physical activity and exercise training have become increasingly important and widely accepted as part of therapy and rehabilitation programmes in cystic fibrosis ( cf ) management .
physical activity refers to any body movement produced by the skeletal muscles and occurs in a variety of forms ( i.e. , free play , exercise , organised sports ) , resulting in a substantial increase in energy expenditure .
exercise training , however , can be defined as regular participation in vigorous physical activity to improve physical performance or cardiovascular function or muscle strength or any combination of these three . prior to initiation of any exercise training , detailed exercise testing is recommended , not only to monitor disease progression , but also to detect exercise - induced limitations and therefore to provide the patients with safe training recommendations [ 3 , 4 ] .
ideally , exercise training should complement current therapies in cf patient healthcare . in previous reports , however , it has emerged that clinicians lack specific recommendations to instruct their patients appropriately [ 5 , 6 ] .  
several studies report beneficial effects of exercise training on cardiopulmonary fitness ( cpf ) in patients with cf [ 711 ] .
cpf pertains to the functions of both the heart and the pulmonary system , usually expressed as peak oxygen consumption ( peak vo2 ) , the most reliable and reproducible measure of cpf following maximal exercise testing .
recently , bradley and moran examined the effectiveness of exercise training in cf using a systematic cochrane review .
seven randomised controlled trials with a total number of 231 participants were included , investigating the effects of different types of training ( aerobic versus anaerobic training , anaerobic training , aerobic training , and the combination of both ) .
the authors conclude that exercise training is an important part of cf care ; however , there are insufficient numbers of studies published to date to document the benefits of exercise training for people with cf .
nevertheless , the authors state that there is no evidence to actively discourage exercise training . in 2009
highlighted that education of health care providers and implementing exercise in clinical practice are needed .
regular exercise training may improve pulmonary function , increase aerobic and anaerobic capacity , strengthen ventilatory muscles , and help airway sputum clearance , the latter probably due to enhanced ventilation and vibrations during exercise , leading to mechanical airway clearance [ 7 , 8 , 11 , 1519 ] .
furthermore , it is suspected that moderate intensity exercise blocks the amiloride - sensitive sodium channels of the respiratory epithelium , thus resulting in lower mucus viscosity , simplifying mucus expectoration . moreover , higher activity levels and peak vo2 are positively related to survival in cf [ 2123 ] . types of training ( aerobic versus anaerobic ) may have different effects on improvement in exercise tolerance , but most training studies so far have focused on endurance training , observing improvements in pulmonary function , peak vo2 , breathlessness , and quality of life [ 11 , 18 , 19 , 24 ] .
exercise training including anaerobic ( strength ) exercises can improve muscle strength and muscle size , resulting in weight gain [ 16 , 19 , 25 ] .
therefore , a comprehensive training programme should include a variety of sports activities , adapted to the special needs and preferences of each individual .
however , the effects of training most likely depend on the training methods , as improvements may only persist with continuous training in the long term .
the aim of this paper is to provide a focused update on aerobic and anaerobic responses to exercise and habitual physical activity exclusive to children and adolescents with cf .
this paper will help to strengthen the rationale for the initiation of further clinical trials examining the effects of regular exercise on overall health in the paediatric cf population .
all relevant studies for this paper were identified using electronic search of medline and pubmed databases . a bibliography search of all accessed publications was also performed .
key descriptors were cystic fibrosis , training , rehabilitation , aerobic fitness , children , and adolescents .
the selection of studies presented in the paper was based upon the agreement by all four authors .
we include studies of subjects with cf , independently of their disease severity , and type of exercise training ( aerobic training ; anaerobic training ; combination of aerobic and anaerobic training , as well as inspiratory muscle training ) .  
neither any physical activity nor an exercise task can be considered as solely aerobic or anaerobic .
the nature of a child 's activity requires an interplay of both aerobic and anaerobic metabolism .
an update on aerobic and anaerobic performance in children with cf is outlined below .  
aerobic exercises include any kind of activities using large muscle groups that can be maintained continuously in a rhythmic manner ( e.g. , swimming , cycling , or running ) .
activities with moderate effort can be performed over hours without significant decline in exercise performance ( although there is some variation on individuals ' physical fitness , energy intake during exercise , etc . ) .
