Best Core Stabilization for Anticipatory Postural Adjustment and Falls in Hemiparetic Stroke

Archives of Physical Medicine and Rehabilitation journal homepage: www.archives-pmr.org Archives of Physical Medicine and Rehabilitation 2018;-:-------

ORIGINAL RESEARCH

Best Core Stabilization for Anticipatory Postural Adjustment and Falls in Hemiparetic Stroke Nam G. Lee, PT, PhD,a Joshua (Sung) H. You, PT, PhD,b Chung H. Yi, PhD,b Hye S. Jeon, PhD,b Bong S. Choi, PhD,a Dong R. Lee, PhD,c Jae M. Park, MS,d Tae H. Lee, PT, MS,e In T. Ryu, PhD,f Hyun S. Yoon, PT, MSb,e From the aDepartment of Physical Therapy, College of Health and Welfare, Woosong University, Jayang-dong, Dong-gu, Daejeon, South Korea; b Department of Physical Therapy, Yonsei University, Wonju City, Kangwon-do; cDepartment of Physical Therapy, Honam University, Seobongdong, Gwangsan-gu, Gwangju; dDepartment of Physical Therapy, College of Graduate School, Daejeon University, Yongun-dong, Dong-gu, Daejeon; eDepartment of Rehabilitation Medicine, Chungnam National University Hospital, Daesa-dong, Jung-gu, Daejeon; and fDepartment of Physical Therapy, College of Graduate School, Yongin University, Samga-dong, Cheoin-gu, Yongin, Gyeonggi-do, South Korea.

Abstract Objectives: To compare the effects of conventional core stabilization and dynamic neuromuscular stabilization (DNS) on anticipatory postural adjustment (APA) time, balance performance, and fear of falls in chronic hemiparetic stroke. Design: Two-group randomized controlled trial with pretest-posttest design. Setting: Hospital rehabilitation center. Participants: Adults with chronic hemiparetic stroke (NZ28). Interventions: Participants were randomly divided into either conventional core stabilization (nZ14) or DNS (nZ14) groups. Both groups received a total of 20 sessions of conventional core stabilization or DNS training for 30 minutes per session 5 times a week during the 4-week period. Main Outcome Measures: Electromyography was used to measure the APA time for bilateral external oblique (EO), transverse abdominis (TrA)/ internal oblique (IO), and erector spinae (ES) activation during rapid shoulder flexion. Trunk Impairment Scale (TIS), Berg Balance Scale (BBS), and Falls Efficacy Scale (FES) were used to measure trunk movement control, balance performance, and fear of falling. Results: Baseline APA times were delayed and fear of falling was moderately high in both the conventional core stabilization and DNS groups. After the interventions, the APA times for EO, TrA/IO, and ES were shorter in the DNS group than in the conventional core stabilization group (P<.008). The BBS and TIS scores (P<.008) and the FES score (P<.003) were improved compared with baseline in both groups, but FES remained stable through the 2-year follow-up period only in the DNS group (P<.003). Conclusions: This is the first clinical evidence highlighting the importance of core stabilization exercises for improving APA control, balance, and fear of falls in individuals with hemiparetic stroke. Archives of Physical Medicine and Rehabilitation 2018;-:------ª 2018 by the American Congress of Rehabilitation Medicine

More than 795,000 people in the United States alone suffer a stroke every year,1 which often results in limited balance function,2 limited walking activity,3 and associated high risk of serious falls.4 Anticipatory postural adjustments (APAs) are important neuromuscular biomarkers that predict balance impairment level Supported by a Brain Korea 21 PLUS Project Grant (grant no. 2016-51-0009) from the Korean Research Foundation. Clinical Trial Registration No.: KCT0002126 (Clinical Research Information Service, Republic of Korea). Disclosures: none.

and associated risk of falls and mobility.5 APAs involve a feedforward mechanism in which postural core muscles stabilize the spine against internal and external perturbation forces imposed on body segments during voluntary limb movements.6 Normally, APAs involve a subconscious preactivation of postural core muscles, where the transverse abdominis (TrA)6-8 and the diaphragm muscles9 activate prior to shoulder or hip movements. After a hemiparetic stroke, APA time is delayed or impaired,10 mainly in the erector spinae (ES), latissimus dorsi,11 and hamstring12 of the paretic side. Electromyographic study reported

