The best-resourced human-performance operations on the planet are about to spend a summer managing the circadian clock. Almost all that effort is aimed at a single property of the clock.
There is a second property they are not managing, and it is the one that decides how good the first can ever be.
The 2026 World Cup is, among other things, the largest applied chronobiology experiment ever run in elite sport. Forty-eight squads will converge on a tournament spread across sixteen cities and four time zones, arriving from six continents.
A team travelling from the western Pacific to a North American base camp can cross up to nineteen time zones before its first training session. The peer-reviewed literature on preparation is unambiguous about what that does to a player: it misaligns the biological clock, disrupts sleep, and raises susceptibility to both physical and mental illness, none of which is compatible with performing at the level the tournament demands (Esh et al., 2026).
What is striking is not that the problem exists. Transmeridian travel has degraded athletes since athletes have been flying to compete. What is striking is how seriously, and how publicly, the response is now being taken. England will base its entire campaign in a single central location to limit repeated resynchronisation, and has commissioned individualised sleep provision tailored to body type, thermoregulation, and light exclusion. The consensus guidance teams are working from reads like a chronobiology syllabus: timed bright-light exposure, pre-departure sleep-schedule shifting toward the destination, meal-timing alignment, judiciously timed outdoor training, strategic napping, and managed caffeine and alcohol (Esh et al., 2026; Janse van Rensburg et al., 2021).
This is the moment the category stops being theoretical. When national federations invest in light, timing, sleep, and thermoregulation as competitive variables, the premise underlying HMN24 is no longer something the brand has to argue for. It is something the most sophisticated operators in sport are demonstrating on a global stage. The circadian system is a performance system. That argument is now being made for us.
The pattern is not confined to the tournament. BrainLit, a Swedish biocentric lighting company, reports that its daylight-mimicking systems are now installed at eight English Premier League clubs, alongside teams across the NBA, NHL, and Major League Baseball, typically in the recovery and performance spaces players spend the most time in (BrainLit, 2025). The claim is the vendor's own, and the outcome figures the company publishes are self-measured rather than independently verified, which is worth holding in mind. But the direction of the spend is the signal that matters. Elite sport, at club level as well as international, is beginning to treat the indoor light environment as performance infrastructure rather than a fixed cost. That is the same lever the World Cup protocols reach for, installed permanently into the buildings players occupy between matches.
But there is a precise and important limit to what the World Cup proves, and it is worth being honest about it, because the limit is exactly where HMN24 lives.
What the protocols are actually managing
All of the interventions noted above do essentially one thing. They adjust the timing of the "clock". All three pre-flight methods for adjusting the players' schedules in order to deal with their destination time zone, all three methods for controlling light exposure during travel to control the players' exposure to daylight, and all three methods for providing exogenous melatonin to help regulate the players' circadian rhythms are used to treat a phase problem -- that is, a problem where the timing of the players' circadian cycle is out of sync with the outside world. For example, a football player whose circadian system remains set to the times of the evening in Europe when he plays in the early afternoon of the East Coast in North America will have a phase problem. Essentially, all measures to mitigate jet lag are designed to shift the timing of the clock into synchronisation with the local day.
The clock's timing is the appropriate target for this particular problem. The complaint seems to be that the body performs correctly at incorrect hours. Timing needs to be corrected. There is ample evidence in the scientific literature showing that this approach is effective, and therefore the teams using it are correct.
However, there are more properties of the clock than just phase. Phase refers to the timing of when the rhythm goes up and down; i.e. when it reaches its peaks and troughs. Amplitude refers to how much it goes from one peak to the next trough; i.e. how big a difference exists between biological day and biological night. When a rhythm has a large amplitude, it is characterised by having a sharp drop in core temperature at night and recovery by morning; having a sharp rise in cortisol upon awakening and a decline in cortisol as the day progresses, etc. The overall effect is that the signal sent by the clock to downstream systems is very strong and easy for those systems to read.
On the other hand, a rhythm with low amplitude is characterised by flatter peaks and shallower troughs. The differences between biological day and biological night become less pronounced. The clock continues to keep time. However, instead of sending a strong signal indicating what time it is, it sends a weak signal.
