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00005768-201404000-0000100005768_2014_46_645_nadeau_performance_4article< 152_0_24_5 >Medicine & Science in Sports & Exercise© 2014 American College of Sports MedicineVolume 46(4)April 2014p 645–655Effects of 24 wk of Treadmill Training on Gait Performance in Parkinson’s Disease[CLINICAL SCIENCES]Nadeau, Alexandra1,2; Pourcher, Emmanuelle3,4; Corbeil, Philippe1,21Department of Kinesiology, Laval University, Quebec City, QC, CANADA; 2Centre d’excellence sur le vieillissement de Québec, Centre de recherche du CHU de Québec, Quebec City, QC, CANADA; 3Quebec Memory and Motor Skills Disorders Research Center, Clinique Sainte-Anne, Quebec City, QC, CANADA; and 4Department of medicine, Laval University, Quebec City, QC, CANADAAddress for correspondence: Philippe Corbeil, 2300 Rue de la Terrasse, Université Laval, Quebec City, QC, Canada, G1V 0A6; E-mail: philippe.corbeil@kin.ulaval.ca .Submitted for publication February 2013.Accepted for publication August 2013.ABSTRACTPurpose: Recent studies suggest that walking on a treadmill improves gait, mobility, and quality of life of patients with Parkinson’s disease (PD). Still, there is a need for larger-scale randomized controlled studies that demonstrate the advantages of treadmill training (TT) with control groups that receive similar amounts of attention. Moreover, to date, no study has combined speed and incline as parameters of progression. The aim of the study was to evaluate the effects of 24 wk of TT, with and without the use of incline, on gait, mobility and quality of life in patients with PD.Methods: The sample comprised 34 patients with PD, at the Hoehn and Yahr stage 1.5 or 2. Participants were randomized to speed TT, mixed TT, and control groups. The intervention consisted of 72 one-hour exercise sessions for 24 wk. The main outcome measures are the Movement Disorder Society–Unified Parkinson’s Disease Rating Scale, the 39-item Parkinson’s Disease Questionnaire, spatiotemporal parameters of gait and 6-min walking distance. The measures were taken at baseline, mid-term and after 6 months.Results: Both TT groups improved in terms of speed, cadence, and stride length during self-selected walking conditions at the study end point. Both groups also showed improvements in distance traveled. Only the Mixed TT group improved their quality of life. The Control group showed no progress.Conclusions: Participants in this study showed significant improvements in walking speed and walking endurance after 6 months of TT. Improvements were observed after 3 months of intensive TT and persisted at 6 months. It appears that individuals with poorer baseline performance may benefit most from TT.Parkinson’s disease (PD) is the second most common neurodegenerative disease (10). This progressive neurological disorder, caused mainly but not solely by a degeneration of the dopaminergic system, results in many physical symptoms, such as resting tremor, rigidity, and slowed movements. The greatest functional disabilities are impaired gait and balance disturbances. Most patients cease to participate in physical activities (1). The detrimental effects of inactivity include decreased functional independence and well-being as well as medical complications such as cardiovascular disease (12). Physical activity is recommended to prevent the complications associated with a sedentary lifestyle, as it often improves PD patients’ symptomatology, in particular, walking and gait-related functions (39). Physical exercise may reinforce neuronal circuits that help gait pacing (24) and may actually promote a neuroprotective effect (1,2,32,49). To optimize the effect of exercise, it is generally recommended that an exercise program include variations in training technique such as specificity, intensity, and volume (41). For instance, to promote the improvement of gait parameters, it is recommended that patients use an exercise specific to walking such as treadmill training (TT) (41). Several studies performed with PD patients have reported that TT, with or without body weight support, is safe (36) and can lead to a more stable walking pattern, improving both walking speed and distance walked (14,24,28,36,38,45,54).Most TT programs for PD patients last less than 3 months, and progressive levels of exercise intensity are mainly controlled through speed adjustment (36). Gait improvements are mostly observed during the first 12 wk (2,36,50). The reason for these limited improvements may be inadequate muscular endurance and strength (27). Very few studies have reported the use of treadmill incline during training in PD. Adjusting the incline creates an uphill climbing effect, making the training more challenging (51). Average and peak electromyographic activities have been found to increase significantly at inclines of 12% and 24% grade for the vastus