Walking dysfunctions are one of the leading health problems in aging adults. Patients with joint problems are particularly affected. Lower extremity pain often leads to reduced mobility and subsequent decline in cardiovascular capacity.1,2 The risk of incurring injurious falls increases as balance capabilities diminish and as sensory reliability and anticipatory reactions diminish.3 It is estimated that approximately 30% of all people older than 65 years have injurious falls at least once a year.3 Specific balance training is recommended to help aging adults maintain activity and avoid fractures and injurious falls.4-6 Many studies have demonstrated that special therapeutic exercise may improve the functional outcome of patients with osteoarthritis,1,7,8 thereby avoiding injurious falls. Closed-chain exercises performed in various positions are recommended.1,9 Up to now, however, there has been no standard training protocol for sensory-motor training. Persons with hip dysfunction may be limited in training by pain; therefore, measuring the effects of sensory-motor training has proven to be difficult in persons with osteoarthritis.10-14
In the face of diminishing resources within the health care system, cost-effective alternatives in the form of exercise programs are necessary.15-17 One example is the Hip School program, a sensory-motor training program that addresses the characteristic impairments of hip osteoarthritis and after hip replacement surgery.9,18 In these programs, 10 to 15 people train once a week for 60 minutes over a 6-month period under the guidance of a physiotherapist. Improvements in endurance, strength, and health-related quality of life were documented among program participants.8,19,20 Supervised group exercise sessions seem to be as beneficial as individual sessions7 and superior to home exercise programs.15
In the present study, we examined the influence of intensive sensory-motor training on balance for individuals with hip dysfunction who participate in “Hip School” programs. Using the Posturomed (Haider-Bioswing, Weiden, Germany) as a measuring device, we created a specific imbalance of the postural system to evaluate the sense of balance.21 Doing so may assist us in understanding whether such intensive balance training may change balance and balance recovery after a sudden disturbance to stance.
PARTICIPANTS AND METHODS
Thirty-five participants of a Hip School program who had a mean age of 58 years (SD 12) were quasi-randomized into a training group (TG) and a control group (CG). All participants, who were tested before beginning the Hip School program, met inclusion/exclusion criteria and signed an informed consent form. Inclusion criteria included uni- or bilateral osteoarthritis of the hip (diagnosed by orthopedic surgeon or physician) or prosthesis of the hip and stable walking without assistive device. Exclusion criteria included cardiovascular disease and limited physical activity (New York Heart Association classes III and IV), neurological disorders resulting in weakness or balance impairments, knee or hip surgery in the preceding 6 months, or loosening of prosthesis.
The TG (n = 14; 7 women and 7 men; mean [SD] age 57  years; mean BMI [SD] 26  kg/m2) was tested before and after completing a 12-week intensive balance training program. The CG (n = 21; 11 women and 10 men; mean [SD] age 59  years; mean BMI [SD] 27  kg/m2) was tested 12 weeks prior to the start of the scheduled Hip School program and remained without any specific training during the 12-week observation period. We used a quasi-randomization method, with the criterion being the month they applied for the Hip School program. By this method we could make sure to get 2 similar clusters of people, but the group size of TG and CG differed because of more interest in the month the CG was recruited. There were no dropouts. The study was approved by the Ethics Committee of the University of Tuebingen in accordance with the Declaration of Helsinki.
Posturomed is used by European physical therapists as a proprioceptive training device. The support platform (12 kg, 60 cm ÷ 60 cm) is suspended on 15-cm-long steel cables, which allow the platform to shift freely along one plane (Figure 1). The displacement characteristics of the platform can be regulated in 3 stages (4, 6, or 8 cables regulating the swinging circle of the platform), the lowest of which was selected for use with participants with hip dysfunction.
A periodic shift of the support platform is suitable to test the participants' ability to control balance22; therefore, we recorded the movements of the platform. The underside of the platform is attached to a contact-free system for recording the platform path (Digimax, Mechatronic, Hamm, Germany). The motions of the platform were recorded in 2 perpendicular directions (x, y) at 100-Hz sample rate and 0.1-mm local resolution. The software used for measurement data logging provides the total distance covered by the platform (Sr) and the path in the x- and y-directions (Sx, Sy) for the measurement interval of 6 seconds in millimeters. Platform movements are termed “balance recovery movements” (BRMs), since they are employed by the participants to counterbalance disturbances to the body's center of balance.
