International Journal of Pediatrics Several studies investigating the eﬀects of exercise train- ing and rehabilitation programmes in CF showed increased peak V˙O2 and peak minute ventilation (peak V˙ E) values, and reduced heart rates (HR) at submaximal workloads, indicating improved CPF [11, 16, 19, 25, 37]. Interestingly, the observed training eﬀects are independent of patients’ disease severity. 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 [34]. Gulmans et al. 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 [38]. 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 140–160 beats per minute (70%–80% of predicted maximal). After the training period, peak V˙ O2 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 participa- tion 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 [38]. Furthermore, in a 12-week randomised and controlled study following a standardised anaerobic training pro- gramme in eleven children with CF, a signiﬁcant increase in peak V˙ O2 (mL·min−1) in the training group was observed. The supervised training consisted of two 30–45 min exer- cise sessions per week of special anaerobic exercises, for example, sprints, chest passes, exchange runs, and so forth. all performed at near maximum intensities. The detailed training programme can be found elsewhere: (http://www .chestjournal.org/content/full/125/4/1299/DC1). In contrast, peak V˙ O2 was signiﬁcantly decreased in the control group (N = 9). After a 12-week follow up all parameters concerning aerobic ﬁtness decreased to pretraining levels [16]. 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 7–19 years were randomly assigned to either an exercise 3 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. Evaluation of training and monitoring was done during telephone and clinical conversations. Exercise capacity was measured during cycle ergometry. At the end of the intervention, no signiﬁcant diﬀerences in the annual rate of decline in peak V˙O2, peak heart rate (peak HR), and peak V˙ E 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 [18]. 2.1.2. Anaerobic Responses to Exercise. 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 [39–41]. Furthermore, children with CF with higher levels of habitual activity have been found to possess increased anaer- obic 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 [42]. Subgroup analysis of subjects with CF revealed that nutri- tional status and sexual maturation rather than pulmonary function may aﬀect anaerobic exercise performance. In their observation, subjects with higher salivary testosterone (>4.0 ng·dL−1) had higher power outputs in both absolute terms and relative to lean body mass compared to subjects and lower salivary testosterone values (<4.0 ng·dL−1). Fur- thermore, 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. Eleven chil- dren with CF lung disease trained 30–45 minutes two times per week. 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 [16]. 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