In chronic disease such as multiple sclerosis (MS), it is important to maintain cardiovascular fitness as much as possible to maximize health and independence. The effects of aerobic exercise in patients with MS have been studied using bicycle ergometers for training and testing cardiovascular fitness.1–6 Bicycle ergometer tests have been used to measure indicators of cardiovascular fitness including, peak oxygen consumption (VO2max) and lactate threshold (LT), and to establish appropriate individualized training intensities.1–6 VO2max reflects the maximal rate at which a person can work aerobically. lactate threshold reflects the rate at which a person can work aerobically without accumulation of acid substances associated with fatigue. Lactate threshold, usually expressed as a percentage of VO2max, occurs around 50% to 60% of VO2max in apparently healthy sedentary subjects and at higher work loads (65% to 80% VO2max) in trained subjects.7 Increases in LT due to training imply that a higher steady-state workload can be performed without fatigue. In patients with MS, bicycle ergometer training with individualized intensity at 60% of VO2max increases VO2max1–3,5,6 and may decrease fatigue.2 Furthermore, bicycle training with individualized intensity at LT increased LT and tended to reduce fatigue.4
Clinicians often recommend that patients with MS do aerobic exercise in a swimming pool rather than on land. The buoyancy of water makes movement easier for individuals with weakness or muscular spasticity. Also, heat dissipation properties of water may minimize exercise-induced elevations in body temperature. In patients who are sensitive to heat, such as some patients with MS, the risk of fatigue or exacerbation of neurological symptoms may be reduced when exercising in cool-water pools.8–10
There is little research on the effects of aquatic exercise on individuals with MS. In one study, 9 subjects with MS completed a single bout of stationary bicycling on land and a single bout of stationary bicycling on a bike placed in a pool.11 The duration and intensity of exercise that the subjects achieved under the 2 cycling conditions were not significantly different. However, subjects reported that their perception of physical stress was less when bicycling in the water. Additional studies involved aerobic dance and resistance exercises in a pool; these included 2 case reports9,10 and 3 quasi-experimental studies.12–14 Outcome measures reported in these studies were tests of muscle performance,10,14 gait,9,10 health-related quality of life,12,13 and fatigue.12,13 The effect of aquatic exercise on cardiovascular fitness in patients with MS was not reported in these studies. In an experimental study by Romberg, et al15 subjects recruited from a MS clinic were randomized to an exercise or control group. The exercise group completed a 3-week inpatient program in which they did aqua aerobics and a 26-week home program in which they performed their preferred mode of aerobic exercise plus resistance exercises on land. Cardiovascular fitness was measured before and after the intervention. Changes over the 6-month period for the exercise and control groups showed a training effect but the effect was not specific for aquatic exercise.
Since aqua aerobics is advocated for people with MS, studies of its effects on patients' cardiovascular fitness are warranted. Aqua aerobics may provide cardiovascular fitness benefits similar to those provided by stationary bicycle exercise (eg, increases in VO2max and LT). Graded exercise testing, with measurements of gas exchange, is recommended for directly assessing cardiovascular fitness and prescribing training intensity when the necessary equipment is available.16 The purpose of the present case report is to describe how graded exercise testing (with measurements of gas exchange) was used to assist with intervention dosing and to measure the outcomes of an aqua aerobics class on 2 measures of cardiovascular fitness (VO2max and LT) and on fatigue for 2 individuals with MS.
Two of 6 participants in an 8-week aqua aerobics class for people with MS are described in this case report as they were the only participants who completed all components of the class. The class, conducted at a local hospital wellness center, included a preintervention examination, 16 exercise sessions (2 classes per week for 8 weeks), and a postintervention examination. Of the 4 other participants not described in the report, 2 were unable to attend all the exercise sessions due to unreliable transportation, 1 did not complete the postintervention cardiovascular fitness examination at the scheduled time, and 1 moved. Written consent and clearance for participation in the class was obtained from each individual and their physician.
The preintervention examination included a medical history, review of systems, Kurtzke's Functional Systems and Expanded Disability Status Rating Scale (EDSS),17 a leg bicycle ergometer graded exercise test on land, and the Fatigue Severity Scale (FSS).18 The graded exercise test and the FSS were repeated following the 8-week intervention.
