Synopsis

Source of validity: Scientific
Rating (out of 5): 2

L-cysteine is a semi-essential amino acid involved in protein synthesis and is a precursor to the antioxidant glutathione. In the context of bodybuilding, its use is primarily justified by scientific understanding of its biochemical roles, albeit with limited direct evidence supporting significant benefits for muscle growth or performance. L-cysteine is thought to help reduce oxidative stress caused by intense exercise, as it is a key component in the synthesis of glutathione, one of the body’s most important antioxidants. Some research suggests that supplementation with N-acetylcysteine (NAC), a precursor of L-cysteine, may reduce muscle fatigue and improve recovery by combating oxidative damage and supporting immune function in athletes.

However, direct studies on L-cysteine supplementation specifically for muscle hypertrophy, strength gains, or other traditional bodybuilding outcomes are sparse. Most available evidence comes from studies on NAC, which show only modest benefits in reducing fatigue and promoting recovery in endurance athletes rather than strength athletes. There is limited evidence that L-cysteine itself, as opposed to NAC, provides significant ergogenic or anabolic effects in the context of bodybuilding.

In summary, while there is a biochemical rationale for L-cysteine supplementation in reducing oxidative stress, the scientific evidence supporting its direct use for muscle growth or bodybuilding performance is weak. Thus, it earns a rating of 2 out of 5 for evidence strength in this context.

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