medialis oblique (125% and 154%), vastus lateralis (109% and 139%), and biceps femoris (53% and 46%); this encourages the use of treadmill incline in rehabilitation (31). Treadmill inclination affects joint kinematics only slightly (30,56,57). It has also been shown that 2.5% increments in treadmill grade effectively increase net oxygen uptake during walks (55). Hence, walking on an incline increases the activity levels in some of the lower extremity muscles and may be an excellent way to improve muscle strength and increase endurance.The aim of this double-blind, randomized, controlled trial was to compare the effect of 24 wk of a speed and incline TT program with a speed only TT program or no TT with light exercise on gait and quality of life. Walking parameters and quality of life were assessed before participation in the training program, at the study midpoint and after 6 months of training. We hypothesized that only the TT groups would exhibit improvements in gait and quality of life after 3 months and that the speed and incline TT group would be the only group to show improvements at 6 months.METHODSStudy populationSubjects were recruited from the local community. A PD support group and word of mouth helped to promote the project. Forty-five patients with idiopathic PD enrolled in the study (Fig. 1). Participants were stage 2 or less on the Hoehn and Yahr scale and between 40 and 80 yr old. They did not have musculoskeletal impairments or excessive pain in any joints that could limit participation in an exercise program, nor did they exhibit signs of dementia (score greater than 24 on the Mini-Mental State Examination). Participation in the project was made available to people living up to 45 min away from the university. Individuals with a major health problem (cancer, heart/lung problem, etc.) were excluded. A neurologist ensured that participants met the inclusion criteria before their acceptance for the project. Informed consent was obtained from each participant in this study. This study was approved by the local institution’s research ethics committee.FIGURE 1. Diagram illustrating recruitment of patients with PD. E1: TT with increase of speed; E2: TT with increase of speed and level, alternately.Study designA 24-wk, double-blind, randomized, controlled trial was conducted between 1 March and 24 December 2011. Participants were randomly assigned to one of the three groups (mixed TT, speed TT, or control [light exercise only]) using a computer-generated sequence. The allocation sequence was concealed from the project director who assigned participants to groups. Participants and research assistants performing the assessments were blind to group assignment; however, exercise trainers were not. The trial was registered at ClinicalTrials.gov (Identifier: NCT01701128). Participants assigned to the TT groups had a choice of two 3-d schedules.InterventionAll three groups had the same recommended training volume. The TT groups had three 1-h supervised sessions per week for 24 wk, for a total of 72 one-hour sessions. The control group had two 1-h supervised sessions per week for the 24 wk and were recommended to perform one 1-h session per week at home during the study period. Participants were asked not to initiate any other structured exercise program during the intervention period. All participants completed a diary recording their daily physical activities for the 24 wk.Treadmill training protocolEach treadmill was equipped with bars and a system shutdown. Subjects were familiarized with the security procedure before the start of the program. There was no harness system. The TT programs were individually tailored to each participant and aimed at improving walking speed. For both TT groups, heart rate and blood pressure were recorded before, midway through, and after the 1-h training session. These measures were used to confirm exercise tolerance, namely, that heart rate did not exceed 75% of the estimated maximum heart rate for the participant (220 − age, [35]) and that blood pressure did not exceed 200/100 mm Hg. In addition, the modified Borg scale (8) was used to determine the perceived effort felt midway through the exercise session. Initial treadmill speed was determined using each participant’s mean preferential walking speed, as obtained during baseline measurements before training. The speed adjustment protocol was derived from a previous study (24). During the first week, the treadmill speed was adjusted to 80% of the participant’s preferential walking speed. In the second and third weeks, all participants were encouraged to reach 90% and 100%, respectively, of their preferential walking speed. When each participant reached 100% of his or her preferential walking speed, treadmill speed was increased by 0.2 km·h−1 at the next session.For the speed TT group, treadmill speed was increased