Substrate, cell volume & training capacity
One of 6 mechanistic pathways to 💪 Build muscle & strength · 20 options
The unglamorous pathway, and the one with the strongest evidence base by an enormous margin. You cannot signal your way past insufficient protein, depleted phosphocreatine or a workout you couldn't finish.
The unglamorous checks that explain most stalled progress. Low ferritin and low B12 both present as 'I just can't train hard any more' with a completely normal full blood count.
Comprehensive Metabolic Panel (CMP)Complete Blood Count (CBC) with DifferentialFerritinVitamin B12Magnesium, RBC🏋️ Athletic Performance & Recovery covers these in one panel →
What engages this pathway
Ordered by how directly each one acts on the mechanism above — never by how much trial evidence exists. Each links to its full breakdown with dosing, half-life and vendor.
🧬 Creatine
Expands the phosphocreatine pool so more ATP is available for high-intensity work, plus a cell-volumizing effect that is itself a hypertrophy signal. Hundreds of trials. Nothing else here is close.
🧬 Creatine HCL
More soluble than monohydrate. The claimed advantage is gastric comfort at lower doses; no trial shows superior outcomes, and monohydrate is the studied form.
🧬 Creatine + Alpha-GPC
Creatine's substrate effect plus Alpha-GPC's demonstrated power-output improvement — two different mechanisms in one product.
🧬 Whey Protein (RecoveryPro)
Fast leucine delivery, the strongest acute mTOR stimulus available from food. Total daily protein matters more than timing, but this is how most people reach total.
🧬 Phosphatidic Acid
Reaches the same mTORC1 node Whey reaches through leucine, but as a membrane phospholipid signaling onto it directly. Human hypertrophy trials exist and are small, the effect sizes are modest, and it only makes sense once protein, creatine and the training itself are already handled.
🧬 Casein Protein
Slow-digesting micellar casein sustains amino-acid availability for hours — the overnight argument, which has modest but real support.
🧬 Plant Protein
Pea/rice blends complement each other's limiting amino acids. Needs a slightly higher dose to match whey's leucine.
🧬 Essential Amino Acids
The nine that must be eaten. Efficient when total protein is constrained; redundant when it isn't.
🧬 HMB
Reduces protein breakdown. Best evidence in untrained or catabolic populations.
🧬 Betaine Anhydrous (TMG)
Trimethylglycine improves power output and body composition in several resistance-training trials; the methyl-donor and osmolyte roles are both plausible mechanisms.
🧬 Beta-Alanine
Raises muscle carnosine, buffering the hydrogen ions that end a set. The benefit is specific to 1–4 minute efforts — meaning higher training volume, not direct anabolism.
🧬 Citrulline Malate
Raises plasma arginine more effectively than arginine does, increasing nitric-oxide-mediated blood flow and reducing perceived exertion across a session.
🧬 Peak ATP
Oral ATP doesn't reach the muscle intact — it acts extracellularly on purinergic receptors to raise blood flow. Small human trials show improved training volume.
🧬 Agmatine
An arginine metabolite that modulates nitric-oxide synthase. The pump effect is the claim; the human evidence is thin.
🧬 Nitrosigine
Inositol-stabilized arginine silicate with better bioavailability than plain arginine and human data for blood flow and cognition.
🧬 Glycerol (HydroMax)
Hyperhydrates the muscle cell osmotically. Real, measurable, and mostly a performance and appearance effect.
🧬 Cluster Dextrin (HBCD)
Highly branched cyclic dextrin — high molecular weight, low osmolality, so it clears the stomach fast at concentrations where maltodextrin sloshes. The training-capacity argument is finishing the session you planned: carbohydrate availability, not a signaling effect.
🧬 Electrolytes
Sodium, potassium and magnesium drive muscle contraction directly. Depletion looks exactly like weakness, and people reach for hormones before they check this.
🧬 Sodium Bicarbonate
Extracellular buffering — the complement to beta-alanine's intracellular buffering. Effective and gastrointestinally brutal if you get the dose wrong.
