Leg muscle volume during 30-day 6-degree head-down bed rest with isotonic and isokinetic exercise training

摘要

Magnetic resonance imaging (MRI) was used to compare the effect of two modes of lower-extremity exercise training on the mass (volume) of posterior leg group (PLG) muscles (soleus, flexor hallucis longus, tibialis posterior, lateral and medial gastrocnemius, and flexor digitorum longus) on 19 men (ages 32-42 years) subjected to intense dynamic-isotonic (ITE, cycle ergometer, number of subjects (N) = 7), isokinetic (IKE, torque egrometer, N = 7), and no exercise (NOE, N = 5) training for 60 min/day during head-down bed rest (HDBR). Total volume of the PLG muscles decreased (p less than 0.05) similarly: ITE = 4.3 /- SE 1.6, IKE = 7.7 /- 1.6, and NOE = 6.3 /- 0.8; combined volume (N = 19) loss was 6.1 /- 0.9. Ranges of volume changes were 2.6 to -9.0 (ITE), -2.1 to -14.9 (IKE), and -3.4 to -8/1 (NOE). Correlation coefficients (r) of muscle volume versus thickness measured with ultrasonography were: ITE r 0.79 (p less than 0.05), IKE r = 0.27 (not significant (NS)), and NOE r = 0.63 (NS). Leg-muscle volume and thickness were highly correlated (r = 0.79) when plasma volume was maintained during HDBR with ITE. Thus, neither intensive lower extremity ITE nor IKE training influence the normal non-exercised posterior leg muscle atrophy during HDBR. The relationship of muscle volume and thickness may depend on the mode of exercise training associated with the maintenance of plasma volume.