Postural control helps strengthen the body against gravity and maintain balance during daily events. Postural control is highly related to the level of independence of individuals and is dependent on how information—received from the visual, vestibular, and proprioceptive systems—is regulated to give appropriate responses on maintaining balance between oneself and one's surroundings (Massion, 1994). Unfortunately, due to aging, individuals may experience neurodegenerative changes that decrease their ability to control posture (Pyykko, Jantti, & Aalto, 1990). Furthermore, recent research has shown that individuals with diabetes mellitus may also experience diminished postural control and mobility, leading to poor outcomes (Morrison, Colberg, Parson, & Vinik, 2012) and contributing to subsequent complications (Schwartz et al., 2002; Tilling, Darawil, & Britton, 2006). Although previous studies have shown that exercise training improves glycemic control and general fitness in individuals with diabetes (Maiorana, O'Driscoll, Goodman, Taylor, & Green, 2002; Tessier et al., 2000), few have explored the effects on balance control and mobility in older adults with type 2 diabetes, and results from those studies showed that exercise produced only a modest improvement (Allet et al., 2010; Morrison, Colberg, Mariano, Parson, & Vinik, 2010; Orr, Tsang, Lam, Comino, & Singh, 2006).
Individuals with diabetes may also have reduced ankle muscle strength, diminished proprioception, and increased ankle joint stiffness in dorsiflexion (Andersen, Nielsen, Mogensen, & Jakobsen, 2004; Giacomozzi, D'Ambrogi, Cesinaro, Macellari, & Uccioli, 2008; van Deursen & Simoneau, 1999). The current authors' earlier findings showed physical characteristics of the ankle are significantly correlated with mobility in older adults with diabetes as measured by the Timed Up and Go (TUG) test (Ng, Lo, & Cheing, 2014). It is therefore logical to deduce that a specific exercise regimen focusing on ankle strength and flexibility training and addressing deteriorated ankle proprioception might improve postural control and mobility in this population.
In addition to center-based training, home exercise has also been demonstrated to be effective in improving mobility of community-dwelling and frail older adults (Matsuda, Shumway-Cook, & Ciol, 2010; Miller, Magel, & Hayes, 2010). However, no studies have previously focused on addressing deteriorated ankle proprioception, enhancing ankle strength, and improving ankle range of motion in individuals with diabetes. The objective of the current study was to design and evaluate the effect of an exercise program that has specific features focusing on ankle characteristics to improve balance in older adults with type 2 diabetes; by extension, improvement in balance would improve mobility and decrease the risk of falls.
Participants were recruited from four local community centers. Inclusion criteria were adults 65 or older with a diagnosis of type 2 diabetes confirmed by blood test with glycated hemoglobin (HbA1c) >6.5%. Participants were self-ambulatory without walking aids and cognitively competent in understanding instructions. Exclusion criteria were the presence of visual impairments, such as retinopathy assessed by Snellen chart; a recent foot lesion or surgery; history of neurological disorders or cognitive disorder; and unstable hypertension by self-report. Ethical approval was obtained from a local university and written informed consent was obtained from all participants before the study began.
The research design of the current study was a pretest–posttest controlled study, with an intervention group of participants in a 10-week exercise program. The program was delivered twice per week in a community setting and included daily home exercise. Registered physiotherapists were engaged to design a 10-week, 60-minute community-based exercise program and daily home exercise program. Compliance with exercise regimens was recorded within the respective setting. The exercise interventions targeted key physical aspects of the ankle to strengthen dorsiflexor and plantar flexor muscles by applying an elastic Theraband® (Ribeiro, Teixeira, Brochado, & Oliveira, 2009). During Theraband exercise application, participants were directed to adjust the tension consistent with perceived skill and exercise tolerance to avoid inflicting injury, thus improving range of ankle dorsiflexion with intense stretching (Christiansen, 2008) and mediating ankle proprioception deficit through visual and vestibular input enhancement.
Visual and vestibular systems were enhanced by using an ankle disc. The ankle disc is a 13-inch latex-free PVC inflatable cushion (Theraband). Participants were directed to stand on the ankle disc with one or both legs while performing ankle movements. The ankle movements were performed separately or in combination with movement of the upper extremities. In addition to using the ankle disc, each exercise session included 15 minutes of rhythmic exercise in which participants were instructed to follow music and perform rhythmic movements, such as walking backwards and sideways, turning, and lunging in different directions.
