Post-exercise protein synthesis rates are only marginally higher in type I compared with type II muscle fibres following resistance-type exercise

We examined the effect of an acute bout of resistance exercise on fractional muscle protein synthesis rates in human type I and type II muscle fibres. After a standardised breakfast (31 +/- A 1 kJ kg(-1) body weight, consisting of 52 Energy% (En%) carbohydrate, 34 En% protein and 14 En% fat), 9 untrained men completed a lower-limb resistance exercise bout (8 sets of 10 repetitions leg press and leg extension at 70% 1RM). A primed, continuous infusion of l-[ring-C-13(6)]phenylalanine was combined with muscle biopsies collected from both legs immediately after exercise and after 6 h of post-exercise recovery. Single muscle fibres were dissected from freeze-dried biopsies and stained for ATPase activity with pre-incubation at a pH of 4.3. Type I and II fibres were separated under a light microscope and analysed for protein-bound l-[ring-C-13(6)]phenylalanine labelling. Baseline (post-exercise) l-[ring-C-13(6)]phenylalanine muscle tissue labelling, expressed as (a,C-13/C-12), averaged -32.09 +/- A 0.28, -32.53 +/- A 0.10 and -32.02 +/- A 0.16 in the type I and II muscle fibres and mixed muscle, respectively (P = 0.14). During post-exercise recovery, muscle protein synthesis rates were marginally (8 +/- A 2%) higher in the type I than type II muscle fibres, at 0.100 +/- A 0.005 versus 0.094 +/- A 0.005%/h, respectively (P < 0.05), whereby rates of mixed muscle protein were 0.091 +/- A 0.005%/h. Muscle protein synthesis rates following resistance-type exercise are only marginally higher in type I compared with type II muscle fibres.