Taking HMB shortly before exercise is linked to higher levels of two specific proteins in muscle tissue that help bring in amino acids and trigger muscle growth pathways.

We analyzed the available evidence and found that taking HMB shortly before exercise is linked to higher levels of two proteins in muscle tissue—SLC36A1 and SLC7A5—that help transport amino acids into muscle cells and may influence muscle growth pathways [1]. This observation comes from one assertion supported by 45.0 data points, with no conflicting findings in our current review. The evidence we’ve reviewed suggests that acute HMB ingestion may influence how muscle cells handle amino acids by increasing the presence of these two transporter proteins. SLC36A1 and SLC7A5 are not enzymes or hormones—they’re like doorways on the surface of muscle cells that help bring in building blocks needed for repair and adaptation after physical stress. When their levels rise, it could mean the muscle is preparing to respond more effectively to the demands of exercise. However, we only have one assertion to work with, even though it’s backed by 45.0 supporting data points. We don’t know how consistent this effect is across different people, doses, or types of exercise. We also don’t know how long the increase lasts or whether it leads to measurable changes in muscle growth over time. What we’ve found so far points toward a possible biological link between acute HMB intake and increased expression of these transporters, but it’s still an early observation. More studies are needed to understand the context, timing, and real-world impact of this effect. If you’re considering HMB before a workout, this suggests your muscle cells might be primed to take in more amino acids—but whether that translates to better results over time remains unclear based on what we’ve seen so far.