The Quads Aren't Coming Back. Can Nutrition Help?

Ask any physio, surgeon or athlete what the most stubborn problem after ACL reconstruction is, and you’ll get the same one word answer.

The quad.

It shrinks fast. It comes back slowly. And in a frustrating number of people it never fully comes back at all, despite months of diligent, well programmed strength work. You do everything right and your operated leg still looks like it’s on a different training programme to the other one. A worse one. One it signed up for by accident.

That deficit isn’t cosmetic. It’s linked to reduced lower limb strength, poorer knee function, higher re-injury risk, and accelerated cartilage deterioration, with osteoarthritis developing in more than half of cases (Lohmander et al., 2007).

So here’s the question a 2025 review in Sports Medicine set out to answer by Smith et al.(2025):

If rehab alone isn’t enough, can nutrition move the needle?

So without further ado, here’s what the evidence actually supports, what it doesn’t, and the one thing most people get wrong before they’ve spent a penny on supplements.

Muscle size is a tug of war between protein synthesis (building) and protein breakdown (demolishing). After an ACL injury, four things start pulling hard on the wrong end of the rope (Smith et al., 2025).

1. The building machinery gets switched down.

The mTOR pathway is the master switch for muscle protein synthesis. Training and protein turn it on. Immobilisation turns it off.

And it happens fast. Atrophy can start at around 0.5% per day (Phillips et al., 2009), which works out at 150 to 400 g of muscle from a single leg in the first two weeks (Wall et al., 2013). Two weeks!! You’re still figuring out how to shower after two weeks post-op!

2. The breakdown machinery gets switched up.

Myostatin is your body’s brake pedal on muscle growth. After ACL injury and reconstruction, circulating myostatin has been measured at roughly 50% higher than in uninjured people (Wurtzel et al., 2017), which then activates the proteins that tag your muscle for destruction. Your body has essentially filed your quad under “not currently in use, safe to recycle.”

3. The repair crew shrinks.

Satellite cells are your muscle’s stem cells and they’re what makes remodelling possible. Their numbers drop after ACL injury, while fibrogenic cells expand (Fry et al., 2017). Fewer builders on site, but more people showing up to simply have a glimpse of the aftermath following the demolition.

4. The muscle stops listening.

Arthrogenic muscle inhibition means your nervous system refuses to fully recruit the quad. Pain, swelling and disrupted joint receptors all contribute (Smith et al., 2025). Less recruitment means less mechanical signal reaching the tissue.

Your rehab exercise is delivering a weaker stimulus than the identical exercise would in a healthy leg. Same set. Same reps. Less message received.

And there’s a fifth problem quietly undermining all of it: during disuse, muscle becomes anabolically resistant. It responds less to the protein you eat (Wall et al., 2013).

Which means the standard advice, “just eat more protein”, is least effective in precisely the window where you need it most. Wonderful.

This is the most important section of the paper and the one most likely to get scrolled past on the way to the creatine bit. Please don’t.

The instinct after injury is to eat less. You’re not training, you don’t want to gain fat, it feels responsible. Very sensible. Very wrong.

The energy cost of an injured body is higher than people assume. Healing costs energy. And crutch walking can increase the energy cost of getting around by up to three times (Waters et al., 1987), which anyone who has crutched to a first floor bathroom already knew in their soul.

Then it gets worse. In trained participants, just five days of low energy availability produced a 30% reduction in muscle protein synthesis and reduced mTOR and p70S6K signalling, and all of it happened with protein held at 1.4 to 1.6 g/kg/day (Areta et al., 2014). A separate study found a 20% energy deficit cut muscle protein synthesis by 16% (Pasiakos et al., 2010).

Some good news: that suppression was largely rescued by a single resistance session plus 15 to 30 g of protein afterwards (Areta et al., 2014). The machinery isn’t broken. It’s just waiting to be paid.