at the next session by 0.2 km·h−1 when participants perceived their physical effort as moderate or less (≤4 on the modified Borg scale) and when their heart rate was less than 75% of the maximum midway through their previous training session. For the mixed TT group, treadmill incline was increased at the next session by 1% when the same progression criteria based on the modified Borg scale and heart rate were met. After that, treadmill speed (+0.2 km·h−1) and treadmill incline (+1%) were increased alternately when the progression criteria were met. This was done in a consistent manner for all participants. Each participant engaged in 5-min warm-up and cool-down periods. Participants were encouraged to walk (without running) for 45 min on the treadmill. Rest was permitted as needed during the sessions. Throughout the training sessions, feedback was given to participants so they maintained proper body posture during the walking exercise.Control group protocolThe Control group’s exercise program was inspired by the “Viactive” physical activity program, which is especially adapted for seniors (Kino-Québec; http://www.kino-quebec.qc.ca/ ). The Viactive program is an awareness program intended to motivate seniors to become physically active. Training for the Control group consisted only of low-intensity exercise routines. These exercise routines included elements of tai chi (breathing and meditation), Latin dance (basic dance steps with a partner), resistance band exercises (offering very little resistance), and coordination movements (tennis ball dribbling). Several exercises are performed in a sitting position on a chair. Exercise intensity was adjusted by increasing the amplitude of movement when possible, and increasing the duration or speed of execution. Each exercise lasted 30–90 s. Participants attended two 1-h supervised sessions per week and were asked to do a third session at home each week based on the instructions in a document they were given.Timing and assessmentsSpatiotemporal gait parameters, including variability, were assessed at the preferential (self-selected) speed using a 4.3-m-long pressure-sensitive mat (GaitRite; CIR Systems, Inc., Havertown, PA). Gait measures recorded with a computerized walkway have shown good validity and test–retest reliability (7). The sampling rate of the system was 80 Hz. Each participant completed eight successive passes (trials) across the instrumented mat, with his or her shoes on. The verbal instructions were standardized: “You will start walking at your self-selected walking speed.” Subjects started and finished the pass 2 m in front of and 2 m past the edge of the mat.Data from the eight trials were averaged. Spatiotemporal parameters assessed in this study included walking speed (cm·s−1), stride length (distance in meters traveled by the heel between two successive steps), cadence (number of steps per minute), and step width (distance in meters between the two feet when in contact with the ground). The coefficient of variation of stride length and the standard deviation of double support time were also calculated. We observed the time in single and double support as percentages of the gait cycle. After trials on the instrumented mat, participants were allowed a 10-min rest. Then, each participant completed the 6-min walking test (4,13). The conditions for performing this test were inspired by a previous study (13). Participants walked along a 30.5-m corridor. Spotters were available to supervise the execution of turns at the ends of the corridor. Subjects were asked to walk as fast as they could for 6 min, without running. They were also advised prior the beginning of the test to slow down or rest when necessary.Motor and nonmotor symptoms of PD, and their influence on daily life, were quantified using the Movement Disorder Society–Unified Parkinson’s Disease Rating Scale (MDS-UPDRS) (18). Cognitive function was assessed using the Mini-Mental State Examination (MMSE) (15). Participants self-assessed depression and mood using the Beck Depression Inventory II (BDI-II) (52). Questions relating to eight different domains were answered using the Parkinson’s Disease Questionnaire (PDQ) (20,39): mobility, daily activities, well-being, stigmatization, social support, cognition, communication, and discomfort. The fear of falling, according to the level of confidence the individual has in performing various daily activities that demand different degrees of balance, was obtained using the Activities-specific Balance Confidence Scale (42).All study outcomes (except the MDS-UPDRS) were assessed at baseline (within 14 d before the training session), after 3 months (1 wk after the 12-wk intervention period) and after 6 months of training (1 wk after the 24-wk intervention period). The MDS-UPDRS was administered only at the beginning and end of the 24-wk program. Physiologists