7 Ways Cognitive Fatigue Steals the Second Half: What Soccer and Tennis Can Learn From the Hospital Night Shift
A science-backed guide to how cognitive fatigue affects decision-making in soccer and tennis, the brain pathways behind it, and the nutrients and emerging supplements being studied for 2026–2027
It's the 70th minute. Your legs still work, your GPS numbers look fine, and yet the pass you'd normally see three moves early just isn't there. In tennis it's the fourth set: the second serve that was automatic in the first hour suddenly feels like a coin flip. Most coaches would call that "tiredness." The research calls it something more specific, and more fixable: cognitive fatigue.
Cognitive fatigue is the drop in mental performance that builds up after long stretches of focus, scanning, and decision-making. It shows up the same way in a pharmacist verifying the 300th prescription of a shift, a physician deep into an afternoon clinic, and a center-mid in the back half of a match. This guide breaks down how cognitive fatigue affects decision-making in soccer and tennis, why it's become a bigger issue since COVID, and what the evidence actually says about nutrients like fish oil, magnesium, B-vitamins, curcumin, mango leaf extract, and citicoline.
Sound familiar?
• Your decisions get slower and "safer" late in matches, even when your fitness testing is strong.
• You lose the picture: scanning drops off and you stop seeing the run behind the defender.
• Your first touch, foot placement, or landing gets sloppy in the final 20 minutes.
• In tennis, your second serve and shot targeting fall apart in later sets.
• You feel foggy, a bit unsteady, or "switched off" after a long day of school, work, or screens before training.
If any of those land, keep reading. Mental fatigue isn't a character flaw. It's biology, and biology can be trained, fueled, and managed.
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1. What Cognitive Fatigue Actually Is (and What It Isn't)
Sports scientists define mental fatigue as a psychobiological state caused by prolonged, demanding cognitive activity. The key finding that changed the field: it doesn't show up where we usually look. In a landmark review, Martin and colleagues noted that heart rate, lactate, and neuromuscular function are essentially unaffected by mental fatigue. What changes is the perception of effort. The same run simply feels harder, so athletes ease off sooner [8].
A 2020 meta-analysis in Sports Medicine pooled the research on prior cognitive exertion and found it reliably impairs subsequent physical performance [37]. In soccer specifically, a 2018 review by Smith, Coutts, and colleagues argued that the cognitive demands of competition likely contribute to the fatigue-related drop-offs seen during and after matches, and not only the physical demands [1].
GOLD NUGGET #1
Mental fatigue barely moves your heart rate or lactate. It changes how hard effort feels and how well you decide. That's why a player can pass a fitness test and still "disappear" late in a match [8].
2. Why Cognitive Fatigue Is a Bigger Problem Post-COVID and in an "Always-On" World
Two things changed after 2020, and both load the same mental budget athletes need on match day.
Screens never really went back down
A JAMA Pediatrics meta-analysis of 46 studies found that youth screen time jumped by about 84 minutes a day during the pandemic, a 52% increase over pre-pandemic levels [15]. For young athletes, that's more scrolling, more notifications, and more task-switching before they ever step on the pitch.
This matters directly for performance. In a randomized crossover study, professional soccer players who spent 30 minutes on social media or video games right before a simulated match made worse passing decisions than when they watched neutral videos [4]. The phone in the locker room isn't neutral.
Long COVID left a cognitive footprint
A meta-analysis in Brain, Behavior, and Immunity found that about 32% of people reported fatigue and about 22% showed cognitive impairment 12 or more weeks after a COVID-19 diagnosis. Several included studies linked these symptoms to heightened inflammation [14]. For an athlete or student who's had COVID, baseline mental stamina may not be where it was.
Post-COVID pain points we hear from players and staff:
• "I'm recovered physically, but my focus fades much faster than it used to." • "I'm on my phone between classes, training, and travel, and I never feel mentally fresh." • "Video sessions, tactics boards, and school all stack up before kickoff."
GOLD NUGGET #2
Thirty minutes of social media or video games right before a match measurably worsened professional soccer players' passing decisions in a randomized study [4]. Protecting the pre-match window is one of the cheapest performance gains available.
