Time-of-day effects on force control during object manipulation.

Area of Science:

• Human motor control
• Chronobiology
• Biomechanics

Background:

• Human motor performance exhibits diurnal variations.
• Understanding these variations is crucial for optimizing tasks requiring precise force control.

Purpose of the Study:

• To investigate time-of-day effects on grip force control during a manipulative task.
• To analyze variations in grip force, arm acceleration, and their relationship with load force throughout a 26-hour cycle.

Main Methods:

• Participants performed continuous up and down movements with an instrumented object over two days.
• Measurements included grip force, load force, arm acceleration, and subjective sleepiness.
• Data were collected across a 26-hour period with 2-hour intersession intervals, including overnight sleep.

Main Results:

• A significant time-of-day effect was observed for grip force level and arm acceleration, both increasing in the morning.
• The ratio of grip force to load also showed modulation, suggesting grip force adjustments partly independent of acceleration.
• The synchronicity and cross-correlation between grip and load force remained constant, indicating consistent predictive coupling.

Conclusions:

• Grip force control and arm movement dynamics are influenced by circadian rhythms.
• While the magnitude of grip force varies, the ability to predictively couple grip force to load remains stable across the day.