In addition to leaving the issue of phase vs amplitude unaddressed, most World Cup protocols also fail to address another important aspect of circadian regulation. Circadian research treats phase shifting and amplitude enhancement as two distinct interventions aimed at addressing separate problems. While a person may need to shift his/her phase if they have difficulty falling asleep at the appropriate time, a person who falls asleep at the appropriate time but experiences difficulty staying asleep or suffers from chronic daytime fatigue and inadequate nighttime sleepiness would likely require amplitude-enhancing treatment rather than a phase-advancement treatment (Walch et al., 2024). Thus, while a tournament-grade jet-lag treatment program can provide a team member with the correct phase, it may also continue to allow him/her to operate on a flattened curve.
Why is amplitude the harder and the more important, problem
There's a particular reason for that focus. Phase is more controllable, and therefore much easier to measure and model, and to shift with time and light in a somewhat predictable way. In comparison, amplitude is far more difficult to deal with across all fronts. First and foremost, it is much harder to measure amplitude outside a laboratory; secondly, amplitude is much harder to define clearly; and thirdly, at present, there have been no clinical trials conducted to intentionally increase central circadian amplitude in healthy humans. The researchers who formally distinguished phase from amplitude have described the lack of such studies as an important omission in the literature (Walch et al., 2024).
The field deals with what it can measure. Since the phase is measurable, it is being addressed.
In contrast, amplitude is the more deeply relevant variable; it is often left implied. However, evidence is mounting regarding why we should care about amplitude. For example, simulated low circadian amplitude has been linked to metabolic disturbances and weight gain in very large populations. Additionally, in the UK Biobank cohort, sleep regularity (the modelling associates sleep regularity with maintained amplitude) was found to be a better predictor of mortality than sleep duration (Walch et al., 2024). Irregular sleep timing shifts light exposure out of its correct zones of the daily cycle, and thus, instead of supporting the oscillations, suppresses them. As a result of this suppression, the rhythmic amplitude of the oscillations flattens.
Stated simply: A clock may be perfectly timed but still be silent. Simply adjusting timing will do nothing to change the volume.
The thing the tournament circles but does not name
Read the World Cup preparation strategy through this lens, and a pattern emerges. The single base camp, the individualised sleep environment, the light management, the consistent training and meal schedule: these are not only phase tools. Sleep regularity and stable, well-timed light are precisely the conditions the modelling associates with preserved circadian amplitude (Walch et al., 2024). The best-prepared teams have arrived, by the logic of the problem, at protocols that protect amplitude. They’re just not describing them that way because amplitude is not yet the language the field reaches for or indeed the press.
That gap between what the best operators are doing and the variable they have a name for is the whole of HMN24's territory. Amplitude is the property of the tournament's circadian effort, which its circling but without implicitly naming it. It is the difference between a clock that keeps time and a clock that keeps time loudly, and it is the variable that determines whether all the phase management in the world translates into a body that actually performs across the full day.
The World Cup will validate, in front of a global audience, that the circadian system is a serious performance system worth real investment. It won’t, on its own, name the variable that decides how much that investment returns.
That naming is the work. It is the work HMN24 exists to do, and it is the work the brand should be doing loudly while the largest applied chronobiology experiment in the history of sport plays out across a North American summer.
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References
BrainLit (2025) Bringing the daylight indoors: BrainLit expands to New Zealand with lighting pioneer Venkatesh Kannan. Company announcement, 12 September. Available at: https://www.brainlit.com (corporate source; client list and outcome figures are company-reported and not independently verified).
Esh, C.J., Carter, S., Bougault, V., Girard, O., Janse van Rensburg, D.C., Chrismas, B.C.R., Meyer, T. and Taylor, L. (2026) 'The 2026 Men's FIFA Football World Cup: evidence-based guidelines to protect player health and performance from environmental challenges', Sports Medicine. Available at: https://doi.org/10.1007/s40279-026-02398-4 (Open access).
Janse van Rensburg, D.C., Jansen van Rensburg, A., Fowler, P., Fullagar, H., Stevens, D., Halson, S.L., Bender, A., Vincent, G., Claassen-Smithers, A., Dunican, I., Roach, G.D., Sargent, C., Lastella, M. and Cronje, T. (2021) 'Managing travel fatigue and jet lag in athletes: a review and consensus statement', Sports Medicine, 51(10), pp. 2029–2050.
Walch, O., Tavella, F., Zeitzer, J.M. and Lok, R. (2024) 'Beyond phase shifting: targeting circadian amplitude for light interventions in humans', SLEEP, 48(1), pp. 1–7. Available at: https://doi.org/10.1093/sleep/zsae247.
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