PHYS THER
Vol. 88, No. 8, August 2008, pp. 928-935
DOI: 10.2522/ptj.20070296
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Research Reports

Changes in Functional Walking Distance and Health-Related Quality of Life After Gastric Bypass Surgery

James Tompkins, Pamela R Bosch, Rochelle Chenowith, Judy L Tiede and James M Swain

J Tompkins, PT, DPT, CP, is Physical Therapist, Department of Physical Medicine and Rehabilitation, Mayo Clinic, 5777 E Mayo Blvd, Phoenix, AZ 85054 (USA).
PR Bosch, PT, PhD, is Associate Professor, Physical Therapy Program, Arizona School of Health Sciences, AT Still University, Mesa, Arizona.
R Chenowith, PT, DPT, PES-NASM, CPT, is Physical Therapist, Elite Sports Medicine and Orthopaedic Center, Nashville, Tennessee.
JL Tiede, RN, MSN, RNFA, is Registered Nurse, First Assist, Department of General Surgery, Mayo Clinic, Phoenix.
JM Swain, MD, is Director of Bariatric Surgery, Department of General Surgery, Mayo Clinic, Phoenix.

Address all correspondence to Dr Tompkins at: tompkins.james{at}mayo.edu


Submitted October 3, 2007; Accepted April 17, 2008


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Abstract
 
Background and Purpose: Early physical functional changes after gastric bypass surgery (GBS) are unclear, and the relationship between these changes and health-related quality of life (HR-QOL) has not been reported. We measured distances from a 6-minute walk test (6MWT) and scores on the 36-Item Short-Form Health Survey (SF-36) before and after GBS.

Subjects and Methods: Twenty-five people undergoing GBS completed the SF-36 and 6MWT presurgically and at the 3-month and 6-month follow-up visits. Ratings of perceived exertion (RPE) were measured during 6MWTs.

Results: Presurgical walking distance (X±SD; 414.1±103.7 m) was 55%±14% of normative values. Distances increased significantly at 3 months (505.2±98.0 m) and at 6 months (551.5±101.2 m). Final RPEs decreased significantly, and HR-QOL improved significantly. Both physical and mental health components of the SF-36 improved significantly. Distance was inversely correlated with body mass throughout the study and positively correlated with the SF-36 Physical Component Summary change from 3 to 6 months.

Discussion and Conclusions: Improved functional capacity was associated with enhanced HR-QOL. At 6 months, walking distances remained 75% of those for age-matched peers who had normal weight.


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Introduction
 
Obesity prevalence is rapidly rising to epidemic proportions in the United States, resulting in a corresponding increase in health care costs.1–3 Estimates from the World Health Organization indicate that more than one billion adults are overweight and that 300 million of them are clinically obese. The sequelae of obesity may include hypertension, cardiovascular complications, type 2 diabetes mellitus, respiratory complications, liver and gallbladder diseases, osteoarthritis, cancer, integumentary complications, decreased health-related quality of life (HR-QOL), and an increased risk of premature death.2,4–6

Gastric bypass surgery (GBS) is an accepted and effective means of managing morbid obesity, not only for weight loss but also for reducing or eliminating associated comorbid conditions.7,8 These benefits may result in improved HR-QOL, enhanced functional abilities, and improved cardiorespiratory fitness.

Although changes in HR-QOL and a reduction in comorbid conditions related to obesity have been documented after weight-loss surgery,2,9,10 one question that has not been addressed is the early postoperative effect of GBS on physical function as measured by over-ground walking at self-selected speeds. The 6-minute walk test (6MWT) is widely used by physical therapists as a measure of functional exercise tolerance.11–18 There are currently no normative values for functional walking distances for patients with obesity. Therefore, we were interested in whether 6MWT distances varied for patients before and after GBS. In addition, we wanted to examine the relationship between functional walking distances and patients’ perceptions of HR-QOL before and after GBS.

Specifically, we hypothesized that: (1) patients with obesity would walk a shorter distance in a 6MWT compared with normative data; (2) the distance walked during the 6MWT would increase significantly at 3 months and at 6 months after GBS compared with before GBS; (3) the patients’ rating of perceived exertion (RPE) at the end of the 6MWT would decrease significantly at 3 and 6 months after GBS compared with before GBS; and (4) the perceptions of patients about HR-QOL, as assessed with the 36-Item Short-Form Health Survey (SF-36), would improve significantly at 3 and 6 months after GBS compared with before GBS.


