Legal Performance Boosters: What Each One Is Really Worth

The marginal gains menu

Every few years a new product promises to knock minutes off your personal record (PR). Some deliver. Others work in a lab but not on a road, and a few are mostly marketing with a study attached.

This article ranks the most talked-about legal aids by the percentage improvement the research supports, then converts those percentages into race times. We cover:

• Super shoes
• Caffeine
• Beetroot juice (dietary nitrate)
• Sodium bicarbonate
• Heat training
• Nomio broccoli sprout shots

None of these come close to the gains from consistent training, eating enough and sleeping well. A runner who adds 5 miles (8 km) a week for a year will improve far more than any shoe or supplement can deliver, so treat everything here as the last 1–3%, not the first.

What a percentage is worth

Small percentages sound trivial until you apply them to a race. This is what each step is worth for a runner targeting a 25-minute 5K or a 4-hour marathon:

Keep this table in mind as you read. For most people, a “small” 1% gain is still a new PR.

The ranking at a glance

The ranges are our reading of the research, not guarantees. Individual responses vary widely for almost everything on this list.

1. Super shoes

Realistic gain: about 1–3% for most runners.

Super shoes, also called advanced footwear technology, combine a thick, light, highly bouncy foam with a stiff plate (usually carbon fiber) or rods. The foam returns more of the energy you put into it, and the geometry reduces the work your calf and foot muscles have to do.

What the research shows

The landmark study came from Hoogkamer and colleagues in 2018. They tested a prototype of Nike’s Vaporfly against two top racing flats, and found it reduced the energy cost of running by an average of 4%. Every one of the 18 runners improved, at every speed tested.¹

A 4% saving in energy doesn’t mean you run 4% faster. As you speed up, air resistance rises, so each extra bit of speed costs more. Modeling by Kipp and colleagues suggests that at elite marathon pace, a 4% economy gain translates to roughly a 2.5–3% faster race.² At slower paces the same economy saving is worth proportionally more speed, because air resistance matters less.

For recreational runners, the economy gain itself is less predictable. Studies at slower paces still find meaningful benefits on average,³ but the spread is wide: some runners gain more than elites do, and a few gain nothing. Heavier runners, runners with a very different foot strike, and those who simply don’t get on with the shoe tend to see less.

How to use them

Race in them, and do some of your key sessions in them too. Your legs need time to adapt to the different feel, and your calves may be sore the first few times. The foam loses some of its bounce with mileage, so many runners keep a pair for races and a few big workouts and do the rest of their training in standard shoes.

Fit matters more than brand. A super shoe you find unstable or uncomfortable won’t help you, and our guide to choosing the right running shoes covers how to judge fit.

If you race seriously, mind the rules. World Athletics limits road shoe stack height to 40 mm (about 1.6 in). Nearly every shoe sold as a racer complies, but check if you’re entering an event run under its rules.

2. Caffeine

Realistic gain: about 2%.

Caffeine is the cheapest, best-studied and most reliable supplement on this list. It works mainly on the brain, reducing how hard a given pace feels, so you can hold a faster pace for longer.

What the research shows

A 2018 meta-analysis of 46 studies found that moderate doses of caffeine improved endurance time-trial performance by an average of about 2.2%.⁴ The International Society of Sports Nutrition (ISSN) position stand concludes that caffeine consistently improves endurance performance, with the most effective dose between 3 and 6 mg per kg of body weight.⁵

The International Olympic Committee (IOC) consensus statement on supplements lists caffeine among the handful with good evidence of improving performance.⁶

How to use it

• Dose: 3 mg per kg (about 1.4 mg per lb) is enough for most runners. For a 150 lb (68 kg) runner that’s roughly 200 mg, or a large coffee. Going above 6 mg per kg adds side effects, not speed.
• Timing: about 60 minutes before the start. For a marathon, some runners take part of their dose as a caffeinated gel in the second half.

Practice with it first. Caffeine can cause jitters, a racing heart and a sudden need for a restroom, and a long run or tempo session is the place to find that out, not race morning. It also lingers for hours, so keep it away from evening sessions to protect your sleep, as we explain in Sleep and Running Performance.

Regular coffee drinkers still benefit. You don’t need to cut caffeine out beforehand, although a few low-caffeine days before a race may make race-day caffeine feel a little stronger.

3. Heat training

Realistic gain: large in hot races; possibly a few percent in cool races with several weeks of heat training, but that’s not yet proven.

Heat training means deliberately exposing yourself to heat so your body adapts. It can do two different jobs, on two different timescales.

Heat acclimation takes about 10–14 days. Your blood plasma volume rises, you start sweating sooner and more, your heart rate at a given pace falls, and your core temperature runs lower. This mainly helps you race in the heat.

