In vivo evaluation of the effects of continuous exercise on skeletal muscle triglycerides in trained humans

Magnetic resonance spectroscopy (H-1 MRS) and imaging (MRI) were used to in vestigate the effects of a bout of moderate prolonged exercise on intra (IM CL)- and extramyocellular lipid (EMCL) utilization in the soleus, tibialis anterior, and gastrocnemius muscles of five trained human subjects. MRI and H-1 MRS measurements were obtained before and after a 90 min run on a cali brated treadmill at a velocity corresponding to 64 +/- 1.5% of each subject s' maximal rate of oxygen consumption. There were significant decreases in IMCL following exercise in the tibialis (pre: 22.37 +/- 4.33 vs. post: 15.7 6 +/- 3.25 mmol/kg dry wt; P< 0.01) and soleus (pre: 36.93 +/- 1.45 vs, pos t: 29.85 +/- 2.44 mmol/kg dry wt; P < 0.01) muscles. There was also a decre ase in the gastrocnemius muscle, although this did not reach the level of s ignificance (pre: 33.78 +/- 5.35 vs. post: 28.48 +/- 5.44 mmol/kg dry weigh t; P< 0.10). No significant changes were observed in EMCL or subcutaneous f at. In conclusion, this study showed that IMCL were significantly utilized in the tibialis and soleus muscles of aerobically endurance-trained humans. The absence of significant utilization of IMCL in the gastrocnemius may re flect differences in fiber type and/or intensity of contraction for each mu scle group.