A displacement mechanism was attached to one side of the device to lock the platform 10 mm outside of the resting position in the x-direction. When the lock is released, the platform swings back into its resting position, simulating “disturbances of stance.”21
Measurement and Test Procedures
Participants took up a standardized single-limb stance position for the measurements: arms hanging freely at their sides, supporting leg in the center of the measurement platform (position marked with tape), and nonsupporting leg slightly bent without contacting the supporting leg (Figure 1). Participants stood upright with their eyes directed at the opposite wall; they were not permitted to look at the platform or the displacement mechanism during testing.
To eliminate effects from habituation, participants stood on the Posturomed during instructions to become accustomed to the unsteady platform. Before the actual measurements, an unrecorded trial was conducted to increase the participants' familiarity with the procedure. All measurements were carried out with participants standing in stocking feet on 1 leg.
Three to five 6-second measurement repetitions were carried out for each leg. The average value of all successful trials was taken as the value for each leg, a minimum of 2 successful completed trials was required for each leg, and no patient had to be excluded. There were 20-second rest intervals between measurements. During each trial, a 6-second interval was recorded. Patients were asked to lift the nonsupporting leg 2 seconds before the actual measurement started.
A measurement was counted as a failed attempt if participants touched either their hand or nonsupporting leg to the guardrail or the platform or if the supporting leg was moved from its starting position. Failed attempts were noted in the measurement record and excluded from analysis. First, the anterior-posterior (AP, path signal Sy) and medial-lateral (ML, path signal Sx) motions of the platform were measured during “1-leg static standing” without any perturbation of the platform. Then, the platform was moved 10 mm right in the frontal plane locked in place and then released to perturb stance equilibrium. Participants had to counterbalance this sudden but expected disturbance, using compensatory equilibrium reactions. Disturbances to stance were applied first in the AP direction and then in the ML direction (anterior displacement in the sagittal plane), and the amount of platform movement generated by participants' equilibrium responses to counterbalance the disturbance was recorded.
The TG did Hip School activities once per week, supervised by a physiotherapist. In addition to the training within the group, participants performed balance exercises, using balance pads on their own at home several times a week. Participants of the TG were provided with an exercise handout and a training diary. They kept a journal of their training frequency; 3 participants trained twice a week, 11 participants trained 3 to 5 times per week. The entire training program took approximately 20 minutes to complete. The program included 4 exercises: 1-legged stand for 15 to 30 seconds (5 repetitions on each leg), 1-leg balance with movement of the nonsupporting leg (1–3 sets of 15–25 repetitions), hip lift (3 sets of 15–25 repetitions), and 2-leg-tiptoe stand (hold high position for 3 seconds, 1–3 sets of 15–25 repetitions).18 The principle of progression was followed, and the participants increased their exercise volume and intensity according to their individual capabilities. Participants began all exercises from a stable surface, and after 6 weeks they could increase the level of difficulty by using a balance pad (Thera-Band Stability Trainer).
Acquisition and Analysis of Data
The data recorded by the measuring system was processed and saved using JMP 4.0 (SAS Institute Inc, Cary, North Carolina) statistics software. Using the data from the valid measurements, means were calculated for each participant and each measurement situation (without disturbance, frontal disturbance, and lateral disturbance). To test the hypothesis on path signals (Sr, Sx, Sy), a paired t test was used (α = .05). Changes in the proportion of failed attempts were analyzed using the Fischer exact test (α = .05).
One-Leg Static Balance
Both TG and CG had similar numbers of failed attempts during the pretest (17%–18%). After training intervention, the number of failed attempts decreased to 5% for the TG, whereas the CG remained nearly unchanged at 18% (Figure 2). The TG had a lower percentage of failed attempts after the 12-week training intervention (P = .001).
The total path of the platform (Sr) decreased in the TG (mean [SD] pretest measurement of 83  mm; mean [SD] posttest measurement of 59  mm) and increased in the CG (mean [SD] pretest measurement of 74  mm; mean [SD] posttest measurement of 96  mm). After training intervention, the participants in the TG required fewer BRMs to remain standing during 1-leg static balance (P = .036).