Apart from exercising in community centers, daily home exercise was emphasized in the intervention group. Elastic Therabands with resistance levels based on each participant's physical performance and an exercise pamphlet were distributed to each participant. An exercise pamphlet with photographs and simple descriptions was used to illustrate the exercise training protocol. Home exercises were also practiced during class and individual feedback was given to participants before they practiced at home. A home exercise diary was enclosed in the exercise pamphlet for participants to record their exercise attempts at home.
Participants in the control group were required to maintain their usual daily activities and not to attend any other exercise classes during the 10-week study period. For ethical purposes, identical exercise classes as well as home exercise pamphlets were provided to the control group when the study ended.
Baseline and postintervention assessments were performed. Assessment tools used to evaluate the visual, vestibular, and somatosensory functions key to postural stability maintenance were identified through a computer-based posturography device, Smart EquiTest®. The device features a platform and visual surround with a sway reference, which is a movable platform that participants stand on during the assessment.
Sensory Organization Test. The Sensory Organization Test (SOT) demonstrated good test–retest reliability among community-dwelling older adults in measuring postural control (Ford-Smith, Wyman, Elswick, Fernandez, & Newton, 1995).
During the test, participants were required to stand on the platform with their arms placed by their sides and looking forward. For safety reasons, participants wore a harness to prevent them from falling during the assessment. Participants were tested under the following six conditions: (1) eyes open with fixed support surface; (2) eyes closed with fixed support surface; (3) sway-referenced vision with fixed support surface; (4) eyes open with sway-referenced support surface; (5) eyes closed with sway-referenced support surface; and (6) sway-referenced vision with sway-referenced support surface. Three 20-s trials were conducted in each condition. During each test, the real-time center of pressure of the participant was recorded for calculating the sway of the individual's center of pressure. Data obtained were compared with his/her limit of stability (i.e., the ability to move the center of gravity within the base of support). The maximal performance of the test is by default set at 12.5° (Fong, Tsang, & Ng, 2012). In each of the six testing conditions, an equilibrium quotient was generated. A score of 100 represents no sway during the assessment and a score of 0 represents the participant's center of pressure falling out of his/her limit of stability. The composite score indicates the individual's overall performance. The findings obtained in the sensory score of the visual, vestibular, and somatosensory systems (range = 0 to 100) were also recorded. These scores represent the ability of the participant to use the respective sensory information (Rosengren et al., 2007; Tsang, Wong, Fu, & Hui-Chan, 2004).
Timed Up and Go Test. The TUG test is a sensitive measure for detecting changes in mobility in older adults with high reliability (Steffen, Hacker, & Mollinger, 2002; Van Iersel, Munneke, Esselink, Benraad, & Olde Rikkert, 2008). The test was performed by having participants sit on a chair with their back against the chair and arms placed on arm supports. Participants were advised to stand and walk for 3 m, turn around near the designated floor marker, and return to the chair and resume the original chair position as quickly as possible. The timed activity began when the participant's back left the backrest until the original position was resumed (Shumway-Cook, Brauer, & Woollacott, 2000). Three trials were performed and the mean to the nearest second was calculated for analysis.
Single-Leg Stance Test. The Single-Leg Stance Test (SLST) is a functional test of balance and was found to be a good indicator for fall risk (Hurvitz, Richardson, Werner, Ruhl, & Dixon, 2000). The SLST was performed by first asking participants to stand in an upright position with their arms along their sides. The timer was started once the non-tested leg was lifted and stopped once the foot of the lifted leg touched the floor, the stance foot was displaced, or the participant used the lifted foot to support the stance leg (Hurvitz et al., 2000). Participants were considered to have reached the maximum time if they managed to stand on a single leg for 45 seconds to prevent a ceiling effect (Briggs, Gossman, Birch, Drews, & Shaddeau, 1989; Jonsson, Seiger, & Hirschfeld, 2004). Three trials were taken on each leg, and the mean to the nearest second was calculated for subsequent analysis. Because a significant difference in SLST was not found between both legs in all participants, the average time (in seconds) of both legs was calculated for subsequent analysis.
SPSS version 17.0 was used for the statistical analysis. Independent t test and chi-square test were used to analyze the difference in demographic characteristics, and one-way analysis of covariance (ANCOVA) was used to analyze the between-group difference in the change in performance. Because a significant between-group difference was noted in HbA1c, it was entered as a covariate in all analyses. Intention-to-treat analysis with the last observation carried forward (Portney & Watkins, 2000) was used for participants who did not attend the post-assessment session. The level of significance was set at 0.05.
