the repair and adaptation process following contraction-induce muscle damage remains uncertain, and is an active area of intense investigation. This mini-review summarizes recent findings on the involvement of T-cells in skeletal muscle repair

Muscle Mitochondrial Function at Different Phases of the Menstrual Cycle

The effect of menstrual cycle (MC) phase on muscle recovery from damage has been studied using markers of strength and soreness, but remains inconclusive. Mitochondrial function is essential for muscle recovery, and has been found to be influenced by estradiol (E2). Understanding the relationship between MC phase and mitochondria can provide further insight into women’s muscle health. The PURPOSE of this study was to determine how MC phase affects markers of muscle damage and recovery, with emphasis on mitochondrial function, following electrically-stimulated muscle contractions. METHODS: 22 premenopausal females were recruited and split into two groups, early follicular (EF) and late follicular (LF). After menstrual cycle tracking and phase confirmation, subjects performed a baseline maximum voluntary knee extension contraction (MVC) and provided a muscle biopsy one week prior to test day. On test day, subjects underwent 200 electrically stimulated eccentric muscle contractions (ES). Subjects reported for follow-up strength tests on days 2, 4, and 7 post damage, and gave a final biopsy on day 7. RESULTS: MVC decreased an average of 14 ± 6% immediately following ES and recovered to 6 ± 7% below baseline by day 4, with no differences between groups for percent decrease in MVC (p=.67). Average peak soreness was 4.0 ± 1.9, with no differences between groups (p=.91). Average change in max coupled mitochondrial respiration was -14.3 ± 15.5 pmolO2ᐧs-1ᐧmg-1 for the EF group and 1.3 ± 22.3 pmolO2ᐧs-1ᐧmg-1 for the LF group (p=.03). Average change in fatty acid supported respiration was -3.6 ± 7.4 pmolO2ᐧs-1ᐧmg-1 for the EF group and 7.5 ± 10.5 pmolO2ᐧs-1ᐧmg-1 for the LF group (p=.046). However, these results are complicated by baseline differences in respiration, with max coupled respiration being significantly higher (p=.02) in the mid-luteal phase (EF group baseline) than the early-follicular phase (LF group baseline). CONCLUSIONS: Results show novel findings that baseline mitochondrial respiration and mitochondrial response to damage differ between MC phases. This finding supports previous research relating mitochondrial function and E2 levels, and suggests further research on mitochondrial function throughout the menstrual cycle

Pericyte NF-κB Activation Enhances Endothelial Cell Proliferation and Proangiogenic Cytokine Secretion in Vitro

Pericytes are skeletal muscle resident, multipotent stem cells that are localized to the microvasculature. In vivo, studies have shown that they respond to damage through activation of nuclear-factor kappa-B (NF-κB), but the downstream effects of NF-κB activation on endothelial cell proliferation and cell–cell signaling during repair remain unknown. The purpose of this study was to examine pericyte NF-κB activation in a model of skeletal muscle damage; and use genetic manipulation to study the effects of changes in pericyte NF-κB activation on endothelial cell proliferation and cytokine secretion. We utilized scratch injury to C2C12 cells in coculture with human primary pericytes to assess NF-κB activation and monocyte chemoattractant protein-1 (MCP-1) secretion from pericytes and C2C12 cells. We also cocultured endothelial cells with pericytes that expressed genetically altered NF-κB activation levels, and then quantified endothelial cell proliferation and screened the conditioned media for secreted cytokines. Pericytes trended toward greater NF-κB activation in injured compared to control cocultures (P = 0.085) and in comparison to C2C12 cells (P = 0.079). Second, increased NF-κB activation in pericytes enhanced the proliferation of cocultured endothelial cells (1.3-fold,P = 0.002). Finally, we identified inflammatory signaling molecules, including MCP-1 and interleukin 8 (IL-8) that may mediate the crosstalk between pericytes and endothelial cells. The results of this study show that pericyte NF-κB activation may be an important mechanism in skeletal muscle repair with implications for the development of therapies for musculoskeletal and vascular diseases, including peripheral artery disease

Effects of Running on Femoral Articular Cartilage Thickness for Anterior Cruciate Ligament Reconstruction Patients and Non-ACLR Control Subjects