One-Leg Balance With Disturbance
On average, 9% of the measurements taken during frontal disturbance and 23% during lateral disturbance were counted as failed attempts (TG and CG, respectively). There was no significant difference in the reaction to frontal disturbances after training intervention (TG: pretest 13%, posttest 7%; CG: pretest 10%, posttest 8%). After training intervention, the TG had a lower percentage of failed attempts during reactions to lateral disturbances (TG: pretest 22%, posttest 13%, P = .042; CG: pretest 27%, posttest 24%, P = .324).
Reactions to frontal disturbances (AP displacement) typically required fewer adjusting motions than did reactions to lateral disturbances (ML displacement) (Mean [SD] AP Sr 106  mm vs mean [SD] ML Sr 144  mm, P < .001; Figure 3). During frontal disturbance, the BRMs increased slightly for the TG (mean [SD] pretest measurement of 97  mm; mean [SD] posttest measurement of 103  mm), and distinctly for the CG (mean [SD] pretest measurement of 99  mm; mean [SD] posttest measurement of 124  mm). Analysis of both directions in the total path showed a distinct difference between the TG and the CG (Figure 4). In the nondisplaced direction Sy (ML motions), participants in the TG showed a reduction of the total path during disturbances to stance after training intervention (mean [SD] pretest measurement of 47.7  mm; mean [SD] posttest measurement of 36.1  mm; P < .001), whereas participants in the CG showed an increased total path (mean [SD] pretest measurement of 36.0  mm; mean [SD] posttest measurement of 47.2  mm; P < .001). After training intervention, participants in the TG could control movements in the nondisplaced direction more effectively than participants in the CG.
During balance recovery from ML disturbances, there was also a minor increase in total path for the TG (mean [SD] pretest measurement of 112  mm; mean [SD] posttest measurement of 117  mm) and a distinct increase for the CG (mean [SD] pretest measurement of 118  mm; mean [SD] posttest measurement of 147  mm). The path in the nondisplaced direction, which is in lateral disruption AP BRMs, decreased in the TG (mean [SD] pretest 49.5 ; mean [SD] posttest, 37.0 ; P < .001). There was practically no change in the path signal Sy for participants in the CG (mean [SD] pretest measurement of 38.0  mm; mean [SD] posttest measurement of 39.6 ; P = .33).
The main purpose of this study was to quantify the effectiveness of a Hip School program with additional sensory-motor training. To quantify the training effects, we used the Posturomed as a measuring device. After training intervention, the participants of the TG had a lower percentage of failed attempts and required fewer BRMs to maintain balance on the Posturomed platform.
Discussion of the Methods
The measurement of just the platform displacement without simultaneous derivation of muscle potentials allows us to draw only limited conclusions as to the neuromuscular regulation mechanism. We can only speculate as to whether changes in the path signal reflect changes in reflex patterns or reaction time for muscle activation. As we recorded only BRMs, we cannot verify changes in reflexes and intermuscular coordination,14 but it seems likely that the recorded changes are due to improvements in these regulation mechanisms.
However, defining and recording failed attempts do allow us to draw conclusions from the path signal with respect to neuromuscular regulation mechanisms. A change in balance capabilities can present itself as a change in the number of failed attempts or in the total path covered by the platform; or, if the total path remains the same, as a change in the relationship of both path directions Sx and Sy. A participant who holds on to something or puts down a foot to keep his or her balance shows a much smaller path signal than a participant who employs equilibrium reactions to maintain balance. In this respect, failed attempts are an important criterion for making predictions about changes in the sense of balance. First, it is of interest whether the participant can successfully complete the test. Second, we would like to measure how far the platform must travel in order for the participant to keep his or her balance. As the study design included no follow-up, we have no information about the duration of the training effect. Further studies should include follow-up measurements to monitor long-term parameters of function in these patients. Another limitation was the inclusion of patients with osteoarthritis and after total hip replacement. In this study, we included equal numbers of participants in TG and CT, because in premeasurements, there was no difference in the signals on the Posturomed platform. In a study design with long-term follow-up, there might be differences in the progression of the osteoarthritis but a stable disease in patients after hip replacement surgery, so these participants should be studied separately.
Discussion of the Results
One-leg static balance
After training on stable and unstable surfaces, participants were more stable and better able to maintain 1-leg stance for the full 6 seconds of measurement and had a distinctly lower proportion of failed attempts during postintervention testing than during preintervention testing. The total path of the platform during measurements without displacement decreased in the TG but increased by a similar amount in the CG. These functional changes are relevant as they indicate to slow down the declining process in functional parameters in patients with osteoarthritis.
