A mini-overview of single muscle fibre mechanics: the effects of age, inactivity and exercise in animals and humans

Abstract

Many basic movements of living organisms are dependent on muscle function. Muscle function allows for the coordination and harmonious integrity of movement that is necessary for various biological processes. Gross and fine motor skills are both regulated at the micro-level (single muscle fibre level), controlled by neuronal regulation, and it is therefore important to understand muscle function at both micro- and macro-levels to understand the overall movement of living organisms. Single muscle mechanics and the cellular environment of muscles fundamentally allow for the harmonious movement of our bodies. Indeed, a clear understanding of the functionality of muscle at the micro-level is indispensable for explaining muscular function at the macro-(whole gross muscle) level. By investigating single muscle fibre mechanics, we can also learn how other factors such Ca2+ kinetics, enzyme activity and contractile proteins can contribute to muscle mechanics at the micro- and macro-levels. Further, we can also describe how aging affects the capacity of skeletal muscle cells, as well as how exercise can prevent aging-based sarcopenia and frailty. The purpose of this review is to introduce and summarise the current knowledge of single muscle fibre mechanics in light of aging and inactivity. We then describe how exercise mitigates negative muscle adaptations that occur under those circumstances. In addition, single muscle fibre mechanics in both animal and human models are discussed.

Contractile Properties of MHC I and II Fibers From Highly Trained Arm and Leg Muscles of Cross-Country Skiers

“…At the same time, other investigators have only shown a numerically yet non-significantly higher maximal Ca 2+ activated force produced by MHC II fibers in trained individuals ( Trappe et al, 2001 , 2006 ; Harber et al, 2004 ; Luden et al, 2012 ). In less trained individuals, this inconsistency also exists with fiber type differences observed in some but not all studies – for review see ( Jee and Kim, 2017 ). Reasons for these slight inconsistencies between studies in trained athletes are not clear but may be related to methodological differences (e.g., skinning process, temperature or the composition of the activating solutions), a lack of statistical power needed to detect a difference, different sport-specific demands, or different muscles of investigation.…”

Structural and Functional Changes in the Coupling of Fascial Tissue, Skeletal Muscle, and Nerves During Aging

“…In particular, the locomotory apparatus loses its effectiveness, due to the molecular and cellular changes occurring in the myofascia, the skeletal muscle tissue, the nervous system, and their structural and functional coupling. Genetics, epigenetics, environment, diseases, lifestyle, nutrition, and injuries also have a prominent role in tissue remodeling occurring with aging (Jee and Kim, 2017). Thanks to recent scientific progress, many phenomena and mechanisms associated with aging have been defined, but still much remains to be investigated.…”

“…Experimental studies indicate a negative effect of aging also on skeletal muscle plasticity, which is the potential of this tissue to modify its structural and functional features in response to environmental changes (Verdijk et al, 2007;Jee and Kim, 2017;Suetta, 2017). The regrowth response to physical inactivity-induced atrophy is also hindered in aged muscles (Pisot et al, 2016).…”

“…Moreover, in old adults, besides a weakened ROS scavenging system, dietary intake of antioxidants is often reduced (Damiano et al, 2019). In this context, data from studies in humans and animal models indicate that muscular activity and/or dietary supplementation with antioxidant compounds, such as l-ascorbic acid, tocopherols, carotenoids, flavonoids, or polyphenols, exert some beneficial effects on age-related skeletal muscle decline (Cesari et al, 2004;Pierno et al, 2014;Anton et al, 2015;Cartee et al, 2016;Jee and Kim 2017;Muhammad and Allam, 2018;Damiano et al, 2019). However, it should be taken into account that the effects of physical exercise and/or dietary supplementation with antioxidants on skeletal muscle aging are still debated due to discordant results (Marcell, 2003;Ji, 2015;Cartee et al, 2016;Flack et al, 2016;White et al, 2016;Distefano and Goodpaster, 2018;Damiano et al, 2019;Szentesi et al, 2019).…”

Aberrant redox signalling and stress response in age-related muscle decline: Role in inter- and intra-cellular signalling

“…However, others have suggested that remaining muscle fibres are not weaker [14,15], possibly due, at least in part to the fact that this loss is not consistent across the whole body. Thus, whether a defect occurs at the level of the single fibre remains unclear, with studies showing conflicting findings (see [16] for review).…”