Ninety-three participants were recruited (intervention group: n = 48, mean age = 71.4 years; control group: n = 45, mean age = 72.8 years) from four community centers. The mean duration of diabetes history was 10 years and participants in both groups were obese according to their body mass index (Table 1). Except for HbA1c level, there were no significant differences between groups in demographic characteristics.
No adverse effects were reported during center-based and home exercise. None of the participants in the intervention group withdrew from the program. However, two participants in the intervention group and two participants in the control group did not attend the reassessment session after the 10-week exercise program (Figure). The mean rate of attendance for the center-based exercise was 75.5%, which was lower than expected.
Flow diagram of study enrollment and participation.
Baseline, postintervention assessment, and change in performance after exercise training are presented in Table 2. As HbA1c was set as a covariate, adjusted values were also calculated after eliminating the effect of HbA1c (Table 2). For the SOT, there was a trend of improvement in the intervention group in the equilibrium quotients, with improvements from 0.6 to 11.0 in different conditions, whereas the control group showed approximately no change. By analyzing the between-group difference in the change of performance after the 10-week exercise program using one-way ANCOVA, the intervention group was found to demonstrate significantly greater improvement in Condition 4 (eyes open, sway-referenced support surface) (5.9 vs. −0.4), Condition 5 (eyes closed, sway-referenced support surface) (11.0 vs. −0.2), composite score (overall performance of individual) (4.4 vs. 0.3), and visual ratio (i.e., ability to use visual information to maintain balance when somatosensory information was altered) (0.1 vs. 0.002), and vestibular ratio (i.e., ability to use vestibular information to maintain balance when somatosensory information is altered and visual information is removed) (0.1 vs. 0.003) (all p < 0.05). For the TUG test, the intervention group showed a greater trend of improvement compared to the control group (−0.3 s vs. −0.01 s; p = 0.26). For the SLST, the intervention group showed a trend of being able to stand for a longer period of time at the end of the exercise training (1.8 s vs. −1.5 s; p = 0.15).
Change in Balance and Mobility between Intervention and Control Groups
The current study examined the effectiveness of an exercise program with a specific focus on postural control and mobility in older adults with type 2 diabetes. Exercise training targeting the ankle was found to produce significantly greater improvement in postural stability. The intervention group also demonstrated a trend of improvement in mobility and balance in the SLST.
As older adults with diabetes are prone to have deteriorated mobility and balance (Morrison et al., 2012; Schwartz et al., 2002; Tilling et al., 2006), the performance of the control group was expected to possibly deteriorate after the 10-week study period. However, the results in Table 2 suggest that the deterioration was not significant. Although the changes in the intervention group were modest, the study showed the clinical importance of this tailor-made exercise approach in “reversing” the deteriorating process of mobility and balance in this population.
The integration or synthesis of visual, vestibular, and somatosensory input/data is essential to postural equilibrium. Failure to correct information received from dynamic environmental conditions may lead to falls. Liu, Hsu, Lu, Chen, and Liu (2010) identified a decrease in ankle proprioception in older adults prior to the onset of neuropathic symptoms. This finding suggests that older adults with diabetes are at greater fall risk regardless of diabetes complications. Therefore, the risk of falls among older adults with diabetes should not be underestimated, even for those without peripheral neuropathy. To compensate for the decline in ankle proprioception inputs, the current exercise program emphasized enhancing the use of visual and vestibular systems for postural control.
Sensory Organization Test
Significant improvements were noted in Conditions 4 and 5 of the SOT (i.e., visual and vestibular ratios and the composite score). It is of interest to review how much the participants improved in using the visual and vestibular systems in postural control after the exercise training. Improvement in visual and vestibular ratios indicated that participants tended to avoid using the conflicting somatosensory information, relying more on the vestibular and visual information to maintain postural stability.
Visual information allows one to have spatial orientation and helps detect movements between the environment and oneself (Redfern, Yardley, & Bronstein, 2001). To facilitate the use of visual information, participants were trained to use visual fixation while standing on the ankle disc and performing movements. Participants directed their gaze on a target during the respective movements; the ankle disc served as the media to disrupt proprioception and diminished mobility and balance. By visually fixating on a target, participants were able to distinguish the change in body orientation and their surroundings.
