BACKGROUND AND PURPOSE
Intensive mobility training (IMT) is an intensive therapeutic approach for neurological functional recovery employing repetitive, task-specific training in a mass practice schedule. The novelty of IMT is the intensive nature of the intervention. Participants engage in several hours of therapy, over multiple consecutive days, with limited rest periods. This approach differs greatly from traditional outpatient physical therapy in which the therapy is provided fewer days per week, and the daily dosage per session is less.1,2 Owing to the departure from a typical dose and the associated additional burden in terms of cost, participant obligation, and personnel requirements, it is important to determine whether the IMT approach is feasible, and whether there are benefits of this type of intervention.
IMT methodology borrows concepts of massed practice and intensive scheduling from other therapies that have been successful in employing these motor control principles, such as constraint-induced movement therapy (CIMT).3 Although many effective rehabilitation studies have used longer training periods, when intervention time is calculated in terms of hours, the majority offer only between 12 and 30 hours of therapeutic intervention.4–9 Therefore, having the participants perform a shorter, more intense 10-day intervention does not significantly alter the amount of time (in hours) that the participant engages in rehabilitation. Thus, IMT provides similar dosage (30 hours) in a shorter, more intense intervention period. This is consistent with the principle of massed practice, wherein a therapeutic intervention is offered in a concentrated, and often condensed, manner, with shorter rest breaks between sessions.10
To best promote motor learning, the participant must be active and be provided with opportunities for repetitious task-specific practice. For example, an early study of weight bearing on the paretic leg in individuals with stroke demonstrated improvements in standing balance after subjects were trained to shift weight onto the paretic limb; however, improvements in standing balance did not transfer to improvements in walking.11 Therefore, if improved walking function is the goal of the treatment, then the individual must practice walking. Another example is when training balance for walking, the use of a walker significantly modifies the balance requirements needed for walking. As balance is a corequisite of the task of walking,12 retraining balance for walking may be more effective if the training occurs without upper-extremity support, thereby making the balance training more specific to the task of walking upright.13
As the relearning of motor tasks is dependent on the repetitive practice of specific tasks,14–17 IMT employs various activities to address relearning. With body weight–supported treadmill-based locomotor training (BWSTT),18–22 the goal is to provide a safe, task-specific environment to improve the task of walking. However, specificity of practice during BWSTT concentrates primarily on the repetitive practice of linear gait and focuses less on balance, transitional movements, full weight bearing, and nonlinear gait, all of which are essential components of walking mobility. To address these additional components of walking mobility, principles of intensive and task-specific training in a massed practice schedule are included in IMT, with a focus on addressing deficits in balance and mobility.
Although IMT was developed with the intention of providing a comprehensive therapeutic approach to address gait, balance, and mobility deficits in individuals with chronic neurological conditions, the intensive nature of the therapy could potentially limit the feasibility of implementing such an intervention. Therefore, the purpose of this case series was to examine (1) whether the intensive nature of IMT was a feasible rehabilitation strategy to be used with 4 individuals with diverse chronic neurological conditions; (2) whether improvements could be attained specifically in the areas of gait, balance, and mobility; and (3) whether improvements could be maintained over time once the intervention has concluded.
This study was approved by the University of South Carolina, Institutional Review Board. Prior to participation, all participants reviewed and signed an informed consent.
Participants with incomplete spinal cord injury (ISCI), Parkinson's disease (PD), stroke (CVA), and cerebral hemispherectomy (HEMI) were selected for participation in this feasibility study because of characteristic deficits in gait, balance, mobility, and the chronic nature of each of these neurological conditions. Participants were recruited from the community, through internet postings, and via professional contacts. All participants, with the exception of the participant with PD, were participants in larger, diagnosis-specific trials for IMT, but were selected for the case series as they met the following inclusion criteria: the ability to ambulate 10 ft (approximately 3 m) with or without an assistive device with only minimal assistance, and the ability to stand with an assistive device for 5 minutes. Participants were excluded if they had been diagnosed with a secondary neurological condition, or is they were unable to communicate location or presence of pain. If selected from a larger trial, they were the first participants in those trials to meet the above criteria. The neurological diagnosis and functional status of each participant are illustrated in Table 1.