Anterior cruciate ligament reconstruction (ACLR) patients are more likely to develop posttraumatic knee osteoarthritis than non-ACLR counterparts. The effect of running on femoral articular cartilage thickness is unclear. PURPOSE: The purpose of this study was to compare how 30 minutes of running influences femoral articular cartilage thickness for ACLR patients and non-ACLR control subjects. We hypothesized that running would deform the femoral articular cartilage more for the ACLR patients than for the control subjects. METHODS: We recruited 20 individuals with primary unilateral ACLR and 20 matched non-ACLR controls. ACLR patients and control subjects were matched based upon age, gender, BMI, and weekly running mileage. The present procedures were approved by the appropriate institutional board and all subjects provided informed consent before data collection. We used ultrasound imaging to measure femoral articular cartilage thickness before and after 30 minutes of running. The ultrasound images were manually analyzed using ImageJ software by the same investigator. Total femoral articular cartilage cross-sectional area of each image was segmented into three regions: medial, lateral, and intercondylar. Deformation due to the run was compared between the ACLR patients and control subjects for each region using independent t tests (P \u3c 0.05, adjusted for multiple comparisons). RESULTS: The 30-minute run resulted in more deformation for the ACLR patients (0.03 ± 0.01 cm) than the matched controls (0.01 ± 0.01 cm) for the medial region (p \u3c 0.01) of the femoral articular cartilage. Identically, the 30-minute run resulted in more deformation for the ACLR patients (0.03 ± 0.01 cm) than the matched controls (0.01 ± 0.01 cm; p \u3c 0.01) for an average of the entire articular cartilage area (medial, lateral, and intercondylar). No significant differences existed between groups for the lateral or intercondylar regions. CONCLUSION: Thirty minutes of running deformed medial and overall femoral articular cartilage more for ACLR patients than non-ACLR control subjects

Femoral Articular Cartilage Quality, but Not Thickness, Is Decreased for Anterior Cruciate Ligament Reconstruction Patients Relative to Control

Anterior cruciate ligament reconstruction (ACLR) patients are at risk of developing posttraumatic knee osteoarthritis (OA). The etiology of posttraumatic knee OA is complex, potentially involving biomechanical and biochemical factors. Changes in femoral cartilage thickness and composition are associated with knee OA, while current research is ambiguous on cartilage in ACLR patients. PURPOSE: This study aimed to compare femoral cartilage thickness and T2 relaxation time (a compositional measure) between ACLR patients and healthy controls in a resting state. We hypothesized that ACLR patients would exhibit thinner femoral cartilage and increased T2 relaxation times. METHODS: Twenty ACLR patients (6-24 months post-surgery) and 20 matched healthy controls were recruited following institutional board approval. Ultrasound and magnetic resonance imaging data were collected on two separate days, allowing cartilage thickness and composition measurements to be made, respectively. Statistical analyses, including independent t-tests and Holm-Bonferroni corrections, were performed on selected regions of interest. RESULTS: The ACLR group showed increased T2 relaxation times in four of eight femoral regions compared to controls. No significant differences in femoral cartilage thickness were observed between the groups. The primary finding from this study is that ACLR patients did not show differences in femoral cartilage thickness (a morphological measure), but displayed prolonged T2 relaxation times (a compositional measure) compared to controls, at rest. This finding suggests that compositional changes precede morphological shifts in femoral cartilage in early post-ACLR periods (6-24 months). CONCLUSION: These early compositional changes may indicate articular cartilage that is more compressible and subject to increased strain on the solid components of the joint. While ultrasound is a more accessible imaging method, magnetic resonance imaging may provide a more accurate and early evaluation of cartilage quality. Further research is needed to develop practical tools for early detection and monitoring of cartilage degradation in ACLR patients before progression into knee osteoarthritis

Running Biomechanics and Knee Cartilage Health in ACLR Patients

Anterior cruciate ligament reconstruction (ACLR) patients are more likely to subsequently suffer from knee osteoarthritis than non-ACLR counterparts. Exercise is thought to influence articular cartilage, however, it is unclear how running biomechanics are associated with femoral cartilage thickness and composition in ACLR patients. PURPOSE: The purpose of this study was to investigate relationships between running biomechanics and measures of femoral articular cartilage condition (thickness and composition) in ACLR patients and control subjects. METHODS: We used ultrasound and MRI (T2 mapping sequence) to measure articular cartilage thickness and composition, respectively, for 20 ACLR patients (age: 23 ± 3 yrs; mass: 70 ± 10 kg; time post-ACLR: 14.6 ± 6.1 months) and 20 matched controls (age: 22 ± 2 yrs; mass: 67 ± 11 kg). After these measures, all participants completed a 30-minute run on a force-instrumented treadmill. Correlational analyses were used to explore relationships between running biomechanics (vertical ground reaction force (vGRF)) and femoral cartilage thickness and composition (T2 relaxation time). The present procedures were approved by the appropriate institutional board and all subjects provided informed consent before data collection was performed. RESULTS: Significant positive correlations existed for the control subjects only between peak vGRF and overall (r = 0.34; p \u3c 0.01), medial (r = 0.23; p \u3c 0.01), lateral (r = 0.39; p = 0.02), and intercondylar (r = 0.31; p \u3c 0.01) femoral thickness. The ACLR patients showed significant negative correlations between T2 relaxation time for the central-medial region of the femoral condyle, and peak vGRF (r = −0.53; p = 0.01) and vertical impulse due to the vGRF (r = −0.46; p = 0.04). CONCLUSION: These findings offer some limited support for the idea that femoral articular cartilage benefits from increase vGRF during running. This is evidenced by the increased thickness for the control subjects and decreased T2 relaxation time (indicative of increased free-flowing water in the cartilage) for the ACLR patients, as running vGRF increased