aerobic capacity of children with cf over a long period of time is less researched , indicating the dearth of data regarding longitudinal assessment of peak vo2 .
investigated the longitudinal relationship between peak vo2 , pulmonary function , and body composition in 65 children with mild cf lung disease ( 10.5  2.9 years of age ; forced expiratory volume in 1  s ( fev1 ) 92.6  20.5% predicted ) over two years .
the authors found that longitudinal changes in lung function were associated with functional changes in peak vo2 and to a lesser extent with fat free mass ( ffm ) .
while ffm is a critical determinant of maximal exercise capacity , ffm may be important for maintaining overall functional capacity and to improve long - term outcome in cf [ 26 , 27 ] .
peak vo2 during maximal exercise is an established prognostic marker in cf [ 2123 ] . in particular
, longitudinal data of peak vo2 in children with cf indicate a decline in peak vo2 over time ; however , those with higher peak vo2 values have a prolonged survival . in comparison to healthy subjects , children with
cf show reduced maximal exercise performance , decreased respiratory function , malnutrition , and physical inactivity as well as intrinsic abnormalities of the skeletal muscle , all likely to be contributing factors [ 28 , 29 ] .
diminished efficiency of mitochondrial oxidative adenosine triphosphate ( atp ) synthesis or abnormalities in myofibril mechanics may also affect maximal exercise capacity in cf [ 26 , 30 ] .
it has also been reported that peak vo2 and early oxygen consumption ( vo2 ) recovery are significantly related in children with chronic lung disease , implying that the greater the aerobic fitness , the faster the rate of recovery following exercise .
hebestreit et al . reported slower vo2 kinetics at the onset of exercise in children with cf compared to healthy children , probably due to an impairment in oxygen delivery .  
improvements in cpf require individual dosages of training stimuli and vary among individuals . however , the optimal training modes for patients with cf have not yet been identified .
it has been demonstrated that the time spent on physical activity in children with cf is similar to that of healthy children , but healthy children spend more time exercising at vigorous intensities . in contrast , selvadurai et al . observed differences in activity behaviours between prepubertal and pubertal children with cf of different stages of disease severity and their healthy peers using accelerometry and activity diaries .
prepubertal and pubertal children with mild cf lung disease were more active compared to their healthy controls .
interestingly , between prepubertal children with moderate - to - severe cf lung disease and a control group no differences were found .
gender differences occurred between pubertal girls and boys with cf , as girls ' habitual physical activity levels were significantly lower .
however , compared to healthy controls , pubertal children with moderate to severe cf disease were significantly less active .
gender differences in habitual physical activity levels between healthy girls and boys are well known , not only when comparing to chronically diseased children [ 35 , 36 ] .
several studies investigating the effects of exercise training and rehabilitation programmes in cf showed increased peak vo2 and peak minute ventilation ( peak ve ) values , and reduced heart rates ( hr ) at submaximal workloads , indicating improved cpf [ 11 , 16 , 19 , 25 , 37 ] .
thus , even patients with severe cf lung disease are able to improve their cpf .
furthermore , it has been established that children with cf had higher activity levels , greater aerobic fitness , enhanced nutritional status , and significantly lower progression of disease .  
investigated the effects and acceptability of a 6-month home - based cycling programme in 14 children ( age 14.1 years ) with mild - to - moderate cf lung disease .
the programme consisted of 5 ergometer cycling sessions per week for 20  min each with the training intensity progressively increasing over time . in the first week
the training intensity started at 50% of maximal workload , increasing up to 60% in the following weeks until the next measurement was up to 70% of maximal workload . once a week , the programme was supervised by a physiotherapist .
hr was measured every three minutes , and the workload was adjusted to reach target training intensities between 140160 beats per minute ( 70%80% of predicted maximal ) . after the training period , peak vo2 per kg body mass as well as per kg ffm increased significantly .
moreover , leg muscle strength for knee extensors and ankle dorsiflexors significantly increased during the training period .
unfortunately , the acceptability of the programme was low , probably due to the somewhat  monotonous  cycling programme . in general
, adherence to treatments is challenging in cf , especially adherence to regular exercise and physical activity .
however , the participation in the prescribed exercise training programme has been shown to increase perceived competence and self - esteem in the children as important mediators to adherence behaviour .
this seems of particular relevance for patients in terms of maintaining an active lifestyle and adherence to training into the long term .