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Method
 
Subjects

Prospective subjects with a minimum body mass index (BMI) of 35 were recruited as volunteers from a group of patients scheduled for GBS at a local hospital that specializes in this type of procedure. Exclusion criteria included inability or unwillingness to return to the clinic at 3- and 6-month intervals after GBS, uncontrolled medical conditions, inability to walk, and pregnancy. Before data collection, all subjects signed an informed consent form that was approved by both the hospital's and the university's institutional review boards.

Twenty-eight women and 2 men, ranging in age from 31 to 58 years (X±SD=44±6.3 years) and with a mean±SD BMI of 45.5±6.9, agreed to participate in the study. Of these 30 subjects, 25 completed all components of the investigation. Four subjects were excluded from the 6MWT and SF-36 analyses because they did not participate in both follow-up sessions, and a fifth subject was lost to follow-up.

Each subject participated in 3 testing sessions. The first session occurred on the day before surgery (pre-GBS) after the preoperative appointment with the bariatric surgeon, the second session took place after a 3-month postoperative follow-up appointment with the surgeon (3 months after GBS), and the final session took place 6 months after GBS.

Measures

Before each testing session, the surgical nurse measured the subjects’ height and weight for the BMI calculation. The subjects then completed the SF-36 and participated in a 6MWT.

BMI.
The BMI is the most common method of estimating an individual's body composition, and it is calculated by dividing body weight in kilograms by height in meters squared (kg/m2).15,19 Regardless of sex, adults with a BMI of 25.0 to 29.9 are considered overweight, those with a BMI of 30.0 to 39.9 are considered obese, and those with a BMI of 40.0 or higher are considered morbidly obese.6,19 All weights were measured on an SR555, Stand-on Scale System (1,000 lb capacity),* whereas the initial heights were measured using a wall-mounted Seca 222 stadiometer.{dagger}

SF-36.
The SF-36 has been used to describe the health status and physical ability of people with numerous impairments who are receiving physical therapy.13 This questionnaire is a generic measure of HR-QOL, with high content and external validity. Reliability values (Pearson r) range from .89 to .94 for the Physical Component Summary (PCS) and from .84 to .91 for the Mental Component Summary (MCS).20 The questionnaire contains 36 questions grouped into 8 scales, and these scales are further clustered into the PCS and MCS components. The PCS includes scales to measure physical functioning, role limitations due to physical health problems (role–physical), bodily pain, and general health. The MCS includes scales to measure vitality, social functioning, role limitations due to personal or emotional problems (role–emotional), and mental health. Validity studies suggest an advantage of the PCS and the MCS over individual scales when interpreting health outcomes.20 At each testing session of our study, subjects were given the SF-36 before doing the 6MWT. Test scores were normalized according to the instructions provided in the SF-36 user manual.20

6MWT.
The 6MWT is a performance-based, submaximal test that estimates cardiorespiratory endurance. Intraclass correlation coefficients for the second and third administrations of the 6MWT have been reported to range from .96 to .99.21 Gibbons et al11 developed a regression equation for estimating 6MWT distance for people 20 to 80 years of age who are healthy, and this formula was used to generate the normative reference for each of our subjects.

The 6MWT was conducted according to the protocol of the American Thoracic Society.22 All testing was conducted indoors on a 114.3-m (125-yd) uninterrupted level surface covered with thin industrial carpeting. The distances were measured to the nearest foot and were then converted to meters. Subjects were wheeled in a wheelchair to the testing site, where baseline heart rate, blood pressure, and oxygen saturation levels were measured as recommended by the American College of Sports Medicine (ACSM) guidelines.23 These vital recordings were obtained again at the end of the 6MWT for the purpose of monitoring the subjects’ safety. Specific instructions for the 6MWT were read aloud to the subjects. They were asked to walk at their own pace but to try to cover the greatest distance possible in 6 minutes. Resting stops were allowed. In addition to these instructions, standardized verbal encouragement was given at the end of minutes 1 through 5, according to the protocol. The 6MWT was administered twice for each subject during the initial visit, with the highest attained value recorded, per the protocol. Subjects rested a minimum of 30 minutes between trials or until the heart rate returned to within 5% of its baseline value. Additionally, no subjects were retested until their blood pressure had returned to prewalk values.

Borg RPE scale.
A standardized Borg RPE scale of 6 to 20 was used according to the recommendations of the ACSM.23 The RPE test-retest correlation coefficients have been reported to range from .71 to .99.24 Subjects were familiarized with the RPE scale using standardized instructions.24 The RPE was recorded at rest before each 6MWT. At the end of each minute during the 6MWT, a laminated copy of the standardized RPE scale was displayed, and the subjects were asked to "rate the level of perceived exertion."

