This systematic review researched the effect of dual tasking on postural stability, focused on elderly and PD patients. Only thirteen studies met the groups inclusion criteria for detailed review. Five studies focused on PD patients, describing the effect of dual tasking on postural stability through visuomotor, VR or balance exercises. The remaining eight studies focused on elderly, showing the effect of dual tasking on balance or postural control through balance, dance and cognitive exercises.
The level of evidence is found to be moderate to high, as the average PEDro score for all of the articles combines was 7.2/11. Only 5 of the 13 articles used were under the mean PEDro score as can be seen in the results table but were still high enough to pass the groups’ screening method. This means that the overall quality of the articles is moderate and reliable. The two highest graded articles received a score of 10/11. The higher the grade of the article the more reliable it is. It was discovered that the biggest factors in determining what made an article the most reliable was its’ method of blinding (single, double, triple) and the measures of at least one key outcome obtained from more than 85% of the subjects initially allocated to groups. All of the articles that were a part of our inclusion criteria had at least a single blinded component
A total of seven studies were found to have balance or postural control as an outcome. Smith-Rey et al. (2015) conducted a research on the effects of computer-based cognitive exercising on gait and balance. The patients endured a ten-week intervention in which the results showed that the 10m gait speed improved (P= 0.016)). Although the improvement seems significant, the author states that a larger sample and a longer period is needed to detect significant differences in 10MDGS.
Another study (Wong et al., 2015) describes an eight-week balance or upper limb exercises on the BBS and Dual task TUG. The trial period lasted 1,5 year with a population of 84 participants in total. The outcomes of the study revealed that the balance training group improved significantly compared to the upper limb group (p=<0.05). The trial period lasted 1,5 year with a population of 84 participants in total.
O’shea et al. (2012) showed a significant effect in footstep patterns of 15 people with PD and 15 comparison subjects without PD. The walking patterns of all subjects were tested under 3 conditions: (1) free walking (“free”), (2) coin transference while walking (“coin”), and (3) digit subtraction while walking (“digit”). Subjects walked 3 times under each condition, and the order of conditions was randomly allocated. The results demonstrated a decrease in their stride length with the coin and digit tasks. However, the group with PD demonstrated a much greater decline in stride length in both dual task conditions, as indicated by the group × task interaction effect for stride length (P=0.007). Although the outcomes of the study seems positive, the limitations are something to keep in mind. The findings cannot be generalized to all people with PD, because only subjects with gait hypokinesia and mild to moderate impairments were included. The author states that further research is needed to examine the effects of dual task performance during walking for subjects with other movement disorders such as akinesia, dyskinesia, and postural instability.
Jacobs et al. (2014) investigated the response of stepping in response to large, backward displacements of the support surface, with and without performing a fluency task of listing items in a category. They recorded the percentage of trials with freezing of gait, foot-lift latencies, and trials with falls into a safety harness. A total of 20 participants (PD and elderly) joined the trial over a period of 24 hours. The results show that for the group with PD, performing the fluency task during protective step responses, significantly increased the percentage of trials with falls (P= 0.024). The study has shown to be of moderate quality, this due to lack of blinding, it must also be said that the sample size was small.
Another article with low quality is Laessoe et al. (2015) due to lack of blinding. The study was conducted during a one-week intervention-serie on elderly and youngsters, which consisted of 25 repetitive tasks in which the 46 participants needed to exceed their limit of stability in order to touch one out of eight lights.
The young group improved significantly compared to the elderly (p=<0.001). The author explains that lack of possibility to make a criterion validation by comparison of the test with respect to an established test, as there exists no “gold standard” for the evaluation of dynamic postural control serves as a limitation to this study.
Two articles with moderate evidence, collected data through the use of a forceplate on elderly. Sukits et al. (2010) conducted a search in which ten participants needed to stand on a forceplate while doing three different cognitive tasks during a twelve week intervention. Results of this study showed that balance improved when the subject- specific dual-task was administered during quiet stance, also more sway was visible compared to standing with eyes closed and performing a forward or backwards subject-specific dual-task (P=0.04). The authors seem to be elated with the outcome, but state that further research and larger sample size needs to be done to disentangle this effect.
Zhou et al. (2015) carried out a three week study in which twenty patients had two different tasks (single task vs dual task) on transcranial Direct Current Stimulation (tDCS) versus sham therapy on a forceplate. The results showed that the dual task time of the control group (tDCS) improved (P= 0.02). The authors explain that those with impaired postural control (i.e., lower COP complexity) may stand to benefit more from tDCS-induced facilitation of cortical excitability. Future, larger-scale studies are therefore warranted to delineate the influence of baseline postural control characteristics on the effectiveness of tDCS as a therapeutic strategy. The overall conclusion of the Postural control/balance- exercise programs is that cognitive training may be an efficacious approach toward improving balance and gait in older adults known to have a history of falls (Smith-Rey et al. 2015). Also, a multi-dimensional balance training program can enhance balance and dual-task gait performance up to 12-month follow-up in people with PD (Wong et al., 2015). The authors of this review believe that future studies should evaluate whether these tests can identify elderly and PD patients with poor postural control who may be at increased risk of falling.
