Lean mass accumulation research typically investigates compounds that promote anabolic activity in skeletal muscle — whether through the androgen receptor, growth hormone pathways, or myostatin inhibition. RAD-140, LGD-4033, YK-11, and MK-677 represent the four most extensively studied compounds in this category, each with distinct mechanisms and evidence quality.
For lean mass research requiring the most robust published human clinical data, LGD-4033 (Ligandrol) is the clear leader. The Basaria et al. 2013 Phase I trial provides double-blind, placebo-controlled data demonstrating dose-dependent lean mass gains (+1.21 kg at 1 mg/day over 21 days) in healthy men — unique in the SARM literature. Viking Therapeutics' subsequent VK5211 Phase II trial in hip fracture patients further established lean mass gains in a clinical population. LGD-4033 is a full AR agonist at doses substantially lower than other potent SARMs.
RAD-140's preclinical data suggests a higher anabolic-to-androgenic selectivity ratio than LGD-4033 in some assays, making it an important research compound for lean mass protocols. Its Phase I/II breast cancer trials (Bardia et al., 2020) provide some human data, though at doses and in populations different from lean mass research contexts. Its ~16-hour half-life enables once-daily dosing. Preclinical primate studies document significant lean mass effects with minimal prostate changes.
YK-11's unique mechanism — partial AR agonism combined with Follistatin-mediated myostatin inhibition — makes it theoretically distinct from all other compounds in lean mass research. The in vitro Kanno 2013 data demonstrating greater myoblast anabolic activity than DHT is compelling, but the lack of in vivo and human clinical data is a significant limitation. YK-11 protocols are generally considered higher risk due to the absence of in vivo safety characterisation.
MK-677 approaches lean mass through an entirely different axis — stimulating growth hormone and IGF-1 rather than activating the androgen receptor. Published human trial data (Murphy et al. 1998; Nass et al. 2008) documents lean mass preservation and gains in older subjects. Crucially, MK-677 does not suppress endogenous testosterone, making it mechanistically distinct and enabling co-administration with AR-targeting SARMs without additive suppression concerns.
| Compound | Human evidence level | Suppression | Mechanism |
|---|---|---|---|
| LGD-4033 | Phase I (healthy men) | Moderate–significant | AR full agonist |
| RAD-140 | Phase I/II (oncology) | Moderate–significant | AR full agonist |
| YK-11 | In vitro only | Significant (expected) | AR + Myostatin inhibition |
| MK-677 | Multiple Phase I/II | None | GH secretagogue |
Per milligram, LGD-4033 produces the most clearly documented lean mass gains in published controlled human research. RAD-140's preclinical selectivity data suggests high potency, but its human data comes from cancer patients at oncology-range doses. YK-11 has the most compelling theoretical potency but the least in vivo evidence.
Yes, and this is commonly studied. Since MK-677 acts via GHSR-1a rather than the AR, it does not add to the testosterone suppression burden of an AR-targeting SARM. The additive anabolic effects of GH/IGF-1 elevation alongside AR activation represent a meaningful combination for lean mass research.