The second effect, an altitude-like blood boost, takes about five weeks or more. With regular heat sessions over several weeks, your body appears to make more red blood cells, raising your total hemoglobin mass (hemoglobin is the oxygen-carrying protein in your blood). That’s the same adaptation altitude camps aim for, and in theory it helps in any weather.

What the research shows: hot races

If your race is hot, heat training is the single biggest gain on this list. Heat slows everybody down, and slower runners, who are out in it for longer, tend to slow the most.⁷ A meta-analysis of heat acclimation studies found consistent, meaningful improvements in exercise performance in hot conditions after acclimation.⁸

It doesn’t have to mean running in the heat. In one study, men who sat in a 104°F (40°C) bath for 40 minutes straight after an easy run, for six days, ran a 5K time trial in the heat about 5% faster afterward. Their 5K in cool conditions didn’t improve.⁹

What the research shows: cool races

Short blocks of heat training do little for a cool race. A 2010 study found that 10 days of heat training improved cyclists’ time-trial performance in cool conditions by around 6%,¹⁰ and that result launched the idea of heat as “the poor man’s altitude.” But a well-controlled follow-up found no extra benefit in cool conditions over normal training,¹¹ and a 2024 meta-analysis of post-exercise heat exposure found only a trivial effect on performance in cool conditions.¹²

Longer blocks are where the altitude comparison comes in, because ten days is too short for your body to build new red blood cells. Elite cyclists who did about an hour of easy riding in a 100°F (38°C) heat chamber five times a week for five weeks increased their hemoglobin mass by about 5%, while a control group training in cool conditions saw no change.¹³ A follow-up found similar gains of about 2.5% whether riders trained in a heat chamber or wore a heat suit in normal conditions, and three heat-suit sessions a week were enough to keep the gain afterward.¹⁴ This is why some elite endurance athletes now make heat-suit sessions a regular part of training.

Whether that makes you faster is less clear. In the five-week studies, the heat-trained riders improved lactate threshold power and other lab measures a little more than the control groups, by about 3 percentage points in a combined performance score.¹⁴ But their maximal oxygen uptake (VO2max) didn’t improve more than the controls’,¹³ and another five-week study found heat training was no better than normal training for a time trial in cool conditions.¹⁵ None of these studies tested runners or actual races. If you’re not racing in the heat, treat long-term heat training as a promising extra with a possible gain of a few percent, not a sure thing.

How to use it

For a hot race, start about two to three weeks before. Most acclimation arrives within 10–14 days and fades over a few weeks without top-ups. For the altitude-style effect, plan on about five weeks of four to five heat sessions a week, then around three a week to hold on to it. That makes it a training block rather than a race-week tweak.

The usual methods are easy runs at the hottest time of day, running in extra layers or a heat suit, or a hot bath or sauna for 20–40 minutes straight after an easy run. Keep hard sessions in cooler conditions so their quality doesn’t suffer. Expect heat sessions to feel harder at first, with a higher heart rate at your usual pace; slow down and keep easy runs easy.

To stay safe:

• Drink to thirst.
• Stop at any sign of dizziness, confusion, nausea or chills.
• Don’t combine heat sessions with alcohol.
• Talk to your doctor first if you have a heart condition, high or low blood pressure, or are pregnant.

4. Beetroot juice (dietary nitrate)

Realistic gain: about 0.5–1%, less for highly trained runners.

Beetroot is rich in nitrate. Bacteria in your mouth convert it to nitrite, and your body then converts that to nitric oxide, which widens blood vessels and makes muscle contraction a little more efficient. The result is a small reduction in the oxygen cost of running.

What the research shows

A 2020 meta-analysis found that nitrate supplementation produced a small but consistent improvement in exercise performance compared with a placebo.¹⁶ In practice, that’s in the region of 1% in time trials, with the clearest benefits in efforts of roughly 5 to 40 minutes.

The important caveat is fitness. The benefit tends to shrink as runners get fitter, and many studies in highly trained endurance athletes find little or no effect.¹⁷ Recreational and mid-pack runners are the group most likely to gain.

How to use it

The usual dose is about 6–8 millimoles (mmol) of nitrate, which is one or two concentrated beetroot “shots” of around 2.4 fl oz (70 ml) each. Regular beet juice from the grocery store contains far less, and nitrate content varies by brand. Take it 2–3 hours before the start. Some evidence suggests taking it daily for 3–7 days beforehand gives a slightly larger effect.

A few practical points:

• Skip antibacterial mouthwash. It kills the mouth bacteria that convert nitrate, and largely blocks the effect.
• Pink urine afterward is harmless and common.
• Concentrated shots upset some runners’ digestion, so test your stomach in training.