Ms. A was a 40-year-old female who worked in an office and was diagnosed with MS 12 years prior to participating in the aqua aerobics class. She reported that her most disabling symptoms were frequent back pain, numbness in her hands and feet, occasional blurred vision, depression, and fatigue. Her medications included Avonex, BuSpar, and Effexor. Ms. A's EDSS score, 2.5/10, is assigned to individuals who exhibit minimal disability in 2 categories of the Functional Systems Scale, are fully ambulatory without aid, and able to work a full day. Ms A exhibited minimal disability in sensory and visual function. She was able to walk more than 1,000 meters without symptoms affecting the quality of her gait.
During the previous 2 years, she participated regularly (2 days per week) in an aqua aerobics class for senior adults with arthritis. She stated that she enjoyed socializing with the members of this class, however, she believed that the class was ‘too easy’ for her. She reported that she was afraid to join a class attended by able-bodied individuals because she thought it would be ‘too difficult’ for her. Her goal for participation in an aerobic class for persons with MS was to learn how to safely exercise at an intensity level higher than that to which she was accustomed
Ms. A was 169 cm tall, weighed 88.3 kg, and her Body Mass Index (BMI) was 30.9. Her resting heart rate and blood pressure were 72 bpm and 136/83 mmHg, respectively.
Ms. B is a 51-year-old female who was not employed outside the home and was diagnosed with MS 11 years prior to participation in the study. Ms. B stated that fatigue, numbness in her hands and feet, stiffness in her right leg, and occasional blurred vision were her most disabling symptoms. She also reported that her symptoms were exacerbated by heat. She was receiving medical treatment for fibromyalgia and depression as well as MS. Her medications included Elavil, Serzone, and Premarin. Ms. B's score on the EDSS, 3.0/10, is assigned to individuals who are fully ambulatory and who are able to work a full-day but have moderate disability in one category of the Functional Systems Scale or have mild disability in 3 or 4 categories. Ms. B exhibited mild disability in sensory, visual, and motor function. She walked 1,000 meters; however, at approximately 500 meters, her walking speed decreased as increased spasticity in her right quadricep and ankle plantar flexor musculature were observed. Furthermore, she reported that, when walking in the community, she had ‘to stop and rest frequently.’ She had not exercised on a regular basis for several years. She reported that she now had more time to participate in an exercise class and wanted to know how to do so safely.
Ms. B's height, weight, and BMI were 167 cm, 101.4 kg, and 36.3, respectively. Her resting heart rate was 67 bpm and blood pressure was 137/88 mmHg.
TESTS AND MEASURES
Aerobic capacity was determined using a continuous maximal graded exercise test (GXT) performed on a Monark 828E leg cycle ergometer. Heart rate and rhythm were measured continuously during the GXT using a standard 12-lead electrode configuration. Brachial blood pressure was measured at the end of each phase of the GXT using a manual sphygmomanometer. Borg Rating of Perceived Exertion (RPE), evaluated on a 6–20 scale, was recorded at the end of each exercise stage. Gas exchange measurement was conducted breath-by-breath using an open circuit spirometer (SensorMedics 2900 Metabolic Cart). Exercise values for oxygen uptake, carbon dioxide production, and pulmonary ventilation were calculated from 2-sec averages of the breath-by-breath data. Before each GXT, the metabolic cart was calibrated using a standard 3-L syringe and known gas concentrations.
