Age-dependent Muscle Adaptation after Chronic Stretch-shortening Contractions in Rats

Abstract

Age-related differences in contraction-induced adaptation have been well characterized especially for young and old rodent models but much less so at intermediate ages. Therefore, additional research is warranted to determine to what extent alterations in adaptation are due to maturation versus aging per se. The purpose of our study was to evaluate muscles of Fisher 344XBrown Norway rats of various ages following one month of exposure to stretch-shortening contractions (SSCs). With exposure, muscles mass increased by ~10% for 27 and 30 month old rats vs. ~20% for 3 and 6 month old rats (P < 0.05). For 3 month old rats, maximum isometric force and dynamic peak force increased by 22 ± 8% and 27 ± 10%, respectively (P < 0.05). For 6 month old rats, these forces were unaltered by exposure and positive work capacity diminished by 27 ± 2% (P = 0.006). By 30 months of age, age-related deficits in maximum isometric force, peak force, negative work, and positive work were apparent and SSC exposure was ineffective at counteracting such deficits. Recovery from fatigue was also tested and exposure-induced improvements in fatigue recovery were indicated for 6 month old rats and to a lesser extent for 3 month old rats whereas no such effect was observed for older rats. Alterations in fatigue recovery were accompanied by evidence of substantial type IIb to IIx fiber type shifting. These results highlight the exceptional adaptive capacity for strength at a young age, the inclination for adaptation in fatigue recovery at early adulthood, and diminished adaptation for muscle performance in general beginning at late adulthood. Such findings motivate careful investigation to determine appropriate SSC exposures at all stages of life.

Efficacy of Age-Specific High-Intensity Stretch-Shortening Contractions in Reversing Dynapenia, Sarcopenia, and Loss of Skeletal Muscle Quality

“…However, this phenomenon is very distinct from cases where maladaptation results, such is the case in physical work and exercise-induced events, and is accompanied by transient soreness and discomfort following loading of soft tissue [12,35,36]. These latter disorders have been reported in both humans [37] and animals [13,38] and typically present with no known etiology, while representing cases where functional loss occurs in the absence of any underlying obvious pathophysiology (i.e., overt inflammation, degeneration, etc.). Obviously, both overt skeletal muscle injury as well as maladaptation may occur at any age [35]; yet, specifically, with respect to maladaptive events incurred during aging, the conditions known as dynapenia and sarcopenia as well as skeletal muscle quality will be examined in this context.…”

“…For these reasons and with these limitations in mind, fundamental, in vivo animal models that are valid and representative of the human exposure-response relationship with respect to aging and exercise are an essential tool for investigating and quantifying these phenomena due to the exquisite control they allow over the biomechanical loading exposure as well as providing a means to evaluate, characterize, and quantify the integrated skeletal muscle response systematically. Interestingly, only recently have investigations begun to question and quantify the impact age-specific RTET imparts on skeletal muscle quality and whether this specific and sensitive outcome metric (i.e., "biomarker") is modifiable with aging [13,38,66,86]. Initial studies by Cutlip and colleagues provided a basis for investigating non-injurious SSC RTET exposure in a validated, fundamental rodent model of aging, which quantified the adaptive and maladaptive response in young and old skeletal muscle, respectively [13].…”

Nutritional Cognitive Neuroscience: Innovations for Healthy Brain Aging

“…Differential effects of aging are particularly evident in the cerebral cortex, in which the superior frontal, middle frontal, and superior parietal cortex are most susceptible to steady age-related atrophy (Lockhart and DeCarli, 2014 ). Other cortical regions have fluctuating rates of change, with some areas showing accelerated atrophy early in aging, others demonstrating accelerated atrophy late in aging, and others showing a combination of early and late acceleration (Figure 1 ; Lockhart and DeCarli, 2014 ; Claassen et al, 2016 ). Subcortically, the caudate nucleus, cerebellum, and hippocampus show susceptibility to age-related structural degeneration (Raz et al, 2005 ).…”

“…Regions highlighted in yellow show decline late in aging (remain structurally intact early in aging but decrease quickly late in aging). Modified from Claassen et al ( 2016 ) in Aging and Disease licensed under CC BY.…”

Prevalence estimation and familial tendency of common forefoot deformities in Turkey: A survey of 2662 adults

“…The absolute prevalences of these deformities are not known accurately, prevalance studies for HV presents a wide range from 3 to 74% with acute differences owing to a number of factors including age, gender and race/ethnicity. 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 …”