Three studies focused on the effect of cognitive or visuomotor exercises on balance. Bier et al. (2014) showed an intervention consisting out of two different exercises, a visual detection and alphanumeric tasks, these were performed separately and in combination. The results showed non-significant improvements after conducting a 3 week intervention. It must be said that this study was limited to a small number of participants and not it does prove whether these improvements are maintained or fade over time as the study did not include long-term follow-ups. The second study (Lamoth et al., 2011) investigated the effect of impaired cognition and dual tasking on gait variability and stability in geriatric patients. The total amount of patients counted 26, making this study limited in evidence. The RCT was performed in 1 day, as the patients walked on normal pace for 3 minutes per trial. The patients performed a single task (walking) and dual task (wording while walking) during these 3 minutes. The study concludes that both groups showed an increase in trunk accelerations and decrease in gait speed (p=<0.05). The final visuomotor study is from Wu et al. (2015), he explains the flow of information throughout the brain of PD versus elderly patients. The study composed of using functional MRI (fMRI) to investigate the underlying neural changes at both local activity and network levels when attending to movements that could be made automatically in PD patients and healthy subjects. This study promotes understanding about the role of the striatum in shifting, execution, and storage of automatic movements. Wu et al. (2015) states that, although PD patients at a relatively early stage can use different strategies, such as compensation from the anterior putamen, to achieve automaticity, this modified automatic mode is not stable and can be disrupted by attention. The researcher found that the reaction times in PD patients were longer than that in controls in each stage; however, the differences were not significant (P = 0.39). The limitations of this study show that the group did not compare the difference of neural activity at the rest condition, even though their previous study showed that neural activity in the resting state is different between PD patients and controls (Wu et al. 2009). An overall conclusion of the visuomotor/visual distraction-exercise program is that for PD patients, at early stage can achieve automaticity with compensatory efforts (Wu et al., 2015). The conclusion for the exercise program on elderly confirm that attentional control capacities can be improved when appropriate training is provided (Bier et al., 2014). Also walking under dual task conditions and quantifying gait using dynamical parameters can improve walking disorders (Lamoth et al., 2015). The authors believe that Patients at early stage can achieve automaticity with compensatory efforts, but more research with a larger population needs to be investigated in order to see the effectiveness of a visuomotor (dual) task.
Two studies used dancing as intervention, Wen Lan et al. (2015) explains that stride length and walking velocities decreased significantly as the dual-task (walking plus hand button pressing tasks) were applied for both the comparison and exercise groups. The results of the study show that the training effects of a Chinese traditional exercise, Yuanji-Dance, on walking balance and the associated attention demand in the healthy elderly can benefit the general cognitive and perceptual-motor functions of elderly people and not influence the dynamic walking balance. The reduction of response time would be effective in preventing a fall after a trip as response time plays a huge role and an important factor in affecting success of recovery after the trip. Pichierri et al. (2012) studied the effect of a dance (video game) in foot placement accuracy and gait while dual tasking on elderly. The dance group showed a significant decrease in single support time (p=0.029). Interestingly, this result seems to be conclusive, the between-group comparison resulted in non-significant.
Yen et al. (2011) studied the effects of Virtual Reality- balance training on postural control. The study chose to go with an arithmetic (cognitive) task for all three groups in order to provide an equal level of difficulty. The task consisted of VR training modes, these included 10 minutes of 3D ball-rolling game and 10 minutes of indoor-outdoor virtual activities. The training program was designed to progress from simple to complex, and upper extremities were held to the side of the trunk or on the waist. The study showed a significant improvement of the SOT-5 and SOT-6 score in the conventional balance (p=<0.001). The overall conclusion of the Dance/Virtual Reality- exercise programs is that both VR and CB training improved sensory integration for postural control in people with PD, especially when they were deprived of sensory redundancy, while cognitive-motor interventions may result in more improved gait under dual task conditions in comparison to a traditional strength and balance exercise program. The authors hypothesize that Chinese Yuanji-Dance practice and Dance (video games) for elderly may improve their personal safety when walking, especially under the condition of multiple task demand.
Limitations of this study
Several limitations persisted in the systematic review, which are to be considered while interpreting the results. The average quality of the included studies according to PEDro methodological quality scale was found to be 7.2, indicating a fair quality of the studies. A high risk of bias prevailed because of the limited number of RCTs. The restriction of search strategy limited to English and Dutch language might have resulted in omission of relevant research. Inability to retrieve descriptive statistics from the respective studies was also a limitation of this study.
This present study did not impose restrictions on the type of included dual task, in order to analyze the differential effects of complexity of dual task. Therefore, a higher chance of biasing and differential outcomes can be expected. Likewise, the systematic difference between the population group base statistics related to age, weight, gender, and disease severity led to difficulty in comparing studies. A majority of the incorporated studies had a small sample size, which generates a high possibility of error. The conclusions derived in the review based on incorporation of dual-task training in rehabilitation protocol are based on limited research.
Originally published 15.10.2019