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Why does IGF-1 LR3 stop working after ~6 weeks?


Jun 18, 2023
Can anyone provide a biological explanation for why IGF-1 LR3 stops working after 6 weeks or so? I did a search but was unable to find this information, so if it has already been discussed, please just post a link.
Stops working.??
What are you basing this off of??
Is there an effect that you get the first 4-6 weeks that stops??
Can anyone provide a biological explanation for why IGF-1 LR3 stops working after 6 weeks or so? I did a search but was unable to find this information, so if it has already been discussed, please just post a link.
What are you basing this off of?

Sorry, I thought IGF-1 LR3 desensitization after 4-8 weeks was common knowledge. I always heard IGF-1 LR3 cycles should be 4-8 weeks on followed by 4-8 weeks off, then repeat. You guys run IGF for longer periods without taking time off?

Here is what I found from a quick Google search.

https://pramahtampa.com/igf-1-lr3/#... can and does occur,course of IGF1/LR3 again .

Desensitization can and does occur around 6 weeks after initial time of use. It is recommended to take 20-40 days off prior to starting another course of IGF1/LR3 again .


LR3 will cause desensitization after about 4 weeks of use


Cycle Length – IGF-1 LR3 cycles typically last 4-6 weeks. Any longer than 6 weeks is not recommended due to potential desensitization.


Desensitization was shown to occur at around 40 days or roughly 4 weeks.

Copy and pasted from a member here @BigTex ….


Bamman MM, Shipp JR, Jiang J, Gower BA, Hunter GR, Goodman A, McLafferty CL Jr, Urban RJ. Mechanical load increases muscle IGF-I and androgen receptor mRNA concentrations in humans. Am J Physiol Endocrinol Metab. 2001 Mar;280(3):E383-90.

Full study

The mechanism(s) of load-induced muscle hypertrophy is as yet unclear, but increasing evidence suggests a role for locally expressed insulin-like growth factor I (IGF-I). We investigated the effects of concentric (CON) vs. eccentric (ECC) loading on muscle IGF-I mRNA concentration. We hypothesized a greater IGF-I response after ECC compared with CON. Ten healthy subjects (24.4 +/- 0.7 yr, 174.5 +/- 2.6 cm, 70.9 +/- 4.3 kg) completed eight sets of eight CON or ECC squats separated by 6-10 days. IGF-I, IGF binding protein-4 (IGFBP-4), and androgen receptor (AR) mRNA concentrations were determined in vastus lateralis muscle by RT-PCR before and 48 h after ECC and CON. Serum total testosterone (TT) and IGF-I were measured serially across 48 h, and serum creatine kinase activity (CK), isometric maximum voluntary contraction (MVC), and soreness were determined at 48 h. IGF-I mRNA concentration increased 62% and IGFBP-4 mRNA concentration decreased 57% after ECC (P < 0.05). Changes after CON were similar but not significant (P = 0.06-0.12). AR mRNA concentration increased (P < 0.05) after ECC (63%) and CON (102%). Serum TT and IGF-I showed little change. MVC fell 10% and CK rose 183% after ECC (P < 0.05). Perceived soreness was higher (P < 0.01) after ECC compared with CON. Results indicate that a single bout of mechanical loading in humans alters activity of the muscle IGF-I system, and the enhanced response to ECC suggests that IGF-I may somehow modulate tissue regeneration after mechanical damage.

We report for the first time changes in muscle mRNAs associated with tissue growth and repair after a single bout of resistance exercise in humans. The novel approach of studying high-intensity CON and ECC loading separately enabled us to test the influence of ECC action on the IGF-I and AR responses to mechanical load. The results indicate that high-intensity
lengthening and shortening contractions both induce muscle IGF-I and AR gene transcription. Moreover, the enhanced IGF-I activation after ECC loading supports the concept that IGF-I is somehow involved in tissue regeneration after mechanical load-induced damage.

Kind of blows the theory of desensitization and shut down of AR and IGF-1R doesn't it? However, while exercise increase AR and their sensitivity, there is still probably a saturation point where the more you use the greater the side effects and the less the benefits. This is the same concept with peptides. We know through research that 1mcg/kg/bw is saturation level. The higher you go up past saturation levels the less the benefits and the greater the unwanted side effects.