The IMT was scheduled to be performed 3 hours per day for 10 consecutive weekdays for a total of 30 hours. During each 3-hour session, the initial hour was dedicated to BWSTT (StepGain GF body weight support system, Robomedica, Robomedica Inc, Mission Viejo, CA.), with the remaining 2 hours of therapy focused on therapeutic interventions intended to improve balance (1 hour) and activities designed to develop coordination, strength, and range of motion within task-specific contexts of gait, balance, and mobility (1 hour). For example, if a participant was having difficulty with walking due to the inability to eccentrically control knee flexion, then eccentric quadriceps strengthening activities would be incorporated with emphasis on closed kinetic chain functional activities.
The goal was to limit rest time to approximately 30 minutes per 3-hour session. In an effort to standardize the amount of therapy, the 30 minutes of rest was divided evenly between each hour of therapy, resulting in a target goal of 50 minutes of gait, 50 minutes of balance, and 50 minutes of strength, range of motion, and coordination activities, for a total goal of 150 minutes spent in therapeutic activities per daily treatment session.
The BWSTT protocol was adapted from that used in a previously published case series of individuals with spinal cord injury.23 The handrails were removed from the treadmill so that the participants were not able to use them for assistance. Body weight support was used for all participants, and the amount of support was determined by the therapist on the basis of observed knee biomechanics (eg, buckling, hyperextension), posture, and/or participant comfort. A consistent level of body weight support was not used across all participants, but rather was adjusted to the unique requirements of each participant. The primary goal during treadmill-based locomotor training was to approach normal temporal parameters of gait (ie, increasing walking speed on the treadmill) and to achieve near-normal joint kinematics (as assessed by observation) through manual assistance applied primarily at the hips, knees, and ankles. Once the optimal gait was achieved at the fastest pace possible for the participant, the BWSTT was advanced by decreasing the amount of body weight support, and reducing manual facilitation efforts. This sequence of advancement was followed by progressively increasing treadmill speeds over the course of training as walking function improved.
Following 1 hour of BWSTT, the remaining 2 hours of the intervention were dedicated to balance (1 hour) and to strength, range of motion, and coordination activities (1 hour). Only the time of the intervention was standardized; the specific therapeutic activities were individualized according to the participant's level of function, performance, fatigue, frustration, and interest (similar to the approach with CIMT). The tasks practiced by each individual varied, but included tasks such as overground gait training with and without an assistive device, sit-to-stand, stair climbing, tandem or unilateral balance activities on various surfaces, targeted functional stretching activities, and coordination tasks such as targeting an object with the lower extremities (see Video, Supplemental Digital Content 1, https://links.lww.com/JNPT/A13, for examples of tasks). As participants improved in performance, tasks were progressed with increasing difficulty and complexity by altering the time spent on a specific task, altering the height, distance, or speed at which the task was performed (such as moving the target farther from their base of support to further challenge balance), changing the support surface on which the task was performed, or reducing the amount of physical assistance needed to complete the task. The trainer used clinical judgment to decide when to progress the difficulty of the activity. To maintain the participant's attention on the task, the goal for each task was to challenge the participant sufficiently to have a risk of failure. For example, if the participant was completing a task to address balance deficits, such as standing on a foam pad, and the participant was not experiencing intermittent loss of balance, then either the support surface would be adjusted to a more compliant and challenging surface or an additional task such as a ball toss would be incorporated to increase the difficulty of the task. Participants received intermittent verbal feedback to encourage more normal movement and mechanics and to acknowledge improvements in task performance. The intervention was provided by physical therapists (PT) and senior level doctor of physical therapy (DPT) students; different interventionists were used for different participants, but all were supervised by the same PT. The intervention was similar to that of our prior study, wherein specific examples of the intervention are described;24 the current study added BWSTT as part of the intervention.