0003-9993/18/$36 - see front matter ª 2018 by the American Congress of Rehabilitation Medicine https://doi.org/10.1016/j.apmr.2018.01.027

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N.G. Lee et al

delayed APA activation of the ipsilateral ES, latissimus dorsi, and lower trapezius muscles during paretic and nonparetic arm flexion tasks.11 The National Institutes of Health have underscored the need for clinical investigations to evaluate the effectiveness, optimal timing, and dosage of stroke rehabilitation therapies for postural control and risk of falls.13 The present Stroke Core Stabilization trial was hence designed to identify the most effective therapies by comparing 2 different commonly used core stabilization exercises. One Stroke Core Stabilization intervention was a conventional core stabilization exercise program that involved an abdominal hollowing technique. This technique contains a conscious feedback mechanism that improves postural stabilization through selective activation of the TrA/internal oblique (IO) muscles to create a sandglass-like stabilization cylinder.14-16 Such stabilization can increase intra-abdominal pressure (IAP), allowing localized lumbar segmental stability. However, this sandglass-like stabilization limits the natural descending movements of the diaphragm, which affects normative breathing. Another Stroke Core Stabilization intervention involved a subconscious dynamic neuromuscular stabilization (DNS) exercise program for retrieving postural core stability from stroke-related neuromuscular impairments, including altered postural motor control strategies and balance deficits. Specifically, the DNS contains a feedforward mechanism by which the postural stabilization cylinder beltdthe diaphragm, pelvic floor muscles, abdominal muscles, and spinal extensorsdbecomes synergistically orchestrated to create optimal IAP17,18 and is associated with postural stability in response to internal or external perturbation during dynamic limb movement. However, the neuromuscular control mechanism of postural core stabilization for enhancing APA, balance, and fear of falls in hemiparetic stroke remains unknown. It is also unclear whether postural core stabilization exercises emphasizing postural adjustment through the subconscious training of the TrA and diaphragm are superior to conventional core stabilization exercises that stress conscious training of the core muscles for APA improvements, associated balance performance, and confidence after falls in individuals with hemiparetic stroke. The purpose of this study was to compare the effects of conventional core stabilization and DNS on APA time, balance performance, and fear of falls in chronic hemiparetic stroke through the Stroke Core Stabilization trial.

List of abbreviations: AD APA BBS DNS EO ES FES IAP IO MANOVA RA TIS TrA

anterior deltoid anticipatory postural adjustment Berg Balance Scale dynamic neuromuscular stabilization external oblique erector spinae Falls Efficacy Scale intra-abdominal pressure internal oblique multivariate analysis of variance rectus abdominis Trunk Impairment Scale transverse abdominis

Methods Participants Twenty-eight adults with chronic hemiparetic stroke (13 women; mean age
SD, 57.7
8.5y) were recruited from a hospital rehabilitation center. The study design was a single-blinded, randomized controlled trial. The Consolidated Standards of Reporting Trials flow diagram is provided in figure 1. The institutional review board (approval no. 1041549-140307-SB-04) at a participating center approved the protocol, and all participants provided written informed consent. Our inclusion criteria for participants were (1) >6 months after the onset of hemiparetic stroke, (2) score >24 on the cognitive Mini-Mental State ExaminationeKorean version, (3) >10m of independent ambulation with or without a walking aid, (4) score 4 on Brunnstrom Stages of Motor Recovery, (5) score <21 on the Trunk Impairment Scale (TIS), (6) score <45 on the Berg Balance Scale (BBS), (7) the ability to raise the paretic and nonparetic arm (>60 ), and (8) the ability to understand and follow simple verbal instructions.19 Participant demographic and clinical characteristics are presented in table 1.

