What question did this study set out to answer?

To investigate the effectiveness of oral amino acid tracers in measuring myofibrillar protein synthesis rates under different feeding and exercise conditions.

March 6, 2026

Oral amino acid tracer delivery detects feeding and exercise changes in myofibrillar protein synthesis rates in male adults.

Key Points

To investigate the effectiveness of oral amino acid tracers in measuring myofibrillar protein synthesis rates under different feeding and exercise conditions.
Participants were randomized into three groups: rested-fasted, rested-fed, and exercise-fed.
Fed groups consumed a carbohydrate and amino acid beverage containing tracers before and after exercise.
Blood samples were collected every 30 minutes for 5 hours to analyze tracer precursor enrichment.
Muscle biopsies were taken before and at 120 and 300 minutes post-ingestion to measure protein synthesis.
LEUMyoPS was significantly higher in the exercise-fed and fed groups compared to the fasted group.
PHEMyoPS was also greater in the exercise-fed and fed groups than in the fasted group.
A strong correlation was found between LEUMyoPS and protein synthesis rates.

Abstract

The efficacy of oral administration of leucine and phenylalanine tracers to measure MyoPS (LEUMyoPS and PheMyoPS, respectively) in response to varying anabolic stimuli was investigated. Participants were randomized to a rested-fasted (FAST), rested-fed (FED), or exercise-fed (EXFED) condition. FED and EXFED consumed a mixed carbohydrate and AA beverage enriched with L-1-13Cleucine (25%) and L-ring-2H5phenylalanine (30%) at rest or after a bout of resistance exercise, while FAST consumed only the equivalent tracer dose. Blood samples were obtained every 30 min for 300 min to determine tracer precursor enrichment with muscle biopsies obtained before and at 120 and 300 min after tracer ingestion to determine MyoPS by the precursor-product method. LEUMyoPS over 300 min was greater (p < 0.01) in EXFED (0.090 ± 0.024%/h; mean ± SD) and FED (0.067 ± 0.028%/h) compared to FAST (0.024 ± 0.015%/h). PHEMyoPS over 300 min was greater (p < 0.01) in EXFED (0.128 ± 0.034%/h) and FED (0.098 ± 0.020%/h) compared to FAST (0.056 ± 0.012%/h). There was a positive correlation (r = 0.81, p < 0.0001) between LEUMyoPS and. Oral essential amino acid tracer ingestion can be used as an alternative method to detect changes in MyoPS in response to mixed macronutrient feeding and feeding plus exercise and may be an option for the study of human muscle protein synthesis where intravenous isotope administration is logistically difficult or prohibitively expensive.

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Cite This Study

Mazzulla et al. (Sun,) studied this question.

synapsesocial.com/papers/69aa70e7531e4c4a9ff5b2ea https://doi.org/https://doi.org/10.14814/phy2.70776

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