# Beyond Simple Tapping: Is Timed Body Movement Influenced When Balance Is Threatened?
## 1 Introduction  
The ability to temporally align/synchronize body movements with external auditory stimuli (metronome or musical beats) plays a fundamental role in human motor performance across a range of activities, from everyday functional work activities and social tasks (e.g., dance) to recreational or competitive sports [1; 2; 3; 4]. This phenomenon, known as timed movement [5], encompasses three fundamental timing aspects, all of which contribute to effective temporal alignment of bodily actions to external rhythmic cues (e.g., auditory cues): entrainment, synchronization, and pace stability [5; 6]. Entrainment refers to the general capability of matching movement frequency with an external cue, such as a metronome or music, without necessitating the exact concurrence of a discrete motor event to a discrete sound event [4; 6; 7]. It reflects the broader ability to match the pacing period or movement frequency over time, typically assessed through metrics like the relationship between the inter-response interval (IRI) and the inter-stimulus interval (ISI) [4; 6; 8; 9]. The accuracy of entrainment is often quantified using the IRI synchronization error, which measures the difference between IRI and ISI, thereby highlighting the concept of period correction, where adjustments are made to match IRI with ISI [6; 8], with higher IRI error values indicating lower entrainment accuracy. Synchronization differs from entrainment by requiring the accurate alignment of self-initiated movements with specific points in the external pacing source. This process involves sophisticated sensorimotor adjustments and error correction mechanisms [8]. Synchronization accuracy is measured by the synchronization error metric, which quantifiesthe temporal discrepancy between the stimulus pacing event (e.g., auditory beat onset) and the movement event (e.g., movement onset) [4; 6; 8; 10]. Synchronization error introduces the concept of phase correction, where adjustments are made to align specific movement points with specific pacing events [8]. Pace stability evaluates the consistency of movement timing without explicit reference to a cue, and it is quantified by assessing the within-subject variability in IRI using the coefficient of variation of IRI (IRI CoV) [11; 12]. This metric underscores the ability to maintain rhythmicity despite inherent variability in motor execution. While not directly related to aligning with external cues (as in entrainment and synchronization), pace stability provides valuable insights into the underlying mechanisms allowing for the maintenance of consistent movement timing. [PERSON] and coworkers [11] highlight the temporal goal of the task as more crucial for pace stability and movement organization than movement scale, timing strategy, and accuracy demands. Similarly, [PERSON] and [PERSON] [2] found that longer interval durations are associated with greater variability in timing performance. The classical studies of timed movement use the established finger-tapping paradigm [2; 4; 8; 11; 13]. Although this approach has provided valuable insights into timing control, it simplifies movement mechanics by minimizing force, limiting motion, and offering clear spatial endpoints [2; 4; 11; 13; 14]. Consequently, finger tapping cannot fully capture the complexity of larger-scale movements, where distinct strategies naturally emerge, such as when moving a finger between targets aligned with auditory cues [2; 11] or performing more complex movements such as timed multi-segmental (or single-segment) body movements, as often occurs in physical fitness and rehabilitative modalities. Evidence suggests that movement complexity may influence the process of temporal correction under a synchronization constraint, with simpler movements showing larger corrections (e.g., finger tapping in place) than more complex ones (e.g., stepping in place) [15].