Endurance Exercise as a Countermeasure for Aging

Abstract

Objective: We determined whether reduced insulin sensitivity, mitochondrial dysfunction and other age-related dysfunctions are inevitable consequences of aging or secondary to physical inactivity.

Research Design and Methods: Insulin sensitivity was measured by hyperinsulinemic-euglycemic clamp and ATP production in mitochondria isolated from vastus lateralis biopsies in 42 healthy sedentary and endurance trained young (18-30 years) and older (59-76 years) humans. Expression of proteins involved in fuel metabolism was measured by mass spectrometry. Citrate synthase activity, mitochondrial DNA abundance (mtDNA), and expression of nuclear-encoded transcription factors for mitochondrial biogenesis were measured. SIRT3, a mitochondrial sirtuin linked to lifespan-enhancing effects of caloric restriction was measured by immunoblot.

Results: Insulin-induced glucose disposal and suppression of endogenous glucose production were higher in the trained young and older people but no age-effect was noted. Age-related decline in mitochondrial oxidative capacity was absent in endurance-trained individuals. Although endurance trained individuals exhibited higher expression of mitochondrial proteins, mtDNA, and mitochondrial transcription factors there were persisting effects of age. SIRT3 expression was lower with age in sedentary but equally elevated in endurance trained individuals.

Conclusions: The results demonstrate that reduced insulin sensitivity is likely related to changes in adiposity and physical inactivity rather than an inevitable consequence of aging. The results also show that regular endurance exercise partly normalizes age-related mitochondrial dysfunction, although there are persisting effects of age at the level of mtDNA abundance, nuclear transcription factors, and mitochondrial protein expression. Furthermore, exercise may promote longevity through pathways common to effects of caloric restriction.