monitored TT exercise intensity, exercise adherence and exercise-related adverse events. At-home exercise was assessed in the Control group by self-report.Statistical analysisANOVAs and Student’s t-tests were used for baseline comparisons. The dependent variables were entered in a mixed ANOVA with repeated measures to detect differences between groups and within assessments. The equality of the variances in each group was first verified with the Levene test. Preplanned post hoc comparisons were carried out with nonorthogonal contrast analysis to verify the difference between baseline and 3 months for the control, speed TT, and mixed TT groups and to compare 3- versus 6-month TT results. Tukey’s post hoc test was used to make group and other comparisons within the experimental design. Multivariate analysis was performed using a forward stepwise linear regression (with Fenter = 3.84 and Fremove = 2.71) to delineate independent predictors of training response (relative changes from baseline to 6 months) for both TT groups. Independent variables included demographic characteristics and baseline results of the MMSE, quality of life, fear of falling, and BDI-II, as well as walking parameters including walking speed and 6-min walking distance. All results are expressed as means ± SD for descriptive statistics. Computations were performed using Statistica version 7.0 (Statsoft Inc., Tulsa, OK). The degree of significance for all tests was set at P < 0.05.RESULTSParticipant characteristicsOf 297 persons screened for eligibility, 204 met one or more exclusion criteria, 48 refused to participate, and 45 were enrolled. The recruitment flow chart is presented in Figure 1. A total of 36 participants with PD completed the 6-month training protocol; 30 participants (83%) were at stage 2 on the Hoehn and Yahr scale (range = 1.5–2, median = 2; Table 1). One person with an MMSE score of 22 was allowed to participate in this study because of the presence of a close relative at all exercise sessions who provided attention and help when needed. Five participants were moved from their initial group due to a change in their schedule and because of the presence of a known relative participating in the same study. No adverse events occurred during training or testing. Two participants were excluded from the analysis: one had a stroke after the end of the training but before the final assessment, and the other had a change in medication during the 6-month training (medication error due to a dosage mistake). The level of attrition was 20% (13.3% at 3 months and 6.7% at 6 months): two participants in the control group, four participants in the speed TT group and three participants in the mixed TT group dropped out. Reasons for dropping out were scheduling conflicts (n = 4), musculoskeletal injuries (n = 3), serious health problem (n = 1) and a motor vehicle accident with major traumatic injury (n = 1). Neither the musculoskeletal injuries nor the major health problem was directly attributable to the exercise program.TABLE 1 Demographic, functional, and physiological data on participants with PD.The control group attended a mean of 33.8 of 45 (75.1%; minimum = 67%, maximum = 87%) sessions and performed a mean of 46.4 (193.3%; minimum = 100%, maximum = 387%) home exercise sessions, whereas the minimum required was 24. The speed TT and mixed TT groups attended, respectively, 87.3% (minimum = 75.0%, maximum = 97.2%) and 87.8% (minimum = 81.9%, maximum = 94.4%) of the 72 prescheduled exercise sessions. A mean of eight absences per participant was recorded. The causes of absenteeism included holidays, minor health problems, high blood pressure recording at the beginning of an exercise session, and poor road conditions.Baseline demographic characteristics are presented in Table 1 and were evenly distributed among treatment groups. No differences between groups were observed for MMSE score, quality of life or fear of falling at baseline (P’s > 0.13). Groups were comparable in their level of depressive mood at baseline as measured by BDI-II score (P = 0.07). The speed TT group had a higher score on the physical examination of motor and nonmotor symptoms (UPDRS) and their effect on daily life (P < 0.05). The speed TT group also had a lower self-selected walking speed and showed less walking endurance as measured by the 6-min walking test (P’s < 0.05). When participants completing the study (n = 35) were compared with those who dropped out (n = 9), no significant differences for any baseline measures were found (P = 0.11–0.89).TT progression of speed and inclineRelative to the initial self-selected speed, treadmill speed increased by a mean of 61.4% (minimum = –4.5%, maximum = 250%) in the speed TT group and by a mean of 24.2% (minimum = –10.7%, maximum = 50%) in the mixed TT group after 6 months (Fig. 2). For the second group, the mean