The protocol for testing cardiovascular fitness began with 3 minutes of rest for the participant to become accustomed to the breathing mask. The participant began exercise with a warm-up period pedaling the leg ergometer at 40 rpm and 0-load for 2 minutes Following the warm-up period, the resistance on the ergometer was increased by 0.5 kp (workload increase = 20 watts) every 2 minutes until one of the following 3 indicators for termination of the exercise test occurred: (1) volitional exhaustion, (2) achievement of VO2max, or (3) symptoms indicating a risk to the health of the subject as defined by ACSM guidelines.19 Volitional exhaustion was defined as the time at which the subject could no longer maintain a pedal rate of 40 rpm because of muscle fatigue. Achievement of VO2max was defined as having met any of the following 3 criteria for VO2max: a plateau in oxygen uptake with increasing workload; a respiratory exchange ratio ≥ 1.5; or heart rate increases to within 10 beats/min of the subject's age-predicted maximum heart rate.19 Values obtained for aerobic capacity are referred to as VO2peak rather than VO2max when a subject's GXT performance is limited by volitional exhaustion.19
LT served as an indicator of cardiovascular fitness and, in addition, each participant's preintervention LT measurement was used to establish their individualized training intensity. Procedures for the latter use of LT are described in the intervention section. LT can be determined directly from blood samples or estimated noninvasively from ventilatory and gas exchange measurements obtained during a GXT. In the present case report, LT was estimated by the SensorMedics 2900 Metabolic Cart software using the Modified V-slope Method.20 The Modified V-slope method has been shown to provide a reliable estimate of LT in sedentary adults.21 In this report LT is expressed as: a percentage of the participant's VO2peak, the participant's oxygen consumption (VO2 at LT), and the metabolic equivalent level (METs).
The Fatigue Severity Scale18 (FSS) was administered prior to and after the intervention. The FSS subjectively assesses a person's perception of the impact of fatigue on their daily activity. Participants rate their fatigue using a 7-point scale for 9 statements. The score on the FSS is equal to the average score for the 9 items. A score of ‘7’ on the FSS indicates that the subject strongly agrees that fatigue has an effect on their daily activity and a score of ‘1’ denotes that he or she strongly disagrees that fatigue has an effect on them. The FSS is a valid and reliable assessment of fatigue for people with MS.18
Preintervention GXT data for Participants A and B including measurements of heart rate, blood pressure, RPE, and oxygen consumption at the end of each test stage are shown in the Table 1 and Table 2, respectively.
Participant A exhibited normal, linear increases in heart rate and oxygen consumption in the initial GXT (Table 1). Her blood pressure measurements also were normal. The GXT was terminated at volitional exhaustion when she could no longer maintain the test pedal speed (Table 1). Participant A did not meet objective criteria for a true maximal test. Ms. A's initial aerobic capacity (VO2peak = 23.4 ml/kg/min) was higher than the mean aerobic capacity reported for 61 women with MS (21.7 ± 5.5 ml/kg/min), the majority of whom, similar to Ms. A, exhibited mild disability.22 In the latter study, 51 of the 61 subjects had EDSS scores less than or equal to 3.5/10. However, her initial VO2 peak was below the 50th percentile (30.9 ml/kg/min) for healthy women in her age group.19
Spasticity in Participants B's right ankle plantar flexor musculature interfered with her ability to ride the bicycle ergometer. Foot straps, toe clips, and a low seat height were used to maintain her right foot on the pedal. Similarities existed between preintervention performances of the case subjects. Like Participant A, Participant B displayed normal heart rate and blood pressure responses during the initial GXT (Table 2). Furthermore, her GXT was stopped at volitional exhaustion and she also did not meet objective criteria for achieving maximal effort (Table 2). Ms B's initial VO2peak (17.6 ml/kg/min) was very low and met criteria established by the Social Security Administration for disability (18 ml/kg/min).19
Participant A's LT expressed as VO2 at LT (11.70 ml/kg/min or 3.34 METs) occurred at 50% of her VO2peak (Table 1). Ms A's LT was sufficient for walking at normal speed (ie, 3 mph) and for performing most daily activities but not large enough to perform moderately vigorous activities of daily living (such as climbing stairs which requires 4 METs) without breathlessness and accumulation of metabolic products associated with muscle fatigue.23
Participant B's preintervention LT (Table 2), expressed as VO2 at LT (7.32 ml/kg/min or 2.09 METS), was equivalent to the value considered necessary for performing light housework or walking about 2 mph.23 Her low LT and low VO2peak at baseline indicated that she was significantly deconditioned and, as a result, exercise beyond light house work or slow walking would be difficult for her.
