Dr. William Seeds on Muscle: The Science Is More Interesting Than the Hype
Thomas DeLauer gets a lot of fitness content creators on his show, but Dr. William Seeds is different. He is a board-certified orthopedic surgeon and one of the founding members of the International Peptide Society. When he talks about peptides for muscle building, he is coming from a place of deep research familiarity and clinical application, not bro-science speculation. This conversation covers ground that most peptide discussions online completely miss.
Seeds starts by reframing the conversation. Most people think of peptides for muscle in terms of growth hormone, and while GH is part of the picture, it is not the whole story. He explains that muscle growth is regulated by a complex web of signaling pathways, including mTOR, AMPK, myostatin, follistatin, and various growth factors. Different peptides interact with different parts of this web, and the results you get depend on which pathways you activate and when.
The growth hormone secretagogue approach, using peptides like Ipamorelin and CJC-1295 to boost natural GH output, is the most popular entry point. Seeds explains that elevated growth hormone increases IGF-1 production in the liver, and IGF-1 is a direct driver of muscle protein synthesis. But the relationship is not linear. Doubling your GH does not double your muscle growth. There are diminishing returns, and at very high levels, the side effects (water retention, joint pain, insulin resistance) start outweighing the benefits.
This is where Seeds gets into territory that separates him from most commentators. He discusses the role of mechanical growth factor (MGF), a splice variant of IGF-1 that is produced locally in muscle tissue in response to exercise. PEG-MGF is a synthetic version that some researchers are studying for its ability to activate satellite cells, the muscle stem cells that are responsible for creating new muscle fibers, not just enlarging existing ones. This distinction between hypertrophy (bigger fibers) and hyperplasia (more fibers) is one of the holy grails of muscle physiology.
BPC-157 and TB-500 for Recovery: Why Athletes Care
Seeds pivots to recovery peptides, and this is where his orthopedic surgery background adds real value. He has treated professional athletes and sees firsthand how injuries respond to different interventions. BPC-157, he explains, works partly through upregulation of growth hormone receptors in damaged tissue. This means it does not just promote healing directly, it makes the tissue more responsive to your own growth hormone, amplifying the repair process.
The mechanism of BPC-157 involves several pathways: it promotes angiogenesis (new blood vessel formation) at injury sites, it modulates the nitric oxide system, and it has been shown to upregulate key growth factors including VEGF, FGF, and EGF. In animal studies, it has accelerated healing of tendons, muscles, ligaments, bones, and even the gastrointestinal tract. Seeds notes that the tendon repair data is particularly compelling because tendons are notoriously slow to heal due to their limited blood supply.
TB-500 complements BPC-157 through a different mechanism. It promotes cell migration, which is the process by which repair cells move to the site of damage. It also reduces inflammation through downregulation of inflammatory cytokines and upregulation of anti-inflammatory factors. Seeds uses the analogy of BPC-157 building the roads (blood vessels) and TB-500 moving the construction workers (repair cells) down those roads.
For athletes and serious trainees, the practical application is straightforward. Use these peptides during periods of high training volume or when recovering from specific injuries. Seeds typically runs cycles of 4-6 weeks, with subcutaneous injections near the affected area when applicable. He mentions that some practitioners are experimenting with oral BPC-157, which may be effective for gut healing but likely has lower bioavailability for musculoskeletal injuries compared to injection.
The Myostatin Connection
One of the more fascinating segments covers myostatin inhibition. Myostatin is a protein that limits muscle growth. It is basically your body saying "that is enough muscle, stop building." Animals with myostatin mutations are freakishly muscular, think of the Belgian Blue cattle breed that looks like it was designed in a video game. Follistatin is a natural myostatin inhibitor, and some researchers are exploring synthetic peptides that modulate this pathway.
Seeds is cautious here. He notes that myostatin inhibition sounds amazing in theory, but the clinical reality is more complicated. Complete myostatin blockade can cause tendon and ligament problems because these connective tissues do not strengthen at the same rate as the muscle. You end up with muscles that are stronger than the structures attaching them to bone, which is a recipe for injury. Partial modulation is the goal, enough to tip the balance toward muscle growth without overwhelming the connective tissue.
There are also cardiac concerns. Myostatin is expressed in heart muscle, and its role there is not fully understood. Blocking it systemically could have unintended cardiovascular effects. Seeds advocates for targeted, moderate approaches rather than aggressive myostatin blockade.
Practical Protocols for the Non-Professional Athlete
DeLauer asks Seeds what a regular person, not a pro athlete, should actually do. Seeds recommends starting with the basics before considering peptides. If your training is inconsistent, your nutrition is poor, and your sleep is bad, peptides will not fix those problems. They amplify what you are already doing. If what you are already doing is suboptimal, you are amplifying garbage.
Assuming your fundamentals are solid, Seeds suggests a growth hormone secretagogue like Ipamorelin as a reasonable first peptide. It has a clean side effect profile, it improves sleep quality, and the modest GH elevation supports both recovery and body composition. Standard dosing is 200-300mcg subcutaneously before bed, cycled five days on and two days off.
For people dealing with a specific injury or chronic tendon issue, BPC-157 at 250-500mcg twice daily near the injury site for 4-6 weeks is his standard recommendation. He often combines it with TB-500 at 2mg twice weekly for the first two weeks, then 2mg once weekly for the remaining four weeks.
He strongly recommends against sourcing peptides from random websites or social media sellers. The risk of contamination, incorrect concentrations, or outright fake products is too high. Compounding pharmacies that require a prescription or well-established research suppliers with third-party testing are the only sources he trusts.
Blood Work and Monitoring: Non-Negotiable
Seeds closes with monitoring recommendations. Before starting any peptide protocol for muscle building, get baseline IGF-1, fasting insulin, fasting glucose, a complete metabolic panel, and a lipid panel. GH secretagogues can worsen insulin sensitivity in some people, and you need to catch that early.
At 6 weeks, repeat the IGF-1 and fasting insulin. If IGF-1 has risen into the upper third of the reference range and fasting insulin is stable, the protocol is working as intended. If IGF-1 has barely moved, the peptide may be underdosed, counterfeit, or your pituitary may not be responding. If fasting insulin is climbing, you need to adjust.
At 12 weeks, do a full repeat panel. Also track your functional metrics: strength numbers, body composition (ideally via DEXA), recovery time between sessions, and sleep quality. The blood work tells you what is happening biochemically. The functional metrics tell you whether that is translating into real-world results.
Seeds is exactly the kind of voice the peptide space needs: scientifically rigorous, clinically experienced, and willing to say "we do not know yet" when the data is not there. His conversation with DeLauer is one of the best introductions to peptides for muscle building available, and it avoids the usual trap of promising miracles while ignoring limitations.