treadmill incline reached 4.7% (minimum = 2%, maximum = 7%) at the end of the program (Fig. 2A). For analysis, the highest values of speed and incline were averaged for the last 4 wk. Negative minimum values indicate that individuals felt the need to reduce speed during this period. Final speed was less than the initial speed in three cases.FIGURE 2. Progression of speed and incline across the weeks for the two TT groups (upper panel, A) and mean preferential walking speed at baseline, after 3 months and after 6 months for each exercise group (lower panel, B). *P < 0.05.The percentage of the estimated maximum heart rate during exercise was similar for both TT groups for the study duration (speed TT = 73.5%; mixed TT = 71.8%, P = 0.52). Similarly, there was no significant difference in the intensity level during the first 3 months (speed TT = 72.7%; mixed TT = 70.9%, P = 0.50) and the last 3 months (speed TT = 74.3%; mixed TT = 72.6%, P = 0.60).Changes in spatiotemporal gait parametersThe speed TT and the mixed TT groups showed a mean 12.1% (minimum = –5.6%, maximum = 56.3%) and 6.3% (minimum = –6.0%, maximum = 21.3%), respectively, improvement in walking speed after 3 months of training (P’s < 0.01; Fig. 2B). Changes in walking speed ranged from –10.6% to 11.2% among control subjects during the first 3 months of training (P = 0.90). Walking speed improved by an additional 10.3% (minimum = –6.9%, maximum = 28.2%, P < 0.001) in the speed TT group and by 6.2% (minimum = –1.1%, maximum = 20.6%, P < 0.01) in the mixed TT group from the third to the sixth month (control: –1.2%; minimum = –10.6%, maximum = 4.2%, P = 0.33). Similar improvements were also observed in cadence and stride length (Table 2).Table 2 Spatiotemporal gait parameters during self-selected speed condition and walking distance during the 6-min walk test.With regard to temporal gait parameters, there was a main effect of time (P’s < 0.001), but there were no significant interactions between factors (P = 0.08–0.20). Gait changes included an increased percentage of gait cycle spent in single support phases and a decreased percentage of time spent in double support. These changes were observed from baseline to 3 months and from baseline to the study end point (P’s < 0.05).A nonsignificant increase in stride length variability was observed in the control group and in the mixed TT group at the study midpoint, whereas the speed TT group showed significant improvement (P < 0.05; Table 2) for the same period. No change was observed in any of the groups for the last 3 months. The standard deviation for time spent in double support also changed between assessments for the speed TT group only (P < 0.01; Table 2). More specifically, a significant decrease in the standard deviation for double support time was observed from baseline to 3 months.Changes in walking enduranceWe observed a significant interaction between group and time for the distance traveled during the 6-min walk test, indicating that improvements were observed only in the speed TT and mixed TT groups after 6 months of training (P < 0.05). The improvements reached 9.9% in the speed TT group (minimum = –0.7%, maximum = 29.4%) and 5.5% in the mixed TT group (minimum = –5.2%, maximum = 13.5%) after 6 months of exercise. During the same period, a nonsignificant increase in performance on the 6-min walk test was observed in the control group (4.5%, P = 0.07).PDQ-39, UPDRS, and other questionnairesAt the end of the study, TT showed a trend toward improving quality of life as measured by the total score on the 39-item PDQ (PDQ-39; speed TT = 8.5%; mixed TT = 25.4%, P = 0.07). No change in quality of life was observed in the control group. A significant interaction between group and time was observed for the mobility and stigmatization sections of the PDQ-39 (Table 3), indicating that the mixed TT group was the only group that showed improvement in these functions with exercise (mobility: 41.5% increase from baseline to 3 months, minimum = –42.1%, maximum = 100%; stigmatization: 43.6% increase from baseline to 6 months, minimum = –50.0%, maximum = 100%, P’s < 0.05). No change was observed in the control or speed TT groups (P’s > 0.15). For all groups, the frequency and severity of motor and nonmotor symptoms, and their subsequent effects on daily living, improved at the study end point (P < 0.001; Table 3). A positive effect was also observed for mood and depression as indicated by a decrease in BDI-II scores after 6 months of training (P < 0.05).TABLE 3 Data from questionnaires of subjects with PD.Predictors of training responseThe level of cognitive functioning did not influence the response to training at the study end point. For walking parameters, only baseline walking speed and performance on the 6-min walk test were significant predictors of a positive response to training in the TT groups (walking speed: β = –0.70, coefficient of determination (R2) = 0.48, P < 0.01; distance traveled in the 6-min walk test: β = –0.46, R2 = 0.39, P < 0.05). Slower walking speeds and shorter distances before training were associated with greater gains during training.DISCUSSIONParticipants in this study showed significant improvements in walking speed and walking endurance after 6 months of TT. Improvements were observed after 3 months of intensive TT and persisted at 6 months. It appears that individuals with poorer baseline performance may benefit the most from TT. This study did not detect any differential effects of treadmill regimen on spatiotemporal gait parameters; however, health-related quality of life improved by the end of the study for participants who trained on treadmills with both speed and incline adjustments. The specific TT programs were superior to the nonspecific exercise program with respect to their impact on walking speed, gait pattern, walking endurance and gait variability, Parkinson-specific symptoms, and health-related quality of life. The aforementioned gait parameters are important for a steady gait and have major effects on mobility.As reported in previous studies (14,24,37,38,43), the majority of patients with mild to moderate PD showed improvements in gait performance after 3 months of TT. For instance, Herman et al. (24) showed a 4%–20% improvement in walking speed, a 5%–10% improvement in walking distance, and a 4%–14% increase in stride length. Similar improvements were also observed after body weight support TT (17,37,38,44) and Nordic walking and standard walking training programs (45). However, whereas other studies reported that gains in walking speed were mostly attributable to an increased stride length (14,36), in the present study, walking speed was also found to be attributable to an increase in cadence.After 3 months of TT, benefits were also observed in terms of quality of life. These improvements were slightly smaller than those reported in other studies with similar training regimens (24,51). This may be explained by the 3-wk titration period that permitted participants to reach 100% of their preferential walking speed. However, the results do confirm that TT, consisting of 45-min sessions, three times a week, with an intensity of up to 75% of the estimated maximum heart rate, is specific enough to result in mobility gains for patients with PD after 12 wk.Very few studies have looked at the effects on PD patients of a training program lasting more than 3 months. States et al. (53) tested a training program for PD patients consisting of four blocks of 10 wk. Note that TT sessions were only added in the last two blocks. These authors reported no change in gait parameters at the end of the study, even when TT was added after the 20th week of the program, but they did note a significant improvement in distance traveled after the first 20 wk as well as a trend toward improved walking distance after 40 wk. In another study, improvements in gait pattern, stride length, gait variability, and maximum walking speed were reported in PD patients after the completion of a 6-month Nordic walking and standard walking training program (three exercise sessions per week) (45). The results of the present study clearly indicate that a structured regime of treadmill walking resulted in specific adaptations with regard to gait patterns. An important finding in the current report concerns the significant changes in spatiotemporal gait parameters that occurred between the third and sixth months of TT.Regarding other treatment modalities, improved gait performance in people with mild to moderate PD has also been observed as the result of a resistance training program (34): 9% improvement in walking speed (33), 21% improvement in walking endurance (11), and 14% increase in stride length (48). Others have observed improvements in walking endurance in patients with mild to moderate PD with the use of dance (19): a 16% increase with tango dancing and a 14% increase with waltz/foxtrot. The use of tai chi as therapy to improve walking speed and stride length has also been shown to be beneficial (up to 10% improvement) (33). Evidence from those studies and the data from the present study suggest that a specific walking program and other high-intensity training programs (both aerobic and nonaerobic exercise) are superior to programs aimed at promoting flexibility, relaxation, and low-intensity physical activity when it comes to improving walking speed and gait parameters (33,45). It is important to highlight that TT without body weight support is a very efficient and cost-effective way of improving gait performance. A treadmill is a low-cost piece of fitness equipment that can be installed at home or used in a gym or recreation facility.Similar improvements in spatiotemporal parameters and walking