Effect of 14 Day Bed Rest on Health Outcomes in Young and Older Participants

Twenty-three healthy men, of which 7 young (YM; aged 18-30 years) and 16 older adults (OM; aged 55-65 years) were recruited for the study. All participants underwent medical examination and routine blood and urine analysis. Exclusion criteria were: smoking; regular alcohol consumption; ferromagnetic implants; history of deep vein thrombosis with D-dimer > 500 μg·L-1; acute or chronic skeletal, neuromuscular, metabolic and cardiovascular disease conditions; pulmonary embolism. Participants were informed of the purpose, procedures and potential risk of the study before signing the informed consent. The study was performed in accordance with the ethical standards of the 1964 Declaration of Helsinki and was approved by the National Ethical Committee of the Slovenian Ministry of Health on April 17, 2012.

The study was conducted in controlled medical environment of the Orthopedic Hospital of Valdoltra, Slovenia. The participants were housed in standard air conditioned hospital rooms and were under constant surveillance with 24-hour medical care. For 14 days, the participants performed all daily activities in bed and received eucaloric controlled meals three times a day. Dietary energy requirements were designed for each subject multiplying resting energy expenditure by factors 1.2 and 1.4 in BR and ambulatory period, respectively. The resting energy expenditure was calculated as done in previous studies. The macronutrient food content set at 60% of carbohydrates, 25% fat, and 15% of proteins, according to the scheme of the so called "mediterranean diet" and adopted also in previous bed rest protocols. Energy balance was checked weekly by fat mass assessment. The daily protein intake was 1.1-1.25 g kg-1 in both groups, in BR and recovery period respectively, except the subgroups of OM who received a supplementation (see below).

After the BR, participants underwent a rehabilitation protocol (R) that consisted of 4-week supervised multimodal exercise program with 3 sessions per week. In each session, participants performed 12-minute warm-up, 15-20 minutes of balance and strength training, and 20-30 minutes of endurance training.

Inclusion criteria

• Body mass index < 28 kg/m2
• Short physical performance battery score >= 9

Exclusion criteria

• smoking;
• regular alcohol consumption;
• ferromagnetic implants;
• history of deep vein thrombosis with D-dimer > 500 μg·L-1;
• acute or chronic skeletal, neuromuscular, metabolic and cardiovascular disease conditions.