Author(s): MERAS SERRANO, H., RAVIER, G., GUEUGNEAU, N., Institution: UNIVERSITÉ MARIE ET LOUIS PASTEUR, Country: FRANCE, Abstract-ID: 841

INTRODUCTION:
Goal-directed motor actions rely on an optimal balance between movement speed and accuracy. This relationship is classically described by Fitt’s law, which predicts systematic changes in movement duration as a function of task difficulty [1]. While this speed-accuracy trade-off has been extensively studied within single experimental sessions [2], relatively few studies have adopted a longitudinal approach. Moreover, little attention has been paid to the fluctuation of biological factors over time, such as sex hormones, and their potential influence on motor control. Fluctuations in ovarian hormones across the menstrual cycle (MC) are known to potentially influence sensorimotor processing [3], yet their impact on fine motor actions remains largely unexplored. Consequently, the present study investigates whether the speed-accuracy trade-off in arm pointing tasks varies across different phases of the MC.
METHODS:
Ten active women were recruited with a natural MC. Experimental sessions were conducted across different hormonal phases. Testing took place during the early follicular phase (EF), the late follicular phase (LF) and the mid luteal phase (ML). In each session, participants completed 80 pointing movements toward targets of varying sizes : 40 executed and 40 imagined. Movements had to be performed as quickly and accurately as possible in both executed and imagined modalities. Motor imagery was used to isolate motor planning from peripheral execution factors. Movement duration, Fitt’s parameter (b and R²), and an isochrony index (executed/imagined duration) were analysed using linear mixed-effects models, with participants as a random intercept. Movement duration was tested for phase*condition*target size, Fitt’s parameters for phase*condition, and isochrony for phase*target size.
RESULTS:
For movement duration, there was a significant main effect of target size (F(2,207) = 108.2, p<0.001, n²p = 0.61) and a significant condition*target size interaction (F(3,207) = 6.8, p<0.001, n²p = 0.09), with post hoc comparisons showing longer durations for smaller targets (p<0.05, d=0.69 – 3.74). For Fitt’s parameters, condition significantly influenced both the b parameter (F(1,45) = 40.3, p<0.001, n²p = 0.47 ) and r² (F(1,85) = 11.6, p<0.001, n²p = 0.12). Post hoc analyses revealed higher b values (p<0.001, d =1.639) and R² (p=0.001, d=0.523) in real compared to imagined movement. Isochrony showed significant effects of phase (F(2,99) = 3.94, p=0.023, n²p = 0.07) and target size (F(3,99) = 10.7, p<0.001, n²p = 0.25), with lower ratios in the EF than in the ML phase (p=0.018, d=-0.628) and a higher ratio for the smallest target compared to larger target sizes (p<0.01, d=0.979 – 1.294).
CONCLUSION:
Our findings suggest that the MC does not affect sensorimotor control during fine motor actions. However, the results for motor imagery indicate a mild impairment in motor planning processes during the EF phase.

1. Fitts, 1954 2. Shmuelof et al., 2012 3. Jang et al., 2025