Te initial FSS scores for our participants (Participant A = 5.4/7, Participant B = 5.6/7) were both above the mean score reported for healthy women of the same age and equivalent to means reported for individuals with MS and a similar EDSS ranking.4,24
EVALUATION AND DIAGNOSIS
Te Guide to Physical Therapist Practice Pattern 6B: Impaired Aerobic Capacity/Endurance Associated with Deconditioning served as an outline for management of the case participants.25 Both participants exhibited a low level of disability as defined by their EDSS scores. However, tests of cardiovascular fitness revealed that they both had impaired endurance large enough to impact their daily and recreational activity.
Te PT diagnosis for both participants was impaired endurance resulting in functional limitations and disability. Te prognosis for improvement in aerobic capacity following the intervention (an 8-week aqua aerobics class for people with MS) was good for both participants. It seemed plausible, based on the fact that individual A had not trained at a high enough intensity and individual B was deconditioned, that aqua aerobics at an appropriate exercise dose (similar bicycle ergometry) would increase cardiovascular fitness and may reduce fatigue.
Exercise Mode, Frequency, and Duration
Each participant attended an aqua aerobics class for people with MS. Te class was held 1 hour, 2 times per week for 8 weeks. Each class consisted of a 10-minute warm-up, 30 minutes of aerobic exercise, followed by a 20-minute cool-down period. Te warm-up and cool-down period included low-intensity aerobic exercises. Te cool-down also included resistance exercises in the pool. Te duration and structure of each class were based upon guidelines for exercise prescription with modifications specific for MS.16,26 Te number of classes per week and the program duration, 8 weeks, were determined by availability of the facility and staff. A physical therapist assistant with a certification in aqua aerobics served as the class leader and a physical therapist monitored the participants' exercise intensity.
During the 30 minute aerobic portion of the class, the participants exercised at an intensity equal to their LT. Training at LT overloads the peripheral vasculature and active muscles and increases the steady-state workload a person can perform without fatigue. This would appear to be beneficial for patients with MS and reduced activity level due to fatigue. Measurements of gas exchange, used to determine participants' LT, were not practical while exercising in the pool. Therefore, during the 30-minute aerobic portion of the class the participants were instructed to exercise at a heart rate equal to their heart rate at LT previously determined in their preintervention examination. This practical method for training at LT (ie, using heart rate at LT) is commonly used by competitive distance runners27 and has been employed in a bicycle ergometer training study involving patients with MS.4
Published guidelines for individualizing exercise intensity for people with MS (barring symptoms that require modification of the prescription intensity) are an intensity equivalent to (1) 50% to 70% of VO2peak or (2) 65% to 75% of HRpeak determined in a maximal graded exercise test.16,26 There are no specific guidelines related to the use of LT in individualizing exercise intensity for patients with MS. Te prescribed exercise intensity for Participant A (HR at LT = 115 bpm) occurred at 75% of her HRpeak and 50% of her VO2peak (Table 1). Te prescribed intensity for Participant B occurred at 72% of HRpeak and 41.3% of her VO2peak (Table 2). For both participants the prescribed exercise intensity was within existing guidelines.
VO2peak for Participant A
Similar to the pretest, in the post test Participant A exhibited normal cardiovascular responses (ie, heart rate, blood pressure, and oxygen consumption) to graded exercise (Table 3). Te amount of time Participant A was able to bicycle before reaching volitional exhaustion increased following the intervention and she achieved a higher fnal workload in the post-test (Table 3). Participant A's VO2 peak increased 11.4% from the pre- to the post-test (Table 3). However, despite improvement, Ms. A's VO2peak was still below the 50th percentile for healthy women in her age group.19
VO2peak for Participant B
Like Participant A, Participant B displayed normal cardiovascular responses during the post-test (Table 4). After training, Participant B was able to bicycle at a higher work load before reaching volitional exhaustion. Her post intervention VO2peak (20.60 ml/kg/min) was still slightly below the mean value reported for women with MS22 and was well below the 50th percentile for healthy women the same age range (28.2 ml/kg/min).19 Te intervention, however, increased her VO2peak 14.6% and to a value above the criteria for disability.