Pain and fatigue scores, as well as the amount of rest/activity time needed for each participant were used to assess participant tolerance of the activities and the feasibility of the intervention. Feasibility was also determined by whether the participant was able to reach 80% of activity (144 minutes) during the 180 minutes of therapy. In addition, to assess the benefits of IMT, standardized clinical outcome measures were selected to evaluate gait, balance, and mobility. Because of the varying diagnoses, outcome measures to address the constructs of gait, balance, and mobility were selected that were well represented in the literature across various neurological conditions. The measures included spatial and temporal parameters of gait (velocity, step symmetry, and step length) based on the average of 3 trials at self-selected gait speed captured by a computerized gait analysis system (GAITRite, CIR Systems Inc, Havertown, PA25–28 Berg Balance Scale (BBS),29–32 Dynamic Gait Index (DGI),33–35 Timed Up and Go test (TUG; average of 3 trials),36–38 and the 6-Minute Walk test (6MWT).39–41 Assessments were performed in the Rehabilitation Lab at the University of South Carolina by a PT or trained senior-level DPT student. To improve reliability, the same evaluator performed the pre- and posttest assessment for each participant. The evaluators for the standardized assessments were not interventionists for the study. The timing of the evaluation sessions and the training sessions were kept consistent for all participants, this was most important for the Participant with PD for standardization relative to his medication cycle.
Data Collection and Analysis
Data used to determine the feasibility of the intervention was collected daily throughout the course of the intervention. Self-report information related to pain and fatigue were collected before and after each session, using the traditional 0 to 10 rating scale, where 0 indicates no symptoms and 10 indicates extreme symptoms. In addition, the average minutes spent in activity and at rest for each day of therapy were documented and tabulated to assess participant tolerance for the therapy.
Gait, balance, and mobility outcome assessments were collected at 3 time points: (1) preintervention, (2) postintervention (1 to 2 days following completion of the intervention), and (3) follow-up (1 to 6 months following the intervention). Follow-up time periods varied between participants due to scheduling conflicts and the availability of the participant. Percent change scores ([(post − pre)/pre] × 100) were calculated between pre- and posttests to indicate changes following the intervention; percent change scores between pretest and follow-up were used to assess the maintenance of improvements over time.
Feasibility data suggests that all participants were able to tolerate the therapy without substantial change in pain each day (see Table 2). Three of the 4 participants did not experience any increase in average daily pain from pre- to posttherapy, whereas 1 participant (with HEMI) reporting an average increase of 3 points on the 10-point scale. The average daily change in fatigue score had a wide range of variability among participants with CVA, ISCI, PD, and HEMI, reporting an average increase in daily fatigue of 0, 1, 3, and 7, respectively.
Individual participants' average time of physical activity ranged from 134 to 157 minutes per day. Across the 4 participants, the average proportion of available activity time spent in activity was 80% (144 minutes of the 180 possible minutes), with 2 participants exceeding the 80% goal and 2 participants (ISCI and PD) falling short of this goal by an average of 10 and 9 minutes per day, respectively. The average rest time needed per day varied from 16 to 45 minutes.
Functional improvements in gait, balance, and mobility measures from pre- to posttest and from pretest to follow-up test are shown in Table 3.
All participants had an improvement on at least 2 of the 3 spatiotemporal gait parameters (velocity, step symmetry, and step length) following the intervention. These improvements remained above pretest values at the follow-up test. With 2 exceptions, posttest performance in all participants demonstrated improvement compared with pretest values in gait velocity (ranging from a 2% to 19% increase), step symmetry (ranging from a −5% to −77% improvement, indicative of more symmetrical steps), and step length (ranging from a 2% to 13% increase). The exceptions were gait velocity in the participant with ISCI, and step symmetry in the participant with PD (who had normal symmetry at pretest). Similarly, with 2 exceptions, follow-up performance in all participants was improved compared with pretest values, indicating that gains were maintained. The exceptions were step symmetry in the participant with PD, and gait velocity and step length for the participant with CVA.
