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* From the Departments of Pediatric Physical Therapy (Drs. Klijn, van der Net, and Helders), Pediatric Gastroenterology (Dr. Oudshoorn), and Pediatric Pulmonology (Drs. van der Ent and Kimpen), Wilhelmina Children’s Hospital, University Medical Center, Utrecht, the Netherlands.
Correspondence to: Janjaap van der Net, PhD, Department of Pediatric Physical Therapy, Wilhelmina Children’s Hospital, University Medical Center, Suite KB02.056.0, PO Box 85090, 3508 AB Utrecht, the Netherlands; e-mail: J.vandernet{at}wkz.azu.nl
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Abstract |
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Design and methods: Twenty patients were randomly assigned to the training group (TG) [11 patients; mean (± SD) age, 13.6 ± 1.3 years; mean FEV1, 75.2 ± 20.7% predicted] or the control group (CG) [9 patients; mean age, 14.2 ± 2.1 years; FEV1, 82.1 ± 19.1% predicted]. The TG trained 2 days per week for 12 weeks, with each session lasting 30 to 45 min. The training program consisted of anaerobic activities lasting 20 to 30 s. The control subjects were asked not to change their normal daily activities. Body composition, pulmonary function, peripheral muscle force, habitual physical activity, aerobic and anaerobic exercise performance, and quality of life were reevaluated at the end of the training program, and again after a 12-week follow-up period.
Results: Patients in the TG significantly improved their anaerobic performance, aerobic performance, and quality of life. No significant changes were seen in other parameters, and no improvements were found in CG. After the follow-up period, only anaerobic performance and quality of life in TG were significantly higher compared to pretraining values.
Conclusions: Anaerobic training has measurable effects on aerobic performance (although not sustained), anaerobic performance, and health-related quality of life in children with CF. Therefore, anaerobic training could be an important component of therapeutic programs for CF patients.
Key Words: anaerobic training • cystic fibrosis • nutritional status • pulmonary function • quality of life
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Introduction |
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TOPAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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Several studies789101112 have shown reduced anaerobic performance in children with CF. In addition, children with CF do not participate in activities with high intensity as much as do healthy control subjects.13
It has been shown that healthy children’s anaerobic performance can be enhanced through participation in structured exercise programs.1415 Rotstein and colleagues14 reported an increase in aerobic and anaerobic performance after an anaerobic training program. It is not clear whether anaerobic training can improve anaerobic and aerobic fitness in children with CF.
Improvement of anaerobic performance could be important for the daily functioning of children with CF. The aim of this study was therefore to investigate the effects of an anaerobic training program on anaerobic and aerobic performance, lung function, body composition, peripheral muscle strength, and health-related quality of life (HRQOL) of children with CF.
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Materials and Methods |
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TOPAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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Study Protocol
After the baseline measurements, the tests were repeated within 7 days after the training program was finished, and again 12 weeks later. The study was designed as a randomized controlled trial. After the pretraining tests, the children were randomly assigned by concealed opaque envelopes to either the training group (TG) or the control group (CG). The control subjects were asked to continue their normal daily activities as well as their physiotherapy regime. The primary researcher was blinded for the experimental condition.
Nutritional Assessment
Anthropometric measurements were made prior to exercise testing. Fat-free mass (FFM) was determined in fasting condition using bioelectrical impedance techniques. Body weight (BW) was measured using a platform beam balance (Mettler; Greifensee, Switzerland) with an accuracy of 0.02 kg. Height was measured with a stadiometer (Holtain; Crymich, UK) with an accuracy of 0.1 cm. Body mass index (BMI) was determined (weight/height2).
Pulmonary Function Tests
Pulmonary function tests were performed after the inhalation of 800 µg salbutamol via metered-dose inhaler with a spacer in order to rule out important bronchial hyperreactivity. FVC, FEV1, and forced expiratory flow between 25% and 75% of expiratory vital capacity were obtained from maximal expiratory flow-volume curves (Masterscreen; Jaeger; Wuerzburg, Germany). Residual volume and total lung capacity were measured in a volume-constant body plethysmograph (Masterlab; Jaeger) and the residual volume/total lung capacity ratios were calculated from the actual values. Values are expressed as the percentage of predicted values.16
Peripheral Muscle Strength
Isometric muscle force measurements were performed for four muscle groups (ie, shoulder abductors, elbow flexors, hip-extensors, and knee extensors) according to the description of Backman et al.17 Results for peripheral muscle force are presented as the total maximal muscle force (ie, summed maximal force in four muscle groups, since factor analyses showed a single-factor solution [eigenvalue, 2.7; 68% of total variance]).