To enhance the use of vestibular systems, the center-based exercise program included rhythmic movements, which involved rotating the head or turning the whole body according to the beat of the music. Participants were required to change their base of support during the dynamic movements and combine the movement of their upper limbs while looking at their hands to enhance the adaptability of the vestibular system, which is one strategy for vestibular rehabilitation (Herdman, 1993).
The vestibular system allows one to detect the orientation of the head and its movement in relation to gravity. Because the direction of gravity remains unchanged, the vestibular system provides the true afferent information in the face of conflicting visual and somatosensory information (e.g., walking on an uneven ground surface in a dark environment). As older adults face deterioration in ankle proprioception, the vestibular system would be the last resort of afferent input in this target population when they are facing an environment with conflicting visual information or when in a dark environment. Older adults who have poor ankle proprioception rely on the use of the vestibular system in dark environments and have a higher fall risk (Connell & Wolf, 1997).
As the vestibular and visual ratios were obtained by comparing the data in two testing conditions (both were compared with Condition 1), the contribution from motor systems was eliminated, and therefore, it can be concluded that the improvements were purely due to change in the use of sensory systems. A 7.1% improvement was noted in the composite score of the intervention group, whereas no change was noted in the control group. Increased ankle muscle strength and range of motion might be accountable for such improvement in the intervention group, as well as the improvement in the use of sensory systems. Spink et al. (2011) demonstrated that ankle muscle strength and range of motion were associated with the amplitude of sway during postural control during quiet standing. However, the changes in ankle strength and range of motion were not assessed in the current study; therefore, future study is required to prove this hypothesis.
Timed Up and Go Test
Sufficient muscle strength of the ankle dorsiflexor and plantar flexors are correlated with walking and turning speed in older adults (Orendurff et al., 2006; Tiedemann, Sherrington, & Lord, 2005). The increase in stiffness of ankle dorsiflexion range of motion not only affects toe clearance during walking, but also results in poor joint alignment of the ankle during sitting, causing an increase in the traveling distance of the center of mass for rising during the initial phase of the TUG test (Mueller, Minor, Schaaf, Strube, & Sahrmann, 1995; Perry, Marchetti, Wagner, & Wilton, 2006). Therefore, participants in the intervention group were expected to show significant improvement after the exercise program.
Despite the contribution of increased ankle muscle strength and stiffness in mobility, the intervention group tended to have a modest effect in TUG test scores and only showed a greater trend of improvement compared to the control group (Table 2). This result can be explained by the fact that the intervention group did well in the baseline assessment and took an average of 9.8 s to complete the TUG test. The cut-off score to indicate fall risk is 12 s for the TUG test (Bischoff et al., 2003); therefore, the baseline performance of the intervention group was considered satisfactory, which might have caused a ceiling effect. The result may limit the generalizability of the current findings to individuals with diabetes who have relatively poorer mobility. Future studies may need to recruit participants with poorer mobility to increase the generalizability of results.
Single-Leg Stance Test
The SLST is another functional test for detecting fall risk in older adults (Hurvitz et al., 2000). The intervention group showed a trend of improvement (11.5%) in contrast to the deterioration observed in the control group (8.9% decrease), which might be explained by the improvement in using visual information after the exercise training. Hazime et al. (2012) found that visual information had a main effect on single-leg standing. Moreover, ankle dorsiflexor and plantar flexors strength was related to the anterior-posterior and medial-lateral sway during single-leg standing (Judge, Schechtman, & Cress, 1996). A previous study (Reimer & Wikstrom, 2010) reported a wide range of SLST performance (6.9 to 32.9 s) observed among older adults ages 70 to 79 years, but there is no consensus on the cut-off score.
The current study protocol comprised tasks with increasing difficulty according to the progress of individual participants to challenge their balance control (Tiedemann et al., 2005). The duration and frequency of the exercise classes were designed based on previous successful balance programs (Cheung, Au, Lam, & Jones, 2008; Kaesler, Mellifont, Swete Kelly, & Taaffe, 2007). The modest effect of exercise in SLST and TUG test scores might be due to insufficient exercise duration.
There were several limitations in the current study. Randomization was not feasible in the local community settings, which may have impacted the withdraw rate. Participants were allocated into different groups based on their availability. In addition, follow up was not performed, as most participants refused to commit to such a long study period.
At the end of the 10-week training period, the reported average compliance rate with home exercise was 53.5%, whereas the average center-based training compliance was 75.5%; both rates were lower than the authors' expectations. In addition, some participants stated that they had forgotten to record their exercise compliance in their exercise diaries; therefore, the actual compliance of home exercise may be higher than the reported figure. Moreover, the true effect of the exercise protocol could have been underestimated, and further action will be taken in a future study to solve this potential bias.