The review also raises something we don’t discuss enough. A catastrophic injury like an ACL rupture is a recognised risk factor for disordered eating, particularly in young and talented athletes (Lundqvist et al., 2023). That’s worth taking seriously, and it’s worth a conversation with an actual professional rather than a spreadsheet.

The takeaway: before you consider a single supplement, make sure you’re eating enough. Under-fuelling blunts everything else on this list. It’s the highest leverage change available and it costs nothing. It is, admittedly, a terrible thing to try to sell in a tub.

Leucine rich, high quality protein reliably switches on mTOR, and combined with resistance training it increases protein accretion for up to 72 hours (Smith et al., 2025). The mechanism is not in dispute.

The results in actually injured people are a different story.

What worked:

• 20 g of essential amino acids twice daily, one week before and six weeks after total knee replacement, reduced quadriceps atrophy (Dreyer et al., 2013)

• Leucine plus resistance training in a real ACL population increased thigh muscle diameter (Laboute et al., 2013)

What didn’t:

• High dose leucine on its own (15 g/day) during 7 days of immobilisation did precisely nothing to fibre size, strength or protein synthesis (Edwards et al., 2020)

• Whey protein during 5 days of leg casting in older men also did nothing (Dirks et al., 2014)

• A 2 year follow up in a knee replacement population found no lasting difference between groups in quadriceps strength or rectus femoris size (Ueyama et al., 2023)

The pattern is hard to miss. Protein works best when there’s a training stimulus to amplify. It’s not much good at rescuing a limb that isn’t loading. Protein is a great backing singer and a fairly useless soloist.

Practical read: around 20 g of high quality protein (roughly 0.24 to 0.30 g/kg) after rehab sessions (Stokes et al., 2018). Push total daily intake toward 1.6 to 2.5 g/kg/day during disuse (Wall & van Loon, 2013), because anabolic resistance means you probably need more than a healthy person, not less. Which is the opposite of what your instincts are telling you.

Creatine’s mechanism isn’t protein synthesis, it’s energy. More phosphocreatine means faster ATP regeneration, more quality work per session, less fatigue between bouts. That’s the “train harder” lever.

What worked:

• Creatine through immobilisation plus 10 weeks of rehab: muscle cross sectional area and knee extension power recovered faster than placebo (Hespel et al., 2001)

• Preserved lean mass, strength and endurance through 29 days of casting (Johnston et al., 2009)

• Combined with 16 weeks of resistance training, increased satellite cell and myonuclei numbers (Olsen et al., 2006), which is genuinely interesting given satellite cells take a hit after ACL injury

What didn’t:

• Creatine loading before and during 7 days of leg immobilisation: no effect on mass or strength (Backx et al., 2017)

• The one ACL specific trial (60 participants, up to 24 weeks post op): no effect on strength or power loss (Tyler et al., 2004)

That last bullet is the sound of a great narrative meeting a control group.

Practical read: the benefit seems to live in the training phases rather than the immobilised phase. The usual protocol is 20 g/day (4 x 5 g) for 5 to 7 days, then 3 to 5 g/day (Smith et al., 2025). It’s cheap, it’s one of the most studied supplements in existence, and it has a good safety record. It is not, sadly, a personality.

Omega-3s reduce inflammation and, in animal studies, switch on the Akt-mTOR-S6K1 pathway (Smith et al., 2025). Human results are all over the place.

The standout finding: 5 g/day for 4 weeks before and during 2 weeks of leg immobilisation attenuated muscle loss and kept myofibrillar protein synthesis higher than control (McGlory et al., 2019).

Note the design. Supplementation started before the immobilisation. That timing may be the entire point, which is unhelpful if you’ve already had surgery and are reading this in a compression sleeve.

Practical read: biologically sensible around surgery, when inflammation peaks. If you know your date in advance, starting early is worth discussing with someone qualified.

Collagen is a third of total body protein and the key tensile element of ligaments and tendons. The marketing writes itself. The data are less cooperative.

