Reaction time (RT) is defined as the interval between the presentation of a stimulus and the initiation of an appropriate voluntary response. This process involves multiple stages, including sensory input, cognitive processing, and motor execution, and can be influenced by various physiological and pharmacological factors¹˒². In women, the menstrual cycle introduces significant endogenous hormonal fluctuations, which may affect neural and motor responses; however, its impact on RT remains inadequately explored and inconsistently documented in existing research³.

The menstrual cycle, characteristic of humans and primates, typically spans around 28 days, though it can vary among individuals⁴. It is divided into distinct phases:

• Follicular Phase (Day 1 to ovulation): Includes the Menstrual Phase (Day 1–5), characterized by bleeding and shedding of the uterine lining, followed by the Proliferative Phase (Day 5–14), marked by regrowth and thickening of the endometrium.
• Ovulatory Phase (around Day 14): Triggered by a surge in luteinizing hormone (LH), leading to the release of an ovum.
• Luteal or Secretory Phase (Day 14–28): Dominated by increased progesterone levels, supporting potential implantation.

These phases are regulated by cyclic fluctuations in reproductive hormones, notably gonadotropins such as Follicle-Stimulating Hormone (FSH) and LH, along with estrogen and progesterone⁴. These hormonal changes may influence sensorimotor integration and cortical processing speed, thereby affecting both Auditory Reaction Time (ART) and Visual Reaction Time (VRT).

The present study aims to assess how different phases of the menstrual cycle influence ART and VRT in young women.

Study Design and Ethical Considerations

This observational study was conducted in the Department of Physiology at a reputed medical college in North India, following approval from the Institutional Human Ethics Committee. All participants provided written informed consent prior to inclusion in the study.

Participants

Eighty-one healthy female medical and paramedical students, aged 17–25 years, were enrolled. Inclusion criteria encompassed:

• Age between 17 and 25 years
• Regular menstrual cycles (28 ± 2 days)
• Absence of auditory or visual impairments
• No use of medications affecting reaction times
• No history of acute or chronic illnesses
• No neuromuscular or sleep disorders
• No excessive fatigue, fasting, smoking, or alcohol consumption

Participants were instructed to have a light breakfast, avoiding stimulants such as tea, coffee, or other caffeinated beverages, and to ensure adequate sleep the night before testing.

Study Procedure

Reaction times were measured on the 1st, 7th, 14th, and 21st days of the menstrual cycle. Testing was conducted between 8:00 AM and 10:00 AM in a quiet room within the Department of Physiology. Prior to testing, participants underwent three practice trials for each stimulus modality.

Reaction Time Measurements

Auditory Reaction Time (ART) and Visual Reaction Time (VRT) were assessed using the Audiovisual Reaction Time Apparatus (Medisystem, Yamunanagar, India), which offers 100% display accuracy and a resolution of 0.1 seconds. The apparatus provides two modes of stimulus:

1. Visual Stimulus: Red and green lights
2. Auditory Stimulus: High and low-frequency tones

Each participant responded to both visual (Red light) and auditory stimuli(high frequency tone). The operator initiated the stimulus, and the participant responded by deactivating it as quickly as possible. The time interval between stimulus onset and participant response was recorded as the reaction time. Three consecutive readings were taken for each stimulus modality, and the lowest value was considered the final reaction time.

Statistical Analysis

Data were analyzed using appropriate statistical methods to assess variations in reaction times across different phases of the menstrual cycle. Statistical significance was set at p < 0.05

Tukey HSD Post Hoc Comparisons of ART Scores Between Time Points

Tukey HSD Post Hoc Comparisons of VRT Scores between Time Points

In the present study both ART and VRT showed significant variation(p<0.0001) on different days of menstrual cycle. Both ART and VRT were fastest on day 21(190.74±23.226 msec and 209.01±27.231msec respectively) and slowest on day 14 (232.72±28.680 msec and 258±36.370 msec respectively).

The comparison between Day 1 and Day 14 showed a statistically significant RT increase (Mean Difference = -26.30 ms, p < .001), indicating slower responses during ovulation compared to the early follicular phase. A similar pattern was observed when comparing Day 7 and Day 14, with a mean RT increase of -33.33 ms (p < .001), reinforcing the trend of reaction time slowing toward mid-cycle. In contrast, RT significantly decreased from Day 14 to Day 21, with a large mean difference of 49.14 ms (p < .001), indicating improved responsiveness in the luteal phase.

Interestingly, no significant difference was observed between Day 1 and Day 7 (p = .299), suggesting that RT remains relatively stable during the early to mid-follicular phase. This aligns with previous findings indicating low and stable hormone levels (estrogen and progesterone) during this phase (5,6)

While estrogen has often been associated with cognitive enhancement and faster motor responses (7,8), the present findings do not support this straightforward relationship. Instead, RT peaked during ovulation (Day 14), when estrogen is at its highest—contrary to expectations of enhanced performance during this period. One possible explanation is that while estrogen may improve verbal and memory-related cognitive domains, its effect on motor response speed may be less predictable or may interact with transient neuroendocrine changes in dopaminergic systems (9).

In contrast, the fastest RTs during the luteal phase challenge older models that associate elevated progesterone with cognitive slowing (10). More recent research suggests that progesterone may enhance GABAergic modulation in ways that reduce anxiety and facilitate motor performance in certain tasks (11). Moreover, inter-individual variability and task-specific demands may account for such deviations from traditional expectations.

There are few studies suggestive of variation in both auditory and visual reaction time during different phases of menstrual cycle but it was not statistically significant.(12)

Practical Implications

The findings may have important implications for cognitive-motor performance in real-world settings. Athletes, drivers, and professionals in high-stakes environments might experience subtle but meaningful changes in reaction ability depending on menstrual cycle phase. Understanding these fluctuations could inform personalized training, scheduling, and workload management.

Limitations and Future Directions

This study's limitations include its reliance on calendar-based menstrual tracking rather than hormonal assays to determine cycle phases. Future studies using salivary hormone assays and more granular reaction time tasks (e.g., simple vs. choice RT) are recommended to validate and expand these findings.

The study demonstrates significant cyclical variation in reaction time across the menstrual cycle, with slower responses around ovulation and faster responses in the luteal phase. These findings underscore the nuanced impact of hormonal fluctuations on motor-cognitive function and warrant further investigation using biologically verified phase tracking and diverse task paradigms.

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