After intervention, LT increased for both individuals (Tables 3 and 4). Participant A's LT (15.7 ml/kg/min or 4.5 METs) had improved to the level required to comfortably sustain moderately vigorous daily and recreational activities.23 Participant B's LT (11.2 ml/kg/min or 3.18 METS) had improved to the level considered necessary for walking at a normal speed (ie, 3 mph).23
Fatigue Severity Scale
Te case subjects' scores on the FSS before and after training were as follows: Participant Abefore = 5.4/7, Participant Aafter = 3.6/7; Participant Bbefore = 5.6/7, and Participant Bafter = 5.6/7. Participant A reported a decrease in fatigue following endurance training, while Participant B reported no change in fatigue. After training, the participants FSS scores were still above the mean score reported for healthy women of the same age and equivalent to means reported for individuals with MS with similar EDSS rankings.24
This case report illustrates the use of metabolic and cardiovascular data obtained during a maximal GXT to (1) measure maximal aerobic capacity and estimate lactate threshold at baseline, (2) establish an appropriate exercise training intensity using HR at LT, and (3) measure the effects of an 8-week aqua aerobics class on indicators of cardiovascular fitness in 2 individuals with MS. Baseline exercise testing showed that both participants had a low aerobic capacity. Participant B's aerobic capacity was lower than Participant A's aerobic capacity. Participant B's higher level of disability, greater number of comorbidities, and lower level of physical activity, compared to A, likely accounted for her lower aerobic capacity. In general, people with MS, even people with low disability, have reduced aerobic capacity compared to healthy people.11,22 Furthermore, the magnitude of disparity between healthy people and people with MS appears to be related to the severity of MS.22,28 In addition to disability, factors such as comorbidities and participation in exercise may influence aerobic capacity.22
Following the 8-week aqua aerobics class, each participant's cardiovascular fitness increased as demonstrated by VO2peak and LT. Increases in VO2peak observed in this case report (11.4% for Participant A and 14.6% for Participant B) enabled the participants to perform more vigorous daily and recreational activities without breathlessness. The observed increases were within the range expected for sedentary healthy adults following land and aquatic exercise training (ie, 10% to 20%).29 For the MS population, improvements in VO2peak following land-based bicycle training have ranged from 10% to 22%.1–3,5,6 Table 5 summarizes studies that have measured cardiovascular adaptations to bicycle training in the MS population. The largest training effects were observed in studies involving combined leg and arm bicycle ergometer training, a higher training frequency (3 days per week vs. 2 days per week) and a longer training duration (> 8 weeks). In one bicycle training study involving 21 subjects with mild to moderate disability, the mean increase in aerobic capacity was 22%.2 The study subjects performed 30 minutes of combined leg and arm bicycle ergometry at 60% of VO2max 3 days a week for 15 weeks. In another training study, the investigators reported a 21% improvement in 13 subjects with MS and mild to moderate disability range following 15 weeks of training including 40 minutes of leg/arm ergometry at 60% of VO2max 3 times a week.1 The mean increase in aerobic capacity was 10% in the study in which 15 subjects with MS performed leg-only bicycle training at 60% of VO2max 2 times per week for 8 weeks.6
Since the principle of specificity of testing was not followed in this report (ie, the mode of exercise for testing and training were different), improvements achieved by the case subjects were expected to be less than improvements reported in previous studies in which subjects were tested and trained on a bicycle ergometer. Standardized protocols exist for testing aerobic capacity on land (eg, bicycle, treadmill, and step tests) but there are no tests that mimic aqua aerobics. Increasing the frequency and duration of the aqua aerobics class in this case report may produce even larger gains in aerobic capacity.