Both balance measures revealed improvement across all participants following the intervention. With the exception of the follow-up BBS score for the participant with ISCI, all participants maintained improvements above pretest values at the follow-up period.
All participants demonstrated improvement in the 6MWT, with percent change scores ranging from 4% to 17% following the intervention (data not collected for participant with PD). Maintenance of change at the follow-up test was observed for both the participants with ISCI and HEMI; however, improvements in the 6MWT were not maintained over time for the participant with CVA. All participants, except for the participant with CVA, displayed improved TUG times at the follow-up test; however, only the participant with PD displayed improved time in the TUG at posttest (−27%).
The unique feature of IMT is the intensive nature of the intervention, in which participants engaged in 3 hours of mobility therapy per day, for 10 consecutive days with limited rest periods. This approach differs from what has been reported in the literature for the traditional distribution of therapy,1 which is delivered across weeks, and wherein the within-session dosage is lower and often of less intensity. Because of this intensity and concerns over participants' ability to tolerate these demands, this case series sought to examine the feasibility of IMT. Our findings suggest that this intensive, task-specific intervention is a feasible and viable therapeutic option for various neurologic diagnoses and that, on average, participants are able to tolerate 144 minutes of activity during a 180-minute session.
Factors such as pain, fatigue, required rest, and time spent in activity were used as indices of the participants' ability to tolerate this intensive intervention. The results indicated that changes in pain and fatigue from pre- to posttherapy were minimal for all participants except for the participant with HEMI. Although this participant had an average increase of daily fatigue of 7 points by the end of a training session, he had a concurrent average rest time of only 16 minutes during the 3-hour training period. This participant had no lasting effects of fatigue, as he returned on the following day with a fatigue score back to “zero.” Rest time was primarily based on participant's request for a break, diminished ability to perform tasks due to observed fatigue, or safety issues (e.g., marked rise in blood pressure). The limited reports of fatigue indicates that these 4 participants were able to tolerate the higher dosage of therapy associated with IMT.
The average time spent in therapeutic activities ranged from 134 to 157 minutes, demonstrating that these participants were able to tolerate activity levels well above what is reported in the literature for typical physical therapy session.1 When reviewing the daily notes for the participants with ISCI and PD, the increased rest time occurred during the 1 hour of BWSTT. This may be more aptly classified as “nonactivity time” rather then rest time because the breaks were often for harness readjustment for comfort. Clinically speaking, these unplanned events will arise, and the primary question is, are we able to accomplish 80% of activity during a 3-hour window of time to reach goals of massed practice and repetition of task practice? In addition to the intensity being greater than what is typical, the scheduling format used in IMT may offer increased convenience for patients who must travel long distances or who need to take time off from work or school to participate in therapy.
Although the main goal of this study was to investigate feasibility of the intensive intervention, there were positive changes that occurred in at least 2 of the 3 spatial and temporal gait parameters assessed (velocity, symmetry, and/or step length) after just 10 days of IMT, and some of these improvements were maintained over time. In addition there were positive changes in both BBSS and DGI from pre- to posttest. Unfortunately, there is limited information regarding minimal detectable change (MDC) scores across diagnoses used in this case series. Although there are some diagnosis-specific MDCs,42 that may be applied to individual patients, a general an improvement of 0.05 m/s in walking speed43 is considered a change beyond error, and 0.1 m/s44 is associated with increased survival; 2 of the 4 participants exceeded these scores from pre- to posttest. The participant with HEMI exceeded the 54 m defined as MDC for the 6MWT,41 and 2 of the 4 participants met or exceeded the 5-point MDC for the Berg Balance Score.31 Although there is no MDC established for the DGI, all participants started at 19 or less points on the DGI which has been reported as a cutoff for falls risk on this assessment; following the intervention, all participants surpassed 19 points.45
Overall, the improvements in gait, balance, and mobility outcome measures indicate that all participants, despite differences in chronic neurological conditions, were able to make modest gains in each of the target areas of gait, balance, and mobility following 10 days of intensive therapy. Although the magnitude of these changes were relatively small, the possibility of change exists for these individuals with chronic disability (3 of the 4 participants were greater than 10 years postincident). The possible physical benefits of this intervention may hold promise; however, as a case series the results cannot be directly attributed to the intervention. A randomized control trial of this intervention is warranted to assess the efficacy of IMT for improving gait, balance, and mobility. In addition, examining the dosage of the intervention, for instance, examining whether a longer daily session or more number of days of intervention could provide more opportunity for improvements, may provide further insight.