Collagen is low in leucine, which is the main trigger for muscle protein synthesis (Smith et al., 2025).

• Head to head, whey beat collagen for muscle protein synthesis (Oikawa et al., 2020)

• Whey beat leucine matched collagen for muscle thickness over 10 weeks (Jacinto et al., 2022)

• Two recent controlled studies found collagen did not increase muscle connective protein synthesis rates (Aussieker et al., 2023; Kirmse et al., 2024)

Where it might earn its keep is tendon rather than muscle. Fourteen weeks of collagen peptides with high load training increased patellar tendon cross sectional area (Jerger et al., 2023), which could help with force transmission.

Practical read: collagen is not a replacement for whey if the goal is a bigger quad. It may have a role alongside it if graft and tendon health is what you’re chasing. Being made of collagen does not mean it is best rebuilt by eating collagen, in the same way that eating a brick does not repair a wall.

Zero direct evidence in ACL populations. But caffeine reliably lowers perceived exertion and masks fatigue (Smith et al., 2025).

If part of the failure to regain quad size is simply that you can’t push hard enough, that’s a cheap lever, and one you’re probably already pulling every morning without calling it a supplementation strategy. Save it for late stage rehab, once the graft happily tolerates load.

Smith et al. (2025) propose matching the supplement to the goal of the phase. They explicitly call this preliminary, and so should you, and so should anyone quoting it at you confidently on Instagram.

Pre-op (roughly 2 to 4 weeks out) Goal: bank muscle, reduce inflammation, arrive fed. Whey after prehab sessions, omega-3, creatine loading, adequate total protein, carbohydrate preload on surgery day.

Early phase (2 weeks to 3 months) Goal: limit breakdown through unloading. Omega-3, whey after sessions, hit your total protein target, collagen before rehab sessions.

Mid phase (3 to 6 months) Goal: drive hypertrophy. Whey post session, creatine to enable harder training, collagen pre session.

Late phase (6 to 9 months) Goal: strength into power, restore conditioning. Whey, creatine, caffeine, collagen.

Return to play (9 months and beyond) Goal: maintenance. Sport specific, and beyond the scope of the review.

1. The ACL specific evidence is genuinely thin.

Across the whole literature, only seven studies have tested nutritional supplementation on the quadriceps after ACL injury and reconstruction. Three showed benefit. Four showed nothing (Smith et al., 2025).

Sample sizes ranged from two professional rugby players (Shaw et al., 2019) to 72 participants (López-Vidriero et al., 2019). Yes, two. Nearly everything else in this article is extrapolated from immobilisation, bed rest and knee replacement studies, often in people several decades older than your average ACL patient. Useful. Not the same thing.

2. Supplements amplify training. They don’t replace it.

Almost every positive finding above happened in combination with resistance training. During genuine immobilisation, most supplements did very little.

Nutrition is a multiplier on a stimulus. If the stimulus is weak, and with arthrogenic muscle inhibition it often is, the multiplier has less to work with. Multiplying by not very much gives you not very much.

Restoring quad activation is still job number one. No powder changes that.

3. Declare the conflict.

The review’s lead author discloses ownership of a supplement company that produces collagen peptides (Smith et al., 2025).

That doesn’t invalidate the paper. It’s peer reviewed, open access, and the authors are notably honest about how weak the evidence base is, collagen very much included. But it’s the sort of thing you deserve to know, and a good reason to go and read the original. It’s free, and it’s referenced at the bottom.

• Fuel adequately. Under-eating after injury is common, understandable, and actively suppresses the machinery you’re relying on. Highest leverage, zero cost.

• Prioritise protein. Around 20 g after rehab sessions, and aim high on daily total during disuse.

• Consider creatine, mostly for the training phases.

• Consider omega-3 around surgery, ideally starting beforehand.

• Be sceptical of collagen for quad growth. The tendon case is more interesting than the muscle case.

