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Strong Support

causal

History

In young men who do not regularly lift weights, performing resistance exercise increases muscle protein synthesis by about 41% two hours after the workout. Consuming leucine-enriched amino acids and...

Pro

Against

Mechanism

Synthesis from 1 study

How it works

After lifting weights, your muscles are ready to grow, but they need the right fuel. Leucine from protein and sugar from carbs work together to flip a master switch that tells your muscles to build new proteins much faster. Without this fuel, growth is modest; with it, protein production jumps...

Most probable mechanism

In Simple Terms

After lifting weights, muscle cells are primed to build new proteins. When you drink a shake with leucine and sugar, the leucine directly turns on a key growth switch inside the cell, while the sugar triggers insulin release, which turns on the same switch through a different route. Both signals combine to fully activate this switch, which then tells the cell’s protein-making machinery to start working much harder, pulling in more building blocks to make new muscle proteins faster.

Causal chain

Leucine from ingested essential amino acids enters muscle cells and activates class III PI3K (hVps34), initiating a signaling cascade that converges on mTOR

Verified by multiple studies

which leads to

Carbohydrate ingestion elevates blood insulin, which activates PI3K-Akt signaling, leading to phosphorylation and inhibition of TSC2

Verified by multiple studies

which leads to

Inhibition of TSC2 releases mTOR from suppression, allowing it to be fully activated by converging signals from leucine and insulin

Supported by evidence

which leads to

Activated mTOR phosphorylates S6K1 and 4E-BP1, promoting ribosomal biogenesis and releasing eIF4E to form the translation initiation complex

Verified by multiple studies

which leads to

Phosphorylated S6K1 increases translation efficiency, while freed eIF4E enables assembly of the eIF4F complex to initiate mRNA translation

Verified by multiple studies

which leads to

Enhanced translation initiation increases the rate of amino acid incorporation into newly synthesized muscle proteins

Verified by multiple studies

Evidence from Studies

Supporting (1)

Community contributions welcome

Leucine-enriched essential amino acid and carbohydrate ingestion following resistance exercise enhances mTOR signaling and protein synthesis in human muscle.

Randomized Controlled Trial

Human

2008 Feb

Contradicting (0)

Community contributions welcome

No contradicting evidence found

Gold Standard Evidence Needed

According to GRADE and EBM methodology, here is what ideal scientific evidence would look like to definitively prove or disprove this specific claim, ordered from strongest to weakest evidence.

Source Study

Leucine-enriched essential amino acid and carbohydrate ingestion following resistance exercise enhances mTOR signaling and protein synthesis in human muscle.

Score: 46

DOI: 10.1152/AJPENDO.00582.2007

Similar Assertions

If young men who don't usually work out drink a special protein-and-sugar shake about an hour after lifting weights, their muscles build protein much faster—nearly triple the rate—compared to just working out without the shake.

91%

If young men who don’t usually lift weights drink a special protein-and-sugar shake one hour after working out, their muscles build protein much faster—nearly triple the rate—than if they just worked out alone, probably because the shake turns on key muscle-building signals in their cells.

90%

Consuming a specific combination of amino acids and carbohydrates one hour after a resistance workout in young, untrained men leads to a measurable increase in muscle protein synthesis and activation of key signaling proteins involved in protein production, compared to performing the workout without this nutritional intake.

84%

Eating more protein after working out makes your whole body build more protein - the more protein you eat, the more protein your whole body builds.

84%

Eating protein after working out only affects the muscle's signaling pathways for about 4 hours - after that, the signaling goes back to normal even though muscle building continues.

84%