Caffeine ingestion improves morning neuromuscular performance to evening levels in healthy females.

Drinking caffeine in the morning increases core body temperature and enhances physical performance. Regular caffeine use over time does not affect muscle growth because the body adapts to its presence.

In healthy young women, consuming 6 mg of caffeine per kilogram of body weight increases muscle electrical activity during knee extension exercises without changing nerve signal speed, indicating greater neural activation from the brain rather than changes in muscle function.

In healthy young women, taking 6 mg of caffeine per kilogram of body weight 45 minutes before exercise increases muscle strength by 33–45% and extends the time they can sustain effort by 43% during a specific knee extension task, bringing morning performance up to evening levels through increased neural signaling to muscles, without changes in body temperature or muscle fatigue markers.

When healthy young women consume 6 mg of caffeine per kilogram of body weight before performing fatiguing isometric exercise, their perception of effort decreases by about 20%, and their core body temperature does not change.

In healthy young women, muscle strength and endurance are lower in the morning compared to the evening when no supplements or treatments are used, with peak torque reduced by 28–30% and time to exhaustion reduced by 31%.

In healthy young women, caffeine improves morning muscle performance without changing the median frequency of muscle electrical signals, meaning the improvement is not due to changes in how fast nerve signals fire or how quickly muscle fibers conduct those signals.