Role of skeletal muscle‐fibre type in regulation of glucose metabolism in middle‐aged subjects with impaired glucose tolerance during a long‐term exercise and dietary intervention

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Abstract
Aim:  The aim of this study was to investigate the role of skeletal muscle fibre type in the regulation of glucose metabolism in middle‐aged obese subjects with impaired glucose tolerance (IGT) during a 2‐year exercise and dietary intervention.Methods:  Muscle biopsies (musculus vastus lateralis) were taken from 22 subjects belonging to the intervention group of the Finnish Diabetes Prevention Study [1]. According to their myosin heavy chain (MHC) profile at the baseline, the subjects were divided into two groups: IGTslow (n = 10) with a high proportion of MHC I isoforms and IGTfast (n = 12) with a high proportion of MHC II isoforms in the vastus lateralis muscle. The intervention consisted of dietary counselling, strength and power training and/or aerobic exercise. The amount of exercise was the same in both groups; the exercise frequency was 5.1 ± 2.7 h/week in the IGTslow and 5.1 ± 2.8 h/week in the IGTfast group.Results:  Fasting glucose (p < 0.05), 2‐h glucose (p < 0.05), fasting insulin (p < 0.05), haemoglobin A1c (HbA1c) (p < 0.01) and insulin resistance (p < 0.05) [homeostasis model assessment for insulin resistance (HOMA‐IR)] decreased in the IGTfast group, whereas only the 2‐h glucose and HbA1c concentrations decreased in the IGTslow group. The amount of the glycogen synthase kinase‐3‐αβ (GSK‐3‐αβ) decreased in the IGTfast group (p < 0.05). Exercise training increased the lactate dehydrogenase (LDH) (p < 0.01), LDH‐1 (p < 0.05) and citrate synthase (CS) (p < 0.05) activities in the vastus lateralis muscle in the IGTslow group, but only the CS activity (p < 0.05) in the IGTfast group.Conclusions:  The glucose metabolism improved both in the IGTslow and IGTfast group during the 2‐year exercise and dietary intervention. The change was more prominent in the IGTfast group than in the IGTslow group, associated with the decrease of the GSK‐αβ protein expression in skeletal muscle. The exercise training improved both glycolytic and oxidative capacity in the vastus lateralis muscle. The glycolytic capacity improved in the IGTslow group and the oxidative capacity in both groups.