# The Task Dependency of Spontaneous Rhythmic Performance in Movements Beyond Established Biomechanical Models: An Inertial Sensor-Based Study

## TL;DR

This study shows that the rhythm of spontaneous movements changes depending on the task, with complex exercises having slower and more variable rhythms than simple movements like walking.

## Contribution

The study reveals that spontaneous motor tempo adapts to task-specific biomechanical demands, suggesting a flexible internal timing mechanism.

## Key findings

- Complex, full-body exercises have slower and more variable tempos compared to simple movements like walking.
- Relative phase durations in movement cycles remain stable at a 1:1 ratio, indicating a shared neural control mechanism.
- Individuals show high timing precision with low variability during complex exercises, suggesting robust internal timing.

## Abstract

What are the main findings?

Spontaneous motor tempo (SMT) is task-dependent: Complex, full-body exercises have slower and more variable tempos compared to simple, established movements like walking, hopping, and tapping.

Consistent Relative Timing: Despite variations in overall tempo, the relative duration of a movement cycle’s phases remains stable, typically at a 1:1 ratio. This points to a shared, underlying neural control mechanism.

High Performance Stability: Individuals maintain a high degree of timing precision with low individual variability, even during complex, full-body exercises.

What are the implications of the main findings?

Internal timing mechanisms are adaptable and adjust to task-specific biomechanical demands, providing insights into motor control beyond simple rhythmic movements.

The findings provide a basis for designing personalized exercise and rehabilitation programs that account for an individual’s natural, task-specific rhythmic variability.

Spontaneous rhythmic performance is a fundamental feature of human movement, well established in biomechanical models (EBMs) but less understood in complex physical fitness exercises (PFEs). This study examined the task dependency of spontaneous rhythmic performance across three EBMs (walking, hopping, finger tapping) and seven PFEs (hip abduction, back extension, sit-up, push-up, shoulder abduction, squat, lunge). A total of 15 men and 15 women performed each task at a self-selected pace while wearing inertial sensors. Measures included spontaneous motor tempo (SMT), temporal structure metrics, and their within- and between-trial individual variability (%CV) (ANOVA, SPSS 28.0, p ≤ 0.05). SMT was task-dependent, with EMB tasks being near ~2 Hz (walking: 1.82 ± 0.10 Hz; hopping: 2.08 ± 0.22 Hz; finger tapping: 1.89 ± 0.43 Hz) and PFEs being slower (0.36–0.68 Hz). Temporal structure mirrored these differences with shorter cycle and phase durations in EBM than PFE tasks, with relative phase durations consistently at about a 1:1 ratio. Τhe overall low %CV indicated stable performance (within-trial: 1.4–7.5%; between-trial: 0.5–7.8%). The results highlight the task dependency of SMT and temporal structure, as well as the robustness of an overarching internal timing framework supporting rhythmic motor control across diverse movement contexts.