Exercise Testing
Subsequent anaerobic and aerobic exercise tests were performed on an electronically braked cycle ergometer (Lode Examiner; Groningen, the Netherlands). All subjects were familiar with the different tests and equipment used. During the tests, heart rate was monitored continuously by three-lead ECG (Hewlett-Packard; Amstelveen, the Netherlands) and oxygen saturation by pulse oximetry (200 E; Nellcor; Breda, the Netherlands). Verbal encouragement was given throughout the tests to stimulate maximal performance.
Each subject performed a Wingate anaerobic test (WanT) to assess anaerobic performance.18 The WanT is a valid and reliable test to evaluate short-term anaerobic power in healthy children, and in children with CF and other chronic illnesses.7111819 The subjects were instructed to start pedaling as fast as possible after a 1-min warm-up against 15-W resistance, while at the same time the full breaking force was applied through an integrated computer program. Anaerobic performance indexes were reported as mean power (MP [power averaged for > 30 s]) and peak power (PP [highest power during the test]).
After the WanT, the subjects rested for at least 45 min before aerobic fitness was assessed by a standard progressive incremental exercise test. Workload was increased by 15 W at 1-min intervals. The maximal workload (Wmax) was defined as the highest workload maintained during 30 s. Continuous respiratory gas analysis and volume measurements were performed breath by breath with a triple V valveless mouthpiece, and were stored in a computerized exercise system (Oxycon Champion; Jaeger). Internal gas and volume calibrations were made before each test. Measurements taken included oxygen uptake (
O2), carbon dioxide production, ventilation, and respiratory exchange ratio (ie, carbon dioxide production/O2). The highest O2 achieved during the last 30 s of exercise was taken as the peak O2 (O2peak).8
Efforts were considered to be at a maximum level if subjects showed clinical signs of intense effort and were unable to maintain speed at > 50 revolutions per minute,20 and if at least one of the following two criteria were met: (1) cardiac frequency of > 180 beats/min; or (2) maximal respiratory exchange ratio of > 1.0.2122 Predicted O2peak values were obtained from an age-matched and gender-matched Dutch reference population.23
Lactate
Blood samples were drawn 3 min after peak aerobic exercise from an antecubital vein and were collected in tubes (Vacutainer; Becton Dickinson; Franklin Lakes, NJ) and subsequently analyzed (Vitros 250 analyzer; Johnson & Johnson Clinical Diagnostics; Rochester, NY).
Daily Physical Activity
Physical activity was assessed with the habitual activity estimation scale.24 This scale reviews the subject’s activity level for 2 weekdays during the previous 2 weeks. The total percentage of time spent being active is presented. The habitual activity estimation scale has been used in studies of children with CF2526 and in other studies of children with chronic disease.27
Quality of Life
Quality of life was measured with a disease-specific HRQOL questionnaire, the CF questionnaire (CFQ). The CFQ consists of a 47-item teen/adult version and a 35-item child version.2829 The CFQ takes into account the different developmental stages, and makes it possible to monitor the health status and quality of life of patients with CF from 6 years of age throughout adulthood.2829
Anaerobic Training Program
The subjects in the TG trained on a individual basis, and the standardized training sessions were led by the children’s own physiotherapist. Specific written instructions in the form of a booklet were given to the physiotherapists. The TG trained 2 days per week for 12 weeks. Each session lasted 30 to 45 min. Guidelines based on a review of anaerobic training studies in children were used.30 The training program consists of eight basic training sessions that were repeated every 4 weeks. The training program is described in more detail at www.chestjournal.org/cgi/content/full/125/4/1299/DC1. Individual scores and changes in training overload were carefully recorded in a logbook. The children were constantly encouraged to exercise at maximal speed.
Statistical Analysis
The data are presented as mean ± SD. All data were tested for normality with the Shapiro-Wilks test. The analysis of variance for repeated measures was used for within-group and between-group comparisons. Between-group comparisons were made with an unpaired t test. Changes within the two groups were analyzed with a two-tailed paired t test. Pearson correlation analyses and linear regression analyses were performed for HRQOL with aerobic and anaerobic indexes. Data were analyzed using the a statistical software package (SPSS, version 9.0; SPSS; Chicago, IL).