Clinical tests The TIS is a standardized assessment of trunk movement control and balance performance.20 Specifically, the TIS measures static sitting balance, dynamic sitting balance, and coordination, and TIS scores range from 0 (fall or compensate) to 23 (successful). The BBS is a widely used clinical test of an individual’s static and dynamic balance functions. Success on 14 balancing tasks is scaled to a scoring system from 0 (unable to maintain balance) to 4 (independent). Because the BBS scores of the participants fell under medium fall risk (score of 21e40) in this study, close supervision was provided during the BBS. The Falls Efficacy Scale (FES) is a standardized measure of fear of falling used to determine a participant’s confidence in his or her ability to maintain balance. FES scores range from 1 (very confident) to 10 (not confident). The reliability and validity of the TIS, BBS, and FES are well established.20-25

Electromyographic measurement of APAs during rapid shoulder flexion A wireless surface electromyographa was used to measure onset times of bilateral external oblique (EO), TrA/IO, ES, and anterior deltoid (AD) muscles during rapid shoulder flexion. For the EO, the electrode was placed halfway between the iliac crest and the 12th rib at a slightly oblique angle running parallel to the muscle fibers. The TrA/IO electrode was located approximately 2cm medial and inferior to the anterior superior iliac spine. The ES electrode was placed on the skin over the muscle mass approximately 2cm from the lumbar (L3) spine. Finally, for the AD, the electrode was placed on the anterior aspect of the arm, approximately 4cm below the clavicle.26 After the electromyographic testing preparation was ready, subjects stood quietly with both feet pelvic-width apart; on hearing a computergenerated auditory cue, they performed a unilateral shoulder flexion to approximately 60 as quickly as possible.7,11 Resting intervals between trials were provided as needed. All subjects completed 10 practice trials, and data were collected for the www.archives-pmr.org

Best core exercise for anticipatory balance

3

Assessed for eligibility Excluded (n=16) - Did not meet inclusion criteria (n=7): Impaired cognition, hemineglect or shoulder pain

(N=46 hemiparetic stroke)

- Declined to participate (n=9): Medical issue (diabetes, Moyamoya disease et al.)

Random assignment (n=30)

Allocated to dynamic neuromuscular stabilization (DNS) intervention (n=15)

Allocated to conventional core stabilization (CCS) intervention (n=15)

Lost to follow-up (n=1)

Lost to follow-up (n=1)

discontinued=1, declined=0

discontinued=1, declined=0

Analyzed (n=14) Excluded (n=0)

Analyzed (n=14) Excluded (n=0)

Fig 1

Consolidated Standards of Reporting Trials flow diagram.

following 10 consecutive test trials, first with the paretic and then with the nonparetic shoulder flexion. Two investigators provided close supervision to ensure safety of the subjects throughout the entire experimental test. The raw electromyographic data were collected at a sampling rate of 1000Hz, processed with a 60-Hz notch filter and a 20- to 1000-Hz bandpass filter. Electromyographic amplitude was determined by calculating the root-mean-square (50ms time constant) over the same contraction period for each muscle. The mean amplitude and SD were computed to determine the onset time and to calculate APA time. The onset time was determined by a computer-based algorithm, generated

Table 1

from the point at which the mean amplitude of 50 consecutive samples reached 3 SDs from the mean of the baseline amplitude recorded immediately before the auditory movement stimulus. The APA time was defined as a relative response time in each postural EO, TrA/IO, and ES muscle electromyographic activation in relation to the initial AD onset time during rapid shoulder flexion.7

Intervention Depending on the randomized group assignment, 15 participants received the standardized conventional core stabilization, and

Participant demographic and clinical characteristics

Parameters

DNS Group (nZ14)

CCS Group (nZ14)

P

Sex (male/female) Age (y) Height (cm) Weight (kg) Poststroke duration (mo) MMSE score TIS score BBS score (score >40) Type (hemorrhage/infarct) Brunnstrom stage (4/5) Paretic side (right/left)

7/7 57.5
9.2 164.3
7.5 66.1
14.4 17.1
5.2 27.1
1.5 14.7
3.4 39.7
3.0 (71.4%) 3/11 11/3 7/7

8/6 57.9
8.1 166.6
9.5 65.4
10.9 15.2
5.4 26.8
2.8 14.3
4.3 39.5
3.2 (78.6%) 5/9 9/5 7/7

.592 .914 .488 .872 .344 .739 .771 .856 >.999 >.999 >.999

NOTE. Values are mean
SD, n, or as otherwise indicated. Abbreviations: CCS, conventional core stabilization; MMSE, Mini-Mental State Examination

