Energy variables, such as metabolic cost and energy expenditure, are important characteristics of motor activities. Alterations in these characteristics, such as an increase in the metabolic cost of walking, might lead to reduced physical activity and health in individuals poststroke. However, characterization of typical motor activities in individuals poststroke has focused mainly on the kinematic and kinetic features of the movements, although much less is known about their energy characteristics. To the best of our knowledge, this study is the first to describe the energy variables of various typical motor activities among individuals in the chronic phase poststroke.
The metabolic cost is a measure of oxygen consumption (
O2) for a given quantity of activity.1–4 The importance of the metabolic cost is demonstrated by its elevation in individuals poststroke, specifically for comfortable walking (walking-c).1–4 The metabolic cost of walking-c, either overground or on a treadmill, was found to be 1.5 to 2 times higher in individuals poststroke than in age-matched healthy individuals.1–4 In addition to its value in understanding movement performance, the metabolic cost of walking-c has been used as an outcome measure of physical activity interventions (eg, gait training) and walking aids.5–8 Such interventions can modify the metabolic cost.5 The uses of the metabolic cost in the characterization and evaluation of motor performance indicate that it is important to know the metabolic cost of an activity. However, the metabolic cost of activities other than slow, comfortable, and fast walking over even surfaces has not been documented.
Energy expenditure can be transformed from
O2 to metabolic equivalents (METs), which represent the aerobic effort relative to rest, or can be presented relative to the maximal
O2 of the individual to represent the aerobic effort.9 It has been suggested that in individuals poststroke the increased energy expenditure of daily activities in addition to lower values of maximal
O2 could lead to exhaustion and therefore reduced daily activity.10 However, this assumption was based on the energy expenditure reported by the compendium of physical activity, which reflects the energy expenditure of daily motor activities in able-bodied adults.11 Actually, previous studies in older adults or people with motor impairments have shown that the energy expenditure during daily motor activities in these populations is lower than the values reported by the compendium of physical activity. In individuals poststroke, the actual energy expenditure of typical motor activities, except walking, has not been reported.
Knowledge about the energy expenditure of an activity can also have implications for the promotion of physical activity and health. It is recommended that for health promotion, individuals poststroke should routinely engage in physical activity at a moderate to high intensity.9,12,13 In addition, the effect of the physical activity on various health aspects has been associated with the intensity of the physical activity.14–16 Engagement in typical motor activities might be useful for promoting moderate-intensity physical activity and health among individuals poststroke; however, further investigation is required to determine if engagement in typical motor activities can provide the energy expenditure required for health promotion.
Therefore, the primary objectives of this study were to describe the metabolic cost and energy expenditure of daily motor activities of individuals in the chronic phase poststroke and to compare them with those of able-bodied individuals. We hypothesized that the metabolic cost would be higher and the energy expenditure would be lower for the participants poststroke relative to the able-bodied participants.
Eleven poststroke and 8 able-bodied individuals participated in this study (Table 1). The participants poststroke were recruited from community stroke support groups and by word of mouth, and the able-bodied participants were recruited from our institution by word of mouth and a flyer advertising the study. The number of participants is representative of the number of participants in other studies designed to describe the energy variables of walking and gaming activities among individuals poststroke.1,3,4,17–20 In addition, an a-priori power calculation to detect the difference of 2 METs between the groups indicated that at least 8 individuals should be included in each group. Determinants for the calculation were a standard deviation = 1 for both groups,19 α = 0.01 one-tail, and power = 0.85. As light and moderate activities are measured in 3 MET intervals, we considered a 2 METs difference would place the energy expenditure either in a different MET category or substantially increase within that category.
The inclusion criteria for the individuals poststroke were an age range from 25 to 75 years; an onset of stroke greater than 6 months before entry into the study; and an ability to walk 50 ft without the assistance of another person, with or without a walking device or brace. The exclusion criteria for both the poststroke and the able-bodied individuals were any medical condition other than the stroke that affected their walking; a history of severe heart disease, myocardial infarction, valve replacement, coronary artery bypass surgery, severe lung disease, or uncontrolled diabetes; or an inability to follow directions. All participants poststroke were cleared to participate in the study by their primary physician. The study protocol was approved by the institutional review board, and the participants signed a written informed consent before testing.