3. Lessons From the Hospital: Decision Overload in Medicine and Pharmacy
Healthcare is a near-perfect lab for studying cognitive fatigue because every shift is a long string of high-stakes decisions. The pattern that emerges there maps almost perfectly onto sport.
Decisions degrade across a single shift
Researchers at Brigham and Women's Hospital analyzed more than 21,000 primary care visits and found that clinicians' likelihood of prescribing antibiotics for acute respiratory infections rose steadily across each morning and afternoon clinic session, including for infections where antibiotics were never indicated. The authors interpreted this as decision fatigue: as the session wore on, it got harder to resist the easier, lower-effort choice [10].
The same logic applies to pharmacy. A pharmacist's shift is hundreds of verification decisions, interaction checks, and interruptions. When the brain's control systems tire, people default to shortcuts. In medicine that's an unnecessary prescription. On the pitch, it's the safe square pass instead of the line-breaking ball.
Back-to-back shifts and the immunoinflammatory load
When shifts stack up, sleep gets cut, and the stress and immune systems get involved. Resident physicians in one study showed elevated high-sensitivity C-reactive protein (hs-CRP, a marker of low-grade inflammation) and blunted morning cortisol compared with attendings who didn't work nights. Their chronic sleep curtailment was associated with greater impulsivity, slower cognitive processing, and weaker executive function [11]. A 2024 study of 303 healthcare workers found hs-CRP and white blood cell counts were significantly higher in night shift staff than day-shift staff [12].
Fact check: the inflammation picture isn't uniform. A Norwegian study of 390 nurses found no clear association between shift schedules and most inflammatory biomarkers [13]. The fair reading is that sleep loss and circadian disruption can push inflammation and cognition in the wrong direction, but individual responses vary.
The healthcare-to-sport translation:
• One long shift ≈ one match: decisions slide toward the easy option as the clock runs.
• Multiple shifts in a row ≈ a congested fixture list or tournament week: fatigue carries over, especially when sleep and travel are disrupted.
• In professional padel, mental fatigue measurably increased from pre- to post-match across successive World Padel Tour matches [39].
4. The Second Half and the Fifth Set: How Cognitive Fatigue Affects Decision-Making in Soccer and Tennis
Soccer
Soccer is one of the most cognitively demanding team sports: constant scanning, anticipating, and choosing under time pressure. In a controlled study, well-trained players who completed 30 minutes of a demanding mental task (the Stroop test) were less accurate and slower on a soccer-specific decision-making test than after reading magazines [2]. A systematic review found that mental fatigue reduced distances covered in physical tests, weakened synchronization between teammates, hurt individual defensive tactical performance, and slowed and degraded decision-making in video-based tests [3]. A separate meta-analysis concluded that mental fatigue significantly impairs overall technical performance in soccer players [38].
Now picture the second half. Players have already spent 45-plus minutes scanning, communicating, and making split-second choices. Mental load stacks on physical load. The result looks like the clinic: the brain starts favoring the lower-effort option.
Tennis
A 2024 systematic review of racket sports found mental fatigue affected stroke speed, accuracy, and faults in table tennis, and in tennis it specifically impaired second-serve accuracy while leaving first-serve speed and accuracy intact [5]. A 2025 study found acute mental fatigue decreased attention and groundstroke targeting performance in male tennis players [7]. In table tennis, mentally fatigued players lost accuracy and hit the ball more slowly [6].
That's the essence of how cognitive fatigue affects decision-making in soccer and tennis: the body may still have gas, but the brain's ability to select, aim, and time the right action erodes first.
GOLD NUGGET #3
In tennis, mental fatigue showed up on the second serve first, the shot that depends most on precise control under pressure, while the first serve held up [5]. If your second-serve percentage collapses late, think brain before legs.
5. What It Does to Vision, Balance, Energy, Foot Mechanics, and Seeing 2–3 Moves Ahead
Vision and scanning
Interestingly, the classic soccer study found mentally fatigued players were slower and less accurate at deciding even though their visual search patterns didn't clearly change [2]. In plain terms, your eyes may still be looking in the right places, but your brain is slower to turn what you see into the right choice. Tennis players under mental fatigue also showed reduced attention [7].