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N.G. Lee et al Table 2

Comparison of APA times (ms) between DNS and CCS groups during paretic and nonparetic shoulder flexion DNS Group

CCS Group

P

Task

Variable

Pretest

Posttest

Pretest

Posttest

Time Main Effect

Group Main Effect

Paretic shoulder flexion

Paretic EO Nonparetic EO Paretic TrA/IO Nonparetic TrA/IO Paretic ES Nonparetic ES Paretic EO Nonparetic EO Paretic TrA/IO Nonparetic TrA/IO Paretic ES Nonparetic ES

71.0
54.8 31.4
32.5 51.1
33.7 24.1
26.5 48.5
31.4 e0.9
32.1 36.9
27.3 76.9
33.7 35.5
18.5 59.4
24.9 27.9
44.7 46.9
33.1

12.8
35.1 e3.3
23.7 31.8
20.4 e13.5
27.7 22.5
26.0 9.4
33.1 1.1
38.0 41.5
24.0 e17.4
45.1 27.1
22.7 7.7
17.2 19.4
20.5

61.7
24.4 29.5
27.2 51.8
18.3 28.3
12.7 49.6
27.8 e14.0
21.4 42.6
29.7 62.6
26.6 30.8
25.1 59.1
25.6 40.0
25.3 78.0
32.0

56.9
27.9 21.7
25.6 50.9
24.5 11.3
21.9 48.8
30.2 e16.3
21.0 34.3
20.0 59.1
26.6 18.5
14.6 64.3
22.1 39.0
24.5 75.9
34.7

.003* .005* .136 <.001* .090 .589 .012* .007* .038* <.001* .076 .188

.088 .122 .144 .022* .082 .011* .826 .017* .006* .044* <.001* .009*

Nonparetic shoulder flexion

NOTE. Values are mean
SD or as otherwise indicated. Negative values represent earlier electromyographic activation relative to the deltoid muscle. Abbreviation: CCS, conventional core stabilization. * 22 mixed model MANOVA was significant at P<.05.

another 15 participants received the DNS exercise. One participant in each group discontinued the intervention during the study. Both interventions were equally comprised of a total of 20 sessions, 30min/d, 5d/wk for 4 weeks. Further description about the interventional procedure is presented in appendix 1.

were random with a chi-square test or an independent t test. The level of significance was set to aZ.05 for clinical tests and demographic analyses.

Results Statistical analyses We calculated descriptive statistics including the means and SDs. The sample size of 28 was determined with a specific effect size and a power of .08 at P<.05 to detect a meaningful difference using the software G*Power 3.0.10.b An independent 22 mixed model multivariate analysis of variance (MANOVA) was performed between group (DNS vs conventional core stabilization) and with time (pretest vs posttest) on 6 dependent variables (APA times of the bilateral TrA/IO, EO, and ES muscles) during paretic or nonparetic shoulder flexion. When an MANOVA revealed significant differences, univariate tests were used to determine a significant interaction or main effect at a significance level of aZ.05. Two-way repeated-measure analyses of variance were used to assess any statistical difference in the TIS, BBS, and FES between the groups across pretest, posttest, or 2-year follow-up. The Bonferroni post hoc test was performed at an adjusted aZ.008 (APA time, TIS, and BBS) or aZ.003 (FES) to account for the type I error associated with multiple comparisons. We confirmed that group assignments

Table 3

Comparison of APA times between DNS and conventional core stabilization groups during paretic shoulder flexion During paretic shoulder flexion, MANOVA showed significant differences in APA times between the DNS and conventional core stabilization groups (Wilks LZ.695, F6,47Z3.430, PZ.007, h2Z.305) and between pretest and posttest (Wilks LZ.676, F6,47Z3.747, PZ.004, h2Z.324). However, no significant interaction effect between group and time (Wilks LZ.808, F6,47Z1.856, PZ.109, h2Z.192) was revealed. Significant time main effects were noted for the APA times on the paretic EO (PZ.003, h2Z.160), nonparetic EO (PZ.005, h2Z.139), and nonparetic TrA/IO (P<.001, h2Z.279). Significant group main effects were observed in the APA times on the nonparetic TrA/IO (PZ.022, h2Z.097) and nonparetic ES (PZ.011, h2Z.118) (table 2). A further post hoc analysis using the Bonferroni test showed that the APA times on the bilateral EO, nonparetic TrA/IO, and paretic ES muscles

