Association Between Meeting Physical Activity Time-Intensity Guidelines With Ambulation, Quality of Life, and Inflammation in Claudication : Journal of Cardiopulmonary Rehabilitation and Prevention

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Peripheral Artery Disease

Association Between Meeting Physical Activity Time-Intensity Guidelines With Ambulation, Quality of Life, and Inflammation in Claudication

Gardner, Andrew W. PhD; Montgomery, Polly S. MS; Wang, Ming PhD; Shen, Biyi MS; Zhang, Shangming MD; Pomilla, William A. MD

Author Information
Journal of Cardiopulmonary Rehabilitation and Prevention: November 2022 - Volume 42 - Issue 6 - p E82-E89
doi: 10.1097/HCR.0000000000000686
  • Free

Peripheral artery disease (PAD) is a significant medical concern, as it is highly prevalent worldwide affecting over 237 million people.1 Additionally, PAD is costly,2 and is associated with a high rate of all-cause and cardiovascular disease (CVD) mortality.3 The most common symptom of PAD is claudication,4 which impairs ambulation,5 physical function,6 daily physical activity (PA),7 and health-related quality of life (HRQoL).8

Physical activity is important for patients with claudication because higher PA levels are associated with lower risks of all-cause mortality, CVD mortality, and CVD events.9–11 The 2018 PA time-intensity guidelines for Americans recommend that adults should perform 150-300 min/wk of moderate-intensity aerobic PA.12 Patients with PAD and claudication have very low functional capacity,13–15 and therefore the intensity of PA performed needs to be considered in relative terms. Walking at a cadence of ≥60 steps/min represents a level beyond purposeful stepping in adults,16,17 and is equivalent to a moderate intensity of walking in patients with claudication compared with their maximal cadence of approximately 95 steps/min during a 6-min walk test (6MWT).18 Fewer patients with claudication met the older PA time-intensity guidelines than healthy controls, and this group difference was most evident in patients with the lowest self-reported ambulatory function.19 There is limited information available on whether meeting the current PA time-intensity guidelines is associated with better ambulation, HRQoL, and vascular outcomes in patients with claudication. Additionally, it is not clear how many steps/d are necessary for patients with claudication to meet the PA time-intensity guidelines. The current study was focused to addresses these knowledge gaps.

The first aim of this investigation was to determine whether meeting the 2018 PA time-intensity guidelines was associated with better ambulatory function, HRQoL, vascular function, and inflammation than failing to meet the PA guidelines in patients with PAD and claudication. The second aim was to determine the optimal number of total steps/d and the optimal number of steps/d taken at a moderate cadence that were needed to meet the PA time-intensity guidelines in PAD patients with claudication. We hypothesize that patients who meet the PA time-intensity guidelines will have significantly greater ambulatory function, HRQoL, vascular function, and lower inflammation than patients who fail to meet the PA guidelines, and that these group differences will persist after adjustment for demographic variables, comorbid conditions, CVD risk factors, and severity of PAD.

METHODS

The procedures of this study were approved by the institutional review board from the University of Oklahoma Health Sciences Center. Written informed consent was obtained from each patient prior to beginning the investigation.

PAD patients who had claudication (Fontaine stage II)4 were recruited from vascular clinics and vascular laboratories. Patients with exercise-limiting claudication were evaluated in the Clinical Research Center, and were enrolled in this study. Patients were screened on inclusion and exclusion criteria that have been described previously.20

MEDICAL SCREENING THROUGH HISTORY AND PHYSICAL EXAMINATION

On the initial study visit, patients arrived at the Clinical Research Center in the morning fasted, but were permitted to take their usual medications prior to arrival. Vital signs, demographic information, education level, height, weight, body mass index, anthropometric measurements, waist circumference, and ankle-brachial index (ABI) were obtained according to standard guidelines.21 Subsequently, blood samples were drawn and sent to a central laboratory for analyses of fasting complete metabolic panel, lipid panel, and measurements of insulin, high-sensitivity C-reactive protein, and fibrinogen levels.

Patients then underwent a medical history and physical examination by study physicians, in which claudication history, comorbid conditions, CVD risk factors, and current medications were recorded. Based on this battery of baseline assessments, patients were coded on CVD risk factors according to standard definitions for hypertension, dyslipidemia, diabetes mellitus, obesity, abdominal obesity, and metabolic syndrome.22 Additionally, coronary artery disease, cerebrovascular disease, and chronic kidney disease23 were coded according to standard definitions, as previously described.24 Patients were further characterized on the history and symptoms of arthritis, chronic obstructive pulmonary disease, and PAD.