Data Analysis

Repeated-measures analyses of variance (ANOVAs) were used to compare the variables at 3 time points (at baseline and at 3 and 6 months after surgery) in BMI, 6MWT distance, and RPE (final score at minute 6). Additionally, changes in the PCS and MCS clusters of the SF-36 from baseline to 3 and 6 months after surgery were analyzed with repeated-measures ANOVAs. The 8 scales of the SF-36 were not analyzed separately because of the risk of an inflated alpha level due to the small sample size. In the event of violation of the sphericity assumption, Greenhouse-Geisser corrections were applied. Planned comparisons were conducted using simple effects contrasts that compared baseline measurements with measurements obtained at 3 and 6 months post-GBS.

The Pearson correlation was used to determine the association between the percentage change in weight and 6MWT distance, and the Spearman rho correlation was used to determine the association between the percentage change in SF-36 scores and 6MWT distance. The SPSS version 14.0 statistical software program{ddagger} was used to conduct all analyses.


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Results
 
Our final sample comprised 23 women and 2 men; the preponderance of women is typical of the population choosing this procedure.12,14 Data were preliminarily tested with a Kolmogorov-Smirnov test and found to be substantially normal (P<.05), except for 2 SF-36 percentage change values. As expected, all 25 subjects had a considerable reduction in BMI during the course of the study, with significant differences between pre-GBS and 3-month post-GBS BMI values (P<.001) and between pre-GBS and 6-month post-GBS BMI values (P<.001). The BMI values are presented in Table 1.


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  		Table 1. Characteristics of Subjectsa

SF-36

Statistical comparisons of the PCS and MCS clusters and the SF-36 scale scores are reported as normative values. Mean values for all 8 scales, and for the PCS and MCS summary scores that subsume them, are displayed in Table 2; published normative values are provided for comparison.20


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  		Table 2. Findings on the 36-Item Short-Form Health Surveya

Scores on the PCS of the SF-36 improved significantly from before GBS to the 3-month follow-up (P<.01) and the 6-month follow-up (P<.01). The MCS scores also improved significantly from before GBS to the 3-month follow-up (P<.05) and the 6-month follow-up (P<.01).

6MWT

Four of the 25 subjects who completed all test sessions refused a second attempt at the 6MWT during the first visit because of fatigue. Because scores were highly correlated for those subjects who did complete 2 trials (Pearson r=.97, P<.01), we felt confident in using the data of subjects who completed only one session. The average (±SD) pre-GBS walk distance was 414.1±103.7 m, which represents 55%±14% of normal for adults older than age 20 years who are healthy.11 Walking distance increased significantly by the 3-month follow-up (P<.001) and the 6-month follow-up (P<.001). These values represent 68%±12% and 75%±13% of the normal values for 3- and 6-month follow-ups, respectively. Table 1 shows the mean values for the distance walked at each time point.

RPE

During the pre-GBS trial, the final RPE (X±SD) for the 6MWT was 14±3 (14 is "somewhat hard"). This rating decreased significantly to 11±3 (11 is "light") at the 3-month follow-up (P<.001) and to 10±3 (10 is "very light") at the 6-month follow-up (P<.001). The Figure shows the mean RPE values for each minute of the 6MWT.


Figure 1
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  		Figure. Rating of perceived exertion during the 6-minute walk test. All paired comparisons were significantly different (P<.03), except at 1, 2, and 4 minutes for before gastric bypass surgery (GBS) and 3 months post-GBS.

Correlations

There were no significant correlations between percentage changes in 6MWT distance and weight loss over time. There was a significant positive correlation between the percentage change in 6MWT distance and scores for the PCS component of the SF-36 from the 3-month follow-up to the 6-month follow-up (r=.41, P<.05). There were no significant correlations over time between percentage change in the 6MWT results and scores for the MCS component of the SF-36 or between percentage change in weight and the SF-36 PCS or MCS summary scores.


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Discussion and Conclusions
 
The objectives of this study were to measure the distance walked during a 6MWT by people who were morbidly obese preparing for GBS, to assess the relationship between this measure of physical function and their perceptions of HR-QOL at 3- and 6-month postsurgical follow-ups, and to compare it with preoperative measurements. The results showed that subjects with morbid obesity had functional walking distances that were only 55% of those of age-matched people who were healthy. However, after undergoing GBS, the subjects had marked functional improvement, as measured by the 6MWT distances at both 3- and 6-month follow-ups. Enright25 reported that people with a BMI of greater than 30 walked a substantially shorter distance compared with a control group of people of normal weight and that BMI negatively affected the 6MWT distance.