Characterization of Participants
Participants underwent a clinical evaluation session before the testing sessions. Height and weight were measured using a wall-mounted body meter (Seca 206, Hamburg, Germany) and a digital scale (Contek WCS-8, Los Angeles, California), and were used for the calculation of body mass index. In addition, the characteristics of walking-c, including speed, distance, energy expenditure, and metabolic cost, were measured over 6 minutes of walking.18 Participants sat for 10 minutes and were then instructed to “walk at your usual comfortable speed”21 back and forth over a 25-m walkway for 6 minutes. The level of motor impairment in the participants poststroke was evaluated using the motor section for the upper and lower extremities of the Fugl-Meyer assessment.22
The study consisted of 4 activities: (1) sit to walk (sitTW) and walk to sit (walkTS) (STWTS); (2) walking-c; (3) walking indoors across obstacles (walking-o); and (4) standing on a foam cushion while reaching forward with one hand to move paper clips into a box (standing-r). The STWTS, walking-c, and walking-o tasks were selected to simulate community-based mobility activities. The standing task was added to simulate tasks with dynamic balance demands while eliminating mobility-related actions.
For STWTS, the environment was set up as a 5-by-2-m rectangle with 3 chairs on one side of the rectangle and 2 on the other. Next to each chair was a stand with big Lego blocks of different colors for each chair and a box located on one end of the rectangle. Participants were instructed to grab a Lego, stand, walk to the opposite chair, sit, exchange the Lego blocks, stand up again, and repeat the process with each chair. Once they reached the end of the rectangle, they placed the Lego in the box, walked back to the beginning, and repeated the process. Participants were told to place as many Legos as possible into the box. In the walking-o task, the participants walked along a 26.5-m hallway and negotiated a variety of obstacles, including stepping over 4 lines marked on the floor 0.8 m apart, walking on a mat, and walking around 6 cones. Participants were instructed to complete as many laps as they could. In the standing task, the participants stood on a foam cushion and reached forward with one hand to move paper clips from a table and place them into a box positioned on the other side of the table. Participants were requested to move as many clips as they could.
The study consisted of 3 testing sessions, separated by at least 2 days. During the testing sessions, the participants performed typical motor activities and also played activity-promoting video games. Data for the gaming activities are reported elsewhere.23 Participants were instructed to avoid eating or drinking for 2 hours and to abstain from caffeine consumption for 12 hours before the sessions. The number and order of activities within each session was fixed, with the anticipated lowest energy-demanding activity performed first and the expected highest energy-demanding activity performed last. The order of the 3 testing sessions was counterbalanced. At the beginning of each testing session, the participants sat still with their eyes closed in a quiet, dimly lit room for 10 minutes. Then the activities were each performed continuously for 8 minutes with a rest break of 8 to 10 minutes provided in between.
Measurements of Outcome Variables
O2 was collected using the breath-by-breath measurement technique with a portable telemetric gas analysis system (COSMED K4b2, COSMED, Rome, Italy).24 The system was calibrated before each session according to the manufacturer's instructions.
The metabolic cost and energy expenditure, as presented by the METs, were used to characterize each activity. The first 2 to 3 minutes of each activity was used to achieve a steady state of the metabolic variables. The
O2 data were extracted from the last 4 minutes of the walking-c and the last 5 minutes of all other activities. Visual inspection of the data was performed to ensure a steady state in
The metabolic cost was calculated as the mean
O2 of an activity divided by the gait speed for STWTS, walking-o, and walking-c, and divided by the number of reaching repetitions for standing-r. It should be noted that for STWTS, 1 m consisted of one transfer from sitTW, walking over 1 m, and one transfer of walkTS. The MET values were calculated by dividing the mean
O2 of each activity by 3.5 mL/kg/min.25,26 Each MET value was assigned an MET intensity level on the basis of the classification system described by the American College of Sports Medicine.27
Mean and standard deviation of the outcome variables were used to characterize each activity. The Shapiro-Wilk test for normality showed that all variables were normally distributed. Independent t tests were used to test for between-group differences in the level of performance. Repeated-measures analysis of variance was used to test for interaction and main effects of activity and group on the metabolic cost and MET values. Separate models were applied for the metabolic cost and the METs. Repeated contrasts were performed as a post-hoc analysis when indicated by interaction effects (the order of activities in the repeated-measures model was from high to low in regard with the metabolic cost and MET values). When main effects of group were identified, independent t tests were performed to test for between-group differences in each activity. Standing-r was not included in the metabolic cost model, as it was measured in different units; however, the groups were compared for this activity by independent t tests. The level of statistical significance was set at 0.05 for all effects, and at 0.01 and one-tail for post-hoc analyses. Statistical analyses were performed with SPSS, version 18 (SPSS Inc, Chicago, IL).
The participants poststroke had a moderate severity of motor impairment, as indicated by their Fugl-Meyer scores,28 and were all unlimited community ambulators.29 The average time poststroke was equal to 6.2 ± 4.3 years. The demographic and clinical characteristics of the participants are presented in Table 1.
All the participants successfully completed the study protocol. Data of walking-c of one able-bodied participant were excluded because of technical problem during the data collection. No adverse exercise effects occurred. The distance covered or number of repetitions performed within the 8 minutes of activity was significantly lower among the participants poststroke (Table 2).
