Beta-alanine: the scarce half of the buffer inside the fibre

Carnosine is a dipeptide, beta-alanine joined to histidine, and skeletal muscle is full of it. The enzyme that makes it, carnosine synthase, is coded by CARNS1. It spends ATP to stitch the two amino acids together. Histidine is rarely the piece that runs out, because meat, fish and the rest of an ordinary diet keep that pool topped up. Beta-alanine is the scarce half. The fibre can only make as much carnosine as the beta-alanine supply allows, which is why feeding beta-alanine raises the muscle store and feeding extra histidine, in someone who already eats protein, usually does not. Harris and colleagues put that on a biopsy in 2006. The store climbed over weeks, not over an afternoon, and it climbed more in the fast fibres, which are the ones that empty glycogen when a set gets hard.

In short. Carnosine is two amino acids joined up, and muscle makes it. Beta-alanine is the half that is usually missing, so taking it fills the store over weeks. The fast fibres, the ones that burn in a hard set, hold the most.

What the store is for, in a set, is the hydrogen ion. Glycolysis turns glucose into pyruvate and, when the mitochondria cannot take pyruvate as fast as the set is making it, into lactate. The chemistry that people call the burn releases hydrogen ions into the cytosol. pH falls. The cross-bridge and the calcium release both get worse at the lower pH, which is one reason the rep dies. The burn page is that story. Carnosine is the local answer. The imidazole ring on the histidine half has a pKa near 6.8, right in the range a working fibre actually reaches, so the ring takes the proton up and holds it. That is a buffer. Bicarbonate does this job in the blood, outside the fibre. Carnosine does it inside, next to the filament. They are not substitutes. One of them cannot reach the compartment the other lives in.

In short. A hard set dumps acid inside the fibre. Carnosine soaks that acid up, because part of the molecule is built to take a hydrogen ion at exactly that acidity. Bicarbonate does the same job in the blood, not inside the muscle.

A single heavy rep does not live here. It lives on phosphocreatine, which is the creatine page: a few seconds, a phosphate handed to ADP, no time for a pH crisis. A long easy ride does not live here either. Type I fibres are already handing pyruvate to mitochondria, hydrogen ions are not piling up, and a bigger carnosine store is a fire extinguisher in a room that is not on fire. The window where the trials keep finding a difference is the work that lasts from about half a minute to about ten minutes, and the last reps of sets that have already gone glycolytic. Hill's rowing work, and the meta-analyses after it, land in that band. You get a few more strokes, a slightly slower fade, not a new one-rep max and not a marathon. People who already have a high store, often those who eat a lot of meat and have trained the fast fibres for years, have less room. Vegetarians start lower, as they do with creatine, and have more ceiling.

In short. It helps efforts that burn, from about thirty seconds up to ten minutes, and the last reps of a hard set. A single max and a long easy run are the wrong jobs. Creatine owns the short one. Mitochondria own the long one.

The tingle is the other thing everyone meets in the first week, and it is not an allergy. Beta-alanine in a sudden peak activates MrgprD, a receptor on sensory neurons in the skin, the same family of receptors that registers certain itches. The neuron fires. The skin prickles for twenty minutes or so. Spread the dose, or use a slower tablet, and the peak never gets high enough to ring that bell, while the muscle store still fills across the month. Histamine is a different molecule. An antihistamine is the wrong tool for a receptor that was never histamine's. The paraesthesia is annoying and it is informative: it means a bolus just hit a nerve ending. It does not mean the fibre has filled. The fibre fills on the slow clock, a gram-scale daily intake for four weeks and more, and it empties on a similar clock when you stop. Missing a day does not wipe it. Stopping for a month does.

In short. The tingle is a nerve ending in the skin, not an allergic reaction. Slowing the dose stops the tingle and still fills the muscle. The muscle itself takes weeks to fill and weeks to empty.

Creatine and carnosine sit in the same fibre and do different seconds of the same set. Phosphocreatine rebuilds ATP at once. Carnosine holds the pH up once glycolysis is the one paying. Taking both is two stores, not one store taken twice. Beta-alanine does not phosphorylate anything at the myosin head, and creatine does not buffer a hydrogen ion. Sodium bicarbonate is the third, extracellular, and it can add to carnosine in the events long enough for blood pH to matter, with a gut that sometimes objects to the salt load. None of these writes a sarcomere. They let you complete work. The growth is still the tension and the protein, on the food page and the fibre page. A scoop that lets you get two more reps is useful exactly to the extent that those reps were heavy.

In short. Creatine covers the first seconds. Carnosine covers the burn after that. Bicarbonate covers the blood. All three buy work. None of them is the bar, and none of them is the meal.

There is a rodent finding that very large beta-alanine intakes compete with taurine for a transporter and can lower tissue taurine. The human supplemental amounts used in the performance trials have not reproduced a taurine deficiency anyone can diagnose on a person. It is worth knowing, because the transporter is real, and it is not a reason to invent a second supplement out of a mouse dose. Carnosine itself also binds metals and reactive carbonyls, which is why the ageing literature keeps sniffing around it. That is a slow chemistry. It is not why a set of twelve felt shorter. The set of twelve felt shorter, when it did, because a proton was caught by an imidazole ring a few nanometres from the filament, and the cross-bridge got a few more cycles before the pH called time.

In short. Huge doses in rodents can crowd out taurine. Ordinary human amounts have not done that in any way you could see. The gym effect is the acid being buffered, not an anti-ageing story.