🧬 Leucine
The only amino acid with a named intracellular sensor: Sestrin2 binds it and releases GATOR2, which is how mTORC1 is switched on. Two predictions follow. The response saturates, so adding leucine to a meal already carrying 30 g of complete protein should do nothing; and the signal is permission rather than material, so it cannot build anything the rest of the amino acid pool does not supply. A meta-analysis of 17 randomized trials in older adults found effects that are modest and inconsistent.
What actually decides this outcome, in order of size
This is the best-evidenced pathway on the goal and the trials all share a design feature nobody mentions: the responder started low. Ranked by how much of the outcome each one owns:
- Training stimulus and its progression, which nothing here replaces. Every supplement below was tested as an addition to a resistance program, and in the absence of the program none of them has a hypertrophy result at all. The International Society of Sports Nutrition position stand on creatine is explicit that the effect is on training capacity Kreider 2017, which is a statement about what the program then does with it.
- Habitual protein intake, because the whey literature is a repletion literature. Whey supplementation moves body composition and strength outcomes Khalafi 2025 and improves strength and physical function in older adults Al-Rawhani 2024, and the populations in which it does most are the ones eating least. Adding protein to somebody already eating plenty is the clearest example on this site of a supplement whose effect is a property of the baseline.
- Starting muscle creatine content, which is measurable in a laboratory and predicts the response. Muscle creatine loading in men was characterized directly Hultman 1985, and the people whose muscle total creatine rises most are the ones who began furthest from saturation. That is the mechanistic reason vegetarians respond more and why a heavy meat eater may notice almost nothing.
- Which form, because the field has been surveyed and the answer is boring. Bioavailability, efficacy, safety and regulatory status of creatine forms have been reviewed together Kreider 2022. The monohydrate is the one with the evidence and the lowest price, and the premium salts are competing against it rather than adding to it.
- The rest of the shelf, last, and it is ergogenic rather than anabolic. Beta-alanine raises muscle carnosine and buffers, and its effects are confined to a specific effort duration Cesak 2023. Sodium bicarbonate does the same job extracellularly Curran-Bowen 2024. Neither builds tissue.
The order to run these in, and what has to be true first
Program first, protein second, creatine third, and the buffering agents only if the sport actually lives in the window they act on. This order is the same one the evidence was generated in.
- Get the program and the food right, because they are the denominator. Nothing below has been shown to work without progressive loading, and the whey trials are comparisons against a background intake rather than against nothing Khalafi 2025. This step is free and it is where most of the outcome lives.
- Creatine as monohydrate, first among the supplements. The position stand covers safety and efficacy Kreider 2017 and the forms review covers why the alternatives have to justify themselves Kreider 2022. Creatine HCL and Creatine + Alpha-GPC are solubility and convenience arguments, not efficacy ones.
- Loading is optional and the pharmacology says why. Muscle stores saturate either quickly at a high intake or slowly at a maintenance intake, and the endpoint is the same saturation Hultman 1985. The choice is between reaching it in days with more gastrointestinal upset or in weeks without.
- Whey Protein (RecoveryPro) or a plant blend, chosen on leucine content rather than on grams. Peripheral amino acid appearance differs between whey, pea and fava preparations Kozior 2023, which is the mechanistic reason a plant protein is usually dosed higher to match. Casein Protein, Plant Protein and Essential Amino Acids are the same decision at different digestion rates.
- HMB only in the population its umbrella review covers. The ergogenic benefits of beta-hydroxy-beta-methylbutyrate have been examined at umbrella level Bideshki 2025, and the signal is clearest in untrained and older participants. In a trained lifter eating enough leucine it is the clearest example of a supplement whose population you have already left.
- Beta-Alanine and Sodium Bicarbonate belong to efforts lasting roughly one to four minutes. Carnosine buffers intracellular protons Cesak 2023; bicarbonate buffers extracellular ones, and combining them has been examined as a question in its own right Curran-Bowen 2024. A systematic review and multilevel meta-analysis found no ergogenic effect of beta-alanine on repeated sprint ability Liang 2026, which is a specific negative about a specific test.