To achieve a difference in PP per kilogram BW of 10% with an SD of 0.8 W/kg and a statistical power of 80%, it was calculated that eight patients had to be included in each study group.
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Results |
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Effects of Exercise Training
Body Composition, Pulmonary Function, Muscle Force, and Habitual Physical Activity:
At the end of the 12-week training period, a significant within-group increase was found for height (TG, 1.5 ± 0.9 cm [p < 0.001]; CG, 1.1 ± 1.0 cm [p < 0.05]) and weight (TG, 0.4 ± 0.6 kg [p < 0.05]; CG, 0.8 ± 1.0 [p < 0.05]). Within-group and between-group comparisons revealed no significant differences for body composition, pulmonary function, peripheral muscle force, and habitual physical activity at the end of the training period.
Anaerobic and Aerobic Performance:
The changes observed after the 12-week training period for anaerobic and aerobic performance are shown in Table 3
. The TG showed significant improvements in absolute PP (11.7%) and MP (12.4%), in PP and MP per kilogram BW (10.9% and 10.1%, respectively), and in PP and MP per kilogram FFM (11.8% and 11.9%, respectively). With respect to aerobic measurements, the TG showed significant improvements in O2peak (5.2 mL/min and 5.7% predicted), Wmax (7.9%), and serum lactate levels (26.1%), while the increase in O2peak per kilogram FFM (5.2%) was not significant. In the CG, a significant decrease was found for O2peak per kilogram BW (– 1.5%) and per kilogram FFM (– 5.6%), while other parameters were unchanged.
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Regression analysis in the TG indicated that the change in PP accounted for 41% of the variance in the physical functioning domain (p < 0.05). Changes in MP or O2peak were not independent correlates of changes in quality-of-life scores.
Effects of Follow-up Period
Comparing the pretraining period and the end of the follow-up period, a significant increase was found for mean height (TG, 2.8 ± 1.0 cm [p < 0.001]; CG, 2.1 ± 1.2 cm [p < 0.01]), weight (TG, 1.7 ± 1.5 kg [p < 0.01]; CG, 1.7 ± 1.3 kg [p < 0.01]), and FFM (TG, 2.0 ± 2.3 kg [p < 0.05]; CG, 1.7 ± 1.2 kg [p < 0.05]), but no changes were found for habitual physical activity. However, between-group comparisons of changes observed at the pretraining assessment compared with the end of the follow-up period were not significant. BMI, pulmonary function, peripheral muscle force, and habitual physical activity did not change significantly in both groups.
The TG showed significant higher follow-up levels of absolute PP (54.6 ± 47.7 W; p < 0.001) and MP (24.9 ± 73.5 W; p < 0.01) when compared with pretraining levels. The increase in the CG was not significant compared to baseline values (PP, 21.7 ± 15.6 [p = 0.34]; MP, 12.7 ± 34.4 [p = 0.31]). All other anaerobic indexes decreased to baseline values.
With respect to aerobic performance, no significant differences were found in the TG between values at baseline and at the end of follow-up period. The CG showed significantly lower O2peak (BW decrease, 1.5 ± 1.7 mL/kg/min [p < 0.05]; FFM decrease, 3.0 ± 1.9 mL/kg/min) and serum lactate levels (decrease, 1.2 ± 1.2 mmol/L; p < 0.05) when comparing values in the pretraining period and at the end of the follow-up period. At the end of the follow-up period, the domain of physical functioning in the TG (8.3 ± 8.4; p < 0.01) was still significantly higher compared to pretraining values.
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Discussion |
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TOPAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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To our knowledge, this is the first study to do-cument that children with CF are able to improve their anaerobic exercise capability through a high-intensity training program. These results are in agreement with those of anaerobic training studies in healthy children.141531 The TG increased their PP by 12.2%, which compares favorably with the results of the study by McManus and colleagues32 after an 8-week sprint-running training program performed three times per week in healthy girls (PP, 9.7%). Rotstein and colleagues14 reported an increase in PP and MP per kilogram BW (14% and 10%, respectively) after a 9-week training program that was performed three times per week. These results are consistent with the increase found in our study (PP/kg BW, 11%; MP/kg BW, 10%). Grodjinovsky and colleagues15 reported much lower improvements in MP per kilogram BW (3 to 4%) and PP per kilogram BW (4%) after a 6-week anaerobic training program that was performed three times per week in healthy children who were 11 to 13 year old. Although guidelines for anaerobic training in children have not yet been clearly established,30 the outcomes of these findings suggest that a minimal time period of approximately 8 weeks would be likely to induce a substantial improvement in pediatric anaerobic fitness.