Genetic variation and exercise-induced muscle damage: implications for athletic performance, injury and ageing.

Prolonged unaccustomed exercise involving muscle lengthening (eccentric) actions can result in ultrastructural muscle disruption, impaired excitation-contraction coupling, inflammation and muscle protein degradation. This process is associated with delayed onset muscle soreness and is referred to as exercise-induced muscle damage. Although a certain amount of muscle damage may be necessary for adaptation to occur, excessive damage or inadequate recovery from exercise-induced muscle damage can increase injury risk, particularly in older individuals, who experience more damage and require longer to recover from muscle damaging exercise than younger adults. Furthermore, it is apparent that inter-individual variation exists in the response to exercise-induced muscle damage, and there is evidence that genetic variability may play a key role. Although this area of research is in its infancy, certain gene variations, or polymorphisms have been associated with exercise-induced muscle damage (i.e. individuals with certain genotypes experience greater muscle damage, and require longer recovery, following strenuous exercise). These polymorphisms include ACTN3 (R577X, rs1815739), TNF (-308 G>A, rs1800629), IL6 (-174 G>C, rs1800795), and IGF2 (ApaI, 17200 G>A, rs680). Knowing how someone is likely to respond to a particular type of exercise could help coaches/practitioners individualise the exercise training of their athletes/patients, thus maximising recovery and adaptation, while reducing overload-associated injury risk. The purpose of this review is to provide a critical analysis of the literature concerning gene polymorphisms associated with exercise-induced muscle damage, both in young and older individuals, and to highlight the potential mechanisms underpinning these associations, thus providing a better understanding of exercise-induced muscle damage

Cellular and molecular changes following skeletal muscle damage: A role for NF-κB and muscle resident pericytes

Skeletal muscle is dynamic and actively regenerates following damage or altered functional demand. Regeneration is essential for the maintenance of muscle mass and, when dysregulated as a result of disease or aging, can lead to losses in functional capacity and increased mortality. Limited data exist on the molecular mechanisms that govern skeletal muscle regeneration in humans. Therefore, the overall objective of this dissertation was to characterize early molecular alterations in human skeletal muscle to strenuous exercise known to induce a muscle regenerative response. Thirty-five subjects completed 100 eccentric (muscle lengthening) contractions (EC) of the knee extensors with one leg and muscle biopsies were taken from both legs 3 h post-EC. The sample from the non-EC leg served as the control. A well-powered transcriptomic screen and network analysis using Ingenuity Pathway software was first conducted on mRNA from the biopsy samples. Network analysis identified the transcription factor NF-kappaB (NF-kB) as a key molecular element affected by EC. Conformational qRT-PCR confirmed alterations in genes associated with NF-kappaB. A transcription factor ELISA, using nuclear extracts from EC and control muscle samples showed a 1.6 fold increase in NF-kB DNA binding activity following EC. Immunohistochemical experiments then localized the majority of NF-kB positive nuclei to cells in the interstitium, which stained positive for markers of pericyte cells and not satellite cells. To ascertain the mechanistic significance of NF-kB activation following muscle damage, in vitro analyses were carried out using a novel primary pericyte/myoblast co-culture model. Primary pericyte/myoblast co-culture experiments demonstrated that pericytes, transfected with a DNA vector designed to drive NF-kB activation, enhanced proliferation and inhibited myogenic differentiation of co-cultured skeletal muscle myoblasts. Furthermore, reduced NF-kB activation led to enhanced myogenic potential of primary pericytes. Taken together, the data in this dissertation suggest that NF-kB dependent signaling in pericytes regulates myogenic differentiation in a cell- and non-cell autonomous manner and may affect the early regenerative response following muscle damage by inhibiting differentiation and promoting proliferation of muscle satellite cells