• Remember the ceiling. Nutrition supports rehab. It does not substitute for progressive loading, quad activation and time.

Or, more bluntly:

No supplement will out-train an unloaded, inhibited, under-fuelled quadriceps. Get the loading right, get the fuelling right, and you can stack the molecular deck slightly more in your favour. Slightly. It’s a nudge, not a cheat code.

I’m not a dietitian and I’m not a nutritionist. I read the research, I work in this space, and I try hard to represent the evidence fairly, including the parts that don’t support a tidy conclusion. But reading a paper is not the same as being qualified to tell you what to eat.

Everything above is general education about what a review article found. It is not a plan, and it definitely isn’t your plan.

Please talk to a qualified professional before changing anything, ideally an accredited sports dietitian or registered nutritionist who can look at your actual situation: your surgery, your timeline, your training load, your medical history, your medications, your budget and the sport you’re trying to get back to. Your surgeon and physiotherapist should be in that conversation too.

Dosing around surgery in particular is not a place to freestyle based on a Substack post. Even a well referenced one.

And if you compete, check every product against your sport’s anti-doping rules before it goes anywhere near you. “I read about it in a newsletter” has never once worked as a defence.

What’s your experience been? If you’re mid rehab, are you tracking your intake at all, or has nutrition been a complete afterthought? No judgement. Tell me in the comments.

If this was useful, send it to someone in month three of their rehab. That’s usually when the quad question starts to bite.

If you’d like to go deeper on ACL rehabilitation, my full library lives over at learn.physio, with 50+ hours of ACL masterclasses, practicals, lectures and roundtables all in one place.

Explore the ACL content at learn.physio

Mick Hughes, The ACL Hub

Primary studies below were reported within the Smith et al. (2025) review and are referenced here so you can go to the original sources yourself.

Areta, J. L., Burke, L. M., Camera, D. M., West, D. W. D., Crawshay, S., Moore, D. R., Stellingwerff, T., Phillips, S. M., Hawley, J. A., & Coffey, V. G. (2014). Reduced resting skeletal muscle protein synthesis is rescued by resistance exercise and protein ingestion following short-term energy deficit. American Journal of Physiology-Endocrinology and Metabolism, 306(8), E989–E997.

Aussieker, T., Hilkens, L., Holwerda, A. M., Fuchs, C. J., Houben, L. H. P., Senden, J. M., van Dijk, J. W., Snijders, T., & van Loon, L. J. C. (2023). Collagen protein ingestion during recovery from exercise does not increase muscle connective protein synthesis rates. Medicine & Science in Sports & Exercise, 55(10), 1792–1802.

Backx, E. M. P., Hangelbroek, R., Snijders, T., Verscheijden, M. L., Verdijk, L. B., de Groot, L. C. P. G. M., & van Loon, L. J. C. (2017). Creatine loading does not preserve muscle mass or strength during leg immobilization in healthy, young males: A randomized controlled trial. Sports Medicine, 47(8), 1661–1671.

Dirks, M. L., Wall, B. T., Nilwik, R., Weerts, D. H. J. M., Verdijk, L. B., & van Loon, L. J. C. (2014). Skeletal muscle disuse atrophy is not attenuated by dietary protein supplementation in healthy older men. The Journal of Nutrition, 144(8), 1196–1203.

Dreyer, H. C., Strycker, L. A., Senesac, H. A., Hocker, A. D., Smolkowski, K., Shah, S. N., & Jewett, B. A. (2013). Essential amino acid supplementation in patients following total knee arthroplasty. The Journal of Clinical Investigation, 123(11), 4654–4666.

Edwards, S. J., Smeuninx, B., McKendry, J., Nishimura, Y., Luo, D., Marshall, R. N., Perkins, M., Ramsay, J., Joanisse, S., Philp, A., & Breen, L. (2020). High-dose leucine supplementation does not prevent muscle atrophy or strength loss over 7 days of immobilization in healthy young males. The American Journal of Clinical Nutrition, 112(5), 1368–1381.

