# Beyond Simple Tapping: Is Timed Body Movement Influenced When Balance Is Threatened?
## 4 Discussion  
This study aimed to investigate the movement timing beyond the tapping paradigm, employing two large-scale movements commonly performed in physical fitness or rehabilitation modalities, with varying inherent balance threats: the two-legged squatting (low balance threat) and the standing hip abduction (higher balance threat). This study focused on three aspects of movement timing, that is, entrainment, synchronization, and pace stability. Our incentive was that, although the finger-tapping paradigm has provided valuable insights into movement control, it simplifies movement mechanics by minimizing force, restricting motion, and relying on a clear surface contact endpoint. Consequently, finger tapping cannot fully capture the complexity of larger-scale movements, where distinct strategies naturally emerge, such as timed multi-segmental (i.e., two-legged squatting) and single-segment (i.e., standing hip abduction) body movements often employed in physical fitness or rehabilitative modalities. Our findings revealed that while participants demonstrated similar overall entrainment in both the two-legged squatting and the hip abduction (evidenced in their non-significantly different IRI match), significant differences emerged in timing metric manifestations. Specifically, the movement of greater balance threat (standing hip abduction) demonstrated more accurate timing alignment with metronome beats (as evidenced by its smaller synchronization error) but lower entrainment accuracy and movement timing consistency (as evidenced by its greater IRI error and lower pace stability). The shorter IRI in the standing hip abduction than the two-legged squatting was rationally expected due to its lower inertial load [31] and its balance loss vulnerability [32]. Previous research has consistently shown that higher inertial loads are linked to slower movement tempos, while lower inertial loads lead to faster-preferred tempos [31; 33]. While our study did not directly manipulate inertial load, the observed difference in IRIs aligns with this established principle. Also, in situations requiring rapid stabilization, individuals tend to minimize the time spent in a vulnerable position [31]. Entrainment refers to the general phenomenon of matching body movement frequency to the pace of a regular cue, such as metronome or music beats [7], without necessarily synchronizing a particular motor element to a discrete beat [5]. Previous research established the entrainment phenomenon on the simple task of finger tapping [4; 6; 8; 34; 35; 36]. However, there is some evidence that simple tasks like finger tapping may not fully capture the motor complexity of a larger-scale movement such as stepping in place [5; 15]. The similar IRI match values between the two exercises indicate that, regardless of the greater movement complexity in two-legged squatting and the greater balance demands in standing hip abduction, participants were able to align their movement frequency with the external pacing cue. Larger-scale movements, such as the multi-segmental or single-segment body movements used in physical fitness and rehabilitation, involve distinct strategies and additional demands that simpler and smaller movements do not address [2, 11]. Our results challenge the conventional focus on the simple finger-tapping paradigm, underscoring the flexibility of the human motor system in entraining to rhythmic cues, even in more challenging contexts [2, 5, 6, 11]. One could argue that the IRI match should anyways be expected, as the metronome tempo was already set at their preferred frequency. This is a reasonable assumption; however, it is notable that even in entrainment to a metronome stimulus at preferred tempo, the balance threat appears to influence specific timing manifestations, such as the timing consistency. Entrainment accuracy, examined through the IRI error, was lower during the movement under greater balance threat, that is, the standing hip abduction (as expressed with a higher IRI error).