Dileucine for Masters Athletes: Training Through Anabolic Resistance After 40 (2026)

You did not stop competing. You kept lifting, kept racing, kept showing up. But somewhere after 40, the math changed. The same training that used to add muscle now seems to barely hold the line. Recovery takes longer. A missed week costs more than it used to. This is not a motivation problem, and it is not in your head. It is a measurable biological shift called anabolic resistance, and it is the central reason masters athletes have to train and eat smarter than their younger selves to hold the same ground.

This article walks through what the published research shows about why aging muscle responds less to protein and training, how the leucine threshold rises with age, and where dileucine, a leucine-leucine dipeptide, fits into a masters athlete's nutrition strategy.

Aging Muscle Still Declines, Even in Trained Athletes

The first myth worth dismantling is that lifelong training fully protects against age-related muscle and power loss. It does not. It slows the decline, but it does not stop it.

A ten-year longitudinal study of masters sprinters aged 48 to 85 tracked the same athletes across a full decade of continued competition. Over those ten years, 60-meter sprint time increased by 14.2 percent, jumping power fell by 9.5 percent, and maximal knee-extensor strength dropped by 21.0 percent. Critically, the size of these declines was not related to how much the athletes trained, suggesting that training volume alone could not offset the underlying loss of force-generating capacity [Hendrickse 2025 PMID 40289323].

The onset is earlier than most people expect. Reviews of sarcopenia, the age-related loss of muscle mass and function, place the beginning of accelerated decline around the fourth decade of life, near age 40, with the rate of loss becoming more pronounced after 50 [Keller 2014 PMID 24596700]. For a masters athlete, this means the biology is already working against you in your 40s, long before anyone would call you old.

The takeaway is not defeatist. It is strategic. Training remains the single most powerful tool a masters athlete has. But because training cannot fully neutralize the age-related decline, nutrition has to carry more of the load than it did at 25.

Anabolic Resistance: The Core Problem After 40

Anabolic resistance is a blunted muscle protein synthesis (MPS) response to a given dose of protein, amino acids, or exercise. The same stimulus that produces a large anabolic signal in a young athlete produces a smaller one in an older athlete.

Pooled stable-isotope data comparing younger men around 22 years old with older men around 74 years old found that post-meal muscle protein synthesis rates were roughly 16 percent lower in the older group, and that MPS was more than three-fold more responsive to protein ingestion in the young. The authors described this as muscle "anabolic inflexibility" [Wall 2015 PMID 26536130].

The problem reaches down to the signaling level inside the muscle cell. Work comparing younger and older men found that older muscle had reduced sensitivity of MPS to escalating doses of essential amino acids, and that this was linked to lower expression and activation of the key signaling proteins mTOR, p70S6K, and related translation initiation factors [Cuthbertson 2005 PMID 15596483]. In plain terms, the machinery that turns a meal into new muscle protein responds more sluggishly with age.

This is why a masters athlete cannot simply eat the way they did in their 20s and expect the same result. The same protein dose now produces a weaker anabolic response, so the dose, timing, and amino acid composition of each meal all have to be sharper.

The Per-Meal Protein Dose Has to Go Up With Age

The most direct way researchers have quantified anabolic resistance is through dose-response studies, feeding people increasing amounts of protein and measuring where the MPS response plateaus.

A pooled dose-response analysis found that myofibrillar MPS plateaued at roughly 0.40 grams of protein per kilogram of body mass per meal in older men, compared with about 0.24 grams per kilogram in younger men. In other words, older adults need a meaningfully larger relative per-meal protein dose to maximally stimulate muscle protein synthesis [Moore 2015 PMID 25056502].

A separate trial in older men around 73 years old, given 10, 20, or 35 grams of whey protein, found that post-meal muscle protein accretion and synthesis were greatest after the 35-gram dose, supporting the idea that older muscle needs more protein per sitting than the roughly 20 grams that maximizes the response in young adults [Pennings 2012 PMID 22338070].

For a masters athlete, the practical message is to anchor each main meal around a substantial protein dose, on the order of 35 to 40 grams of high-quality protein, rather than spreading small amounts thinly across the day. But total protein is only part of the story. The other lever is leucine.

The Leucine Threshold, and Why It Rises With Age

Leucine is the branched-chain amino acid most directly responsible for switching on muscle protein synthesis. It acts as a nutrient signal that activates the mTOR pathway and the translation-initiation machinery, which is the conceptual basis of the "leucine threshold" or "leucine trigger" idea [Norton 2006 PMID 16424142].

In young adults, a per-meal leucine dose of roughly 2 to 3 grams, achievable from about 20 to 25 grams of whey protein, is generally enough to clear the threshold and maximally stimulate MPS. With age, the threshold appears to rise. A systematic review found that the ingested leucine dose was associated with the magnitude of the muscle protein synthesis response in older adults, but not in younger adults, consistent with the idea that older muscle is more dose-dependent on leucine and harder to trigger [Wilkinson 2023 PMID 37537134].