TESTS AND OUTCOME MEASUREMENTS

Patients performed a standardized Gardner-Skinner graded treadmill protocol5 during the initial study visit to determine study eligibility, and then repeated the test on a following visit within 1 wk for the purpose of recording the outcome measures of claudication onset time and peak walking time.5 Peak oxygen uptake was also determined by oxygen uptake obtained during the peak exercise workload with a VO2000 metabolic system (Medical Graphics Inc). Prior to the treadmill test, the patients rested supine for 10 min. The ABI was measured according to standard guidelines.21 After completion of the treadmill test, patients returned to the supine position and the ABI was measured 1 min after exercise. Calf muscle oxygen saturation (StO2) was continuously measured over the medial gastrocnemius muscle of the more symptomatic leg before and during the treadmill test using a continuous-wave, near-infrared spectrometer.25 The exercise time taken to reach the minimum calf StO2 value was recorded.25

Patients performed a 6MWT in which two cones were placed 100 ft apart in a marked corridor.18 A technician provided encouragement every 2 min, and recorded the pain-free distance and total distance. After completing the test, patients evaluated the level of difficulty of the test from a Borg Rating of Perceived Exertion scale.26 None of the patients needed to use a walking assist device during the 6MWT.

Physical performance was measured by the short physical performance battery score ranges between 0 and 12, and is based on completing a repeated chair rise test, a standing balance test, and a 4-m walk test.27

Large artery elasticity index and small artery elasticity index were obtained via diastolic pulse contour analysis by an HDI/Pulsewave CR-2000 Cardiovascular Profiling System (Hypertension Diagnostic Inc) following 5-10 min of rest in the supine position, as previously described.28

Patient-based ambulatory ability was obtained using a validated Walking Impairment Questionnaire (WIQ) for PAD patients that assesses ability to walk at various speeds and distances, and to climb stairs.29

A patient-based, general measurement of HRQoL was assessed from the Medical Outcomes Study Short-Form 36 (MOS SF-36—Rand Version 1.0).30 For each subscale, multiple item scores are standardized into a scale from 0-100, with higher scores reflecting better health states.

Patient-based physical functioning was determined from six activities of daily living (ADL) primarily requiring lower extremity function as the major component.27,31 Patients selected one answer for each ADL from the following three possible choices: no difficulty, some difficulty, or unable to do.

The current health state of each patient was assessed with the EuroQol visual analog scale ranging from a score of 0, representing the worst imaginable health state, to a score of 100, representing the best imaginable health state.32 Balance and fall history were assessed by asking the patients whether they had often stumbled or felt unsteady when they walked over the past year,33 and whether they had fallen over the past year.34

PHYSICAL ACTIVITY GROUPS DETERMINED FROM AMBULATORY ACTIVITY MONITORING

Daily walking was measured using a StepWatch3 activity monitor (Orthoinnovations, Inc) during 7 consecutive days, as we have previously described.7,35 The step activity monitor was strapped around the right ankle above the lateral malleolus using an elastic Velcro strap, and it continuously recorded the number of steps taken on a min-to-min basis. Patients were instructed to wear the monitor during waking hours and to remove it before retiring to bed and while showering. The patients were further instructed to engage in their normal routine daily activities, and were not given any steps/d goals to attain. The step activity monitor does not display the number of steps taken, thereby blinding patients to their daily steps. Only valid days with >10 hr of wear time were included in the analyses, as determined by identifying the first step recorded in the morning and the last step recorded in the evening of each day.36 During this period, we excluded durations in which patients may have removed the monitor by deleting periods with no recorded steps for 180 consecutive min.36 All patients had ≥6 valid d of monitoring.

