Ninety percent of DM1 patients present at adulthood with delayed muscle maturation, distal muscle weakness, wasting, myotonia, cataracts, cardiac abnormalities, smooth muscle dysfunction, insulin resistance, daytime sleepiness, testicular atrophy (low reproductive fitness), ''difficult'' personality, neuropsychiatric disturbances, and frontal balding. Ten percent of the patients present at infancy with hypotonia (floppy infant), oromotor dysfunction, tent-shaped mouth, feeding and respiratory insufficiency (diaphragmatic hypoplasia), arthrogryposis, and mental retardation in those who survive until adulthood (congenital DM). All manifestations show a progressive course. Usually, creatine kinase is elevated. Muscle biopsy shows type 1 predominance, centrally located nuclei, severe fiber atrophy with nuclear clumps, hypertrophic and angulated fibers, and occasionally, necrotic fibers, fibrosis, or fat deposits. Cardiac involvement comprises conduction defects (mostly HV prolongation) and, less frequently, primary cardiomyopathy (wall thickening, hypertrabeculation, dyskinesia, and reduced myocardial tissue velocities). Cerebral MRI shows large Virchow-Robin spaces, white matter lesions, and atrophy. There may also be megacolon, megarectum, and delayed gastric emptying without dyspeptic symptoms. Some patients have hypo-IgG and, in some cases, thyrotropin deficiency. Phenotype severity and age at onset vary greatly between patients.
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The use of dumbbells gives you a much more comprehensive strengthening effect because the workout engages your stabilizer muscles, in addition to the muscle you may be pin-pointing. Without all of the belts and artificial stabilizers of a machine, you also engage your core muscles, which are your body's natural stabilizers.