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Muscle-specific substrate use during cycle exercise at 1 G: implications for astronaut muscle health.

Aviation, space, and environmental medicine (2013-08-10)
Bridget E Lester, Robert A Standley, Jonah D Lee, William J Fink, Scott W Trappe, Todd A Trappe
ABSTRACT

Studies of real and simulated microgravity exposure show the lower limb muscles atrophy to the greatest extent, with the calf muscles being most affected and most difficult to target with exercise countermeasures. This ground-based study examined the metabolic involvement of the thigh and calf muscles during two cycle exercise protocols (moderate and high intensity) central to the exercise countermeasures program on the International Space Station. Intramuscular glycogen and triglyceride levels were quantified in the vastus lateralis and soleus muscles before and after a moderate (current ISS prescription: 45 min at 55% VO(2max), 131 +/- 12 W) and high (proposed ISS prescription: 8 x 30-s intervals at 150% VO(2max), 459 +/- 34 W) intensity cycle exercise bout in nine individuals. During moderate intensity cycling, glycogen was significantly reduced in the vastus lateralis (114 +/- 27 mmol x kg(-1) dry weight) and remained unchanged in the soleus. High intensity cycling significantly reduced glycogen in both muscles, but the vastus lateralis (151 +/- 25 mmol x kg(-1) dry weight) used significantly more (-160%) than the soleus (59 +/- 11 mmol x kg(-1) dry weight). Intramuscular triglycerides were unchanged in both muscles at both intensities. These findings, coupled with other ground-based studies, provide strong support for high intensity cycling being a more appropriate component of the ISS prescription for upper and lower leg skeletal muscle health and cardiorespiratory fitness, although additional exercise paradigms that target the calf are warranted. These muscle-specific findings should be considered when designing exercise strategies for combating conditions of sarcopenia and muscle wasting on Earth.

MATERIALS
Product Number
Brand
Product Description

Sigma-Aldrich
Glycogen from oyster, ≥75% dry basis
Sigma-Aldrich
Glycogen from bovine liver, ≥85%
Sigma-Aldrich
Glycogen from Mytilus edulis (Blue mussel), for DNA precipitations
Sigma-Aldrich
Glycogen from rabbit liver, ≥85% dry basis (enzymatic)
Sigma-Aldrich
Glycogen from Mytilus edulis (Blue mussel), ≥85%
Sigma-Aldrich
Glycogen from oyster, Type XI