Greater implicit flexibility (higher baseline Continuous Relative Phase variability) was associated with lower explicit flexibility (longer joint angle relaxation time) during perturbed walking, indicating that implicit and explicit flexibility are inversely related during perturbed human walking.
Key Findings
Results
Implicit and explicit flexibility were inversely related during perturbed walking, contrary to the study's hypothesis.
Greater baseline Continuous Relative Phase variability (bCRPV) was associated with longer joint angle relaxation times following perturbation
This finding was contrary to the hypothesis that greater implicit flexibility would correspond to faster locomotor reorganization
The inverse relationship was observed across three of the four segment couplings examined
The authors conclude that 'higher bCRPV does not necessarily correspond to faster locomotor reorganization following perturbation'
Results
Moderate positive correlations were observed between bCRPV and relaxation time across three of four segment couplings.
Spearman's rank correlations were used to examine the relationship between implicit and explicit flexibility measures
Positive correlations between bCRPV and relaxation time were found in three of the four segment couplings analyzed
A positive correlation between these measures indicates an inverse functional relationship, as longer relaxation time reflects slower adaptation
The correlations were characterized as 'moderate' in magnitude
Results
Individuals exhibiting greater baseline Continuous Relative Phase variability required more strides to return to regular walking patterns following sudden perturbations.
Implicit flexibility was quantified using baseline Continuous Relative Phase variability (bCRPV) measured during unperturbed treadmill walking
Explicit flexibility was quantified using joint angle relaxation time following perturbation
Participants with higher bCRPV showed longer relaxation times, meaning they needed more strides to recover
This suggests that greater movement variability at baseline does not confer a recovery advantage following unexpected perturbations
Methods
Unexpected unilateral perturbations were introduced via sudden belt accelerations or decelerations during treadmill walking in healthy young adult males.
Participants were healthy young adult males
Perturbations were delivered unilaterally through sudden treadmill belt accelerations or decelerations
Perturbations were unexpected to participants
Walking was performed on a treadmill, allowing controlled perturbation delivery
Methods
Flexibility was operationalized at two distinct levels of movement organization using complementary measures.
Implicit flexibility was defined as the ability of the locomotor system to adopt alternative movement solutions at baseline, quantified by bCRPV
Explicit flexibility was defined as the ability to reorganize movement following perturbation, quantified by joint angle relaxation time
The study characterizes flexibility 'using complementary measures derived from different levels of movement organization'
The authors note that flexibility in locomotion 'remains rarely characterized' despite its theoretical importance
Discussion
The study provides empirical evidence that implicit and explicit flexibility represent distinct and potentially dissociable properties of locomotor adaptability.
The inverse relationship between the two measures suggests they capture different aspects of locomotor flexibility
The authors interpret findings as demonstrating 'the value of characterizing flexibility using complementary measures derived from different levels of movement organization'
Higher movement variability (bCRPV) in baseline walking did not translate to superior recovery capacity after perturbation
The results challenge the assumption that a single measure of flexibility can capture the full scope of locomotor adaptability
What This Means
This research suggests that two different ways of measuring walking flexibility—one based on natural movement variability during normal walking and one based on how quickly a person recovers after an unexpected disturbance—are actually inversely related to each other. The study had healthy young men walk on a treadmill while experiencing sudden unexpected changes in belt speed on one side, simulating real-world perturbations like slips or unexpected surface changes. People who showed more natural variability in their walking patterns (called 'implicit flexibility') actually took longer to return to their normal walking pattern after being perturbed, which was the opposite of what the researchers expected.
This matters because it challenges a common assumption in movement science: that having more movement variability is simply 'better' for adaptability. The findings suggest that being variable in normal, unperturbed walking does not necessarily mean a person will recover more quickly when something unexpected happens. These are two distinct aspects of how the body manages locomotion, and they appear to be governed by different mechanisms.
For fields like rehabilitation, sports science, and fall prevention, this research suggests that assessing walking flexibility may require multiple different measurements rather than relying on a single metric. A person could score well on one type of flexibility measure while performing poorly on another, and both types of information may be important for understanding someone's true ability to navigate a changing environment safely.
Check Your Own Numbers
Upload your bloodwork. We'll cross-reference your results against this study and 4,700 others.
Kwek J, Komar J, Williams G, Chow J. (2026). Implicit and explicit flexibility are inversely related during perturbed human walking in healthy young adult males.. Journal of biomechanics. https://doi.org/10.1016/j.jbiomech.2026.113525