Differing diagnoses and pathophysiologies between participants may be viewed as a limitation of this study; however, the purpose of this case series was to assess the feasibility and possible physical benefits of intensive therapy for individuals with various diagnoses that have similar functional deficits. In addition, the fact that the participants with PD and CVA were both in their 40s when acquiring the diagnoses may not reflect the “typical” age of patients with these disorders. Another limitation of this study was the varying time to complete a follow-up testing session. The participants involved in this study were not all local residents and therefore were scheduled according to travel availability. In addition, although each participant's therapy was not standardized by the traditional definition, the amount of time spent in each target area was similar. Another limitation is that the researchers failed to collect data for the 6MWT for the participant with PD, this information would be helpful for a full picture of the effect of the intervention. Furthermore, the findings could be influenced by experimenter bias because the interventionist collected daily self-report of fatigue and pain. Finally, the reported improvements may not represent actual, meaningful change as this was a case series. Despite the limitations, the findings of this case series suggest that IMT is feasible for these participants and further investigation is warranted to determine the overall effects of the intervention, the optimal schedule intensity, and duration to support improved functional performance through repetitive practice.
The outcomes of this feasibility study indicate that individuals representing different chronic neurological conditions (ISCI, PD, CVA, and HEMI) are able to tolerate IMT intervention 3 hours per day for 10 days. Although the clinical presentation and pathophysiology differed greatly across participants, all had deficits in gait, balance, and mobility. Improvements in some aspects of mobility were observed in all participants, despite the fact that some of these individuals had neurological insult to the CNS more than 10 years prior to participation.
1. Lang CE, MacDonald JR, Gnip C. Counting repetitions: an observational study of outpatient therapy for people with hemiparesis post-stroke. J Neurol Phys Ther. 2007;31(1):3–10.
2. Kwakkel G. Impact of intensity of practice after stroke: issues for consideration. Disabil Rehabil. 2006;28(13–14):823–830.
3. Wolf SL, Winstein CJ, Miller JP, et al. Effect of constraint-induced movement therapy on upper extremity function 3 to 9 months after stroke: the EXCITE randomized clinical trial. JAMA. 2006;296(17):2095–2104.
4. Bastille JV, Gill-Body KM. A yoga-based exercise program for people with chronic poststroke hemiparesis. Phys Ther. 2004;84(1):33–48.
5. Mount J, Bolton M, Cesari M, Guzzardo K, Tarsi J. Group balance skills class for people with chronic stroke: a case series. J Neurol Phys Ther. 2005;29(1):24–33.
6. Pohl M, Mehrholz J, Ritschel C, Ruckriem S. Speed-dependent treadmill training in ambulatory hemiparetic stroke patients: a randomized controlled trial. Stroke. 2002;33(2):553–558.
7. Werner C, von Frankenberg S, Treig T, Konrad M, Hesse S. Treadmill training with partial body weight support and an electromechanical gait trainer for restoration of gait in subacute stroke patients: a randomized crossover study. Stroke. 2002;33(12):2895–2901.
8. Hesse S, Bertelt C, Jahnke MT, et al. Treadmill training with partial body weight support compared with physiotherapy in nonambulatory hemiparetic patients. Stroke. 1995;26(6):976–981.