Dizziness and balance
A 2022 systematic review in Experimental Brain Research found mental fatigue increased postural sway, reduced accuracy on voluntary balance tasks, delayed responses to perturbations, and made balance recovery less effective [16]. That can feel like being "a beat off" or slightly unsteady. Important: true or recurring dizziness has many causes (hydration, blood sugar, blood pressure, concussion, inner-ear issues), so don't write it off as mental fatigue. Get it checked.
Fatigue and effort
Because mental fatigue raises perceived effort without changing heart rate or lactate, the same pressing run simply feels harder, and athletes self-limit earlier [8].
Foot mechanics and landing
This is the hidden injury angle. In amateur male athletes, 45 minutes of a demanding cognitive task reduced dynamic balance and knee proprioception and worsened landing mechanics, factors linked to lower-limb injury risk [18]. A 2025 biomechanics study found mental fatigue partly altered landing patterns associated with non-contact ACL injury risk [17]. Foot placement, cutting, and landing quality in the final stretch of a match deserve as much attention as sprint counts.
Seeing 2–3 steps ahead
Anticipation runs on working memory and cognitive control in the prefrontal cortex. That's exactly the system that tires. Mental fatigue impairs decision speed and accuracy and team tactical synchronization [2, 3], which is what "seeing the game" really is.
GOLD NUGGET #4
Mental fatigue alters balance, proprioception, and landing mechanics [16, 17, 18]. Late match ankle rolls and non-contact knee injuries may have a cognitive component, not just a physical one.
6. The Major Pathways Behind Cognitive Fatigue
Researchers don't think there's one single cause. These are the best-supported pathways right now:
• Adenosine buildup in the anterior cingulate cortex (ACC). Prolonged mental effort is thought to increase brain adenosine, which raises the sense of effort and dampens motivation through its interaction with dopamine [8]. This is the main reason caffeine, an adenosine blocker, is one of the best-studied countermeasures [36].
• Dopamine and catecholamine drain. Motivation and effort-based decision-making depend on dopamine signaling in prefrontal and cingulate circuits. Mental fatigue is theorized to reduce this signaling, and most effective countermeasures appear to work through it [35, 36].
• Glutamate accumulation in the lateral prefrontal cortex. In a Paris Brain Institute study, people who did hours of demanding cognitive work had higher glutamate in the lateral prefrontal cortex by day's end and made more impulsive, low-effort choices [9]. Their model: the buildup makes recruiting cognitive control more costly. The researchers also pointed to rest and sleep as the brain's way of restoring regulation.
• Immunoinflammatory signaling. Sleep loss and night work are associated with higher hs-CRP and altered stress-hormone (HPA axis) function, alongside slower processing and impulsivity [11, 12]. Post-COVID fatigue and cognitive symptoms have also been linked to inflammation [14].
• Brain energy supply. Sleep deprivation alters the brain's high-energy phosphate balance, and creatine research suggests supporting that energy buffer can partially restore performance [32].
GOLD NUGGET #5
After a long, demanding day of thinking, glutamate rose in the brain's cognitive-control region and people shifted toward easier, more impulsive choices [9]. That's the clinic's late afternoon prescribing creep and the second-half safe pass, explained by the same chemistry.
7. The Nutrient Toolkit: Cod Liver Oil, Magnesium, B-Vitamins, and Curcumin With Black Pepper and Oil
Supplements won't replace sleep, smart scheduling, or training, but several have real human data relevant to cognitive fatigue. Here's what holds up, and where the evidence gets thinner.
Cod liver oil (omega-3s: EPA and DHA)
How it may help: DHA is a structural fat in brain and retinal cell membranes, and omega-3s have anti-inflammatory effects.
The research: in a double-blind trial with players from two Spanish women's top-flight teams, 3.5 g/day of DHA-rich fish oil for four weeks improved complex reaction time and efficiency compared with olive oil [19]. That's a decision-speed outcome, directly relevant to match play.