we suggest a training programme that should focus on the individual interests of the children including preferences for sport activities . the study may have benefited by including different activities to maintain motivation and adherence to training .
furthermore , in a 12-week randomised and controlled study following a standardised anaerobic training programme in eleven children with cf , a significant increase in peak vo2 ( mlmin ) in the training group was observed . the supervised training consisted of two 3045 min exercise sessions per week of special anaerobic exercises , for example
in contrast , peak vo2 was significantly decreased in the control group ( n = 9 ) .
after a 12-week follow up all parameters concerning aerobic fitness decreased to pretraining levels .  
schneiderman - walker et al . investigated the long - term effects of regular exercise training in a 3-year study .
children and adolescents with mild to moderate cf lung disease aged 719 years were randomly assigned to either an exercise intervention or control group .
the exercise group was instructed to perform a minimum of 20 minutes in their favourite endurance - related activities three times per week .
in addition , the patients were advised to monitor their hr while exercising at a training intensity of 70%80% of maximum hr .
exercise capacity was measured during cycle ergometry . at the end of the intervention , no significant differences in the annual rate of decline in peak vo2 , peak heart rate ( peak hr ) , and peak ve between either group were found .
however , the intervention group demonstrated a significantly lower annual decline in fev1 and vital capacity ( vc ) .
patients in the exercise group remained compliant during the study period and reported better well - being .  
anaerobic activities are characterised by high intensities of short durations ( lasting typically up to 30 s ) , being predominantly fuelled by nonoxidative sources of atp resynthesis .
previous studies investigating anaerobic performance of children and adults with cf showed lower values compared to healthy subjects [ 3941 ] .
furthermore , children with cf with higher levels of habitual activity have been found to possess increased anaerobic power during the wingate anaerobic test ( want ) .
these higher levels of activity are likely influenced by several factors such as the extent of malnutrition , muscle mass , mitochondrial abnormalities , and cf genotype [ 29 , 30 , 34 , 40 , 42 , 43 ] .  
boas et al . found lower power outputs in the want in 41 male adolescents with cf compared to healthy controls .
subgroup analysis of subjects with cf revealed that nutritional status and sexual maturation rather than pulmonary function may affect anaerobic exercise performance . in their observation , subjects with higher salivary testosterone ( > 4.0  ngdl ) had higher power outputs in both absolute terms and relative to lean body mass compared to subjects and lower salivary testosterone values ( < 4.0  ngdl ) .
furthermore , body mass index ( bmi ) was associated with higher anaerobic performance , indicating higher power output values . categorising
the patients regarding their pulmonary function showed no differences , however , this population had almost normal lung function values ( fev1 , 90.2  24.2% predicted ) .  
another study showed significant improvements in anaerobic parameters in the want following a 12-week individualised anaerobic training programme .
peak power and mean power per kilogram ffm significantly increased in the training group , as anaerobic parameters did not change in the control group .
after a 12-week followup period , anaerobic performance and quality of life remained improved whereas most outcome parameters decreased to pretraining levels .   in another related study ,
selvadurai et al . investigated the relationship between fitness and cf genotype in 79 children with a wide range of disease severity . the class of cf transmembrane conductance regulator ( cftr ) mutation was significantly correlated with anaerobic and aerobic performance , bmi , and pulmonary function .
patients with class i and ii cftr mutation had the lowest peak anaerobic power in the want compared to those with classes iii , iv , and v cftr mutations , respectively .   unfortunately , most training studies in cf are of short duration , and longitudinal data are lacking , especially in the paediatric population .
longitudinal and controlled studies are required to verify training effects in association with disease progression in cf and decline in pulmonary function and peak vo2 .
studies , documenting less or no effects after exercise training on cpf , are most likely due to a low number of study subjects , lack of a control group or lack of training supervision , and poor compliance [ 25 , 44 ] .
further research is warranted to assess the effects of different training methods longitudinally ( aerobic versus anaerobic training versus a combination of both training regimes ) .
more detailed information regarding training protocols ( intensity , duration , and rest periods ) would be advantageous to therapists and health care providers working with children with cf .
furthermore , when working with children the fun component needs to be emphasised , while group activities may be the preferred choice rather than isolated training ( i.e. , cycling or stepping ) , infection control permitting .
