The impact of life-long strength versus endurance training on muscle fiber morphology and phenotype composition in older men
Tiril Tøien, Jakob Lindberg Nielsen, Ole Kristian Berg, Mathias Forsberg Brobakken, Stian Kwak Nyberg, Lars Espedal, Thomas Malmo, Ulrik Frandsen, Per Aagaard, Eivind Wang
Abstract
Aging is associated with loss of fast-twitch type II myofibers, motor unit remodeling, and grouping of myofibers. This study reveals, for the first time, that strength training preserves neural innervation of type II fibers, resulting in similar myofiber type distribution and grouping in life-long strength-trained master athletes as young moderately active adults. In contrast, life-long endurance-trained master athletes and recreationally active old adults demonstrated higher proportion of type I fibers accompanied by more marked grouping of type I myofibers, and more atrophic fibers compared with strength-trained master athletes and young individuals. Thus, strength training should be utilized as a training modality for preservation of fast-twitch musculature, maximal muscle strength, and rapid force capacity (RFD) with advancing age.