Association of Skeletal Muscle Fiber Type Distribution with Lactate Metabolism and Metabolic Health

Abstract

ABSTRACT Background: The metabolic syndrome (MetS) is classified as a combination of risk factors of metabolic origins and increases the risk of cardiovascular disease, type 2 diabetes, atherosclerosis, stroke, and all-cause mortality. Treatment of MetS is expensive and a simple and effective measure is needed for early detection and possible prevention. Blood lactate concentrations can be measured as lactate influences metabolic regulation inside and outside the cell. Higher levels of fasting blood lactate have been shown in people with obesity and type 2 diabetes. Skeletal muscle plays a major role in metabolic homeostasis and the production of lactate, and this is mediated by specialized muscle fibers. Skeletal muscle fiber type determines substrate use and possible metabolic health. Several studies have shown a link between a lower percentage of type I fibers and obesity and type 2 diabetes. Studies have also shown that a higher percentage of type I fibers can be associated with a healthier cardiometabolic phenotype. Purpose: Observe how muscle fiber type distribution relates to blood lactate levels and other factors of metabolic syndrome. Methods: Overweight subjects (n=32) were screened for any pre-existing conditions. Anthropometric and blood metabolite measures were taken for each subject. During one of three visits a muscle biopsy was performed, the muscle was then placed in O.C.T and frozen. Muscle tissue was then sectioned, and fiber type protocol was followed to determine fiber-type distribution. After fluorescent imaging, each image was manually quantified. Results: There was a significant correlation between a higher percentage of type II fibers and higher lactate levels (r=0.43, p=0.02) There was a significant correlation between higher HDL levels and a higher percentage of type I fibers (r=0.42, p=0.02). Higher levels of triglycerides also showed a significant correlation with a higher percentage of type II fibers (r=0.36, p=0.02). Higher HOMA-IR levels have a significant relationship with a higher percentage of type II fibers (r=0.53 p=0.002). Although the correlation of systolic blood pressure to type I (r=-0.24, p=0.2) or type II fibers (r=0.23, p=0.2) showed no significance, higher diastolic blood pressure was significantly correlated with a higher percentage of type II fibers (r=0.39 p=0.03). A higher Android/Gynoid ratio was significantly correlated with a higher percentage of type II fibers (r=0.49, p=0.01). Higher VAT mass (g) was also significantly correlated with a higher percentage of type II fibers (r=0.56, p=0.001). The percentage of body fat did not show any significance in relation to type I (r=-0.13, p=0.49) or type II fibers (r=0.11, p=0.54). VO2max also showed no significance in relation to type I (r=0.32, p=0.08) or type II (r=-0.32, p=0.08) fibers respectively. Conclusion: The results of this study show that there is a significant association between fiber type distribution and lactate levels and other factors of metabolic syndrome. Future studies should explore metabolic enzymatic activity for different skeletal muscle compositions (fiber type distribution) and how it relates to the factors of the metabolic syndrome.