We quantified the total number of steps/d, and the time and steps/d spent at a moderate cadence (ie, intensity) in the community setting, defined as exceeding a cadence of 60 steps/min by patients with claudication.7 This cadence represents a level beyond purposeful stepping in adults,16,17 >60% of the maximal cadence of patients with claudication during a 6MWT,18 and >67% of the average cadence of supervised treadmill exercise training sessions completed by patients with claudication.20 Patients were then grouped according to whether they achieved <150 min/wk of moderate-intensity PA (group 1 = do not meet the 2018 PA time-intensity guidelines) or whether they were above this threshold (group 2 = meet the guidelines). The step activity monitor is considered the gold standard to measure step counts, as it is the most accurate step counting device available on the market,37 with accuracy >99 ± 1% in patients with claudication.7

STATISTICAL ANALYSES

The data were summarized by group as mean ± SD for continuous variables and n (%) for categorical variables (Table 1). The normality assumption for continuous variables was checked based on Shapiro-Wilk tests, and if failed, log transformation was applied. Two-group comparisons were performed based on two-sample t tests or Wilcoxon rank sum tests for continuous variables and Pearson's χ2 tests or Fisher exact tests for categorical variables, as appropriate. For each of primary outcomes, we conducted unadjusted (univariable) and adjusted (multivariable) regressions to evaluate group differences, where the list of confounding variables including age, weight, sex, education, ABI, hypertension, diabetes, abdominal obesity, arthritis, and chronic obstructive pulmonary disease is considered based on group comparisons in Table 1, prior studies, and clinical experience. The P values in model 1 and model 2 were obtained from Wald tests. To evaluate the diagnosis ability of total daily steps and daily steps taken at a moderate cadence that are needed to meet the PA time-intensity guidelines in PAD patients with claudication, the receiver operating characteristic (ROC) curves were generated and its area under the curve was calculated. Thereafter, the optimal numbers were determined by minimizing the distance between the point and the optimal point (0,1) in the ROC plane or maximizing Youden's index. All hypothesis tests were two-sided with the significance level of .05. Data were analyzed using SAS 9.4 Software (SAS Institute).

Table 1 - Clinical Characteristics of Patients With Claudication Grouped According to Their Physical Activity Statusa
Group 1 (Do Not Meet Physical Activity Time-Intensity Guidelines) (n = 397) Group 2 (Meet Physical Activity Time-Intensity Guidelines) (n = 175) P Value
Age, yr 65.7 ± 10.0 67.7 ± 10.7 .041
Weight, kg 83.0 ± 19.5 82.9 ± 14.3 .952
Height, cm 167.5 ± 9.4 170.2 ± 8.8 .001
Body mass index, kg/m2 29.5 ± 6.4 28.7 ± 5.3 .098
Ankle/brachial index 0.65 ± 0.22 0.75 ± 0.22 <.001
Daily steps, steps/d 5 263 ± 2 133 10 202 ± 3 017 <.001
Daily steps at moderate intensity, steps/d 823 ± 447 3 319 ± 1 627 <.001
Time spent in moderate-intensity activity, min/d 11 ± 6 40 ± 18 <.001
Sex, men 178 (45) 115 (66) <.001
Race, Caucasian 206 (52) 99 (57) .346
Education, high school graduate 282 (71) 136 (78) .045
Coronary artery disease 140 (35) 61 (35) .985
Cerebrovascular disease 64 (16) 35 (20) .319
Chronic kidney disease 92 (23) 53 (30) .068
Lower extremity revascularization 191 (48) 71 (41) .104
Current smoking 150 (38) 47 (27) .014
Hypertension 345 (87) 150 (86) .802
Dyslipidemia 369 (93) 146 (83) .001
Diabetes 200 (50) 42 (24) <.001
Obesity 178 (45) 68 (39) .235
Abdominal obesity 228 (57) 71 (41) <.001
Metabolic syndrome 334 (84) 130 (74) .008
Arthritis 214 (54) 93 (53) .782
Chronic obstructive pulmonary disease 100 (25) 46 (26) .780
aData are presented as means ± SD, or n (%) of patients with characteristic present.

RESULTS

The groups were significantly different on age, height, ABI, daily steps, moderate-intensity daily steps, time spent in moderate-intensity activity, sex, education, current smoking, dyslipidemia, diabetes, abdominal obesity, and metabolic syndrome (Table 1).

All ambulatory and functional outcomes were significantly different between the two groups in unadjusted (model 1) and adjusted analyses (model 2) (Table 2).