Clinical tests: TIS and BBS TIS

BBS

Test

DNS

CCS

P (timegroup)

DNS

CCS

P (timegroup)

Pretest Posttest P (time)

14.7
3.4 16.6
2.7*

14.3
4.3 15.4
3.7

.422

39.7
3.0 40.9
2.4

39.5
3.2 40.8
1.9

.871

.005y

.010y

NOTE. Values are mean
SD or as otherwise indicated. Abbreviation: CCS, conventional core stabilization. * Bonferroni test was significant between pretest and posttest at P<.008. y Two-way repeated-measures analysis of variance was significant at P<.05.

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Best core exercise for anticipatory balance were significantly decreased only after the DNS intervention (P<.008), but no significant results were observed for other comparisons.

Comparison of APA times between DNS and conventional core stabilization groups during nonparetic shoulder flexion During nonparetic shoulder flexion, MANOVA showed significant differences in APA times between the groups (Wilks LZ.586, F6,47Z5.533, P<.001, h2Z.414) and between pretest and posttest (Wilks LZ.668, F6,47Z3.889, PZ.003, h2Z.332). However, no significant interaction effect was observed between group and time (Wilks LZ.797, F6,47Z1.996, PZ.085, h2Z.203). Significant time main effects were noted for the APA times in the paretic EO (PZ.012, h2Z.115), nonparetic EO (PZ.007, h2Z.131), paretic TrA/IO (PZ.038, h2Z.080), and nonparetic TrA/IO (P<.001, h2Z.262). Significant group main effects were observed in the APA times on the nonparetic EO (PZ.017, h2Z.105), paretic TrA/IO (PZ.006, h2Z.139), nonparetic TrA/IO (PZ.044, h2Z.075), paretic ES (P<.001, h2Z.356), and nonparetic ES (PZ.009, h2Z.125) (see table 2). The Bonferroni tests showed that the APA times for paretic EO and bilateral TrA/IO muscles were significantly decreased after the DNS intervention. The nonparetic EO and paretic ES muscles revealed more significantly decreased APA times after DNS compared with conventional core stabilization. The APA time for the nonparetic ES muscle was only significantly decreased after conventional core stabilization intervention (P<.008).

Clinical outcome measures Two-way repeated-measures analysis of variance showed nonsignificant interaction effects between time (pretest and posttest) and group (DNS and conventional core stabilization), but significant time main effects were noted for TIS (PZ.005, h2Z.263) and BBS (PZ.010, h2Z.230), respectively. The Bonferroni tests showed greater improvement in the TIS score after the DNS intervention than the baseline pretest (P<.008) (table 3). For the FES measure, a significant timegroup interaction effect (PZ.036, h2Z.234) and main effect (P<.001, h2Z.563) were observed (table 4). The Bonferroni test showed greater decreased posttest and follow-up test FES scores in the DNS group compared with the conventional core stabilization group at an adjusted aZ.003 (.05/15). In the DNS group, the posttest FES score was significantly decreased compared with the pretest score (PZ.003) and remained more decreased at the 2-year follow-up test compared with the pretest score (P<.001). In the conventional core stabilization group, the posttest FES score was significantly decreased compared with the pretest score (P<.001), but no significant difference was achieved at 2-year follow-up test.

Discussion This clinical study demonstrated the effects of DNS and conventional core stabilization exercises on APA time in individuals with chronic hemiparetic stroke. As anticipated, DNS training was more effective for improving APAs via the coordinated neuromuscular activation of postural trunk muscles than conventional www.archives-pmr.org

5 Table 4

Clinical test: FES

Test

DNS

CCS

Pretest Posttest 2-y follow-up P (time)

29.0
11.5 26.3
10.3 20.9
8.8* 21.6
9.8y 18.7
8.7x 22.9
11.0 <.001z

P (timegroup) .036z

NOTE. Values are mean
SD or as otherwise indicated. Abbreviation: CCS, conventional core stabilization. * Bonferroni test was significant between pretest and posttest. y Bonferroni test was significant between pretest and posttest at P<.003. z Two-way repeated-measure analysis of variance was significant at P<.05. x Bonferroni test was significant between posttest and 2-year follow-up.