Fact check: that trial used DHA-rich fish oil, not cod liver oil. Cod liver oil also delivers vitamins A and D. The adult upper limit for preformed vitamin A is 3,000 mcg RAE per day [20], so check labels if you're also taking a multivitamin, and talk to a provider if you're pregnant or on blood thinners.
Magnesium
How it may help: magnesium acts as a natural gatekeeper on NMDA glutamate receptors, which ties it directly to the glutamate pathway above. It's also central to energy metabolism and sleep regulation.
The research: in a 2024 randomized trial, adults with sleep complaints taking 1 g/day of magnesium L-threonate for 21 days improved objective deep and REM sleep scores and reported better energy, mood, and mental alertness versus placebo [22]. A newer six-week trial in poor sleepers reported improvements on some cognitive measures and in sleep-related impairment [23].
Fact check: these trials studied people with sleep problems, not athletes, and used one branded form. The upper limit for supplemental magnesium is 350 mg/day for adults; higher doses commonly cause GI upset [21].
B-Vitamins
How they may help: B-vitamins are cofactors for cellular energy production and for making neurotransmitters, including dopamine.
The research: in a randomized trial of 215 working men, a high-dose B-complex with vitamin C and minerals improved vigor, reduced stress, and led to better performance on a demanding math task. Participants also rated themselves less mentally tired before and after a 60-minute cognitive demand battery [24]. A parallel trial in 216 women found the supplement blunted the negative effect of extended multitasking on mood and fatigue and improved multitasking accuracy [25].
Fact check: benefits are likely largest in people whose intake was suboptimal to begin with.
Curcumin with black pepper and oil
How it may help: curcumin is an anti-inflammatory polyphenol from turmeric, relevant to the immunoinflammatory pathway.
The research: a randomized trial of a lipid-based curcumin formulation (400 mg Longvida, about 80 mg curcumin) improved attention and working memory one hour after dosing, and after four weeks improved working memory and reduced fatigue in healthy older adults [26]. A 12- week replication found lower fatigue scores at 4 and 12 weeks and better working memory at 12 weeks [27].
Why black pepper and oil: curcumin is poorly absorbed on its own. In a small 1998 study, adding 20 mg of piperine (from black pepper) to 2 g of curcumin raised its bioavailability by 2000% in human volunteers [28]. Curcumin is also fat-soluble, which is why lipid formulations and taking it with a meal containing fat make sense.
Fact check: the famous "2000%" figure comes from one small study and hasn't been consistently replicated at that magnitude. Piperine works by slowing the body's breakdown pathways [28], which can also affect some medications, so check with a provider or pharmacist. And the curcumin cognition trials were in older adults, not athletes.
8. Mango Leaf Extract and Citicoline: What the Research Shows
Mango leaf extract (mangiferin)
Mango leaves are rich in mangiferin, a polyphenol. The best-studied extract, Zynamite, is standardized to at least 60% mangiferin and produced by Nektium in Gran Canaria, Spain.
The research: in a double-blind crossover trial of 70 healthy adults aged 18–45, a single 300 mg dose improved overall accuracy across a cognitive battery, with specific gains in "accuracy of attention" and episodic memory [29]. A newer trial of a water-soluble version in 120 university students reported improvements in processing speed, complex task handling, and mental flexibility at lower doses (100–150 mg) [30].
Fact check: promising, fast-acting, and non-stimulant, but research so far centers on one patented extract. Independent replication and athlete-specific trials are still needed.
Citicoline
Citicoline (CDP-choline) supplies choline and uridine, building blocks for brain cell membranes and the neurotransmitter acetylcholine. It's also thought to support dopamine activity.
The research: in a randomized trial of 75 healthy adolescent males, 28 days of 250 or 500 mg/day of citicoline (Cognizin) improved attention and psychomotor speed versus placebo, and higher weight-adjusted doses predicted better attention accuracy and less impulsivity [31]. Attention plus motor speed is a useful combination for youth soccer and tennis players.
Fact check: the study was funded by the ingredient's manufacturer and didn't test athletes or in-game performance.