5. Sodium bicarbonate

Realistic gain: about 1–2% in efforts lasting 1–10 minutes; little benefit for longer races.

Sodium bicarbonate is baking soda. Taken before a hard effort, it increases the blood’s capacity to buffer the acid that builds up during very intense exercise, which can delay fatigue.

What the research shows

The ISSN position stand concludes that bicarbonate improves performance in high-intensity efforts, particularly those lasting from about 30 seconds to 12 minutes.¹⁸ A classic meta-analysis estimated an improvement of about 1.7% in a one-minute sprint at the standard dose.¹⁹ It’s also on the IOC’s short list of supplements with good evidence.⁶

For steady distance running, the picture is much weaker. A 2025 meta-analysis of running studies concluded that a single dose of bicarbonate had a negligible benefit on continuous running performance.²⁰ A 5K sits on the border. Fast 5K runners racing near the 15-minute mark may see something, but for a 25-minute 5K, a half marathon or a marathon, the expected gain is close to zero.

Bicarbonate has had a boost in popularity thanks to newer hydrogel products, such as Maurten Bicarb, designed to reduce the stomach upset that made plain baking soda so unpleasant. They make it more tolerable, but they don’t make it work for events it wasn’t suited to in the first place.

How to use it

The dose is 0.2–0.3 g per kg of body weight. For a 150 lb (68 kg) runner that’s roughly 14–20 g, or 3–4 teaspoons of baking soda. Take it 60–180 minutes before the start, with a carbohydrate-rich meal and plenty of fluid to reduce stomach issues.

Bloating, nausea and diarrhea are common with plain baking soda, so always try it before a hard session first, never for the first time on race day. The dose also contains a large amount of sodium. If you have high blood pressure or kidney problems, check with your doctor.

6. Nomio broccoli sprout shots

Realistic gain: unknown.

Nomio is a Swedish shot made from broccoli sprouts, and it’s become popular in professional cycling. Broccoli sprouts are rich in compounds called glucosinolates, which the body converts to isothiocyanates such as sulforaphane. These switch on the body’s own antioxidant defenses. The company’s headline claim is a reduction of around 12% in blood lactate during exercise.

What the research shows

The key study, from researchers at the Swedish School of Sport and Health Sciences, gave nine healthy volunteers broccoli sprouts or a placebo during a week of very hard training.²¹ With the sprouts, they had lower markers of oxidative stress, lower lactate during moderate exercise, fewer severe drops in blood sugar overnight, and improved performance at the end of the week, while performance didn’t change on the placebo.

That’s interesting, but it’s a long way from a proven PR booster. It’s one small study, of nine people over seven days, with no running study and no race-style time trial. Lower lactate also isn’t the same as running faster. Lactate is a marker of how hard your body is working, not the cause of fatigue, so a drop could mean better energy use or nothing that matters on race day.

There’s a conflict of interest too. Two of the authors hold a patent on using these compounds to enhance training and co-founded a company commercializing them. That doesn’t make the findings wrong, but it’s a reason to wait for independent studies. A follow-up lactate study of 15 people was, at the time of writing, still a preprint that hadn’t been peer reviewed.²²

Broccoli sprouts are food and appear safe for healthy people, so there’s little harm in trying Nomio if you’re curious and don’t mind the price. Just treat it as an experiment. It isn’t on the IOC’s list of supplements with good evidence, and we’d rank every other item in this article ahead of it.

Can you stack them?

Mostly, yes, but the gains don’t simply add up. Caffeine and super shoes work through different routes and combine well. Beetroot and bicarbonate both have smaller effects in well-trained runners, and research on combining supplements is mixed, with some combinations showing no extra benefit.

A sensible approach for most runners targeting a 5K to marathon PR:

1. Race in shoes that suit you, super shoes if they do.
2. Take caffeine at a dose you’ve tested.
3. Heat train if your race is likely to be warm.
4. Try beetroot if you’re a recreational runner and it doesn’t upset your stomach.
5. Keep bicarbonate for track and mile racing.
6. Treat Nomio as an optional experiment, not part of the plan.

Nothing new on race day

Every supplement here can cause stomach trouble in some people. Test each one in a hard training session, then a tune-up race, before trying it in your goal race. A 2% gain disappears quickly if you spend five minutes in a portable toilet.

If you’re drug tested

Everything in this article is legal under World Anti-Doping Agency (WADA) rules. Supplements can still be contaminated with banned substances. If you compete at a level where you might be tested, choose products certified by a third-party program such as Informed Sport or NSF Certified for Sport.

The free gains

Before spending money, make sure you’ve banked the gains that cost nothing. Even pacing comes first, because going out too fast costs more time than any supplement can give back. Fueling and tapering properly matter more than everything above: arriving at the start line fresh and fueled is worth more than the whole list. Running in a group helps too, since tucking in behind other runners reduces air resistance, which is part of why elite races use pacemakers. And sleep improves how every run feels; we rank it as the number one recovery tool.