Although an increase in the total path in the CG was expected because of the degenerative character of osteoarthritis, it was surprising given the relatively short period of 3 months. Other studies describe a much slower rate of decline in functional parameters.15,23 We found no other factors that could account for these changes. The recorded improvements are highly clinically relevant, because increased values for AP and ML movements are associated with lower scores on clinical measures of balance as foot center-of-pressure displacements.24 Postural instability and high postural sway increase the risk of injurious falls.25,26 Similar settings of short-term balance training were effective in improving dynamic balance in healthy participants.27 The training carried out in this study appears to be effective in reducing balance movements and therefore improving stability during 1-leg static balance.
One-leg standing with disturbance
Because of the anatomy of the foot (3 times longer than wide), reactions to frontal disturbances are easier to cope with. This difference between lateral disturbance and frontal disturbance can be seen on the Posturomed not only in the number of failed attempts (23% vs 9%) but also in the total path of the platform (144 mm vs 106 mm).
Current literature cites 3 stereotypical patterns of response to A-P disturbances: ankle, hip, or stepping strategy.28 While ankle and hip strategies are equilibrium responses, stepping or holding on to something is a protective response used when equilibrium responses are not sufficient. In this study, stepping or reaching for support was counted as a failed attempt. The lower number of failed attempts during the posttraining measurement suggests that participants were able to use ankle and hip strategies more effectively to respond to disturbances following sensory-motor training.
From a biomechanical point of view, the disturbance is comparable to the supporting leg slipping. Perturbation to the base of support is one of the most common reasons for falls.29 The disturbance impulse on the Posturomed examines reactions of a participant in a situation similar to slipping or tripping but without a high risk for injurious falls. Insufficient resources for dual tasking could be related to the high risk of injurious falls in the aging adults. Sensory-motor training can improve potential abilities for reacting to such situations.30 Participants in the TG successfully coped with more disturbances and improved their reactions to sudden disturbances.
Against all expectations, the total path of the platform was not reduced in the TG but rather increased slightly during frontal and lateral disturbances. It is possible that displacements that caused participants to lose their balance during the initial measurements (pretest) were successfully overcome at the cost of a higher path signal. It is well known that sensory-motor training shortens the latency period for reflex activity to disturbances.14,31 A faster reflex activity would be another reason for increased neuronal activation of the stabilizing muscles, which leads to an increase in the path signal. This could explain why the BRMs increased, although participants were able to react more effectively to disturbances after training (fewer failed attempts) during the measurements.
The question remains, however, as to why the total path of the CG increased so distinctly. An increase in total path was expected on the basis of the degenerative character of hip osteoarthritis, but the development over such a short period of 3 months was surprising. When can an increase in total path be interpreted as an improvement, and when does it show a deterioration in performance? The improvement in the TG showed that the y-direction is a good indication for the success of the sensory-motor training. When the platform moves in the y-direction, it is only from the participants' BRMs, since test displacement of the platform was applied only in the x-direction. The fewer BRMs needed to maintain balance, the more effective the postural responses of the participant. This hypothesis is supported by the Sy values demonstrated in both groups. The inactive CG had to employ more movement in this direction during the postmeasurement in order to compensate for the disturbance and keep their balance, whereas participants after training intervention had much less motion in the Sy direction. Aging adults with a history of falls show greater amounts of sway in the AP direction.24 During lateral disturbances, the AP path signal decreased after training intervention. It is possible that this shows improved reactions to disturbances that are associated with a reduction of the risk of falling.
Balance training can considerably improve stability during 1-leg static balance. More stability during 1-leg static balance reduces the risk of falling. Anyone who is stable while standing on one leg might be less vulnerable to disturbances through slipping or stumbling. The Hip School training programs for patients with osteoarthritis should include such exercises that improve balance and standing on one leg. The sensory-motor training program we carried out improved participants' stability while standing.
It is possible to quantify a training effect on balance and joint stabilization by using Posturomed. Examining patients at risk of incurring injurious falls during training therapy to prevent falls using the Posturomed as a measuring device would be an interesting basis for a future study. It might be possible to draw conclusions on the risk of falling from changes in the stability of 1-legged standing and reactions to disturbances while standing.
A comparison of the data collected in this study to data from a group of healthy participants of similar age must still be done. Perhaps it would then be possible to examine changes in the total path to identify whether deficits in balance coordination contribute to an increased risk of falling in the aging adults.
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