The subjects in our study had a 33% overall increase in walking distance (mean distance=137 m) from before GBS to 6 months after GBS. An improvement of 70 m has been reported as a clinically meaningful change in functional status.25 Because exercise capacity has previously been established as the strongest predictor of mortality from all causes, even after adjustment for known risk factors such as cardiac disease, smoking, hypertension, obesity, or cholesterol level,15–17,26 improvements in functional capacity have serious long-term implications for these individuals.

In addition to improved functional walking distance, our subjects reported a reduced perception of exertion during both the 3- and 6-month 6MWTs after GBS. These findings suggest that as the subjects lost weight, their perception of effort during functional walking was reduced. In women with moderate to severe obesity, a 10% weight loss through dieting has been shown to increase self-selected walking speed and maximal oxygen consumption and to reduce walking oxygen consumption and perceived exertion during walking.18 Although exercise metabolism was not measured in the current study, decreased energy expenditure also has been reported after weight-loss surgery both at rest27,28 and during self-selected and preset treadmill walking speeds.29 Foster et al30 found that walking energy expenditure in people who were obese was reduced more than expected on the basis of the amount of weight lost. They attributed the disproportionate reduction in energy expenditure to factors such as decreased mechanical work in overcoming friction between the thighs and between the arms and the trunk, as well as to less extraneous motion in swinging the arms and moving the thighs due to reduced girth. A reduction in the energy cost of respiration also was thought to contribute to decreased energy expenditure during walking.

These factors not only represent reduced stress to body systems and structures but also most likely contribute to a person's perception of effort during physical activity. When the Borg RPE scale is used, any change in physiological stimuli may alter the sensation of breathlessness and general exertion.31 Thus, a reduction in energy expenditure combined with the physical benefit of weight loss probably contributed to lower RPEs in our study. A substantial reduction in a person's perception of exertion despite walking at a faster speed is of clinical importance in that the person may be more inclined to initiate and adhere to an exercise program if the individual perceives his or her efforts to be less laborious. Of note, we did not discuss with any subject the RPE reports from previous test sessions, and there was sufficient time between test sessions to preclude subjects from recalling their previous choices. Thus, subjects were not comparing their current RPE selections with those from prior tests, and their RPE reports, therefore, were presumably a true assessment of exertion at a given time.

Not to be underestimated is the effect of excess weight on the HR-QOL of people who are morbidly obese. In a 6- to 12-month follow-up assessment of patients who had undergone GBS, Hooper et al32 found significant improvement in HR-QOL as measured by the SF-36. Sanchez-Santos et al10 observed significant improvement in HR-QOL in patients 5 years after weight-loss surgery, with poorer outcomes in those patients who had lost an insufficient amount of weight. Our results concurred with these findings and with the findings of other studies.33,34 Particularly noteworthy for this population was that improvements in the physical functioning score of the SF-36 reflected a 51% change in scores from before GBS to 6 months after GBS. The SF-36 physical functioning scale assesses the impact of health on physical activities such as walking, climbing stairs, and being active (moderate to vigorous activity). Our subjects’ self-reports of enhanced physical functioning were supported by their measurable increases in walking distance after GBS. There also was a positive correlation between changes in scores for walking distance and for the PCS cluster of the SF-36 from 3 to 6 months after GBS.

Wadden and Phelan34 reported that people who were obese had decreased physical functioning scores, as measured by the SF-36, and that weight loss improved HR-QOL scores, specifically in physical functioning. We found no correlation between percentage of change in weight and SF-36 scores over time, but the subjects’ self-ratings of improved physical well-being were supported by measured improvements in functional capacity.

One unexpected finding in our study was that although the MCS score improved significantly at 3 and 6 months after GBS, no correlation was found between percentage changes in the MCS score and the 6MWT distance. This lack of correlation was interesting because psychological factors have been reported to affect physical performance negatively or positively.35 Our results indicated that perceived physical limitations may be a greater barrier to function than perceived mental limitations. Additionally, it was remarkable that subjects who initially had an MCS score lower than that of the general population before GBS had a score higher than that of the general population at both 3 and 6 months after GBS. Because poor mental health is associated with various health problems, this improvement after GBS represents another benefit of weight-loss surgery. Such early improvements in mental well-being may support overall long-term success after GBS in terms of adherence to the necessary lifestyle modifications, including routine exercise.