trampolining , for example , as a popular although controversial activity , has been discussed in the paediatric population and cf lung disease , especially due to the increased risk potential for injuries [ 4547 ] .
however , providing there is particular focus on safety issues and supervision , trampolining can be an effective adjunct to regular airway clearance techniques or even as part of physiotherapy in cf .
in habitual daily life patients with cf are faced with certain barriers and challenges according to their participation in regular exercise and habitual physical activity .
parents should be encouraged to exercise with their children and serve as role models ( i.e. , aiming to increase habitual physical activity levels ) .
based on the training studies available in children and adolescents with cf , there is no definitive evidence regarding the sustainability of training effects in the long term ( i.e. , months to years ) .
specific risks of exercise training in cf are presented in the table . during prolonged exercise , as a consequence of excessive sweat and sodium losses , children with cf
are advised to drink repeatedly ( i.e. , every 1520  min ) , and ideally including approximately 50  mmoll sodium chloride in their drink .
especially , in hot conditions , children may underestimate their fluid needs with the risk to undergo excessive dehydration .  
for example , cf patients with portal hypertension with significant enlargement of spleen and liver should , as a precaution , be advised against participation in contact sports .
patients participating in physical activities which take place at high altitudes ( e.g. , skiing ) should be monitored , especially if the patient is already hypoxic .
furthermore , episodes of acute right heart failure induced by a combination of altitude and high intensity exercise have been documented . during diving activities
air trapping could occur in patients with lung disease , on ascent the air expands , with risk of development of pneumothorax .
exercise - induced hypoxemia is a potential hazard for patients with cf , thus participation in high - intensity exercise needs consideration .
however , soon after the termination of high intensity efforts , sao2 returns to pre - exercise levels , while there is no evidence that brief exercise - induced hypoxemia causes damage to the child with cf .
cough with sputum may be observed during exercise in patients ; however , this is indicative of airway clearance .  
general guidelines for clinical exercise testing [ 54 , 55 ] and training in patients with chronic disease are beyond the scope of this paper and can be found elsewhere .
the table summarises a selection of recommended exercises , including training intensities for patients with cf .
our recommendations ( see table 1 ) are based on training studies available , as well as , our own clinical and practical experience in the work with children and adolescents with cf .
we support the approach of combining endurance and strengthening activities as well as exercises to improve flexibility , balance , and motor skills .
in addition to exercise training , an active lifestyle is generally recommended to improve exercise capacity , for example , using stairs instead of an elevator .
we therefore recommend including a detailed description of training methods and parameters ( duration , intensity , frequency , and rest periods ) in future studies .
in particular , this may help comparing results of different training studies . despite the beneficial effects of regular ( structured ) exercise , habitual physical activity levels ( activities that can easily incorporated in daily life )
physical activity is well recognized as part of health care and rehabilitation programmes in cf ; however the relationships between activity , fitness , and health are still poorly understood .
higher levels of habitual activity have been associated with higher aerobic and anaerobic capacity , a better quality of life , and improved survival . however ,
longitudinal studies are needed to support and justify programmes of regular exercise on the overall health status of children and adolescents with cf . to date , there is no evidence that children and adolescents with cf should not be physically active in daily life .
moreover , as part of their cf management , it would be desirable to inform patients , and their parents about the beneficial effects of exercise , but also its potential risks , and additionally provide patients with training recommendations .
it is necessary to instruct clinicians , health care support staff , patients and parents regarding adequate exercises and sports activities during rehabilitation programmes that can be implemented in normal daily life .
 physical activity and exercise training play an important role in the clinical management of patients with cystic fibrosis ( cf ) . 
 exercise training is more common and recognized as an essential part of rehabilitation programmes and overall cf care . 
 regular exercise training is associated with improved aerobic and anaerobic capacity , higher pulmonary function , and enhanced airway mucus clearance . 
 furthermore , patients with higher aerobic fitness have an improved survival 
 . aerobic and anaerobic training may have different effects , while the combination of both have been reported to be beneficial in cf . however , exercise training remains underutilised and not always incorporated into routine cf management . 
 we provide an update on aerobic and anaerobic responses to exercise and general training recommendations in children and adolescents with cf . 
 we propose that an active lifestyle and exercise training are an efficacious part of regular cf patient management . 
1. Introduction
2. Method of Review
3. Conclusion