9. New and Emerging Supplements for Cognitive Fatigue in 2026– 2027
These are the compounds getting the most research attention right now. Evidence levels below are our plain-language summary: Moderate = multiple controlled human trials; Emerging = a few small RCTs; Preliminary = one or two small trials.
Supplement | What's new | Evidence level | Results so far |
Creatine (for the brain) | Acute high-dose use under sleep loss | Emerging | A single 0.35 g/kg dose during 21 hours of sleep deprivation improved cognitive performance and processing speed and shifted brain energy markers [32]. Daily 3–5 g is the established safe athletic dose [33]; the one-off brain dose is far higher and less tested. |
Paraxanthine | Caffeine's main metabolite, marketed as a smoother stimulant | Emerging | 200 mg improved some executive-function measures and reduced attentional decline and cognitive fatigue before and after a 10 km run [34]. Mostly industry-linked research so far. |
L-tyrosine | Tested specifically under mental fatigue | Preliminary | In a 2026 crossover trial, 300 mg/kg increased time to exhaustion by about 16% in mentally fatigued cyclists and slowed the rise in perceived effort, without changing subjective mental fatigue [35]. Only 12 participants; the dose is very large. |
Magnesium L threonate | Brain-targeted magnesium form | Emerging | Improved sleep quality and daytime functioning [22] and some cognitive measures in poor sleepers [23]. |
Water-soluble mango leaf extract | Lower-dose, drinkable version | Emerging | Improved processing speed and mental flexibility in university students [30]. |
Caffeine (benchmark) | Not new, but the comparison point | Moderate | One of the best-supported countermeasures to mental fatigue, at roughly 3–6 mg/kg [35, 36]. |
Bottom line: none of these is a magic switch, and athletes subject to anti-doping rules should only use third-party tested products (for example, NSF Certified for Sport or Informed Sport).
10. Five Actionable Steps for Athletes and Students
1. Protect the 30-minute window before kickoff, training, or an exam. No social media or gaming. Use that time for music, a walk, or a calm tactical review. This directly targets the effect seen in pro soccer players [4].
2. Treat sleep as cognitive recovery. Sleep is when the brain restores regulation after long, demanding work [9]. Keep consistent sleep and wake times, especially during
congested fixture weeks or exam blocks, and use a short early-afternoon nap when nights run short.
3. Train your brain under load. Put decision-making drills, small-sided games, or second serve practice at the end of sessions when you're already tired. Brain endurance training, which combines cognitive and physical work, consistently improves endurance performance in studies [40].
4. Fuel food-first, then personalize supplements. Eat oily fish twice a week, leafy greens, nuts and seeds, whole grains, and a carbohydrate source before matches. If you're considering fish oil, magnesium, B-vitamins, curcumin, citicoline, mango leaf, or creatine, review them with a qualified provider and stick to tested products.
5. Monitor it like you monitor GPS load. Rate mental fatigue 0–100 before training, run a quick 3-minute reaction-time test on your phone or laptop, and have staff note late session
landing and foot-placement quality. Trends tell you when to pull back.
Talk to an Integrative Provider
BEFORE YOU START ANY SUPPLEMENT
This article is for education, not medical advice. Cognitive fatigue, dizziness, persistent brain fog, and post-COVID symptoms can overlap with sleep disorders, concussion, nutrient deficiencies, anemia, thyroid issues, and more. We strongly encourage you to see an integrative provider (an integrative physician, sports medicine doctor, or registered dietitian with integrative training) to discuss your symptoms, review labs if needed, check for medication interactions, and build a plan that fits your sport, schedule, and anti-doping requirements.
Fact-Check Notes
• Mental fatigue impairing soccer decision-making, technical performance, and tactical behavior is supported by multiple systematic reviews [1, 3, 38].
• The antibiotic-prescribing study shows an association with time in session; the authors interpret it as decision fatigue but note other factors may contribute [10].
• Inflammation findings in shift workers are mixed [11, 12, 13].
• The piperine "2000%" figure comes from a single small 1998 study [28].
• Curcumin and magnesium cognition trials were not in athletes; mango leaf and citicoline trials are largely industry-supported [26, 23, 29, 31].
References
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