Although stroke is largely considered a condition of the aged, approximately 35,000 new strokes occur annually in individuals under the age of 40 years [
A training program entitled Poststroke Optimization of Walking using Explosive Resistance (POWER) has been developed to target muscle power generation dysfunction in individuals aged 18 to 75 years. This training program has been previously documented as a feasible intervention to improve muscular and locomotor function in this group [
A convenience sample of sixteen individuals (young = 6; older = 10) with chronic stroke (≥6 months) who completed 24 sessions of POWER training were included in this secondary analysis of a larger, ongoing trial investing the effects of POWER training on muscular and locomotor function. Inclusion criteria were the following: (1) ages 18–40 or 60–75 years, (2) residual paresis in lower extremity (Fugl-Meyer lower extremity motor score <34), (3) ability to walk 10 meters without support from another individual, and (4) lower than normal self-selected walking speed (SSWS) (<1.2 m/s). Individuals were excluded if they had history of preexisting neurological, psychiatric, or orthopedic problems that would hinder ability to complete aspects of testing or training. All participants that met inclusion criteria were required to complete an exercise tolerance test and be cleared for participation by the study cardiologist. This study was approved by the Institutional Review Board of the Medical University of South Carolina, and participants provided written informed consent prior to participation.
Subjects completed 24 sessions of POWER training, as previously described [
Participants walked at their SSWS measured using a GAITRite Portable Walking System (GAITRite
Peak muscle power generation of the knee extensors was assessed during isotonic contractions on the Biodex isokinetic dynamometer (Biodex Medical Systems Inc., Shirley, New York), using an external resistance set at approximately 40% of their maximum voluntary isometric contraction. Differences in lower extremity maximal contractile velocity have been reported to occur against this external load (e.g., 40% 1 RM) and are most closely associated with gait velocity in older individuals [
Clinical assessments included Fugl-Meyer lower extremity motor score (FMA-LE) [
Within-group changes were assessed using paired sample
At baseline there were no significant differences in clinical assessments, SSWS, or muscle power generation between young and older groups (Table
Participant demographics and outcome measures (mean ± standard deviation).
Young ( |
Old ( | |||
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Pre | Post | Pre | Post | |
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Age (years) | 28.2 ± 5.2 | — | 65.8 ± 4.2 | — |
Time since stroke (mos) | 59.7 ± 46.7 | — | 27.4 ± 29.0 | — |
FMA-LE (0–34) | 18.8 ± 4.0 | 20.7 ± 5.8 | 22.3 ± 7.1 | 23.1 ± 8.4 |
BBS (0–56) | 44.0 ± 10.2 | 46.5 ± 10.1 | 43.7 ± 10.9 | 42.6 ± 11.1 |
DGI (0–24) | 15.2 ± 4.9 | 16.3 ± 4.0 | 15.6 ± 5.2 | 14.3 ± 6.1 |
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SSWS (m/s) | 0.55 ± 0.32 | 0.86 ± 0.42 |
0.67 ± 0.42 | 0.77 ± 0.45 |
6MWT (m) | 310 ± 157 | 374 ± 123 | 265 ± 143 | 267 ± 152 |
PKP (W/kg) | 77.7 ± 64.9 | 88.9 ± 65.3 |
57.4 ± 31.1 | 72.3 ± 38.3 |
NPKP (W/kg) | 174.9 ± 63.5 | 221.3 ± 78.4 |
131.5 ± 29.4 | 200.7 ± 58.0 |
FMA-LE: Fugl-Meyer assessment-lower extremity motor score, BBS: Berg Balance Scale, DGI: Dynamic Gait Index, SSWS: self-selected walking speed, 6MWT: 6-minute walk test, PKP: paretic knee power, and NPKP: nonparetic knee power.
Young subjects significantly improved SSWS (
Associations between change (Δ) in SSWS (self-selected walking speed) and muscle power generation on nonparetic (a) and paretic (b) sides. Closed circles (solid line) are young subjects; open circles (dotted line) are older subjects.
These results demonstrate that 24 sessions of POWER training can significantly improve lower extremity muscle power generation in both young and older individuals following stroke. Training significantly improved locomotor function in young, but not older, poststroke subjects, even though both groups walked at similar gait speeds prior to training. Despite the relatively short duration of POWER training, young participants reached clinically meaningful improvements in SSWS (0.31 m/s) [
Individuals with poststroke hemiparesis experience deficits in the force generating capacity of muscles, in combination with substantial muscle weakness, that affect complex movement patterns such as walking. Individuals with stroke can be compared to their neurologically healthy aged counterparts, who also experience pronounced velocity dependent muscular deficits that limit mobility [
The results of the present study are consistent with studies in neurologically healthy older adults, in which POWER training enhanced functional outcomes when compared to traditional strength training [
A few limitations are worthy of mentioning in this analysis. Sample size, particularly of the young group, limits generalizability of this study. Our sample size also prohibits testing of normality and thus our analyses are limited in their scope. This is not uncommon in studies using convenience samples and the data should be interpreted with this in mind. Additionally, the cohort in this analysis consisted of high-functioning stroke participants, as seen by high pretraining scores on clinical assessments, which also limits generalizability to individuals of varying functional statuses. This may also explain the lack of significant improvements in clinical assessments (FMA-LE, BBS, and DGI) from pre- to posttraining caused by the existing ceiling effect within the data. Lastly, the inclusion of both resistance training exercises and task-specific exercises impedes our ability to attribute improvements in locomotor performance to one or the other. However, the study intervention was designed with a clinical application in mind and implicates that both resistance training and task-specific training should be utilized.
In conclusion, it is essential to provide evidence-based therapies that address the particular needs of both young and older individuals following stroke, offering unique challenges to clinicians treating this population. The results of this study particularly support the implementation of power training for young individuals with chronic stroke, especially if increasing gait speed is a rehabilitation goal.
The authors declare that there is no conflict of interests regarding the publication of this paper.
This work was supported by AHA-11BGIA7450016, VA RR&D I01 RX000844, and NIH P20GM109040. This paper is the result of work supported in part by the Office of Research and Development, Rehabilitation R&D Service, Department of Veterans Affairs, and the Ralph H. Johnson VA Medical Center, Charleston, SC, USA.