endurance were observed with both treadmill regimens. Inadequate statistical power and a lower baseline walking capacity for patients in the speed TT group may explain the lack of a differential effect between regimens. However, even when we removed the speed TT group participants with the lowest functional capacities from the analysis, improvements remained similar in both groups. Another possibility is that fatigue, induced by the intensive mixed TT program, may have diminished the potential of this training. Posttraining fatigue measurements were not performed, and therefore this explanation is purely speculative. Alternatively, a 6-month study period may have been too short to detect any differing effects of incline and speed training compared with speed only TT. Walking on an incline increases the activity level in select lower extremity muscles and may be an excellent means of increasing endurance and improving muscle strength. Furthermore, using an incline may decrease the monotony associated with repeated TT by varying the type of stimulus across sessions. Likewise, an incline may allow walkers to remain at a given treadmill speed, without running, for a longer period.On the other hand, the majority of patients in the mixed TT group reported improved health-related quality of life at the end of the study, whereas patients in the other groups did not. Interestingly, these patients improved most on subscales 1 (mobility) and 4 (stigmatization). Incline and speed adjustments during TT may promote perceived mobility, and patients may feel less stigmatized or more “empowered” as a result. Longer-term training protocols may provide additional benefits from a perceptual and physical perspective.The present study also showed that TT may help to reduce gait variability. The coefficient of variation for stride length is a good indicator of disturbances in gait rhythmicity and inconsistencies in the locomotor pattern (5,21,22,25,40). Reduced stride length variability and a shorter double support phase are both associated with a lower risk of falling (21,22). In this instance, TT reduced gait variability at the study end point. This may be explained in part by the close relationship between slower walking speeds and increased gait variability (6). The mean values for stride length variability (4.3%–4.7%) reported after 6 months of training were similar to those reported in other studies of PD for nonfallers (4.4% [26]) and well below those for fallers (8.6% [47]). Patients with the greatest gait variability at baseline showed the most improvement by the study end point. In the same way, the participants who benefited most from the TT program were those with a slower walking speed and poorer walking endurance at baseline. Interestingly, this relationship has also been demonstrated in other populations (29). In this study, neither disease duration nor motor and nonmotor symptoms of PD were correlated with improvements in walking speed or distance.It should be noted that after 6 months of low-intensity exercise routines, the control group did not worsen in terms of their gait performance, quality of life, and Parkinson-specific symptoms. There are two possible explanations of this maintenance. The first is that the exercises, although of low intensity, helped to maintain the participants’ general physical condition. Similarly, even though the intensity was low, the control group did almost twice the prescribed amount of exercise at home. The second possibility is that the group’s symptoms simply did not progress throughout the duration of the study, and that the exercises had no impact on them. Other studies, with a duration ranging from 6 to 24 wk, also showed no worsening of gait parameters in their control groups (9,28,45).TT without body weight support proved to be safe for PD patients in the early stages of the disease. Speed was adapted to each participant so that they all felt comfortable at the beginning of each session. Monitoring of vital signs throughout the protocol certainly helped to prevent adverse events, and it should be mentioned that no significant adverse events were reported. Moreover, the musculoskeletal injuries or major health problems causing participants to drop out occurred outside the study.It must be noted that the present study has several limitations. The dropout rate was high, at 20% attrition, and the sample size was relatively small. However, it is important to highlight that no participants left the study as a result of disinterest or because the protocol was too demanding. Attrition rates of other long-term training studies with PD patients have been as high as 43% (9). To maximize participation in TT programs, five participants were moved from their initial group before the beginning of the training program. These participants showed similar improvements in gait