core stabilization training, suggesting improved feedforward activation during perturbation. Most importantly, the fear of falling was reduced and maintained even at the 2-year follow-up point among participants in the DNS group. To date, this study is the only clinical trial highlighting positive benefits of DNS on APA, balance performance, and fear of falling in hemiparetic stroke. Therefore, it was difficult to compare present data with previous data. Our results showed that during paretic shoulder flexion the APA times of the nonparetic TrA/IO muscles after interventions were significantly fast after DNS (pretesteposttestZ37.6ms) compared with conventional core stabilization (17.0ms). Similarly, during nonparetic shoulder flexion, only the DNS group revealed faster APA times on the paretic (52.9ms) and nonparetic (32.3ms) TrA/IO muscles. The baseline APA times of postural trunk muscles were initially delayed (51.1e76.9ms after AD activation), but considerably improved (31.8e41.5ms after AD activation) after intervention. This improved APA time range was consistent with previous APA data in which the range was from 100ms before AD activation to 50ms after AD activation in healthy adults.7 On the contrary, in the conventional core stabilization, no significant change in APA times of postural trunk muscles, excluding the nonparetic ES muscle during nonparetic shoulder flexion, was evident after the intervention. These results suggest a superior effect of DNS on APA compared with conventional core stabilization. Such differential effects in APA times suggest that DNS and conventional core stabilization use distinct motor control mechanisms. Perhaps, the DNS exercise paradigm, which emphasized a subconscious feedforward mechanism,17 was mediated via relatively fast, short-loop latency, thereby mandating fast APA time. On the other hand, the conventional core stabilization exercise paradigm, which focused on a conscious feedback mechanism,27 might have been modulated via a relatively slow, long-loop APA latency. Interestingly, Cordo and Nashner6 examined APA times associated with rapid arm movements induced by variable handle perturbations with a handheld manipulandum in healthy adults. APA responses were modulated on a subcortical level before voluntary movement and were not modified by a conscious-level effort. Recently, only 1 related clinical study examined the effects of neurodevelopmental treatmentebased and DNSecore stabilization exercises on TrA/ IO, EO, and rectus abdominis (RA) muscular activity; TrA/IO muscle thickness; and core stability in individuals with hemiparetic stroke. There was greater TrA/IO electromyographic amplitude (38.70%), muscle thickness (15.38%), and core stability

6 (3.39%) during the DNS core exercise than during the neurodevelopmental treatment core exercise in patients with hemiparetic stroke.32 These results support the notion that the increased TrA muscle thickness was associated with increased TrA/IO electromyographic muscle activity, which was induced by reflex-mediated stimulation of the chest zones during DNS.17,32 Clinical outcome analyses revealed that the DNS intervention was more effective in the FES measure than the conventional core stabilization intervention, but nonsignificant changes in the TIS and BBS scores were observed between the groups. Both groups demonstrated improvements in trunk movement control (TIS) and balance performance (BBS) after the intervention. However, the reliable change index, which is based on defining clinical meaningful change using the statistical convention of exceeding 2 SEs33 indicates that a 1-point increase in the mean BBS data does not reflect meaningful clinical improvement. These findings were in accordance with previous core stabilization studies in subacute and chronic stroke population.34,35 Cabanas-Valde´s et al34 examined the effects of a 5-week core stabilization training on dynamic sitting balance (TIS and Function in Sitting Test) and dynamic standing balance/gait (BBS, Tinetti test, and Brunel Balance Assessment) in individuals with subacute stroke and reported improved dynamic sitting and standing balance/gait after the intervention. Similarly, a 4-week core stabilization training was found to be effective for trunk movement control (TIS) and muscle activity in the RA, EO, IO, and ES muscles in individuals with hemiparetic stroke after the intervention.35 However, to our knowledge, no previous study has investigated the effect of core stabilization intervention on FES in patients with stroke. The present research is the only clinical evidence highlighting the advantageous effect of DNS core stabilization intervention on the FES, which remained even at a 2-year follow-up test. Collectively, trunk movement, balance, and falling confidence were substantially enhanced after both interventions with superior improvements from DNS compared with conventional core stabilization. Certainly, the DNS core stabilization facilitates subconsciously regulating diaphragm descending movement, which reflexively activates the TrA/IOepelvic flooremultifidus chain eccentrically during inspiration. The core chain is isometrically and concentrically activated in coordination with the superficial EO, RA, and ES muscles to generate sufficient cylinder-like IAP for dynamic balance and trunk movement control, thereby increasing falling confidence.33 On the other hand, conventional core stabilization facilitates consciously regulating the selective concentric activation of the deep TrA/IO core muscles in functional supine, quadruped, sitting, and standing positions without necessarily involving diaphragmepelvic floor muscles and superficial EO, RA, and ES muscles. This conventional core stabilization maneuver might have insufficient IAP to stabilize the entire spine, and rather it provides segmental stabilization for the lumbar spine where the selective concentric contraction of the local abdominal muscles were activated.36 This may explain such differential effects on APA times, trunk movement control, balance performance, and falling confidence between DNS and conventional core stabilization.