In other words....enhanced activation of satellite cells by testosterone requires IGF-1. Those Androgens that aromatize are effective at not only increasing IGF-1 levels but also the sensitivity of satellite cells to growth factors.3 This action has no direct effect on protein synthesis, but it does lead to a greater capacity for protein synthesis by increasing fusion of satellite cells to existing fibers. This increases the number of myonuclei and therefore the capacity of the cell to produce proteins. That is why large bodybuilders will benefit significantly more from high levels of Androgens compared to a relatively new user.

So whenever a muscle grows in response to training there is a coordinated increase in the number of myonuclei and the increase in fiber cross sectional area. More myonuclei mean more receptors. The same is most likely true for IGF-1 use. The more mechanical loading during training the more muscle damage, the greater hypertrophy. WIth hypertrophy come more myonuclei/satellite cells thus, more AR. So now we have a greater need for IGF-1. So while there is most likely a saturation level for using IGF-1 Lr3, there is absolutely no evidence that IGF-1R shut down or desensitize after 4 weeks of continual use or longer.

Here is another good study:

Sinha-Hikim I, Taylor WE, Gonzalez-Cadavid NF, Zheng W, Bhasin S. Androgen receptor in human skeletal muscle and cultured muscle satellite cells: up-regulation by androgen treatment. J Clin Endocrinol Metab. 2004 Oct;89(10):5245-55.

**broken link removed**

Androgens stimulate myogenesis, but we do not know what cell types within human skeletal muscle express the androgen receptor (AR) protein and are the target of androgen action. Because testosterone promotes the commitment of pluripotent, mesenchymal cells into myogenic lineage, we hypothesized that AR would be expressed in mesenchymal precursor cells in the skeletal muscle. AR expression was evaluated by immunohistochemical staining, confocal immunofluorescence, and immunoelectron microscopy in sections of vastus lateralis from healthy men before and after treatment with a supraphysiological dose of testosterone enanthate. Satellite cell cultures from human skeletal muscle were also tested for AR expression. AR protein was expressed predominantly in satellite cells, identified by their location outside sarcolemma and inside basal lamina, and by CD34 and C-met staining. Many myonuclei in muscle fibers also demonstrated AR immunostaining. Additionally, CD34+ stem cells in the interstitium, fibroblasts, and mast cells expressed AR immunoreactivity. AR expression was also observed in vascular endothelial and smooth muscle cells. Immunoelectron microscopy revealed aggregation of immunogold particles in nucleoli of satellite cells and myonuclei; testosterone treatment increased nucleolar AR density. In enriched cultures of human satellite cells, more than 95% of cells stained for CD34 and C-met, confirming their identity as satellite cells, and expressed AR protein. AR mRNA and protein expression in satellite cell cultures was confirmed by RT-PCR, reverse transcription and real-time PCR, sequencing of RT-PCR product, and Western blot analysis. Incubation of satellite cell cultures with supraphysiological testosterone and dihydrotestosterone concentrations (100 nm testosterone and 30 nm dihydrotestosterone) modestly increased AR protein levels. We conclude that AR is expressed in several cell types in human skeletal muscle, including satellite cells, fibroblasts, CD34+ precursor cells, vascular endothelial, smooth muscle cells, and mast cells. Satellite cells are the predominant site of AR expression. These observations support the hypothesis that androgens increase muscle mass in part by acting on several cell types to regulate the differentiation of mesenchymal precursor cells in the skeletal muscle.

In summary, although multiple cell types within the human skeletal muscle express AR protein, satellite cells, and myonuclei are the predominant sites of AR expression. ARs aggregate within the nucleoli of satellite cells and myonuclei. Testosterone and DHT up-regulate AR expression in vivo and in vitro. These data are consistent with the proposal that androgens induce skeletal muscle hypertrophy by acting at multiple sites within the muscle through multiple mechanisms, including modulation of pluripotent stem cell commitment and differentiation and regulation of muscle protein synthesis; further studies are needed to elucidate the molecular basis of androgen action on human skeletal muscle.

So when you build muscle using testosterone or other AAS obviously muscle is enlarged and new satellite cells are made therefore AR's are increased in numbers and existing AR are upregulated.

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