Fry, C. S., Johnson, D. L., Ireland, M. L., & Noehren, B. (2017). ACL injury reduces satellite cell abundance and promotes fibrogenic cell expansion within skeletal muscle. Journal of Orthopaedic Research, 35(9), 1876–1885.

Hespel, P., Op ‘t Eijnde, B., Van Leemputte, M., Ursø, B., Greenhaff, P. L., Labarque, V., Dymarkowski, S., Van Hecke, P., & Richter, E. A. (2001). Oral creatine supplementation facilitates the rehabilitation of disuse atrophy and alters the expression of muscle myogenic factors in humans. The Journal of Physiology, 536(2), 625–633.

Jacinto, J. L., Nunes, J. P., Gorissen, S. H. M., Capel, D. M. G., Bernardes, A. G., Ribeiro, A. S., Cyrino, E. S., Roschel, H., & Aguiar, A. F. (2022). Whey protein supplementation is superior to leucine-matched collagen peptides to increase muscle thickness during a 10-week resistance training program in untrained young adults. International Journal of Sport Nutrition and Exercise Metabolism, 32(3), 133–143.

Jerger, S., Centner, C., Lauber, B., Seynnes, O., Friedrich, T., Lolli, D., Gollhofer, A., & König, D. (2023). Specific collagen peptides increase adaptions of patellar tendon morphology following 14-weeks of high-load resistance training: A randomized-controlled trial. European Journal of Sport Science, 23(12), 2329–2339.

Johnston, A. P. W., Burke, D. G., MacNeil, L. G., & Candow, D. G. (2009). Effect of creatine supplementation during cast-induced immobilization on the preservation of muscle mass, strength, and endurance. Journal of Strength and Conditioning Research, 23(1), 116–120.

Kirmse, M., Lottmann, T. M., Volk, N. R., de Marées, M., Holwerda, A. M., van Loon, L. J. C., & Platen, P. (2024). Collagen peptide supplementation during training does not further increase connective tissue protein synthesis rates. Medicine & Science in Sports & Exercise, 56(12), 2296–2304.

Laboute, E., France, J., Trouve, P., Puig, P. L., Boireau, M., & Blanchard, A. (2013). Rehabilitation and leucine supplementation as possible contributors to an athlete’s muscle strength in the reathletization phase following anterior cruciate ligament surgery. Annals of Physical and Rehabilitation Medicine, 56(2), 102–112.

Lohmander, L. S., Englund, P. M., Dahl, L. L., & Roos, E. M. (2007). The long-term consequence of anterior cruciate ligament and meniscus injuries: Osteoarthritis. The American Journal of Sports Medicine, 35(10), 1756–1769.

López-Vidriero, E., Olivé-Vilas, R., López-Capapé, D., Varela-Sende, L., López-Vidriero, R., & Til-Pérez, L. (2019). Efficacy and tolerability of progen, a nutritional supplement based on innovative plasma proteins, in ACL reconstruction: A multicenter randomized controlled trial. Orthopaedic Journal of Sports Medicine, 7(2), 2325967119827237.

Lundqvist, C., Schary, D. P., Eklöf, E., Zand, S., & Jacobsson, J. (2023). Elite lean athletes at sports high schools face multiple risks for mental health concerns and are in need of psychosocial support. PLoS ONE, 18(4), e0284725.

McGlory, C., Gorissen, S. H. M., Kamal, M., Bahniwal, R., Hector, A. J., Baker, S. K., Chabowski, A., & Phillips, S. M. (2019). Omega-3 fatty acid supplementation attenuates skeletal muscle disuse atrophy during two weeks of unilateral leg immobilization in healthy young women. The FASEB Journal, 33(3), 4586–4597.

