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Functional and metabolic early changes in calf muscle occurring during nutritional repletion in malnourished elderly patients^1,2,3

¹ From the Département de Gériatrie du Centre Hospitalo-Universitaire de Bordeaux, Hôpital Xavier Arnozan, Centre Hospitalier-Universitaire de Bordeaux, Pessac, France; Résonance Magnétique des Systèmes Biologiques, Unité Mixte de Recherche 5536, Université Victor Segalen de Bordeaux 2, Centre National de la Recherche Scientifique, Bordeaux, France; and Equipe de Recherche Universitaire EA 487, Université Victor Segalen Bordeaux 2, Bordeaux, France.

Background: Metabolic alterations in skeletal muscle associated with malnutrition and the potential reversibility of such alterations during refeeding are not fully understood.

Objective: We characterized early changes in muscle during refeeding in malnourished, hospitalized elderly subjects.

Design: Muscle function, metabolism, and mass were evaluated in 24 clinically stable patients (11 were malnourished) by using isokinetic plantar flexor torque measurements and nuclear magnetic resonance (NMR) imaging for medial gastrocnemius mass assessment and ³¹P and ¹³C NMR spectroscopy for inorganic phosphate (Pi), phosphocreatine, and glycogen quantitation.

Results: Malnourished subjects had lower muscle mass (P < 0.02) and tended to have lower strength than did control subjects. In malnourished subjects, muscle strength increased after refeeding (P < 0.01) whereas muscle mass was unchanged. The ratio of Pi to ATP was lower in malnourished than in control subjects (P < 0.001) and increased during refeeding (P < 0.01). The mean ratio of phosphocreatine to ATP was lower in malnourished than in control subjects (P < 0.01) and increased to control values after refeeding. Muscle glycogen showed a scattered distribution for malnourished subjects; the mean value did not differ significantly from that of control subjects, either at baseline or after refeeding.

Conclusions: The lower ratio of phosphocreatine to ATP in malnourished subjects could have resulted from either lower total muscle creatine or reduced oxidative capacities. High or normal glycogen associated with a low Pi-to-ATP ratio in malnourished subjects suggested preferential use of lipid over carbohydrate for energy supply, which is known to reduce muscle performance. The data suggest that normalization of muscle metabolite content after refeeding improves muscle strength in malnourished subjects.

Key Words: Nuclear magnetic resonance • phosphocreatine • inorganic phosphate • glycogen • isokinetic peak torque • muscle function • muscle mass • muscle metabolism • elderly • hospital patient • malnourished elderly • malnutrition • refeeding • skeletal muscle • protein-energy malnutrition