9. Plummer P, Behrman AL, Duncan PW, et al. Effects of stroke severity and training duration on locomotor recovery after stroke: a pilot study. Neurorehabil Neural Repair. 2007;21:137–151.
10. Schmidt RA, Lee TD. Motor Control and Learning: A Behavioral Emphasis. 4th ed. Champaign, IL: Human Kinetics; 2005:285–322.
11. Dickstein R, Nissan M, Pillar T, Scheer D. Foot-ground pressure pattern of standing hemiplegic patients. Major characteristics and patterns of improvement. Phys Ther. 1984;64(1):19–23.
12. Patla AE, Prentice SD, Robinson C, Neufeld J. Visual control of locomotion: strategies for changing direction and for going over obstacles. J Exp Psychol Hum Percept Perform. 1991;17(3):603–634.
13. Behrman AL, Bowden MG, Nair PM. Neuroplasticity after spinal cord injury and training: an emerging paradigm shift in rehabilitation and walking recovery. Phys Ther. 2006;86(10):1406–1425.
14. Taub E, Crago J. Overcoming learned nonuse: a new behavioral approach to physical medicine. In:Kikuchi TSH, Saito I, Tsuboi K, eds. Biobehavioral Self-Regulation: Eastern and Western Perspectives. Tokyo: Springer Verlag; 1995:2–9.
15. Mark VW, Taub E. Constraint-induced movement therapy for chronic stroke hemiparesis and other disabilities. Restor Neurol Neurosci. 2004;22(3–5):317–336.
16. Behrman AL, Harkema SJ. Locomotor training after human spinal cord injury: a series of case studies. Phys Ther. 2000;80(7):688–700.
17. Dietz V, Harkema SJ. Locomotor activity in spinal cord-injured persons. J Appl Physiol. 2004;96(5):1954–1960.
18. Hesse S. Treadmill training with partial body weight support after stroke: a review. Neuro Rehabil. 2008;23(1):55–65.
19. Lam T, Eng J, Wolfe D. A systematic review of the efficacy of gait rehabilitation strategies for spinal cord injury. Top Spinal Cord Inj Rehabil. 2007;13(1):32–57.
20. Miyai I, Fujimoto Y, Yamamoto H, Ueda Y, Saito T, Nozaki S, Kang J. Long-term effect of body weight-supported treadmill training in Parkinson's disease: a randomized controlled trial. Arch Phys Med Rehabil. 2002;83(10):1370–1373.
21. Herman T, Giladi N, Gruendlinger L, Hausdorff JM. Six weeks of intensive treadmill training improves gait and quality of life in patients with Parkinson's disease: a pilot study. Arch Phys Med Rehabil. 2007;88(9):1154–1158.
22. Bode S, Mathern GW, Bookheimer S, Dobkin B. Locomotor training remodels FMRI sensorimotor cortical activations in children after cerebral hemispherectomy. Neurorehabil Neural Repair. 2007;21(6):497–508.
23. Behrman AL, Lawless-Dixon AR, Davis SB, et al. Locomotor training progression and outcomes after incomplete spinal cord injury. Phys Ther. 2005;85(12):1356–1371.
24. Fritz SL, Pittman AL, Robinson AC, Orton SC, Rivers ED. An intense intervention for improving gait, balance, and mobility for individuals with chronic stroke: a pilot study. J Neurol Phys Ther. 2007;31(2):71–76.
25. Bilney B, Morris M, Webster K. Concurrent related validity of the GAITRite walkway system for quantification of the spatial and temporal parameters of gait. Gait Posture. 2003;17(1):68–74.
26. Nelson AJ, Zwick D, Brody S, et al. The validity of the GaitRite and the Functional Ambulation Performance scoring system in the analysis of Parkinson gait. Neuro Rehabil. 2002;17(3):255–262.
