This study was designed to describe changes in plasma fatty acyl moieties during a 2-h endurance exercise. Sixteen endurance-trained subjects cycled 2 h at 55% of maximal power output and capillary blood was sampled every 15 min. Fourier-transform infrared (FT-IR) spectrometry was used to determine correlated changes between plasma fatty acyl moieties (FAM) structural characteristics and metabolic parameters (oxygen consumption, respiratory exchange ratio, glucose, lactate, TG, glycerol, and albumin). Opposite changes were found between carbohydrate and fatty acid metabolism during the second hour of exercise, i.e., a decrease of glucose and lactate concentrations while albumin, FAM, and TG increased. For fatty acid metabolism, FAM and TG did not showed the same pattern of changes at the end of exercise, i.e., TG remained constant after 90 min while FAM continued to increase. This late FAM concentration increase was correlated to the changes in albumin concentration and the nu C=C-H/nu(as) CH3 and nu(as) CH2/nu(as) CH3 ratios. These ratios clearly showed that FAM unsaturation increased while chain length decreased. It was hypothesized that PUFA from TG adipose lipolysis ketone bodies (beta-hydroxybutyric acid) from liver may have been released in higher amounts as glycogen stores became depleted after 90 min of exercise.
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