Information regarding exercise training and LT in individuals with MS is limited. Mostart and Kesselring4 showed that 4 weeks of aerobic training in an inpatient rehabilitation setting increased LT in subjects with MS. In their study 26 people with MS (EDSS range = 2.5 to 6.5) were randomly assigned to an exercise or non-exercise group. The exercise group performed five, 30-minute sessions of stationary bicycling per week in addition to physical rehabilitation. The non-exercise group performed physical rehabilitation only. Like the subjects in the present case report, the exercise group trained at an intensity equivalent to their heart rate at LT. The exercise group (n = 13) experienced a mean 12% increase in LT and a trend toward less fatigue (as determined by the FSS).4 There were no changes in LT or fatigue in the non-exercise group. Improvements in LT for our subjects (A= 33.8% and B= 53%) were much higher than the mean improvement reported by Mostart and Kesselring.4 Preintervention values for LT for participants in this case report (Tables 1 and 2) were below the baseline mean (14.29 ml/kg/min) for subjects in the experimental study.4 The case participants lower initial LT levels may explain larger improvements in LT observed in this report. The results of an investigation of the physiological responses of low fit older women to a 12-week aquatic exercise program lends support to this contention.30 Training resulted in a mean 20% increase in LT and furthermore, based upon the standard deviations reported for the mean LT before and after training, improvements as high as 49% may have been seen.30 Although the method used for determining LT in this case report is reliable in healthy individuals20, 31 the reproducibility in patients with MS is unknown. Therefore, a possible limitation of this case report is that random measurement error may also have contributed to the observed large improvements in LT.
Participant A's contention that her previous exercise class was ‘too easy’ was supported by her inability at the beginning of the current class to maintain the prescribed exercise intensity (HR at LT) and by her anecdotal comparisons of intensity of the 2 classes. When the current class began she was not accustomed to exercising at an intensity needed for her to achieve a cardiovascular training effect. Unfortunately exercise testing is not a routine component of community exercise classes in which people with chronic diseases and low disability (like Participant A) may elect to participate. The findings in this case report illustrate the benefits of baseline exercise testing to develop individualized exercise prescriptions and follow-up testing to monitor the effectiveness of an aerobic exercise regimen.
Physical therapists who prescribe cardiovascular exercise for patients with MS typically do not have access to the equipment used in this case report to directly measure maximal aerobic capacity (ie, metabolic cart). Alternatively, physical therapists can estimate aerobic capacity using bicycle exercise testing procedures (recommended for patients with MS) that involve determining the peak workload that the patient can achieve and the patient's heart rate at their peak workload.26 Furthermore, the HR obtained in the final workload can be used to establish an appropriate individualized training intensity.26 Use of age-predicted maximum heart rate (APMHR) to individualize intensity (rather than the actual HR response to graded exercise) is not recommended for the MS population.16,26 In patients who exhibit a blunted HR response to exercise resulting from a cardiovascular autonomic dysfunction use of the APMHR may result in a higher than indicated exercise intensity.16,32
Improvements in VO2 peak and LT in the present report were associated with decreased fatigue in Participant A but not Participant B. A limitation of the present case report is reliance on the FSS and the lack of additional instruments to measure fatigue, such as the SF-36 vitality subscale. The FSS discriminates between levels of fatigue in healthy and patient populations;18 however, the FSS may not be sensitive enough to assess changes in fatigue over time in patients with MS. Anecdotally Participant B said that the intervention made her feel more energetic and she was doing more activities at home. Use of a standardized assessment of self-reported physical activity would have augmented this case report.
The effects of training on fatigue differed for Participants A and B and may be an important factor related to exercise adherence for people with MS. Roehrs and Karst13 found that their 12-week aquatic aerobic program resulted in a significant decrease in fatigue (measured with the fatigue subscale of the Multiple Sclerosis Quality of Life Inventory) in 19 patients with MS (EDSS range = 1.5 to 8). They noted that only 19 of 31 adults with MS who agreed to participate in their study completed at least 25% of the exercise sessions. Issues related to withdrawal or sporadic attendance included poor bladder control, lack of transportation to the pool, and impaired mobility to get from the pool to the bathroom. Likewise, transportation and mobility issues impacted attendance in our aqua aerobics classes. Addressing these barriers appears to be important to promote adherence to aquatic exercise programs for people with MS.
Physical therapists often encourage people with MS to participate in aquatic aerobic exercise; however, little research has been conducted on the efficacy of aquatic aerobic exercise in improving the cardiovascular fitness of patients with MS. In this case report an 8-week aqua aerobic training program whose intensity was determined by exercise testing resulted in improvements in cardiovascular fitness in 2 individuals with multiple sclerosis.
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