- Citrulline Malate, Agmatine, Nitrosigine and Peak ATP are the pump shelf and the critical review is worth reading before buying it Gough 2021. Betaine Anhydrous (TMG), Glycerol (HydroMax), Cluster Dextrin (HBCD) and Electrolytes are hydration and fuel rather than signaling; glycerol additionally has doping-relevant blood effects Polyviou 2012.
- Phosphatidic Acid is the one item here with a signaling claim rather than a substrate one. It is proposed to act on mTOR, which places it with Androgen & anabolic-receptor signaling conceptually and at the bottom of this list evidentially.
What gets bought for this that cannot move it
The category that fails is any of this bought without the program. Creatine increases the work that can be completed and whey supplies the material; neither instructs a muscle to grow. That instruction is mechanical, and the trials that produced these effect sizes all supplied it Kreider 2017. A reader who buys the shelf and trains twice a fortnight has purchased the adjective and not the noun.
Beta-alanine is the item on this page whose sensation most exceeds its window. The paresthesia is immediate, unmistakable and unrelated to the effect, which arrives over weeks as muscle carnosine accumulates Cesak 2023. The effect itself lives in efforts of roughly one to four minutes, and outside that window the honest prediction is nothing — including on repeated sprints, where the pooled answer was negative Liang 2026.
And the replete reader is the one this page fails most expensively. Somebody already eating plenty of protein, already saturated on creatine from three years of use, already training hard, is at the flat part of every dose-response curve on the page. The population effects reported for whey Khalafi 2025 and for HMB Bideshki 2025 include people with room to move, and there is no product here that creates room.
If the limiting factor is somewhere else, so is the page. Recovery capacity and sleep is Recovery, sleep & the anabolic window between sessions. Hormonal signaling is Androgen & anabolic-receptor signaling. Local repair after damage is Satellite cells & local repair. And a reader who cannot finish sessions because of breathlessness rather than muscular fatigue belongs at Endurance & work capacity.
How you would know it was working, on a real read-out and a real timescale
This page makes two predictions that can be wrong. Creatine should add a small, fast, non-contractile mass in the first fortnight and then stop; and total training volume completed should rise over the same period. If body mass rises and volume does not, the water arrived and the training capacity did not, and there is nothing else to wait for.
- Total weekly volume load, recorded every session. Sets times reps times load, summed. This is the read-out that matches the mechanism the position stand describes Kreider 2017, and it is the only one that distinguishes a supplement effect from a motivation effect.
- Morning body mass, same conditions, weekly. Creatine increases intracellular water as stores fill Hultman 1985, so a rise of a kilogram or so in the first two weeks is the expected signature of loading and is not tissue.
- Comprehensive Metabolic Panel (CMP) once before and once at 12 weeks, and read creatinine with the supplement in mind. Creatine raises serum creatinine by increasing its production rather than by impairing its clearance, and the question of creatine-induced kidney dysfunction has been examined directly Longobardi 2023. Cystatin C with eGFR is the escalation, because it is not derived from creatine metabolism.
- Ferritin with Complete Blood Count (CBC) with Differential once, and Vitamin D (25-Hydroxy) once. Both limit training capacity independently of anything on this shelf, and both are commoner in heavy trainers than the shelf implies.
- 4 weeks for creatine, 12 for protein, and the numbers have reasons. Four because muscle stores saturate within days to a few weeks depending on the loading choice Hultman 1985. Twelve because a change in lean mass from a protein intervention is measured against training cycles rather than weeks Khalafi 2025.
What will fool you. The first fortnight of creatine looks like rapid growth and is intracellular water. A raised creatinine in somebody taking creatine looks like kidney injury and usually is not Longobardi 2023, which is why the supplement belongs on the form at the blood draw. Beta-alanine tingling and a citrulline pump are sensations rather than endpoints Gough 2021. Deloads improve every number on this list. And plant and dairy proteins at identical grams are not identical exposures at the muscle Kozior 2023.