Changes in aerobic exercise capacity usually are associated with specific training programs involving several hours per week at submaximal intensity.33 Although the intensity of our training program may be considered very stressful and the duration of the exercises very brief, anaerobic training resulted in an increase in O2peak (5%). This result is in accordance with those of studies1434 in healthy children that have shown an increase in aerobic capacity of 4 to 7% after anaerobic training. These results may be explained by the fact that resynthesis of adenosine triphosphate during high-intensity exercise depends on both aerobic and anaerobic processes.35 Moreover, in children approximately 40% of energy production in the WanT test comes from aerobic metabolism.30 In addition, although an incremental exercise test explores aerobic capacity and is not a valid tool for assessing anaerobic performance,36 the increase in serum lactate values seen in the TG suggests a larger contribution of anaerobic glycolysis during peak aerobic exercise. In other words, improved anaerobic energy metabolism possibly enhanced aerobic power output. This is supported by the finding that during specific aerobic training a decrease is seen in serum lactate concentration.37
Increased anaerobic performance has been linked to biochemical changes in the muscle of children.31 Fournier and colleagues31 reported a 21% increase in anaerobic enzyme activity after sprint training. Subsequently, higher serum lactate values in our study provide indirect evidence in support of improvements in biochemical processes associated with anaerobic metabolism as a result of the training program.
Improvements in HRQOL, as measured by the disease-specific CFQ, were seen in the TG. This is consistent with the results of other studies,538 which found improvements in quality-of-life scores after aerobic training, as measured with a generic measure (ie, the quality of well-being scale). Furthermore, as shown in our study and in other studies,538 changes in HRQOL are related to changes in exercise performance. This emphasizes the need to assess further both HRQOL and exercise performance, which provide valuable information on the multidimensional impact of the disease on patient’s quality of life and can make an important contribution to decision making in clinical practice.3839
In our study, no positive or adverse effects were seen in pulmonary function, FFM, and peripheral muscle strength due to the training program. As could be expected, no change was found in the amount of habitual physical activity, since we asked the participants not to change their activity level during the study period. Until now, the influence of physical training on pulmonary function has not been established clearly. Several studies404142 have shown improvements in pulmonary function after aerobic training. In contrast, other studies123843 have failed to detect improvements in pulmonary function. Eventually, all studies show that training is safe for the patients’ respiratory condition.
Effects of Follow-up Period
The increases found in the study parameters in the TG decreased to baseline values after the 12-week follow-up period, with the exception of anaerobic performance and HRQOL. Generally, the benefits of exercise disappear if physical activity is discontinued. However, as shown in our study and the studies of others,3841 benefits due to training seem to continue for some time in patients with CF, regardless of follow-up training sessions.
Clinical Implications of Anaerobic Training
Up to now, anaerobic exercise has received little attention compared to that for aerobic exercise, although many activities in daily life as well as sport activities are both aerobic and anaerobic in nature.89 Regular exercise is an important part of treatment in patients with CF. Adherence to exercise programs depends on individual motivation and variation in activities. The children enjoyed our training program, which motivated them to attend 98% of the training sessions. Our anaerobic training program offered the necessary variation to enhance adherence to it. The increase in anaerobic and aerobic performance and in HRQOL after anaerobic training indicates that this type of training can be included in the overall physical rehabilitation of children with mild-to-moderate CF. Ideally, an exercise program for children with CF could be made of aerobic, anaerobic, and strength-training activities. This makes it possible to individually tailor the program according to the preference of the participants, thereby improving the levels of exercise adherence.44
In conclusion, our results suggest that children with mild-to-moderate CF can enhance their anaerobic and aerobic performance and HRQOL through participation in a structured anaerobic exercise training program. In addition, aerobic performance increases as well. The improvements in anaerobic performance and HRQOL are maintained through a 12-week follow-up period. Therefore, anaerobic training could be an important component of the rehabilitation program of children with CF.
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Footnotes |
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O2 = oxygen uptake; O2peak = peak O2; WanT = Wingate anaerobic test; Wmax = maximal workload Received for publication January 30, 2003. Accepted for publication October 30, 2003.
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