There is also direct evidence that leucine can rescue a sub-threshold protein dose. In a controlled trial, a low, normally sub-maximal dose of whey protein supplemented with extra leucine stimulated post-meal myofibrillar MPS as effectively as a full whey dose at rest [Churchward-Venne 2012 PMID 22451437]. This is the mechanistic heart of leucine-enrichment strategies: you can push a smaller meal over the anabolic threshold by raising its leucine content rather than its total protein.

Reviews of anabolic resistance in older adults converge on the same practical recommendation: distribute protein across meals, raise the leucine content of each meal, and combine this with resistance exercise [Breen 2011 PMID 21975196]. For masters athletes, leucine is not a nice-to-have. It is the specific lever that the aging-muscle literature keeps pointing back to.

Where Dileucine Comes In: The Paulussen 2021 Trial

Dileucine is the leucyl-leucine dipeptide, two leucine residues joined by a single peptide bond. The question researchers asked was whether delivering leucine in this dipeptide form produces a stronger anabolic signal than the same dose of free leucine.

Paulussen and colleagues at the University of Illinois Urbana-Champaign tested exactly this in a double-blind randomized crossover trial in healthy young men (n=10), published in the Journal of Applied Physiology in 2021. They compared 2 grams of dileucine against 2 grams of free leucine, measuring myofibrillar fractional synthetic rate (FSR) with stable-isotope methodology. Ingesting 2 grams of dileucine raised myofibrillar FSR to approximately 0.075 percent per hour, whereas 2 grams of free leucine did not significantly raise synthesis above the basal rate, at approximately 0.047 percent per hour [Paulussen 2021 PMID 34323596].

That difference works out to roughly a 60 percent greater myofibrillar synthetic rate for the dipeptide compared with free leucine at the same nominal dose. The leading explanation is differences in absorption and delivery kinetics between the intact dipeptide and the free amino acid.

The relevance to masters athletes is mechanistic rather than proven in an aging population, and it is worth being precise about that. This trial was conducted in young men. But it sits on top of a large body of aging-muscle research showing that the leucine threshold rises with age and that leucine content per meal is a key determinant of the anabolic response. A tool that produces a stronger per-gram leucine signal is exactly the kind of lever the anabolic-resistance literature suggests older athletes need.

Wise Choice Supplements Dileucine delivers 2000 mg of pure dileucine per serving, matching the dose used in the Paulussen trial.

Protein and Leucine Supplementation Do Build Muscle in Older Adults

The dose-response and threshold studies explain the mechanism. Longer training trials show the outcome.

A meta-analysis of 22 randomized controlled trials, totaling 680 participants, found that protein supplementation during prolonged resistance training increased fat-free mass by 0.69 kilograms and one-repetition-maximum leg-press strength by 13.5 kilograms, with benefits seen in both younger and older adults [Cermak 2012 PMID 23134885]. The effect of adding protein on top of training was real and measurable across the age span.

In frail elderly adults around 78 years old, a 24-week resistance training program with protein supplementation produced a gain in lean body mass of roughly 1.3 kilograms in the protein group, while the placebo group did not gain lean mass, despite both groups improving in strength [Tieland 2012 PMID 22770932]. This is among the clearest demonstrations that protein supplementation, paired with training, shifts body composition in an aging population that would otherwise be losing muscle.

It is worth being honest that the evidence is not unanimous. Some trials have found that adding modest protein supplementation on top of resistance training did not produce extra muscle or strength beyond training alone, particularly when baseline protein intake was already adequate. The signal across the literature is that protein and leucine matter most when intake is otherwise sub-optimal or when the per-meal dose fails to clear the higher anabolic threshold of older muscle, which is precisely the scenario a busy masters athlete can fall into.

A Practical Framework for the Masters Athlete

Pulling the evidence together, a defensible nutrition framework for a trained athlete over 40 looks like this.

• Anchor each main meal around 35 to 40 grams of high-quality protein, rather than grazing on small amounts, to clear the higher per-meal threshold of aging muscle [Moore 2015 PMID 25056502; Pennings 2012 PMID 22338070].
• Aim for roughly 3 grams of leucine per meal, recognizing that the threshold to trigger MPS appears higher and more dose-dependent with age [Wilkinson 2023 PMID 37537134; Norton 2006 PMID 16424142].
• Use a leucine-rich tool to lift meals that fall short of the threshold, such as a lighter breakfast or a rushed post-training meal, rather than forcing in large amounts of extra whole food [Churchward-Venne 2012 PMID 22451437].
• Keep resistance training as the non-negotiable core. The longitudinal masters data show that training slows but does not erase age-related decline, so the goal is to give muscle every reason and every substrate to stay [Hendrickse 2025 PMID 40289323; Cermak 2012 PMID 23134885].
• Distribute protein across three to four feedings rather than loading it all at dinner, in line with anabolic-resistance recommendations [Breen 2011 PMID 21975196].

Within this framework, dileucine is a per-meal leucine tool, not a replacement for total protein or training. Its role is narrow and specific: to add a strong, low-calorie leucine signal to a meal or a training window where the per-meal threshold might otherwise go unmet.

