Efficacy of 3 days/wk resistance training on myofiber hypertrophy and myogenic mechanisms in young vs. older adults

Abstract

. Efficacy of 3 days/wk resistance training on myofiber hypertrophy and myogenic mechanisms in young vs. older adults. J Appl Physiol 101: [531][532][533][534][535][536][537][538][539][540][541][542][543][544] 2006. First published April 13, 2006; doi:10.1152/japplphysiol.01474.2005.-Resistance training (RT) has shown the most promise in reducing/reversing effects of sarcopenia, although the optimum regime specific for older adults remains unclear. We hypothesized myofiber hypertrophy resulting from frequent (3 days/wk, 16 wk) RT would be impaired in older (O; 60 -75 yr; 12 women, 13 men), sarcopenic adults compared with young (Y; 20 -35 yr; 11 women, 13 men) due to slowed repair/regeneration processes. Myofiber-type distribution and crosssectional area (CSA) were determined at 0 and 16 wk. Transcript and protein levels of myogenic regulatory factors (MRFs) were assessed as markers of regeneration at 0 and 24 h postexercise, and after 16 wk. Only Y increased type I CSA 18% (P Ͻ 0.001). O showed smaller type IIa (Ϫ16%) and type IIx (Ϫ24%) myofibers before training (P Ͻ 0.05), with differences most notable in women. Both age groups increased type IIa (O, 16%; Y, 25%) and mean type II (O, 23%; Y, 32%) size (P Ͻ 0.05). Growth was generally most favorable in young men. Percent change scores on fiber size revealed an age ϫ gender interaction for type I fibers (P Ͻ 0.05) as growth among Y (25%) exceeded that of O (4%) men. Myogenin and myogenic differentiation factor D (MyoD) mRNAs increased (P Ͻ 0.05) in Y and O, whereas myogenic factor (myf)-5 mRNA increased in Y only (P Ͻ 0.05). Myf-6 protein increased (P Ͻ 0.05) in both Y and O. The results generally support our hypothesis as 3 days/wk training led to more robust hypertrophy in Y vs. O, particularly among men. However, this differential hypertrophy adaptation was not explained by age variation in MRF expression. sarcopenia; myogenin; MyoD; myosin heavy chain IT IS WELL ESTABLISHED THAT muscle mass declines with age (termed sarcopenia). In the knee extensors (e.g., vastus lateralis), which are important for ambulation and weight-bearing function, a 30% decrease in whole muscle size occurs between the ages of 50 and 80 yr (15,40). This whole muscle atrophy results from atrophy of type II myofibers (34) and apparent loss of both type I and type II motor units as evidence from cadaveric studies of vastus lateralis indicate the number of myofibers, regardless of fiber type, declines substantially between the sixth and eighth decades (39). In the United States, $18.5 billion of total direct health care costs in 2000 were attributable to sarcopenia (31), and this will undoubtedly increase because the percentage of American adults 65 yr and older is expected to increase from one in nine to 20% of the adult population by 2030 (National Institute on Aging statistics). Resistance training has shown the most promise among interventions aimed to decrease the effects of sarcopenia, as it enhances strength, power, and mobility function and induces varying degrees of skeletal musc...

Potent myofiber hypertrophy during resistance training in humans is associated with satellite cell-mediated myonuclear addition: a cluster analysis

“…Resistance training results based on the independent variables of age and sex have been previously published on 49 (20) and 52 (25) of these 66 subjects, and our laboratory introduced the concept of Kmeans cluster analysis with a 2-cluster model on n ϭ 52 subjects in this earlier work (25). After expanding the sample to 66 subjects, we clustered subjects, independent of age and sex, into three response clusters based on changes in vastus lateralis mean myofiber crosssectional area (MFA; m 2 ): Xtr (n ϭ 17), Mod (n ϭ 32), and Non (n ϭ 17).…”

β-Hydroxy-β-Methylbutyrate Did Not Enhance High Intensity Resistance Training-Induced Improvements in Myofiber Dimensions and Myogenic Capacity in Aged Female Rats

“…Despite its general effectiveness, the degree of RT-induced muscle hypertrophy varies across different age and gender groups Tracy et al, 1999;Welle et al, 1996). We and others have previously observed a blunted hypertrophic response in older females following long-term RT (Bamman et al, 2003;Ivey et al, 2000;Kosek et al, 2006). Although the underlying mechanism has not been well-defined, the divergent extent of hypertrophy in old females may occur in part from reduced myogenic aptitude (Gallegly et al, 2004;Leiter et al, 2011), which could conceivably impair the regenerative processes activated in response to mechanical loading.…”

Link between blood flow and muscle protein metabolism in elderly adults

“…Capillary number to muscle fiber ratio strongly correlates with muscle fiber radius (R 2 = 0.948) and cross-sectional area (R 2 = 0.864) 80) . In younger humans, the cross-sectional area of skeletal muscle fiber is comparable in type I and II muscle 15,81) . However, the characteristics of sarcopenia are type II muscle fiber-specific 15,16) , and a reduction of muscular capillary density in the elderly is only observed around type II muscle fibers 8,9) .…”