Study limitations Potential research limitations should be considered for future studies. In this study, APA times according to electromyographic analyses were relatively variable during rapid shoulder flexion. This variability could be attributed to the speed of arm

N.G. Lee et al movements, altered motor unit recruitments,37 or visually inconspicuous movement compensation. The latter is unlikely because in this experiment we discarded data and repeated data collection if any potential compensatory activation was apparent. Although this study focused on APA control in core muscles in relation to upper extremity (shoulder flexion) movement, the future study should also examine the role of lower extremity postural muscles because of their important APA-mediated regulation.

Conclusions This clinical trial provides promising evidence that DNS exercise is effective for improving balance performance, with DNS offering superior improvements in delayed APA time and associated fear of falling in individuals with chronic hemiparetic stroke. These findings provide conceptual and clinical insights for examining and managing postural core stabilization in individuals with impaired APA control, balance dysfunction, and high risk of falling in chronic hemiparetic stroke.

Suppliers a. TeleMyo 2000 EMG; Noraxon Inc. b. G*Power 3.0.10; University of Kiel.

Keywords Rehabilitation; Stroke

Corresponding author Joshua (Sung) H. You, PT, PhD, Dept of Physical Therapy, Yonsei University, Maeji-ri, Heungeop-myeon, Wonju, Gangwon-do, 26493, South Korea. E-mail address: [email protected].

Appendix 1 Interventional Procedure Specific instructions for the conventional core stabilization procedure were as follows. While pulling the umbilicus up and in toward the spine without pelvic movement and breathing quietly, contract the deep abdominal muscles without excessive contraction of the superficial muscles for 5 seconds.27 The therapist inspected the participant’s movements and made any necessary corrections. Once the participant was able to correctly perform the basic conventional core stabilization exercises as described, the participant progressed to more advanced core stabilization exercises, including unilateral or bilateral shoulder and hip flexion-extension movements in the quadruped; these were performed in sitting and standing positions while maintaining isometric contraction of the TrA.28 Instructions for the DNS procedure were as follows. The patient was instructed to breathe in against the therapist’s hand which is applied around the lower abdominal and inguinal area and maintained it for 5 seconds. The ideal core stabilization response should characterize anterolateral and posterior expansion of the sternum and the 10 to 12 ribs, caudal movement of the diaphragm, and a widening of the www.archives-pmr.org

Best core exercise for anticipatory balance intercostal spaces.29 The therapist inspected the participant’s movements and made manual corrections when necessary. Once the participant was able to successfully perform the basic DNS exercises as described, he or she progressed to more advanced core stabilization exercises, including unilateral or bilateral shoulder and hip flexion-extension movements in the quadruped; these were performed in sitting and standing positions while regulating the diaphragm’s respiratory and IAP core stabilization functions via a coordinated activation of the diaphragmeIOe TrAemultifidusepelvic floor muscles in conjunction with other superficial EO and ES core muscles. The correction activation was visually and manually inspected. Furthermore, an experienced physical therapist (primary investigator) performed the ultrasound measurement monitoring to ensure corrective diaphragm and abdominal muscle activation at each session during conventional core stabilization and DNS interventions.30,31

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