Sources read for these sections
- Kreider RB, et al. International Society of Sports Nutrition position stand: safety and efficacy of creatine supplementation in exercise, sport, and medicine. Journal of the International Society of Sports Nutrition, 2017 · PMID 28615996
- Hultman E. Muscle creatine loading in men. J Appl Physiol (1985) 1996 · PMID 8828669
- Kreider RB. Bioavailability, Efficacy, Safety, and Regulatory Status of Creatine and Related Compounds: A Critical Review. Nutrients 2022 · PMID 35268011
- Longobardi I, et al. Is It Time for a Requiem for Creatine Supplementation-Induced Kidney Failure? A Narrative Review. Nutrients 2023 · PMID 36986197
- Khalafi M. Effects of Whey Protein Supplementation on Body Composition, Muscular Strength, and Cardiometabolic Health in Older Adults: A Systematic Review with Pairwise Meta-Analysis. Healthcare (Basel) 2025 · PMID 41228181
- Kozior M. An Investigation of the Protein Quality and Temporal Pattern of Peripheral Blood Aminoacidemia following Ingestion of 0.33 g kg-1 Body Mass Protein Isolates of Whey, Pea, and Fava Bean in Healthy, Young Adult Men. Nutrients 2023 · PMID 37836496
- Bideshki MV. Ergogenic Benefits of beta-Hydroxy-beta-Methyl Butyrate (HMB) Supplementation on Body Composition and Muscle Strength: An Umbrella Review of Meta-Analyses. J Cachexia Sarcopenia Muscle 2025 · PMID 39797501
- Cesak O, et al. Carnosine and Beta-Alanine Supplementation in Human Medicine: Narrative Review and Critical Assessment. Nutrients 2023 · PMID 37049610
- Liang W. No ergogeniceffect of beta-alanine on repeated sprint ability: a systematic review and multilevel meta-analysis of randomized controlled trials. Frontiers in Nutrition 2026 · PMID 41971372
- Curran-Bowen T. Sodium bicarbonate and beta-alanine supplementation: Is combining both better than either alone? A systematic review and meta-analysis. Biology of Sport 2024;41(4):3-20 · PMID 38952910
- Gough LA, et al. A critical review of citrulline malate supplementation and exercise performance.. European Journal of Applied Physiology 2021 · PMID 34417881
- Al-Rawhani AH. Effectiveness of whey protein supplementation on muscle strength and physical performance of older adults: A systematic review and meta-analysis of randomized clinical trials. Clin Nutr 2024 · PMID 39303495
- Polyviou TP, et al. Effects of glycerol and creatine hyperhydration on doping-relevant blood parameters. Nutrients 2012 · PMID 23112907
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Frequently asked questions
The unglamorous pathway, and the one with the strongest evidence base by an enormous margin. You cannot signal your way past insufficient protein, depleted phosphocreatine or a workout you couldn't finish.
20 options are mapped to this pathway in the Vault, including Creatine, Creatine HCL, Creatine + Alpha-GPC, Whey Protein (RecoveryPro). They are grouped by the mechanism they act through rather than ranked by how much trial evidence exists — 18 carry clinical validation and 2 are mechanistic predictions.
The unglamorous checks that explain most stalled progress. Low ferritin and low B12 both present as 'I just can't train hard any more' with a completely normal full blood count. The markers worth checking are Comprehensive Metabolic Panel (CMP), Complete Blood Count (CBC) with Differential, Ferritin, Vitamin B12.
Unproven is not the same as ineffective. Of the 20 options on this pathway, 18 have clinical validation and 2 are graded theoretical — meaning the mechanism is sound but the specific human trial has not been run, which is true of a great deal of what works in this space. Nothing on this page is ordered by evidence tier, because sorting by trial count would bury the compounds you came looking for.
Where this goes next
Everything above is the free case for Substrate, cell volume & training capacity. The protocol — the dosing, the order to correct things in, the week-by-week schedule and what to retest — is a lesson inside Skool.