MuscleTech Amino 4XL SX-7 Black Onyx Review

MuscleTech Amino 4XL SX-7 Black Onyx

Amino 4XL SX-7 Black Onyx is a BCAA/Amino supplement by MuscleTech which consists of some pretty standard ingredients, not necessarily at the most optimal doses…


Leucine is the most potent of all amino acids when it comes to stimulating muscle protein synthesis.  Thus, it should come as no surprise that MuscleTech included it at a much higher dose than the other two BCAAs (Isoleucine and Valine), as is the case in most BCAA supplements.

Amino 4XL SX-7 Black Onyx contains three types of Leucine: Instantized Leucine, ActiveTR (delayed release Leucine), and PepForm Leucine peptides.  This allows for both immediate and prolonged absorption of Leucine, but with just two grams of total Leucine per serving, the actual impact on muscle protein synthesis may not be particularly profound.

At two servings (2g of Leucine per serving, 4g total), that’s a pretty good dose though…

Isoleucine and Valine

Although Isoleucine and Valine are not potent activators of muscle protein synthesis like Leucine, they may have their own individual functions that make them worth taking as well.  Isoleucine in particular has been shown to induce glucose uptake into muscle cells, and BCAAs in general may also help fight fatigue via competitively reducing Tryptophan uptake into the brain (reducing Serotonin which causes fatigue).  However, at the doses present in Amino 4XL SX-7 Black Onyx (400mg of Isoleucine and Valine per serving), it’s not clear how effective they are.


In the context of Amino 4XL SX-7 Black Onyx, Taurine may help to reduce oxidative damage to muscle tissue that typically occurs during exercise.  Although many of the benefits of Taurine seem to have been exaggerated by bodybuilding supplement companies, those pertaining to exercise recovery are quite reliable.

Taurine has also been shown to synergistically enhance the recovery benefits of BCAAs (particularly by reducing muscle soreness) so it ultimately makes for a fine addition to any Amino/BCAA supplement.


Glutamine levels tend to be depleted by rigorous exercise and this depletion appears to be correlated with a temporary decline in immune function.  Therefore, it stands to reason that Glutamine may be helpful as a recovery-aid, albeit through different mechanisms than Taurine.  However, at the dose present in Amino 4XL SX-7 Black Onyx (500mg per serving), it probably doesn’t make much of an impact.  The doses of Glutamine used in most studies have generally been much, much higher.


Though often referred to as a “pump” ingredient, Citrulline has reliable mechanisms by which it actually enhances muscular endurance.  However, studies showing performance enhancement benefits have used much higher doses of Citrulline (6-9g), usually as Citrulline Malate.  Since Amino 4XL SX-7 Black Onyx contains such a small amount of Citrulline (only 250mg), it’s doubtful that it provides much benefit.

Beyond enhancing muscular endurance, Citrulline also may synergistically enhance the impact of Leucine on muscle protein synthesis, but again, with such a low dose in Amino 4XL SX-7 Black Onyx such benefits likely don’t apply.

Peak ATP

Peak ATP is a bioavailable form of Adenosine Triphosphate (ATP) which Iovate (parent company of MuscleTech) has used in several different supplements over the past couple years.  Studies have shown Peak ATP to significantly increase circulating levels of ATP and ultimately provide some performance enhancement and recovery benefits.

We discuss the benefits of Peak ATP more in-depth here.

The “clinical range” is 200-400mg, with 400mg being the more effective dose, but Amino 4XL SX-7 Black Onyx provides just 100mg per serving.

The Bottom Line

The ingredient profile of Amino 4XL SX-7 Black Onyx is solid, but most of the ingredients are pretty under-dosed relative to what has proven effective in studies.  If money is no option, and you can consume multiple servings at a time, then Amino 4XL SX-7 Black Onyx may be worth a shot, but there are certainly much more effective BCAA/Amino Supplements out there.

If you’re looking for something that will actually help you gain lean muscle, check out our Best Muscle Builders List! exists to educate the supplement community and seperate the science from the hype.

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