performance, quality of life, and Parkinson-specific symptoms to the rest of their respective groups. There was also considerable heterogeneity with regard to the participants’ age, physical capabilities, and medication regimen. Unfortunately, patient characteristics were unevenly distributed among the groups. The speed TT group was characterized by lower functional capacity and more severe motor symptoms than the other groups. However, the fact that statistically significant differences in gait parameters and quality of life were found within individual patients is indicative of the strong effect of the training programs used in this study. Moreover, according to Hauser and Auinger (23), a 2.4-point improvement in UPDRS motor scale score is considered clinically relevant. The speed TT group experienced a mean improvement of 7.0 ± 4.8 points on the UPDRS motor scale, whereas the mixed TT and control groups experienced a mean improvement of 4.1 and 4.5 points, respectively, when compared with baseline. Hence, 83.3% of the speed TT group, 54.5% of the mixed TT group, and 72.3% of the control group improved by more than 2.4 points on the UPDRS motor scale.There is growing evidence from animal and human studies that forced exercise enhances the release of brain-derived neurotrophic factor and may improve neural repair and neuroplasticity (2). Forced exercise is defined “operationally as a mode of aerobic exercise (e.g., TT, tandem cycling) in which exercise rate is augmented mechanically to assist the participant in achieving and maintaining an exercise rate that is greater than their preferred voluntary rate of exercise” (3). Interestingly, forced exercise of the lower extremities during tandem cycling results in improvements in global (UPDRS motor scale) and fine-motor function during a bimanual dexterity task. It is proposed that forced exercise in PD leads to an increase in cortical and subcortical activation, which may indicate an alteration of the central motor control processes (3,46). Peripheral mechanisms of adaptation to exercise may also come into play (i.e., improved corticomotor excitability and enhanced muscle coordination and recruitment) (28,45). These mechanisms may contribute to the beneficial effects of TT in PD, helping to pace retraining and motor learning (14,16,24,43,51). More long-term research is needed to determine whether forced or vigorous exercise could promote a neuroprotective effect in PD and perhaps slow the progression of the disease.CONCLUSIONSBoth TT and flexibility programs had positive effects on motor and nonmotor symptoms of PD in this study, but only TT had positive effects on walking speed, spatiotemporal gait parameters, walking endurance, and health-related quality of life. To improve gait pattern and speed in PD, exercise therapists should be encouraged to organize practice sessions with adequate specificity, progression of intensity, and frequency. Continuous improvements in gait parameters were observed until the end of the 6-month TT period. The use of incline adjustments during training sessions may constitute an interesting way of increasing endurance and improving muscle strength, which may ultimately lead to improved gait patterns and quality of life. Further studies should verify the carry-over effect of this exercise into the daily lives of PD patients. The effectiveness of TT compared with other treatment modalities and the effect of detraining on the symptoms and deficits caused by PD should also be addressed.The authors thank the Clinique Ste-Anne “Mémoire et Mouvement” for its generous donation and the Natural Sciences and Engineering Research Council (NSERC) for support provided through grants to PC. They gratefully acknowledge the editing work and suggestions by Jaime McDonald and Zofia Laubitz. They also thank Yoann Dessery, Annie-Pier Fortin, Nathalie Bourque, and Nadine Savard for their assistance with the data collection and project execution. The results of the present study do not constitute endorsement by the American College of Sports Medicine.The authors have no conflict of interest to declare.The authors declare that, except for income received from our primary employer, no financial support or compensation has been received from any individual or corporate entity for the past 3 yr for research or professional services and there are no personal financial holdings that could be perceived as constituting a potential conflict of interest.The full financial disclosures for the previous 12 months of all authors are as follows:P. Corbeil1. Grants: NSERC, Fonds québécois de la recherché sur la nature et les technologies, and Institut de recherché Robert Sauvé en santé et en sécurité du travail.E. Pourcher1. Advisory boards: Schering Plough, Pfizer, Wyeth Ayers, Janssen Ortho, AstraZeneca, and Biovail.2. 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