A 10-week exercise program focused on ankle strengthening, incorporated with a home exercise program, was effective in improving the postural control in older adults with type 2 diabetes. The program also produced a trend of improvement in mobility and single-leg balance. Clinicians should consider this strategy to reduce the risk of falls among older adults with diabetes. If this protocol can be applied regularly by nursing staff in clinical settings, such as in a diabetes clinic, the results might be more promising; however, further study is required to support this hypothesis.
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|Variable||Intervention Group (n = 48)||Control Group (n = 45)||p Value|
|Age (years)||71.4 (7.9)||72.8 (6.5)||0.36|
|History of diabetes (years)||10.2 (8.7)||10.2 (7.3)||0.99|
|Glycated hemoglobin (HbA1c) (%)||8.0 (1.2)||6.9 (0.8)||<0.001|
|Body mass index (kg/m2)||27.6 (7.9)||25.4 (4.0)||0.10|
|Sex (female) (n, %)||35 (72.9)||33 (73.3)||0.95|
Change in Balance and Mobility between Intervention and Control Groupsa
|Variable||Intervention Group (n = 48)||Control Group (n = 45)||Partial η2||p Valueb|
|Pretest||Posttest||Change||Adjusted Change (SE)||Pretest||Posttest||Change||Adjusted Change (SE)|
| Condition 1||91.3 (4.9)||92.0 (2.3)||0.7 (4.9)||0.8 (0.6)||92.4 (2.6)||91.8 (3.0)||−0.6 (2.3)||−0.8 (0.6)||0.04||0.08|
| Condition 2||90.1 (3.1)||89.8 (2.9)||−0.4 (2.2)||−0.4 (0.4)||90.1 (3.3)||89.8 (3.3)||−0.2 (3.2)||−0.2 (0.5)||<0.001||0.85|
| Condition 3||88.7 (5.8)||89.2 (6.0)||0.8 (3.6)||0.6 (0.7)||89.0 (5.6)||89.5 (3.7)||0.5 (5.1)||0.7 (0.7)||<0.001||0.94|
| Condition 4||68.8 (11.2)||74.5 (7.9)||5.4 (8.6)||5.9 (1.3)||70.7 (9.5)||70.9 (10.4)||0.1 (8.1)||−0.4 (1.4)||0.1||<0.01|
| Condition 5||48.0 (13.1)||59.4 (11.8)||10.9 (12.9)||11.0 (1.8)||59.2 (10.2)||59.1 (10.0)||−0.2 (9.5)||−0.2 (1.9)||0.2||<0.001|
| Condition 6||49.6 (14.5)||55.1 (13.4)||5.3 (15.1)||4.3 (2.1)||56.4 (11.9)||57.1 (11.4)||0.8 (11.0)||1.9 (2.2)||0.007||0.46|
|Composite score||66.3 (12.2)||71.0 (12.4)||4.6 (6.6)||4.4 (0.9)||72.0 (5.7)||72.1 (5.7)||0.1 (4.9)||0.3 (1.0)||0.09||0.01|
|Somatosensory ratio||1.0 (0.1)||1.0 (0.0)||−0.01 (0.1)||−0.02 (0.01)||1.0 (0.3)||1.0 (0.0)||0.004 (0.04)||0.01 (0.01)||0.03||0.13|
|Visual ratio||0.8 (0.1)||0.8 (0.1)||0.1 (0.1)||0.1 (0.01)||0.8 (0.1)||0.8 (0.1)||0.006 (0.08)||0.002 (0.01)||0.08||0.01|
|Vestibular ratio||0.5 (0.2)||0.6 (0.1)||0.1 (0.1)||0.1 (0.02)||0.6 (0.1)||0.6 (0.1)||0.002 (0.1)||0.003 (0.02)||0.1||<0.001|
|TUG (s)||9.8 (3.0)||9.6 (3.0)||−0.2 (1.1)||−0.3 (0.2)||11.5 (3.3)||11.4 (3.3)||−0.07 (1.0)||−0.01 (0.2)||0.01||0.26|
|SLST (s)||15.6 (14.3)||17.4 (16.1)||1.8 (10.3)||1.8 (1.5)||15.8 (13.7)||14.4 (13.6)||−1.4 (8.7)||−1.5 (1.6)||0.02||0.15|