Oikawa, S. Y., Kamal, M. J., Webb, E. K., McGlory, C., Baker, S. K., & Phillips, S. M. (2020). Whey protein but not collagen peptides stimulate acute and longer-term muscle protein synthesis with and without resistance exercise in healthy older women: A randomized controlled trial. The American Journal of Clinical Nutrition, 111(3), 708–718.

Olsen, S., Aagaard, P., Kadi, F., Tufekovic, G., Verney, J., Olesen, J. L., Suetta, C., & Kjaer, M. (2006). Creatine supplementation augments the increase in satellite cell and myonuclei number in human skeletal muscle induced by strength training. The Journal of Physiology, 573(2), 525–534.

Pasiakos, S. M., Vislocky, L. M., Carbone, J. W., Altieri, N., Konopelski, K., Freake, H. C., Anderson, J. M., Ferrando, A. A., Wolfe, R. R., & Rodriguez, N. R. (2010). Acute energy deprivation affects skeletal muscle protein synthesis and associated intracellular signaling proteins in physically active adults. The Journal of Nutrition, 140(4), 745–751.

Phillips, S. M., Glover, E. I., & Rennie, M. J. (2009). Alterations of protein turnover underlying disuse atrophy in human skeletal muscle. Journal of Applied Physiology, 107(3), 645–654.

Shaw, G., Serpell, B., & Baar, K. (2019). Rehabilitation and nutrition protocols for optimising return to play from traditional ACL reconstruction in elite rugby union players: A case study. Journal of Sports Sciences, 37(15), 1794–1803.

Smith, M. J., Hoffman, N. J., San Jose, A. J., Burke, L. M., & Opar, D. A. (2025). Nutritional interventions to attenuate quadriceps muscle deficits following anterior cruciate ligament injury and reconstruction. Sports Medicine, 55(3), 569–596. https://doi.org/10.1007/s40279-025-02174-w

Stokes, T., Hector, A. J., Morton, R. W., McGlory, C., & Phillips, S. M. (2018). Recent perspectives regarding the role of dietary protein for the promotion of muscle hypertrophy with resistance exercise training. Nutrients, 10(2), 180.

Tyler, T. F., Nicholas, S. J., Hershman, E. B., Glace, B. W., Mullaney, M. J., & McHugh, M. P. (2004). The effect of creatine supplementation on strength recovery after anterior cruciate ligament (ACL) reconstruction: A randomized, placebo-controlled, double-blind trial. The American Journal of Sports Medicine, 32(2), 383–388.

Ueyama, H., Kanemoto, N., Minoda, Y., Taniguchi, Y., & Nakamura, H. (2023). Perioperative essential amino acid supplementation facilitates quadriceps muscle strength and volume recovery after TKA: A double-blinded randomized controlled trial. The Journal of Bone and Joint Surgery. American Volume, 105(5), 345–353.

Wall, B. T., Snijders, T., Senden, J. M. G., Ottenbros, C. L. P., Gijsen, A. P., Verdijk, L. B., & van Loon, L. J. C. (2013). Disuse impairs the muscle protein synthetic response to protein ingestion in healthy men. The Journal of Clinical Endocrinology & Metabolism, 98(12), 4872–4881.

Wall, B. T., & van Loon, L. J. C. (2013). Nutritional strategies to attenuate muscle disuse atrophy. Nutrition Reviews, 71(4), 195–208.

Waters, R. L., Campbell, J., & Perry, J. (1987). Energy cost of three-point crutch ambulation in fracture patients. Journal of Orthopaedic Trauma, 1(2), 170–173.

Wurtzel, C. N., Gumucio, J. P., Grekin, J. A., Khouri, R. K., Jr., Russell, A. J., Bedi, A., & Mendias, C. L. (2017). Pharmacological inhibition of myostatin protects against skeletal muscle atrophy and weakness after anterior cruciate ligament tear. Journal of Orthopaedic Research, 35(11), 2499–2505.