Affiliation:
1. Faculty of Kinesiology and Physical Education, University of Toronto, Toronto, Ontario, Canada
2. Toronto Rehabilitation Institute, Toronto, Canada
Abstract
ABSTRACT
Background
Acute exercise increases the incorporation of dietary amino acids into de novo myofibrillar proteins after a single meal in controlled laboratory studies in males. It is unclear whether this extends to free-living settings or is influenced by training or sex.
Objectives
We determined the effects of exercise, training status, and sex on 24-hour free-living dietary phenylalanine incorporation into skeletal muscle proteins.
Methods
In a parallel group design, recreationally active males (mean ± SD age, 23 ± 3 years; BMI. 23.4 ± 2.9 kg/m2; n = 10) and females (age 24 ± 5 years; BMI, 23.1 ± 3.9 kg/m2; n = 9) underwent 8 weeks of whole-body resistance exercise 3 times a week. Controlled diets containing 1.6 g/kg–1/d–1 (amino acids modelled after egg), enriched to 10% with [13C6] or [2H5]phenylalanine, were consumed before and after an acute bout of resistance exercise. Fasted muscle biopsies were obtained before [untrained, pre-exercise condition (REST ] and 24 hours after an acute bout of resistance exercise in untrained (UT) and trained (T) states to determine dietary phenylalanine incorporation into myofibrillar (ΔMyo) and sarcoplasmic (ΔSarc) proteins, intracellular mechanistic target of rapamycin (mTOR) colocalization with ulex europaeus agglutinin–1 (UEA-1; capillary marker; immunofluorescence), and amino acid transporter expression (Western blotting).
Results
The ΔMyo values were ∼62% greater (P < 0.01) in females than males at REST. The ΔMyo values increased above REST by ∼51% during UT and ∼30% in T (both P < 0.01) in males, remained unchanged in females during UT, and were ∼33% lower at T when compared to UT (P = 0.013). Irrespective of sex, ΔMyo and ΔSarc were decreased at T compared to UT (P ≤ 0.026). Resistance training increased mTOR colocalization with UEA-1 (P = 0.004), while L amino acid transporter 1, which was greater in males (P < 0.01), and sodium-coupled neutral amino acid transporter 2 protein expression were not affected by acute exercise (P ≥ 0.33) or training (P ≥ 0.45).
Conclusions
The exercise-induced incorporation of dietary phenylalanine into myofibrillar and sarcoplasmic proteins is attenuated after training regardless of sex, suggesting a reduced reliance on dietary amino acids for postexercise skeletal muscle remodeling in the T state.
Funder
Natural Sciences and Engineering Research Council of Canada
Mitacs Accelerate Postdoctoral Fellowship
NSERC
Publisher
Oxford University Press (OUP)
Subject
Nutrition and Dietetics,Medicine (miscellaneous)
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