As expected, BMI decreased during the 6 months after GBS, with subjects experiencing a mean reduction of 34% in BMI, or a percentage (X±SD) of excess weight loss of 57.7%±14.5%.36 Previous reports have indicated that most weight loss after GBS occurs within the first 6 months.19 Although the mean 6-month BMI of 30.1 would still classify these individuals as obese, we expected that weight loss would continue throughout the first year after surgery because patients are estimated to lose 60% to 70% of their excess body weight by 1 year after surgery.19

The combination of decreasing BMI and increasing functional capacity affords these patients the opportunity to greatly reduce their increased mortality risk associated with obesity. Improvements have been documented after weight-loss surgery in patients with type 2 diabetes mellitus, hypertension, dyslipidemia, and cardiovascular disease.2 Increased functional capacity confers its own benefits.15,17 The 6MWT distances measured for each patient would provide an excellent baseline for establishing the aerobic component of an exercise prescription. Although the recommended way to improve health status is 30 to 60 minutes of daily exercise involving large muscle groups 3 to 6 times per week, health benefits also may accrue to people with decreased functional capacity who perform intermittent bouts of exercise lasting 5 to 10 minutes for 3 to 6 times per day.37

In preparation for GBS, prospective patients are educated extensively about the surgery and alternative treatments for management of morbid obesity.38 Patients also typically undergo 6 to 12 months of counseling and education with a psychologist or nurse counselor, social worker, dietitian, and surgeon.39 They are instructed about psychosocial issues and the required presurgical and postsurgical behavioral changes.40,41 In addition to recommendations about dietary changes, patients receive instructions that exercise must become a routine component of their lives. One limitation of this study was the fact that exercise was not monitored. We, therefore, do not know the extent to which the subjects adhered to a specific program of exercise and what influence any exercise had on the rate of weight loss. It would be useful to measure these components in future studies because they would provide insight into the amount of exercise individuals could perform safely soon after weight-loss surgery.

Additionally, exercise has been shown to have the highest rate of nonadherence at 12-month postsurgical follow-up,40 which suggests that patients may lack specific instruction and guidance about appropriate exercise programs. Physical therapists are uniquely qualified to instruct, monitor, and educate patients about the importance of exercise, including mode, frequency, and intensity of activity for cardiovascular fitness, muscle strength (force-generating capacity), and endurance. Successful GBS outcomes depend, in part, on routine physical exercise.41 Physical therapy examinations and interventions are critical to the implementation of an appropriate exercise program specifically tailored to each client. Understanding early postoperative changes in functional status will help physical therapists develop individualized programs. In addition to addressing cardiovascular function and muscle strengthening, physical therapists can monitor patients for musculoskeletal dysfunction, which has been reported to occur in at least 1 joint in every patient in a presurgical cohort and to continue in 48% of patients at 6 to 12 months after GBS.32

Other limitations of the study were its relatively small sample size, which was, nonetheless, representative of the population that elects to undergo GBS, the limited geographic region from which these patients came, and the treatment of all the patients by the same surgeon. The data collected on 6MWT distances also were insufficient for normative criteria but did provide interesting preliminary information.

In summary, our findings provided indexes of functional capacity in people with morbid obesity before and after GBS. Our subjects experienced a rapid improvement in functional walking distances within a short time after surgery. Such benefits likely could be enhanced through a patient-specific exercise program and by the provision of patient education about the benefits and implications of regular physical activity.


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Footnotes
 
Dr Tompkins, Dr Bosch, and Dr Swain provided concept/idea/research design. Dr Tompkins, Dr Bosch, Dr Chenowith, and Dr Swain provided writing. Dr Tompkins, Dr Chenowith, Ms Tiede, and Dr Swain provided data collection. Dr Tompkins and Dr Bosch provided data analysis. Dr Tompkins provided project management and clerical support. Dr Swain provided subjects. Dr Tompkins and Dr Swain provided facilities/equipment. Dr Bosch and Dr Swain provided institutional liaisons. Dr Tompkins, Dr Chenowith, and Dr Swain provided consultation (including review of manuscript before submission).

Editing, proofreading, and reference verification were provided by the Section of Scientific Publications, Mayo Clinic.

* SR Instruments Inc, 600 Young St, Tonawanda, NY 14150. Back

{dagger} Itin Scale Co Inc, 4802 Glenwood Rd, Brooklyn, NY 11234. Back

{ddagger} SPSS Inc, 233 S Wacker Dr, Chicago, IL 60606. Back


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R. K. Evans
The Role of Physical Activity Participation in Weight Loss Outcomes Following Weight Loss Surgery
American Journal of Lifestyle Medicine, March 1, 2010; 4(2): 124 - 129.
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