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Exercise in the fasted state facilitates fibre type‐specific intramyocellular lipid breakdown and stimulates glycogen resynthesis in humans
Author(s) -
De Bock K.,
Richter E. A.,
Russell A. P.,
Eijnde B. O.,
Derave W.,
Ramaekers M.,
Koninckx E.,
Léger B.,
Verhaeghe J.,
Hespel P.
Publication year - 2005
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.2005.083170
Subject(s) - medicine , endocrinology , glycogen , vastus lateralis muscle , triglyceride , chemistry , carbohydrate , exercise physiology , skeletal muscle , biology , cholesterol
The effects were compared of exercise in the fasted state and exercise with a high rate of carbohydrate intake on intramyocellular triglyceride (IMTG) and glycogen content of human muscle. Using a randomized crossover study design, nine young healthy volunteers participated in two experimental sessions with an interval of 3 weeks. In each session subjects performed 2 h of constant‐load bicycle exercise (∼75%), followed by 4 h of controlled recovery. On one occasion they exercised after an overnight fast (F), and on the other (CHO) they received carbohydrates before (∼150 g) and during (1 g ( kg bw ) −1 h −1 ) exercise. In both conditions, subjects ingested 5 g carbohydrates per kg body weight during recovery. Fibre type‐specific relative IMTG content was determined by Oil red O staining in needle biopsies from m. vastus lateralis before, immediately after and 4 h after exercise. During F but not during CHO, the exercise bout decreased IMTG content in type I fibres from 18 ± 2% to 6 ± 2% ( P = 0.007) area lipid staining. Conversely, during recovery, IMTG in type I fibres decreased from 15 ± 2% to 10 ± 2% in CHO, but did not change in F. Neither exercise nor recovery changed IMTG in type IIa fibres in any experimental condition. Exercise‐induced net glycogen breakdown was similar in F and CHO. However, compared with CHO (11.0 ± 7.8 mmol kg −1 h −1 ), mean rate of postexercise muscle glycogen resynthesis was 3‐fold greater in F (32.9 ± 2.7 mmol kg −1 h −1 , P = 0.01). Furthermore, oral glucose loading during recovery increased plasma insulin markedly more in F (+46.80 μU ml −1 ) than in CHO (+14.63 μU ml −1 , P = 0.02). We conclude that IMTG breakdown during prolonged submaximal exercise in the fasted state takes place predominantly in type I fibres and that this breakdown is prevented in the CHO‐fed state. Furthermore, facilitated glucose‐induced insulin secretion may contribute to enhanced muscle glycogen resynthesis following exercise in the fasted state.