There was a significant interaction between group and activity on the metabolic cost: F(1,17) = 13.4; P = 0.002. Post-hoc analysis revealed a significant interaction effect for only STWTS versus walking-o: F(1,16) = 14.8; P = 0.001 (Figure 1).
The metabolic cost was higher for the individuals poststroke than for the able-bodied participants: F(1,16.4) = 19.2; P < 0.001. Post-hoc analysis showed higher metabolic cost values for the participants poststroke across all activities. Metabolic cost values and between-group post-hoc comparisons are presented in Table 3.
The MET values are presented in Figure 2. There was a significant interaction between group and activity on the METs: F(2,34) = 5.59; P = 0.007. Post-hoc analysis revealed a significant interaction effect for only walking-c versus standing-r: F(1,16) = 12.2; P = 0.003. The MET values were lower for the participants poststroke than for the able-bodied participants: F(1,16) = 15; P = 0.001. Post-hoc analysis showed lower METs for the participants poststroke across all activities (STWTS: mean difference, 1.99 METs; 95% confidence interval (CI), 0.32-3.67; P = 0.01; walking-o: mean difference, 2.38 METs; 95% CI, 1.07-3.7; P = 0.001; walking-c: mean difference, 1.25 METs; 95% CI, 0.5-2; P = 0.007; standing: mean difference, 0.51 METs; 95% CI, 1.02-0.91; P = 0.009).
To the best of our knowledge, this study is the first to describe the energy variables of various typical motor activities among individuals in the chronic phase poststroke. The participants poststroke had moderately severe motor impairment28 and were unlimited community ambulators.29 They were relatively young, but comparable in age with other studies reporting on the metabolic cost of walking in individuals poststroke.1,3,4,30 Of the activities tested, 3 simulated mobility activities and 1 simulated upper extremity functioning while standing balance was challenged. All activities were performed at a self-selected pace. However, to standardize the relative effort with which each individual performed, the participants were instructed to perform using the maximum level of activity possible (except for walking-c).
The current study focused on 2 domains: the metabolic cost of movement and the energy expenditure. Our findings of the increased metabolic cost for a variety of typical motor activities in individuals poststroke extend the knowledge about the metabolic cost of motor activities in individuals poststroke beyond walking and suggest that increases in the metabolic cost are even more pronounced for more complex activities, such as STWTS. These findings emphasize the need to specifically address changes in the metabolic cost by rehabilitation programs.
The activity with the highest metabolic cost for both groups was STWTS. This finding was expected, as STWTS involves more intense activity of the large muscle groups of the lower extremities and has higher balance demands. For the participants poststroke, the metabolic cost of walking-c was 0.24 ± 0.06 mL/kg/m. This value was slightly higher than values that have been previously reported for individuals poststroke with similar gait speeds (0.19 and 0.21 mL/kg/m),3,18 and as expected was lower than values reported for individuals poststroke with lower gait speeds (0.35-0.63 mL/kg/m).1,2,4,30 The metabolic cost of walking-c for the able-bodied participants was in agreement with previous reports.1,2,4 Across all the activities, the metabolic cost was significantly higher for the participants poststroke relative to the able-bodied participants (20%-50% increases). Interestingly, the increase in metabolic cost for standing-r was 50%. This finding emphasizes that changes in the metabolic cost among individuals poststroke are not restricted to mobility-related activities, but also affect upper extremity and standing balance activities.
We also found that although the metabolic cost increased for both groups as the motor complexity of the activity was increased (ie, from walking-c to walking-o to STWTS), this increase was more pronounced in the participants poststroke for STWTS. This finding might reflect compensatory kinetic and kinematic strategy during sitTW and walkTS, leading to a disproportional increase in the mechanical work required. It might also be the result of disproportionally higher balance demands for the participants poststroke during the performance of this activity.
The mechanisms of the increase in metabolic cost after stroke are not fully understood. Possible explanations include changes in the mechanics of movement (eg, increased mechanical work, coactivation, and discoordination),31–33 and pathological stroke-related changes that lead to an inefficiency of movement (eg, reduced oxidative capacity in paretic muscles).34,35 These mechanisms for the increase in metabolic cost could be the target of rehabilitation training. For example, reducing compensatory strategies or improving movement coordination by practice may reduce the mechanical work and thus the metabolic cost.36–38 Muscle endurance training can induce skeletal muscle hypertrophy, which might involve molecular changes in the muscle architecture that influence muscle metabolism.34,39
The other variable tested in this study was the energy expenditure. The MET values were chosen to represent energy expenditure because they can be referenced to the intensity of the aerobic effort relative to the rest (which is equal to 1 MET). In addition, MET values are commonly used in recommendations for physical activity. The MET values for the participants poststroke were lower than for the able-bodied participants across all activities. This finding can be partially explained by the lower level of activity performed by the participants poststroke relative to the able-bodied participants. The lower level of the activity may be due to low aerobic capacity10 or to various stroke-related impairments that hamper their performance,5,40 including muscle weakness and balance impairments. These findings are in accordance with reports about the lower MET values of walking and other daily activities among older adults relative to the MET values reported by the compendium of physical activity,41 and emphasize the need to develop a specific norms for individuals poststroke.
