Feelings of psychological distress, especially in combination with fear of falling, can cause an individual to adopt more cautious gait behaviors, resulting in a more variable gait and an increased risk of falling.1 Over the years, physiological measurements have gained popularity and are used increasingly as part of experimental research designs.2 Chatterjee et al3 in this issue assert that there is a need to include an objective measure of the perceived challenge posed by various walking tasks; they measured skin conductance as a reflection of sympathetic nervous system (SNS) activity, using a portable device that is commercially available for clinical use. Adhesive electrodes on the palmar surface of the index and ring fingers of both hands measured the electrodermal activity or galvanic skin response as a reflection of the participants' elevated levels of physiological arousal and anxiety.

The introduction of objective physiological measurement to the physical therapist's clinical toolbox is important; it can add a new source of useful information to the assessment process. Chatterjee et al3 demonstrated that skin conductance increases during relatively more complex walking tasks. While their study focused specifically on individuals with stroke, their findings may be generalizable to other clinical populations as well. In the context of physical therapy, the increased arousal associated with dual-task performance, or more complex walking tasks, can contribute to gait instability and increased fall risk,2 especially among frail older adults.1 Clinicians may be interested in using skin conductance as an index of anxiety, which can be a potential risk factor for falls.4 It has been suggested that anxiety can increase fall risk in 2 ways. First, anxiety caused by a fear of sustaining a fall and injury during a certain activity could lead people to adopt a slower, more cautious gait that, paradoxically, is less stable than a more natural and confident gait.2 Second, because of the complex interplay between anxiety and attention, anxiety can compete for executive resources required to complete a complex task and may therefore affect the individual's ability to complete the motor task safely.5 Clinicians would ideally want to capture a "real-time" objective assessment of psychological distress, without disrupting the task at hand. Skin conductance offers an important advantage over self-report in this regard, as it may be less likely to be affected by inherent biases such as social desirability, the cognitive ability of a person to make an accurate estimate of his or her walking performance, or task disruptions, which could compete for the already sparingly available attentional resources.

Chatterjee et al3 suggest that skin conductance could be an added outcome variable for clinicians, when evaluating the extent to which a patient might benefit from interventions designed to reduce fear of falling and improve safety while walking. However, as part of this Clinical Point of View, we would like to address some limitations of using skin conductance in clinical practice. It is important to remember that skin conductance is not a direct reflection of the walking task itself but a reflection of the level of autonomic arousal experienced by a specific individual. That is, a person's level of autonomic arousal can be affected by a myriad of factors beyond walking complexity. These factors include thoughts, beliefs, and expectations6 (eg, about the possibility of threat or social embarrassment), methodological factors7 (eg, ambient temperature), personality characteristics,8 and other influences (such as pain9 or anticholinergic medications10) that lead some people to have higher levels of skin conductance than others. Especially in the context of clinical practice, these potentially confounding factors should be considered before relying on skin conductance to assess the perceived challenge of walking.

While the role of psychophysiological measurement in improving physical therapy assessments and outcomes remains to be clarified with additional research, several ideas may be considered. First, individual differences in autonomic responses and different assessment circumstances are likely to induce different levels of arousal. For example, an assessment conducted to determine eligibility for insurance compensation is likely to induce more anxiety than an assessment conducted to make rehabilitation recommendations. As such, it would be important for the clinician to take an individualized approach to assessment. Such an approach would involve comparing each patient's skin conductance scores across tasks and baseline. Comparing scores across patients may be premature, given our current state of knowledge, as well as individual differences and situational variables. Comparisons across patients may lead to less accurate clinical conclusions compared with the individualized approach just described.

Second, when interpreting elevations in galvanic skin response, clinicians should consider variables beyond walking task complexity. While self-report indices are constrained by limitations inherent to any subjective measures, a combined approach might offer substantial advantages over using one measure in isolation. For example, interviewing patients about factors that may be making them tense or worried during the assessment would be useful in interpreting the findings. Therefore, for clinicians interested in measuring autonomic arousal, skin conductance may prove to be a useful adjunct to patients' self-reported anxiety.

In conclusion, while the results of the study by Chatterjee et al3 support the feasibility of measuring galvanic skin responses to gauge the perceived challenge of walking tasks, clinicians should be judicious when using skin conductance in their clinical practice. We do not know whether skin conductance is a reliable physical therapy tool outside of a standardized experimental setting or whether it has sufficient sensitivity to change for longitudinal use in physical rehabilitation. Future research is needed to investigate the relationship between galvanic skin responses and self-report in this context.

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