Table 2 - Ambulatory and Physical Function Outcomes in Patients With Claudication Grouped According to Their Physical Activity Statusa
Variables Group 1 (Do Not Meet Physical Activity Time-Intensity Guidelines) (n = 397) Group 2 (Meet Physical Activity Time-Intensity Guidelines) (n = 175) Model 1b P Value Model 2c P Value
Treadmill test
Claudication onset time, sec 243 ± 209 423 ± 311 <.001 <.001
Peak walking time, sec 427 ± 281 709 ± 359 <.001 <.001
Peak oxygen uptake, mL/kg/min 11.9 ± 3.3 14.2 ± 3.7 <.001 <.001
6-min walk test
Pain-free distance, m 198 ± 123 257 ± 130 <.001 <.001
Total walk distance, m 335 ± 88 415 ± 79 <.001 <.001
Rating of perceived exertion score 13.2 ± 2.7 12.7 ± 2.6 .027 .002
Continuous walking 201 (51) 130 (74) <.001 <.001
4-m walk test
Gait speed, m/sec 1.04 ± 0.21 1.16 ± 0.22 <.001 <.001
Cadence, steps/min 102.6 ± 13.2 109.4 ± 9.3 <.001 <.001
Step length, m/step 0.61 ± 0.12 0.63 ± 0.11 .038 .009
Physical function
Chair stand time, sec 14.20 ± 2.59 12.64 ± 2.30 <.001 <.001
SPPB score, points 8.8 ± 1.4 9.7 ± 1.2 <.001 <.001
Abbreviation: SPPB = short physical performance battery.
aData are presented as means ± SD, or n (%) of patients who completed the 6-min walk test without stopping.
bModel 1: unadjusted.
cModel 2: adjusted for age, weight, sex, education, ankle/brachial index, current smoking, hypertension, dyslipidemia, diabetes, abdominal obesity, arthritis, and chronic obstructive pulmonary disease.

The groups were significantly different in unadjusted and adjusted analyses for the MOS SF-36 questionnaire outcomes of physical function, role-physical, bodily pain, general health, and vitality scores (Table 3). Furthermore, the groups were significantly different in unadjusted and adjusted analyses for the WIQ distance, speed, and stair climbing scores, the PA score via questionnaire, and the ADLs associated with bathing, transferring from a bed to a chair, climbing stairs, and walking a half mile.

Table 3 - Patient-Based Health Outcomes in Patients With Claudication Grouped According to Their Physical Activity Statusa
Variables Group 1 (Do Not Meet Physical Activity Time-Intensity Guidelines) (n = 397) Group 2 (Meet Physical Activity Time-Intensity Guidelines) (n = 175) Model 1b P Value Model 2c P Value
Medical Outcomes Short Form-36 Questionnaire, %
Physical function 44 ± 21 61 ± 22 <.001 <.001
Role-physical 48 ± 41 59 ± 42 .002 .003
Bodily pain 63 ± 24 69 ± 22 .008 .002
General health 57 ± 22 62 ± 21 .010 .007
Social function 81 ± 23 83 ± 23 .203 .260
Role-emotional 75 ± 40 77 ± 36 .560 .560
Mental health 79 ± 17 81 ± 16 .226 .087
Vitality 56 ± 22 63 ± 18 .001 <.001
Walking Impairment Questionnaire, %
Distance 34 ± 30 58 ± 36 <.001 <.001
Speed 34 ± 23 50 ± 26 <.001 <.001
Stair climbing 38 ± 29 55 ± 29 <.001 <.001
Physical activity, falls
Health VAS, % 72 ± 18 74 ± 17 .312 .365
Physical activity score 1.1 ± 1.0 1.8 ± 1.3 <.001 <.001
Falling history 107 (27) 34 (19) .062 .083
Fear of falling 112 (28) 42 (24) .376 .591
Stumble/unsteady while walking 132 (33) 49 (28) .262 .749
ADL
Walking/room 38 (10) 12 (7) .309 .743
Bathing 62 (16) 9 (5) <.001 .036
Transferring 30 (8) 4 (2) .009 .049
Toileting 30 (8) 7 (4) .108 .402
Stairs 270 (68) 80 (46) <.001 <.001
Walk half mile 309 (78) 94 (54) <.001 <.001
Abbreviations: ADL, activities of daily living; VAS, visual analog scale.
aData are presented as means ± SD, or n (%) of patients who have some difficulty or unable to do each ADL and who reported a fall outcome.
bModel 1: unadjusted.
cModel 2: adjusted for age, weight, sex, education, ankle/brachial index, current smoking, hypertension, dyslipidemia, diabetes, abdominal obesity, arthritis, and chronic obstructive pulmonary disease.