How to Use Dileucine

The studied dose is 2 grams, which is the per-serving dose of Wise Choice Supplements Dileucine. Practical patterns masters athletes can use:

• Peri-workout: mix 2 grams into a pre- or post-training shake to reinforce the anabolic signal during the window when muscle is most responsive to feeding.
• With a low-protein meal: add 2 grams to breakfast or a mid-day snack that falls short of the per-meal leucine threshold.
• Alongside whey: a 25-gram whey serving already supplies roughly 2.5 to 3 grams of leucine and often clears the threshold on its own. Dileucine earns its place when whey is absent, when the protein dose is smaller, or when you want to push the per-meal signal higher in the face of age-related anabolic resistance.

Dileucine is a pure, unflavored powder that mixes into water, a shake, or any existing routine. You can order Wise Choice Supplements Dileucine as a standalone powder.

Quality and Testing

Dileucine is a specialty amino-acid ingredient, so identity, purity, and contaminant testing matter. Wise Choice Supplements Dileucine is tested by Eurofins, an internationally recognized third-party analytical laboratory, with a Certificate of Analysis available on request. The pure-powder presentation contains no fillers, sweeteners, or added calories, which keeps it compatible with a masters athlete's nutrition plan.

What the Evidence Does and Does Not Say

To stay honest about the boundaries of the current data:

• The dileucine trial measured myofibrillar synthesis over hours in young men, not body composition over months in masters athletes. No published trial has yet tracked dileucine through a training block in an older population.
• The aging-muscle case for leucine is strong and well replicated, but applying the dileucine finding to athletes over 40 is a mechanistic extrapolation, not a proven outcome.
• Dileucine does not replace total daily protein or resistance training. The trials that moved lean mass in older adults did so through total protein intake combined with training.
• No supplement compensates for inadequate sleep, insufficient training stimulus, or chronically low protein intake.

Bottom Line

Anabolic resistance is the defining nutritional challenge of training after 40. Aging muscle responds less to protein and to training, the per-meal protein dose required to maximize muscle protein synthesis rises, and the leucine threshold needed to trigger that synthesis climbs with age. Masters athletes who want to hold or build muscle have to meet that higher threshold deliberately, meal by meal.

High per-meal protein, adequate leucine, and consistent resistance training form the foundation. Within that foundation, dileucine offers a mechanistically grounded way to deliver a strong leucine signal at a low calorie cost, matching the 2-gram dose shown to outperform free leucine for muscle protein synthesis. For an athlete fighting the slow tax of age, that per-meal precision is exactly where the leverage is.

Train hard, eat your protein, and respect the higher threshold the years have set.

References

1. Hendrickse PW, et al. Longitudinal changes in performance and muscle characteristics in master sprint athletes. Journal of Cachexia, Sarcopenia and Muscle. 2025. PMID 40289323.
2. Keller K, Engelhardt M. Strength and muscle mass loss with aging process. Age and strength loss. Muscles, Ligaments and Tendons Journal. 2014. PMID 24596700.
3. Wall BT, et al. Skeletal muscle atrophy during short-term disuse: implications for age-related sarcopenia, and the relationship between anabolic resistance and inflexibility. PLoS One. 2015. PMID 26536130.
4. Cuthbertson D, et al. Anabolic signaling deficits underlie amino acid resistance of wasting, aging muscle. FASEB Journal. 2005. PMID 15596483.
5. Moore DR, et al. Protein ingestion to stimulate myofibrillar protein synthesis requires greater relative protein intakes in healthy older versus younger men. The Journals of Gerontology, Series A. 2015. PMID 25056502.
6. Pennings B, et al. Amino acid absorption and subsequent muscle protein accretion following graded intakes of whey protein in elderly men. American Journal of Physiology - Endocrinology and Metabolism. 2012. PMID 22338070.
7. Norton LE, Layman DK. Leucine regulates translation initiation of protein synthesis in skeletal muscle after exercise. The Journal of Nutrition. 2006. PMID 16424142.
8. Wilkinson K, et al. The age-related anabolic resistance of muscle protein synthesis and the role of ingested leucine. Physiological Reports. 2023. PMID 37537134.
9. Churchward-Venne TA, et al. Supplementation of a suboptimal protein dose with leucine or essential amino acids: effects on myofibrillar protein synthesis at rest and following resistance exercise in men. The Journal of Physiology. 2012. PMID 22451437.
10. Breen L, Phillips SM. Skeletal muscle protein metabolism in the elderly: interventions to counteract the 'anabolic resistance' of ageing. Nutrition & Metabolism (London). 2011. PMID 21975196.
11. Cermak NM, et al. Protein supplementation augments the adaptive response of skeletal muscle to resistance-type exercise training: a meta-analysis. The American Journal of Clinical Nutrition. 2012. PMID 23134885.
12. Tieland M, et al. Protein supplementation increases muscle mass gain during prolonged resistance-type exercise training in frail elderly people: a randomized, double-blind, placebo-controlled trial. Journal of the American Medical Directors Association. 2012. PMID 22770932.
13. Paulussen KJM, et al. Dileucine ingestion is more effective than leucine in stimulating muscle protein turnover in young males: a double blind randomized controlled trial. Journal of Applied Physiology. 2021. PMID 34323596.