title: Enhancement of Skeletal Muscle in Aged Rats Following High-Intensity Stretch-Shortening Contraction Training.
abstract: Exercise is the most accessible, efficacious, and multifactorial intervention to improve health and treat chronic disease. High-intensity resistance exercise, in particular, also maximizes skeletal muscle size and strength-outcomes crucial at advanced age. However, such training is capable of inducing muscle maladaptation when misapplied at old age. Therefore, characterization of parameters (e.g., mode and frequency) that foster adaptation is an active research area. To address this issue, we utilized a rodent model that allowed training at maximal intensity in terms of muscle activation and tested the hypothesis that muscles of old rats adapt to stretch-shortening contraction (SSC) training, provided the training frequency is sufficiently low. At termination of training, normalized muscle mass (i.e., muscle mass divided by tibia length) and muscle quality (isometric force divided by normalized muscle mass) were determined. For young rats, normalized muscle mass increased by ∼20% regardless of training frequency. No difference was observed for muscle quality values after 2 days versus 3 days per week training (0.65 ± 0.09 N/mg/mm vs. 0.59 ± 0.05 N/mg/mm, respectively). For old rats following 3 days per week training, normalized muscle mass was unaltered and muscle quality was 30% lower than young levels. Following 2 days per week training at old age, normalized muscle mass increased by 17% and muscle quality was restored to young levels. To investigate this enhanced response, oxidative stress was assessed by lipid peroxidation quantification. For young rats, lipid peroxidation levels were unaltered by training. With aging, baseline levels of lipid peroxidation increased by 1.5-fold. For old rats, only 2 days per week training decreased lipid peroxidation to levels indistinguishable from young values. These results imply that, appropriately scheduled high-intensity SSC training at old age is capable of restoring muscle to a younger phenotype in terms of lipid peroxidation levels and muscle quality.
authors.affiliation: 1 Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health , Morgantown, West Virginia.
authors.forename: Erik P
authors.initials: EP
authors.lastname: Rader
authors.affiliation: 1 Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health , Morgantown, West Virginia.|2 West Virginia School of Medicine , Division of Exercise Physiology, Morgantown, West Virginia.
authors.forename: Marshall A
authors.initials: MA
authors.lastname: Naimo
authors.affiliation: 1 Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health , Morgantown, West Virginia.
authors.forename: Kayla N
authors.initials: KN
authors.lastname: Layner
authors.affiliation: 1 Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health , Morgantown, West Virginia.
authors.forename: Alyssa M
authors.initials: AM
authors.lastname: Triscuit
authors.affiliation: 1 Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health , Morgantown, West Virginia.|3 Department of Sports Medicine, Mercyhurst University , Erie, Pennsylvania.
authors.forename: Robert D
authors.initials: RD
authors.lastname: Chetlin
authors.affiliation: 1 Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health , Morgantown, West Virginia.
authors.forename: James
authors.initials: J
authors.lastname: Ensey
authors.affiliation: 1 Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health , Morgantown, West Virginia.
authors.forename: Brent A
authors.initials: BA
authors.lastname: Baker
mesh_terms: D000375:Aging / Q000502:physiology*; D000818:Animals; D015415:Biomarkers / Q000378:metabolism; D005455:Fluorescent Antibody Technique; D015227:Lipid Peroxidation; D008297:Male; D008315:Malondialdehyde / Q000378:metabolism; D009119:Muscle Contraction / Q000502:physiology*; D018485:Muscle Fibers, Skeletal / Q000502:physiology; D018482:Muscle, Skeletal / Q000502:physiology*; D009929:Organ Size; D018384:Oxidative Stress; D010805:Physical Conditioning, Animal; D011914:Rats, Inbred BN
chemical_list: D015415:Biomarkers; D008315:Malondialdehyde
keywords: Fisher 344XBrown Norway rats; dorsiflexor muscles; dynamometer; oxidative stress; repetitive exposure