J Physiol 587.4 (2009) pp 897–904 897
Differential stimulation of myofibrillar and sarcoplasmic protein synthesis with protein ingestion at rest and after
resistance exercise
Daniel R. Moore1, Jason E. Tang1, Nicholas A. Burd1, Tracy Rerecich1, Mark A. Tarnopolsky2
and Stuart M. Phillips1
We aimed to determine whether there is a differential stimulation of the contractilemyofibrillar
and the cellular sarcoplasmic proteins after ingestion of protein and how this is affected by
resistance exercise. Fasted (FAST) muscle protein synthesis was measured in seven healthy
young men with a primed constant infusion of l-[ring-13C6]phenylalanine. Participants then
performed an intense bout of unilateral resistance exercise followed by the consumption of 25 g
of whey protein to maximally stimulate protein synthesis. In the rested (FED) leg myofibrillar
(MYO) protein synthesis was elevated (P<0.01) above FAST at 3 h (∼163%) but not at 1 and
5 h (P>0.05). In contrast, MYO protein synthesis in the exercised (FED-EX) leg was stimulated
above FAST at 1, 3 and 5 h (∼100, 216, and 229%, respectively; P<0.01) with the increase
at 5 h being greater than FED (P<0.01). Thus, the synthesis of muscle contractile proteins is
stimulated by both feeding and resistance exercise early (1 h) but has a greater duration and
amplitude after resistance exercise. Sarcoplasmic (SARC)protein synthesiswas similarly elevated
(P<0.01) above FAST by ∼104% at 3 h in both FED and FED-EX suggesting SARC protein
synthesis is stimulated by feeding but that this response is not augmented by resistance exercise.
In conclusion, myofibrillar and sarcoplasmic protein synthesis are similarly, but transiently,
stimulated with protein feeding. In contrast, resistance exercise rapidly stimulates and sustains
the synthesisofonly themyofibrillarprotein fractionafterprotein ingestion. These data highlight
the importance of measuring the synthetic response of specific muscle protein fractions when
examining the effects of exercise and nutrition.
