Concurrent validity of the use of the Dartfish application to assess motor strategy use in adults

Background: Motor strategy use changes with age, resulting in decreased balance and therefore an increased risk for falls. The importance of motor strategy activation in fall prevention is highlighted in current literature; however, physical therapists do not routinely examine motor strategy activation in clinical practice. There is limited available literature on how to objectively measure motor strategy use within a clinical setting given time and financial resource constraints. However, the use of the smart devices such as an iPad in clinical practice may provide a way to address this problem, and thus two studies were carried out. The purpose of the first study was to investigate the concurrent validity of the Dartfish ProSuite 7.0 software, which has been shown to be comparable to three-dimensional systems, and the Dartfish Express application (app) on an iPad 2 as a tool to measure start and stop ankle position during forward and backward ankle strategy activation. This affordable app has the potential to be used by clinicians in the clinic to objectively assess motor strategy use. The purpose of the second study was to investigate motor strategy use during an anticipatory stepping correction in an older adult sample compared with a younger adult sample using an iPad 2 and the Dartfish Express app. Comparisons of start and stop ankle position following forward and backward motor vi strategy activation and the time from initiation to completion of a stepping strategy were examined.

Participants: 30 young adults (M= 26.5 ± 4.5 years) and 30 older adults (M= 72.6 ± 4.0 years).

Methods: A two-camera set up was used for study one: an iPad 2 and Sony camera lens at equal heights. A one-camera setup with an iPad 2 was used for study two. In both studies, markers were placed on bony prominences on participants’ left side. Participants were read modified Mini-BESTest instructions for forward and backward compensatory stepping corrections. The Dartfish app and ProSuite software was used to measure the ankle start position (degrees) prior to initiation of an ankle strategy, stop position (degrees) immediately following the completion of ankle strategy use, and the time (seconds) it took to initiate and complete a compensatory step.

Results and discussion: In study one, Pearson’s product moment correlation coefficient statistic showed an excellent relationship (r >0.75) between the Dartfish ProSuite 7.0 software and the Dartfish Express app on an iPad 2 for all four positions. Thus, the app’s use is appropriate to assess anticipatory motor strategies. Dependent t-test was used to compare means between the two devices. No significant differences were found between forward stop/start and backwards start/stop positions between devices. Therefore, only the iPad 2 and the Dartfish Express app were used in study two. For the second study, independent t-tests were used to compare the difference in ankle start and stop positions between the older and younger adults. A statistically significant difference vii was found in the forward ankle stop position (p= 0.01) that could be indicative of a more reserved anticipatory postural response from older adults. The reserved anticipatory postural response could be a result of increased fear of falling, decreased confidence in the participant’s ability to regain his or her balance beyond that point, or bias from previous experiences in loss of balance episodes. No other significant differences were found. Independent t-tests were also used to compare differences between forward and backward mean-time from initiation to completion of a stepping reaction; no significant differences were noted between older and younger adults.

Conclusions: Overall, findings of these studies support the use of the Dartfish Express app as a tool to measure motor strategies and reinforce the importance of clinically assessing motor strategies. Further investigations should evaluate the reliability of the Dartfish Express app, as one considers the use of the app as a primary outcome tool for an intervention targeting motor strategy training.