chatGPT:
Summary
This paper tests how well people can cancel an already-started step when a stop signal appears, and whether healthy ageing changes that ability. The authors adapt the classic stop-signal task from finger/button responses to three movement types: finger tap, seated foot tap, and forward step initiation. They studied 27 young adults and 29 healthy older adults.
The key finding is that older adults were slower to start movements, but were not significantly slower at cancelling movements once the task accounted for their slower initiation speed. Stopping speed, measured by stop-signal reaction time, was similar in young and older adults, although stopping a step was slower than stopping a foot tap, and both were slower than stopping a finger tap.
A central biomechanical result is that the early anticipatory postural adjustment — the initial weight shift before lifting the foot — behaves partly like a ballistic, feedforward process. Once that early loading phase has begun, it continues similarly whether the person later completes the step or successfully cancels it. But later in the movement, as weight transfers toward the stance leg, visual stop cues can interrupt the process and prevent foot-lift.
The authors also found evidence that older adults used more proactive inhibition: they slowed down more when there was a chance they might need to stop. This cautious strategy may help preserve stopping success in healthy ageing, even though raw movement initiation is slower.
What is novel
The main novelty is methodological: the paper adapts the stop-signal task to real step initiation, rather than only seated hand or foot responses. This matters because stopping a step is not just a cognitive inhibition problem; it is also a balance and postural-control problem.
A second novelty is the separation of the step into APA and foot-lift phases. The authors show that action cancellation can decouple these phases: a person may begin the preparatory weight shift but still cancel the actual foot-lift. That gives a more precise picture of where the “point of no return” lies during step initiation.
A third novel aspect is the comparison of finger, foot, and full stepping inhibition in the same participants. The moderate correlations between finger and stepping stopping suggest that finger-based inhibition tests may not fully capture lower-limb or gait-relevant stopping ability.
Finally, the study adds to ageing research by suggesting that healthy older adults may preserve cancellation ability through strategic slowing, rather than by maintaining youthful movement speed.
Critique
The study is well designed in several ways. It uses a standard stop-signal framework, includes several response modalities, uses force plates to capture the biomechanics of stepping, and has enough stop trials to estimate stopping speed more robustly than earlier stepping studies. The distinction between movement initiation speed and cancellation speed is also important, because otherwise older adults could appear impaired simply because all their movements are slower.
The main limitation is that the older group was relatively healthy and high functioning. The results should not be generalised to frailer adults, people with Parkinson’s disease, people with falls history, or people with major balance problems. The finding that stopping is preserved may apply mainly to healthy ageing. The authors acknowledge this limitation.
The sample size is modest: 56 participants total. That is reasonable for a biomechanics study but may miss smaller age-related differences in stopping speed. The paper reports non-significant age differences in SSRT, but the possibility of a small real age effect remains.
A deeper issue is that proactive slowing complicates interpretation. Older adults slowed down more when stop cues were possible, and this may have helped them stop successfully. That is interesting, but it means the SSRT may not be a pure measure of reactive stopping capacity. Trial-by-trial feedback discouraging slow responses might have revealed larger age differences. The authors note this explicitly.
The ecological validity is better than a seated button-press task, but still limited. Participants stood in a lab, responded to arrows, and made planned forward steps. Real-world fall avoidance often involves uneven surfaces, lateral steps, obstacles, distraction, fear, dual-tasking, and moving gait rather than step initiation from quiet stance.
Bottom line
This is a useful and fairly novel paper because it moves inhibition research from the hand-button paradigm into a more gait-relevant stepping task. Its strongest contribution is showing that the early postural preparation for a step can begin, yet the later foot-lift can still be cancelled if the stop cue arrives early enough. The ageing conclusion is more cautious: healthy older adults were slower to move, but not clearly worse at stopping, probably because they adopted a more cautious proactive strategy.