IGF-1 (Insulin-like Growth Factor 1)
- Growth factor
- Building
- Recovery
By Mag. Christian Schönbauer, founder of Hardgainer Performance Nutrition®. Training since 1999, started under 50 kg.
IGF-1 is the messenger between growth hormone and your muscle tissue. It supports muscle protein synthesis, together with protein and insulin. For a hardgainer (hard gainer), IGF-1 is a signal in the system, not the switch. Whether it can work is decided by the levers you actually hold: training, surplus and sleep.
Note
This page gives you context and practice, not medical advice or individual treatment recommendations. If you have a medical condition, hormonal questions or take medication, please get it checked by a doctor.
What is IGF-1? The definition in 20 seconds
Your body makes IGF-1 mainly in the liver, triggered by growth hormone. Your muscle also makes IGF-1 locally. At the muscle it drives muscle protein synthesis, especially when enough amino acids are available.
- A signal, not a cure-all: Building stays driven by training and protein. IGF-1 works as a team with insulin, testosterone and cortisol.
- The hardgainer trap: Many suspect a hormone problem when the scale will not move. Usually something simpler is missing: energy. Without a surplus your body has no reason to build, whatever the signal looks like.
- For hardgainers this means: You do not need anything for your hormone axis. You need a lean surplus, progressive training and enough sleep.
The anchors in the system: TDEE, maintenance calories and SRA.
For years I worried about my "GH/IGF-1 axis" because I thought something hormonal must be off: otherwise I would have gained by now. The truth: my surplus was non-existent and my sleep was under 6 hours. Once both were sorted, everything changed, without a single supplement targeting the hormone axis.
What you control and what you don't
You cannot turn your IGF-1 level up directly. What you can control are the conditions that let the signal do its job.
- Training: Heavy compound lifts with progressive overload, volume between MEV and MRV, effort steered by RIR. Without a training stimulus there is nothing for a growth signal to act on.
- Energy: A lean surplus above your needs. Our deliberately cautious starting value is 150 to 250 kcal per day. If you train in a constant deficit, you tend to look for the cause in your hormones instead of on your plate.
- Protein and carbs: 3 to 5 meals with enough protein per serving to hit the leucine threshold. Carbs around training refill your glycogen.
- Sleep and stress: A stable sleep window and less constant stress are the base of your recovery. How sleep and muscle growth connect is covered in the deep dive. Constantly high cortisol works against building.
Practice: the 14-day check
- Day 0, set your base: Lock in your calorie corridor, define your sleep window, set up a training plan with fixed effort and progression.
- Document daily: Morning bodyweight, sleep duration and quality, steps as your measure for NEAT and your training. Build weekly averages. How much your steps burn is shown by the NEAT Calculator.
- Day 14, check the trend: Is your rate of gain flattening or your strength stalling? Then check calories, steps and sleep. Do not reflexively add volume and do not reach for a hormone test.
IGF-1 responds to the whole picture. Trends count, not snapshots.
Common misconceptions
- “More IGF-1 automatically means more muscle.” Within normal ranges, training, energy and protein decide, not the lab value. See hypertrophy.
- “As a hardgainer, something must be off with my hormones.” Many think so. Almost always it is surplus, structure or sleep that is missing. Only once that base has held for weeks is it worth looking at other causes, and then with a doctor.
- “Sleep is secondary.” Sleep is the base of your recovery. If you sleep too little night after night, you slow your progress, however good your training and nutrition are.
- “I need to get my IGF-1 tested.” For training and nutrition you do not need a lab value. Performance, weight trend and recovery tell you more.
Sleep is negotiable. If you train hard and eat enough, five to six hours will do.
False. Sleep is the frame of your recovery, and only inside that frame can a signal like IGF-1 do anything. If you sleep too little night after night, you slow your progress, however good your training and nutrition are.
Common questions
What is IGF-1 and why does it matter for hardgainers?
A growth factor that relays the effect of growth hormone to your muscle tissue and supports protein synthesis there. It matters for hardgainers because many suspect a hormone problem where calories, training or sleep are usually what is missing.
Can I influence IGF-1 through nutrition?
Indirectly. Enough energy, protein and carbs create the frame in which the signal can work. You cannot turn IGF-1 up directly through food. Training, surplus and sleep stay the levers.
Do hardgainers need more IGF-1 than others?
No. Hardgainers mainly need enough energy, including a look at high daily movement, plus structured training and stable sleep. IGF-1 follows these factors, not the other way round.
When is an IGF-1 test useful?
For medical questions, such as growth disorders or hormonal axes, and then with a doctor. For your training, performance, weight trend and recovery are the better indicators.
From term to practice: your tools
The signal follows the base. These three tools give you the numbers for your 14-day check.
See all Hardgainer Tools. If you want more out of your numbers, go with Hardgainer Pro.
What the research says
Two papers behind the claims on this page
IGF-1 acts on muscle, but only together with amino acids and training. These two papers are behind the claims above.
- Together with raised amino acids, IGF-1 increased muscle protein synthesis more than amino acids alone, while insulin improved protein balance only by reducing breakdown. 22 fasted adults, infusion straight into the forearm artery over 6 hours, with the other arm as control. Fryburg et al., Journal of Clinical Investigation, 1995
- More IGF-1 directly in the muscle raised muscle mass by 15 percent on average and strength by 14 percent in young mice. In old mice it prevented age-related decline, with strength 27 percent above untreated old muscles. The IGF-1 was delivered into the muscle by gene transfer. Barton-Davis et al., Proceedings of the National Academy of Sciences of the United States of America, 1998
What the studies do not cover
Fryburg infused IGF-1 artificially into one arm and measured over only 6 hours. Barton-Davis is an animal study using gene transfer, with no training and no nutrition. Neither paper shows that you can or should raise your IGF-1 on purpose in everyday life.
Your takeaway: IGF-1 is a real growth signal, but you steer it through the base. Surplus, progressive training, enough protein and stable sleep.
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Reading & Resources
The terms directly around IGF-1 and the pillars next to it.
Content here is general practice guidance and does not replace individual medical or nutritional advice.