Although the MET values in the current study might mainly reflect the low level of activity performed by the participants poststroke, assessing the MET values relative to maximum exercise capacity can provide an estimation of the aerobic effort made by the participants. The maximal exercise capacity of sedentary individuals in the chronic phase poststroke has been reported to reach 3.9 to 4.5 METs,5,42 in contrast with 8 to 10 METs among healthy individuals. In reference to these generic values, the participants poststroke approached the maximal exercise capacity when performing the STWTS activity and reached approximately three quarters of the maximal exercise capacity for the other walking activities. The able-bodied participants, on the other hand, required less than two thirds of the maximal exercise capacity to perform any of the activities.
Ivey et al10 have previously argued, based on the MET values reported by the compendium of physical activity, that engagement in daily motor activities would require individuals poststroke to work to complete exhaustion. The findings of the current study support this assessment by demonstrating that among the participants poststroke (who were instructed to perform using the highest level of activity possible), involvement in higher levels of typical motor activities would require significant aerobic effort.
The MET values observed in this study should also be referenced to the recommendations for physical activity. In healthy adults, physical activity has been associated with the prevention of chronic diseases, such as diabetes and cardiovascular diseases, and with improved functional and cognitive health and health-related quality of life.16 Initial findings suggest that similar benefits can also be expected for individuals poststroke.13 The promotion of health is dependent on the amount and intensity of physical activity, with low intensities providing some health benefits and higher intensities providing substantial health benefits.43,44 Different modes of activity have been implemented to facilitate moderate to high intensity in the training of individuals poststroke, including ergometer cycling, partial body-weight-support treadmill training, and task-specific training consisting of typical motor activities, such as brisk walking, repeated sit-to-stand, and obstacle negotiation.45 The energy expenditure of task-specific training might be lower relative to the other modes of activity because of stroke-related impairments that govern the intensity of the activity,5,40,46 as well as the nature of its self-selected pace.
The MET values of the mobility activities in this study were at the lower end of the moderate-intensity range for the participants poststroke, although they were at the upper end of the range for the able-bodied participants.27 Based on these MET values, typical motor activities can provide the appropriate energy expenditure needed for health promotion in individuals poststroke as well as in able-bodied individuals. It should be noted that more vigorous intensities of physical activity, which may provide additional benefits for various aspects of health,14,47 have been achieved in individuals poststroke by traditional modes of aerobic exercise.8,14 For the individuals poststroke, the interpretation of the MET values, on the basis of the American College of Sports Medicine classification, may be misleading because it is driven from data in healthy people. As was demonstrated earlier, a specific MET level might represent higher aerobic effort for individuals poststroke as compared with healthy individuals.
The implementation of long-term programs for promoting engagement in physical activity and health in individuals poststroke might benefit from integrating typical motor activities into the programs. The use of activities on the basis of self-selected pace has been associated with less perceived exertion and improved enjoyment.48,49 Moreover, the practice of such activities does not require special equipment or space. Finally, this mode of practice is in accordance with the task-specific principle.
As demonstrated by the metabolic cost and energy expenditure characteristics of the STWTS activity, when implementing typical motor activities into exercise programs, consideration should be given to the selection of activities in order to balance between the high metabolic cost that can lead to exhaustion and the need to achieve physical activity at a moderate intensity. Choosing activities with the high metabolic cost and high energy expenditure could, on the other hand, be seen as an opportunity to target the metabolic cost by repetitive task-specific training while achieving the appropriate energy expenditure for health promotion.
Our study has several limitations. First, given that the maximum aerobic capacity of the participants was not tested, we could only describe the relative aerobic effort in reference to the values reported in the literature. Second, the activities tested in this study simulated the “functional units” of motor activities, namely, obstacle negotiating in the walking-o and transferring from sitting to standing, walking for a short distance, and transferring to sitting in the STWTS. However, except for walking-c, they were not directly equivalent to the activities presented in the compendium of physical activity.50 Finally, the participants were relatively young and were unlimited community ambulators. It is possible that older individuals or individuals with a lower functional level would demonstrate higher metabolic cost and lower energy expenditure.
The metabolic cost is higher for individuals poststroke relative to able-bodied individuals for various motor activities. Rehabilitation programs need to specifically address the high metabolic cost of motor activities. Involvement in typical motor activities is adequate to promote health, but it promotes an energy expenditure that is lower compared with other modes of aerobic exercise.
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