The groups were significantly different in unadjusted and adjusted analyses for the ABI measured 1 min after treadmill exercise, the percentage change in the ABI after exercise, in the exercise time to the minimum calf muscle StO2, and in high-sensitivity C-reactive protein, and in small artery elasticity index (Table 4).

Table 4 - Vascular Outcomes in Patients With Claudication Grouped According to Their Physical Activity Statusa
Variables Group 1 (Do Not Meet Physical Activity Time-Intensity Guidelines) (n = 397) Group 2 (Meet Physical Activity Time-Intensity Guidelines) (n = 175) Model 1b P Value Model 2c P Value
ABI 1 min after exercise 0.37 ± 0.26 0.47 ± 0.29 <.001 <.001
ABI percentage change after exercise, % −47 ± 27 −41 ± 27 .015 .007
Exercise time to minimum calf muscle StO2, seca 227 ± 253 292 ± 347 .021 .006
High-sensitivity C-reactive protein, mg/L 5.9 ± 6.1 3.6 ± 4.5 <.001 <.001
Fibrinogen, g/L 3.6 ± 1.4 3.4 ± 1.2 .095 .066
Large artery elasticity index, (mL × mm Hg−1) × 10 13.4 ± 6.5 14.0 ± 5.6 .291 .122
Small artery elasticity index, (mL × mm Hg−1) × 100 3.2 ± 1.6 3.7 ± 2.4 .017 .035
Data are presented as means ± SD.
Abbreviations: ABI, ankle/brachial index; StO2, oxygen saturation.
aData were log transformed for model assessment.
bModel 1: unadjusted.
cModel 2: adjusted for age, weight, sex, education, ABI, current smoking, hypertension, dyslipidemia, diabetes, abdominal obesity, arthritis, and chronic obstructive pulmonary disease.

The ROC curve shown in Figure 1 indicates that ≥7675 steps/d was the best threshold associated with meeting the PA time-intensity guidelines. The precision or positive predictive value associated with this threshold was 75.9%, and the negative predictive value was 92.1% (Figure 1). The ROC curve displayed in Figure 2 indicates that ≥1660 steps/d taken at a moderate cadence was the best threshold associated with meeting the PA time-intensity guidelines. The precision or positive predictive value associated with this threshold was 93.6%, and the negative predictive value was 100% (Figure 2).

F1
Figure 1.:
Receiver operating characteristic curve for daily steps. The optimal step threshold is ≥7675 steps/d, which is based on the highest sum sensitivity + specificity. Best threshold: sensitivity = 82.9%, specificity = 88.4%. Precision or positive predictive value = 75.9%. Negative predictive value = 92.1%.
F2
Figure 2.:
Receiver operating characteristic curve for daily steps taken at a moderate cadence. The optimal step threshold is ≥1660 steps/d, which is based on the highest sum sensitivity + specificity. Best threshold: sensitivity = 100%, specificity = 97.0%. Precision or positive predictive value = 93.6%. Negative predictive value = 100%.

DISCUSSION

A major finding of this study was that patients with claudication who meet the PA time-intensity guidelines had better ambulation, HRQoL, and vascular outcomes than those who failed to meet the guidelines. These group differences persist after adjustment for demographic variables, comorbid conditions, CVD risk factors, and severity of PAD. Finally, taking ≥7675 total steps/d and ≥1660 steps/d at a moderate cadence were the optimal amounts for patients with claudication to meet the PA time-intensity guidelines.

GROUP DIFFERENCES IN AMBULATION, PHYSICAL FUNCTION, HRQoL, VASCULAR, AND INFLAMMATORY OUTCOMES

Patients who met the PA time-intensity guidelines had better scores on a number of key outcome measures of ambulation, physical function, and HRQoL than those who were less active. For example, the more physically active group had 66% longer treadmill peak walking time, 24% greater 6MWT distance, 10% higher score on the short physical performance battery test, 39% higher HRQoL physical function score, and 71% higher WIQ distance score. Additionally, the patients who met the PA time-intensity guidelines had fewer patients reporting difficulties in completing ADL associated with bathing, stair climbing, and walking a half mile than patients who did not meet the PA guidelines. Collectively, these findings suggests that patients who met the PA time-intensity guidelines had better objective and subjective measures of physical function and HRQoL than the less active group. The current findings support our recent report,38 which found that patients with claudication who walked above daily step count thresholds of 7000 and 10 000 steps/d had greater ambulatory function, physical function, and HRQoL than patients who took fewer steps.