Where to spend your effort

Super shoes (about 1–3%) and caffeine (about 2%) are the best-supported and most widely useful aids. Heat training is the biggest single gain for a hot race, and over five weeks or more it raises hemoglobin mass like altitude training, although it hasn’t yet been shown to make runners faster in cool races.

Beetroot juice offers around 1%, mostly for recreational runners rather than elites. Bicarbonate works for short, very hard efforts, not for half marathons and marathons. Nomio has interesting early research but no running data, so its value for PRs is unknown.

Test everything in training first, and never let any of it replace consistent training, eating enough and sleep.

This article is general information, not medical or coaching advice. Talk to your doctor before using supplements if you have a medical condition or take medication.

References

1. Hoogkamer W et al. A comparison of the energetic cost of running in marathon racing shoes. Sports Medicine, 2018. PubMed
2. Kipp S, Kram R, Hoogkamer W. Extrapolating metabolic savings in running: implications for performance predictions. Frontiers in Physiology, 2019. Frontiers
3. Paradisis GP et al. Recreational runners gain physiological and biomechanical benefits from super shoes at marathon paces. International Journal of Sports Physiology and Performance, 2023. PubMed
4. Southward K, Rutherfurd-Markwick KJ, Ali A. The effect of acute caffeine ingestion on endurance performance: a systematic review and meta-analysis. Sports Medicine, 2018. Springer
5. Guest NS et al. International Society of Sports Nutrition position stand: caffeine and exercise performance. Journal of the International Society of Sports Nutrition, 2021. PubMed
6. Maughan RJ et al. IOC consensus statement: dietary supplements and the high-performance athlete. British Journal of Sports Medicine, 2018. PubMed
7. Ely MR et al. Impact of weather on marathon-running performance. Medicine & Science in Sports & Exercise, 2007. PubMed
8. Tyler CJ et al. The effects of heat adaptation on physiology, perception and exercise performance in the heat: a meta-analysis. Sports Medicine, 2016. PubMed
9. Zurawlew MJ et al. Post-exercise hot water immersion induces heat acclimation and improves endurance exercise performance in the heat. Scandinavian Journal of Medicine & Science in Sports, 2016. PubMed
10. Lorenzo S et al. Heat acclimation improves exercise performance. Journal of Applied Physiology, 2010. PubMed
11. Keiser S et al. Heat training increases exercise capacity in hot but not in temperate conditions: a mechanistic counter-balanced cross-over study. American Journal of Physiology – Heart and Circulatory Physiology, 2015. PubMed
12. Solomon TPJ, Laye MJ. The effect of post-exercise heat exposure (passive heat acclimation) on endurance exercise performance: a systematic review and meta-analysis. BMC Sports Science, Medicine and Rehabilitation, 2025. Springer
13. Rønnestad BR et al. Five weeks of heat training increases haemoglobin mass in elite cyclists. Experimental Physiology, 2021. PubMed
14. Rønnestad BR et al. Heat training efficiently increases and maintains hemoglobin mass and temperate endurance performance in elite cyclists. Medicine & Science in Sports & Exercise, 2022. PubMed
15. Mikkelsen CJ et al. Prolonged heat acclimation and aerobic performance in endurance trained athletes. Frontiers in Physiology, 2019. PMC
16. Senefeld JW et al. Ergogenic effect of nitrate supplementation: a systematic review and meta-analysis. Medicine & Science in Sports & Exercise, 2020. PMC
17. Jones AM, Thompson C, Wylie LJ, Vanhatalo A. Dietary nitrate and physical performance. Annual Review of Nutrition, 2018. PubMed
18. Grgic J et al. International Society of Sports Nutrition position stand: sodium bicarbonate and exercise performance. Journal of the International Society of Sports Nutrition, 2021. Taylor & Francis
19. Carr AJ, Hopkins WG, Gore CJ. Effects of acute alkalosis and acidosis on performance: a meta-analysis. Sports Medicine, 2011. PubMed
20. Miller LE et al. Negligible benefit of oral single-dose sodium bicarbonate on continuous running performance: systematic review with meta-analysis of randomized, double-blind, placebo-controlled trials. Journal of the International Society of Sports Nutrition, 2025. Taylor & Francis
21. Flockhart M et al. Glucosinolate-rich broccoli sprouts protect against oxidative stress and improve adaptations to intense exercise training. Redox Biology, 2023. PubMed
22. Vinge F et al. A glucosinolate-rich beverage lowers blood lactate concentrations during submaximal exercise. bioRxiv preprint, 2025. doi.org