Elite karate athletes lost the most performance at 5pm in week four of Ramadan

Twelve elite male karate athletes were tested at 08:00, 17:00 and 22:00 before Ramadan, during its second week, and during its fourth week. The largest deteriorations in both reaction time and anaerobic running performance appeared in the fourth week at 17:00 [s1].

Morning performance at 08:00 was relatively preserved throughout [s1].

Why the timing structure is the point

Most research on athletic performance during Ramadan tests at one time of day and reports whether performance dropped. That design conflates two different things: the effect of fasting, and the effect of when in the fasting day the test happened.

This study used a within-subject repeated-measures protocol across three periods and three testing times [s1], which separates them. The answer it produces is not "Ramadan reduces performance" but something more specific — that the deficit is concentrated at particular hours and accumulates across the month.

The 17:00 finding makes physiological sense in a way the study is set up to demonstrate rather than merely assert. Late afternoon is the point of maximum elapsed time since the pre-dawn meal, when fluid deficit and glycogen depletion are deepest and the evening meal is still hours away. It is also, in many training programmes, when practice is scheduled.

What was measured

Cognitive testing covered simple reaction time, multiple-choice reaction time, and Stroop performance; physical testing used a 5-metre multiple shuttle run [s1]. Both were assessed before and after a karate-specific aerobic fatigue protocol [s1]. Sleep and dietary intake were monitored throughout each period [s1].

Including a fatigue protocol is what makes this relevant to actual competition. A rested athlete tested in a laboratory is not in the state a karate athlete is in during the later rounds of a tournament.

The sleep and diet findings

Ramadan fasting significantly reduced total sleep time, sleep efficiency, total energy intake, carbohydrate intake and fat intake, while increasing subjective sleepiness and fatigue [s1].

These are the plausible mediators of the performance results, and the study measures them rather than assuming them. But a within-subject design that tracks several variables simultaneously establishes that they moved together; it does not isolate which one is doing the causal work. Shorter sleep, reduced carbohydrate availability and daytime fluid restriction all change during Ramadan at once, and this design cannot separate them.

What happened to performance

Cognitive and physical performance were significantly affected by Ramadan period, time of day, and fatigue state [s1]. The greatest deterioration occurred during the fourth week at 17:00, where both reaction-time and shuttle-run outcomes showed the largest impairments compared with pre-Ramadan values [s1]. Decrements were also observed at 22:00, while 08:00 performance was relatively preserved [s1].

Exercise-induced fatigue further worsened both cognitive and physical outcomes and attenuated the normal time-of-day variation [s1].

That last clause is the subtlest result in the paper. Performance in this protocol varied by time of day [s1]; fatigue flattening that variation means the usual advantage of competing at one's best hour is reduced — the athlete becomes, in effect, uniformly compromised rather than variably capable.

Week four versus week two

The fourth week being worse than the second is consistent with a cumulative effect rather than an acute one. If the deficit were driven purely by same-day fasting, week two and week four should look similar. That they do not suggests accumulating sleep debt or energy deficit, though the study reports the pattern without resolving which.

The limits

Twelve athletes. All male, all elite karate practitioners. Elite athletes are unrepresentative in both directions — better conditioned and better supported than recreational athletes, but also training at intensities that leave less margin.

There is no non-fasting control group. The comparison is to the same athletes before Ramadan, which controls for individual variation but not for anything else that changes across a competitive season. And a study of a religious observance cannot randomise the exposure.

Nothing here is guidance. The authors' recommendation is that training load, recovery strategies, sleep management and nutritional timing be carefully adapted during Ramadan [s1] — addressed to coaching staff and framed as adaptation rather than avoidance. Individual decisions about fasting and training rest with athletes and the clinicians and coaches who work with them.

Why it matters for a region that schedules around it

Athletes across the Middle East train and compete during Ramadan every year, and the practical question for the coaching staff around them is not whether fasting affects performance but when — and a study that finds 08:00 relatively preserved while 17:00 in week four is worst points at a schedule change rather than a training reduction.

What to watch next

Whether the time-of-day pattern replicates in other sports and in female athletes. The mechanism proposed — time since the pre-dawn meal — is not karate-specific, so if it is real it should show up in any sport with a substantial anaerobic or reaction-time component.

Sources

1. Effects of Ramadan intermittent fasting on sleep, cognitive and physical performance in elite karate athletes: A within-subject repeated-measures study — Chronobiology International, 16 June 2026 (primary)