Calorie restriction accelerates the catabolism of lean body mass during 2 wk of bed rest.

Background: Muscle inactivity and low energy intake commonly occur in persons with acute or chronic disease, in astronauts during space flight, and during aging.

Objective: We used a crossover design to investigate the effects of the interactions of inactivity and calorie restriction on whole-body composition and protein kinetic regulation in 9 healthy volunteers.

Design: Lean body mass (LBM) was measured by using dual-energy X-ray absorptionmetry before and at the end of 14-d periods of bed rest (B) and controlled ambulation (A) in patients receiving eucaloric (E) or hypocaloric (H) (approximately 80% of total energy expenditure) diets.

Increased urinary excretion rates of serotonin and metabolites during bedrest.

Astronauts are often on a voluntarily reduced energy intake during space missions, possibly caused by a metabolic or emotional stress response with involvement of the central serotonergic system (SES). We investigated 24 h urinary excretion (24 h-E) of serotonin (5-HT) and 5-hydroxyindol acidic acid as indicators of the SES in healthy males under two different normocaloric conditions: normal physical activity (NPA) and -6 degree head-down-tilt (HDT). HDT or NPA were randomly arranged with a recovery period of 6 months in between.

Short-term bed rest impairs amino acid-induced protein anabolism in humans.

Diminished muscular activity is associated with alterations of protein metabolism. The aim of this study was to evaluate the effect of short-term muscle inactivity on regulation of whole-body protein deposition during amino acid infusion to simulate an experimental postprandial state. We studied nine healthy young volunteers at the end of 14 day periods of strict bed rest and of controlled ambulation using a cross-over design.

Sensitivity of whole body protein synthesis to amino acid administration during short-term bed rest.

We tested the hypothesis that a reduced stimulation of whole-body protein synthesis by amino acid administration represents a major mechanism for the bed rest-induced loss of lean body mass. Healthy young subjects and matched controls were studied on the last day of a 14-day bed rest or ambulatory period, as part of the overall protocol "Short-term Bed Rest - Integrated Physiology" set up by the German Aerospace Centre (DLR) in co-operation with the European Space Agency. A balanced mixture of essential and non-essential amino acids was intravenously infused in the postabsorptive state for 3 hours at the rate of 0.

Reduced resting metabolic rate in athletes with menstrual disorders.

Purpose: This study investigated metabolic and nutritional determinants in association with menstrual disorders in athletes. Athletes with normal menstrual function (AN; N = 21) and athletes with menstrual disorders (AD: N = 12) participated in this study.

Methods: The quality of the menstrual cycle was judged according to salivary progesterone concentrations.