RESUMEN
PURPOSE: Aging and inactivity lead to skeletal muscle metabolic inflexibility, but the underlying molecular mechanisms are not entirely elucidated. Therefore, we investigated how muscle lipid and glycogen stores and major regulatory proteins were affected by short-term immobilization followed by aerobic training in young and older men. METHODS: 17 young (23 ± 1 years, 24 ± 1 kg m(-2), and 20 ± 2% body fat) and 15 older men (68 ± 1 years; 27 ± 1 kg m(-2), and 29 ± 2% body fat) underwent 2 weeks' one leg immobilization followed by 6 weeks' cycle training. Biopsies were obtained from m. vastus lateralis just before immobilization (at inclusion), after immobilization, and the after 6 weeks' training. The biopsies were analyzed for muscle substrates; muscle perilipin protein (PLIN), glycogen synthase (GS), synaptosomal-associated protein of 23 kDa (SNAP23) protein content, and muscle 3-hydroxyacyl-CoA dehydrogenase (HAD) activity RESULTS: The older men had higher intramuscular triglyceride (IMTG) (73 %) and Glycogen (16%) levels compared to the young men, and IMTG tended to increase with immobilization. PLIN2 and 3 protein content increased with immobilization in the older men only. The young men had higher GS (74%) protein compared to the older men. Immobilization decreased and training restored HAD activity, GS and SNAP23 protein content in young and older men. CONCLUSION: Evidence of age-related metabolic inflexibility is presented, seen as body fat and IMTG accumulation. The question arises as to whether IMTG accumulation in the older men is caused by or leading to the increase in PLIN2 and 3 protein content. Training decreased body fat and IMTG levels in both young and older men; hence, training should be prioritized to reduce the detrimental effect of aging on metabolism.
Asunto(s)
Ejercicio Físico , Glucógeno/metabolismo , Inmovilización/efectos adversos , Metabolismo de los Lípidos , Proteínas Musculares/metabolismo , Músculo Esquelético/metabolismo , 3-Hidroxiacil-CoA Deshidrogenasa/metabolismo , Anciano , Proteínas Portadoras/metabolismo , Glucógeno Sintasa/metabolismo , Humanos , Masculino , Músculo Esquelético/crecimiento & desarrollo , Perilipina-1 , Fosfoproteínas/metabolismo , Proteínas Qb-SNARE/metabolismo , Proteínas Qc-SNARE/metabolismo , Adulto JovenRESUMEN
OBJECTIVE: To determine the effect of aerobic retraining as rehabilitation after short-term leg immobilization on leg strength, leg work capacity, leg lean mass, leg muscle fibre type composition and leg capillary supply, in young and older men.Subjects and design: Seventeen young (23 ± 1 years) and 15 older (68 ± 1 [standard error of the mean; SEM] years) men had one leg immobilized for 2 weeks, followed by 6 weeks' bicycle endurance retraining. METHODS: Maximal voluntary contraction, leg work capacity (Wmax), and leg lean mass by dual energy X-ray absorptiometry were measured at inclusion, after immobilization and after 3 and 6 weeks' retraining. Muscle biopsies were evaluated for fibre type, fibre area, and capillarization. RESULTS: Immobilization decreased maximal voluntary contraction (-28 ± 6% and -23 ± 3%); Wmax (-13 ± 5% and -9 ± 4%) and leg lean mass (only in young, -485 ± 105g) in young and older men, respectively. Six weeks' retraining increased maximal voluntary contraction (34 ± 8% and 17 ± 6%), Wmax (33 ± 5% and 20 ± 5%) and leg lean mass (only in young 669 ± 69 g) in young and older men, respectively, compared with the immobilized value. CONCLUSION: Short-term leg immobilization had marked effects on leg strength, and work capacity and 6 weeks' retraining was sufficient to increase, but not completely rehabilitate, muscle strength, and to rehabilitate aerobic work capacity and leg lean mass (in the young men).
Asunto(s)
Terapia por Ejercicio , Extremidad Inferior/fisiología , Fuerza Muscular/fisiología , Adulto , Anciano , Capilares/fisiología , Humanos , Inmovilización , Masculino , Contracción Muscular/fisiología , Fibras Musculares Esqueléticas/fisiología , Músculo Esquelético/irrigación sanguínea , Resistencia Física/fisiologíaRESUMEN
We studied the effect of physical inactivity and subsequent retraining on cardiovascular risk factors in 17 young (Y; 23.4 ± 0.5 years) and 15 older adult (O; 68.1 ± 1.1 years) men who underwent 14 days of one leg immobilization followed by six weeks of training. Body weight remained unchanged. Daily physical activity decreased by 31 ± 9% (Y) and 37 ± 9% (O) (p < .001). Maximal oxygen uptake decreased with inactivity (Y) and always increased with training. Visceral fat mass decreased (p < .05) with training. Concentrations of lipids in blood were always highest in the older adults. FFA and glycerol increased with reduced activity (p < .05), but reverted with training. Training resulted in increases in HDL-C (p < .05) and a decrease in LDL-C and TC:HDL-C ratio (p < .05). A minor reduction in daily physical activity for two weeks increased blood lipids in both young and older men. Six weeks of training improved blood lipids along with loss of visceral fat.