Patients who met the PA time-intensity guidelines also had better scores on a number of key vascular outcome measures than those who were less active. For example, the more physically active group had a 27% higher ABI value 1 min after treadmill exercise, a 29% longer exercise time to the minimum calf muscle StO2, 39% lower high-sensitivity C-reactive protein, and a 16% higher small artery elasticity index. These findings suggest that patients who met the PA time-intensity guidelines had better lower extremity macrovascular function after exercise, better microvascular function of the calf muscle during exercise, lower systemic inflammation, and higher systemic arterial elasticity of the smaller resistance vessels.

The current findings support our recent report,39 which found that patients with claudication who were in the middle and upper tertiles of community-based daily steps taken at a moderate cadence had better calf muscle StO2 and ABI values during and immediately after exercise.

OPTIMAL NUMBER OF DAILY STEPS TO MEET PHYSICAL ACTIVITY TIME-INTENSITY GUIDELINES

A number of health benefits for older adults are associated with performing regular PA, such as lower risk of all-cause and CVD mortality, lower risk of CVD, improved physical function, and improved HRQoL.12 For most optimal results, PA time-intensity guidelines have been established in which adults are recommended to perform ≥150 min/wk of moderate-intensity aerobic PA, or as much as possible if this threshold cannot be achieved.12 In the current study we found that only 31% of patients with claudication met the PA time-intensity guidelines, which is similar to the percentage of patients with heart failure in a recent report.40 The optimal number of total daily steps that patients with claudication needed to take to meet the PA time-intensity guidelines was ≥7675 steps/d, which represented the best combination of sensitivity (82.9%) and specificity (88.4%). The area under the curve was 0.926, which is considered as having excellent discrimination accuracy in determining whether patients with claudication meet the PA time-intensity guidelines.41 Furthermore, the optimal number of daily steps taken at a moderate cadence to meet the guidelines was ≥1660 steps/d, as this value was associated with the best combination of sensitivity (100%) and specificity (97%). The area under the curve was 0.998, which is also considered as having excellent discrimination accuracy.41 From a practical standpoint, patients with claudication need to do some walking at a moderate cadence each day to attain at least 7675 total daily steps. A target to accumulate ≥1660 steps/d at a moderate cadence could be achieved if patients are encouraged to perform bouts of intermittent walking faster than their typical pace for approximately 20-25 min.

LIMITATIONS

As with many clinical studies, there may have been a self-selection bias regarding study participation. Furthermore, the results are only generalizable to patients with claudication. There are limitations associated with the cross-sectional design of the study, which does not provide evidence of causality. Additionally, although our analyses were adjusted for covariates, it is possible that statistically significant findings are due to confounding variables that were not measured or to residual confounding. There is also a limitation associated with our objective assessment of daily step counts, which does not measure other potential physical activities performed throughout the day, such as non-weight-bearing and non-ambulatory activities. However, we believe this limitation is minimal because walking is required to complete many ADLs, and walking is the most common form of exercise of older adults.42 The step activity monitor does not directly measure wear time, and must be estimated according to our described methods. Finally, there are limitations associated with the noninvasive measurements of calf muscle StO2 and diastolic pulse contour analysis, as we have previously described.25,28

CONCLUSIONS

Patients with claudication who meet the 2018 PA time-intensity guidelines for US adults had better ambulation, HRQoL, and vascular outcomes than those who failed to meet the PA guidelines. From a practical standpoint, patients with claudication best achieved the PA time-intensity guidelines by taking ≥7675 total steps/d, and ≥1660 steps/d at a moderate cadence. The clinical significance is that community-based walking to a level that meets the PA time-intensity guidelines is associated with favorable health and vascular outcomes in patients with claudication.

ACKNOWLEDGMENTS

Supported by grants from the National Institute on Aging (R01-AG-24296 and R01-AG-16685).

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Keywords:

exercise; microvascular; near-infrared spectroscopy; peripheral artery disease; step count

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