27. van Uden CJ, Besser MP. Test-retest reliability of temporal and spatial gait characteristics measured with an instrumented walkway system (GAITRite). BMC Musculoskelet Disord. 2004;5(1):13.
28. Salbach NM, Mayo NE, Higgins J, Ahmed S, Finch LE, Richards CL. Responsiveness and predictability of gait speed and other disability measures in acute stroke. Arch Phys Med Rehabil. 2001;82(9):1204–1212.
29. Berg K, Wood-Dauphine S, Williams J. The Berg Balance Scale: reliability assessment with elderly residents and patients with an acute stroke. Scand J Rehabil Med. 1995;27:36–37.
30. Blum L, Korner-Bitensky N. Usefulness of the Berg Balance Scale in stroke rehabilitation: a systematic review. Phys Ther. 2008;88(5):559–566.
31. Steffen T, Seney M. Test-retest reliability and minimal detectable change on balance and ambulation tests, the 36-item short-form health survey, and the unified Parkinson disease rating scale in people with parkinsonism. Phys Ther. 2008;88(6):733–746.
32. Stevenson TJ. Detecting change in patients with stroke using the Berg Balance Scale. Aust J Physiother. 2001;47(1):29–38.
33. Chiu YP, Fritz SL, Light KE, Velozo CA. Use of item response analysis to investigate measurement properties and clinical validity of data for the dynamic gait index. Phys Ther. 2006;86(6):778–787.
34. Marchetti GF, Whitney SL, Blatt PJ, Morris LO, Vance JM. Temporal and spatial characteristics of gait during performance of the Dynamic Gait Index in people with and people without balance or vestibular disorders. Phys Ther. 2008;88(5):640–651.
35. Jonsdottir J, Cattaneo D. Reliability and validity of the dynamic gait index in persons with chronic stroke. Arch Phys Med Rehabil. 2007;88(11):1410–1415.
36. Ng SS, Hui-Chan CW. The timed up & go test: its reliability and association with lower-limb impairments and locomotor capacities in people with chronic stroke. Arch Phys Med Rehabil. 2005;86(8):1641–1647.
37. Faria CD, Teixeira-Salmela LF, Nadeau S. Effects of the direction of turning on the timed up & go test with stroke subjects. Top Stroke Rehabil. 2009;16(3):196–206.
38. Morris S, Morris ME, Iansek R. Reliability of measurements obtained with the Timed “Up & Go” test in people with Parkinson disease. Phys Ther. 2001;81(2):810–818.
39. Steffen TM, Hacker TA, Mollinger L. Age- and gender-related test performance in community-dwelling elderly people: Six-Minute Walk Test, Berg Balance Scale, Timed Up & Go Test, and gait speeds. Phys Ther. 2002;82(2):128–137.
40. Falvo MJ, Earhart GM. Six-minute walk distance in persons with Parkinson disease: a hierarchical regression model. Arch Phys Med Rehabil. 2009;90(6):1004–8.
41. Fulk GD, Echternach JL, Nof L, O'Sullivan S. Clinometric properties of the six-minute walk test in individuals undergoing rehabilitation poststroke. Physiother Theory Pract. 2008;24(3):195–204.
42. Fulk GD, Echternach JL. Test-retest reliability and minimal detectable change of gait speed in individuals undergoing rehabilitation after stroke. J Neurol Phys Ther. 2008;32(1):8–13.
43. Perera S, Mody SH, Woodman RC, Studenski SA. Meaningful change and responsiveness in common physical performance measures in older adults. J Am Geriatr Soc. 2006;54(5):743–749.
44. Hardy SE, Perera S, Roumani YF, Chandler JM, Studenski SA. Improvement in usual gait speed predicts better survival in older adults. J Am Geriatr Soc. 2007;55(11):1727–1734.
45. Shumway-Cook A, Baldwin M, Polissar NL, Gruber W. Predicting the probability for falls in community-dwelling older adults. Phys Ther. 1997;77(8):812–819.