• concurrent exercise;
  • leucine;
  • microgravity;
  • muscle;
  • weightlessness;
  • WISE 2005


Aim:  The goal of this investigation was to test specific exercise and nutrition countermeasures to lower limb skeletal muscle volume and strength losses during 60 days of simulated weightlessness (6° head-down-tilt bed rest).

Methods:  Twenty-four women underwent bed rest only (BR, n = 8), bed rest and a concurrent exercise training countermeasure (thigh and calf resistance training and aerobic treadmill training; BRE, n = 8), or bed rest and a nutrition countermeasure (a leucine-enriched high protein diet; BRN, n = 8).

Results:  Thigh (quadriceps femoris) muscle volume was decreased (< 0.05) in BR (−21 ± 1%) and BRN (−24 ± 2%), with BRN losing more (< 0.05) than BR. BRE maintained (> 0.05) thigh muscle volume. Calf (triceps surae) muscle volume was decreased (< 0.05) to a similar extent (> 0.05) in BR (−29 ± 1%) and BRN (−28 ± 1%), and this decrease was attenuated (< 0.05) in BRE (−8 ± 2%). BR and BRN experienced large (< 0.05) and similar (> 0.05) decreases in isometric and dynamic (concentric force, eccentric force, power and work) muscle strength for supine squat (−19 to −33%) and calf press (−26 to −46%). BRE maintained (> 0.05) or increased (< 0.05) all measures of muscle strength.

Conclusion:  The nutrition countermeasure was not effective in offsetting lower limb muscle volume or strength loss, and actually promoted thigh muscle volume loss. The concurrent aerobic and resistance exercise protocol was effective at preventing thigh muscle volume loss, and thigh and calf muscle strength loss. While the exercise protocol offset ∼75% of the calf muscle volume loss, modification of this regimen is needed.