Discussion
Our results showed that adolescents with FAO and non-FAO adolescents
presented similar aerobic fitness, PAL, peripheral muscle strength, and
HRQoL results. However, the adolescents in the FAO group presented
higher values of expiratory muscle strength than did the non-FAO group.
This study also showed that most adolescents with asthma are physically
deconditioned and sedentary, regardless of whether the condition was
clinically controlled, and FAO was present.
Aerobic fitness and PAL in
children and adolescents with asthma have been studied over the last two
decades (23-25), and the association between PAL and lung function
remains poorly understood (26,
27). Loponen et al. (2018) showed
that a low PAL was associated with a faster decline in lung function in
adults with asthma (8). However, no studies have evaluated the
association between PAL and the decline in lung function in children and
adolescents with asthma. Contrary to our hypothesis, the present study
showed that the FAO and non-FAO adolescents have a similar PAL. Two
hypotheses can explain our findings. First, both groups had controlled
asthma, and this hypothesis is supported by previous studies showing
that subjects with controlled asthma experience fewer asthma symptoms
and therefore have a higher PAL than do subjects with uncontrolled
asthma (28). Second, both groups exhibited a long period of sedentary
behavior and a very short period of moderate-to-vigorous physical
activity (MVPA).
In our study, most adolescents in the FAO and non-FAO groups presented
reduced levels of aerobic fitness, as evaluated by the CPET. All
adolescents terminated the CPET due to fatigue in the lower limbs, and
they also demonstrated cardiac limitations (reduced cardiac reserve).
These results corroborate those in previous studies in either children
or adolescents with asthma and those without asthma (7, 21, 22). Taken
together, these results suggest that physical deconditioning, rather
than asthma or FAO, is the major cause of interruption during maximal
exercise. The reduced levels of
aerobic fitness observed in our study may be explained by the reduced
MVPA levels; however, the opposite result should be observed if the
adolescents participate in a physical training program (29).
Children and adolescents with asthma and their nonasthmatic peers have
been shown to have similar levels of respiratory muscle strength (30).
On the other hand, children and adolescents with severe asthma have
reduced maximal inspiratory pressure (MIP) compared to those with
nonsevere asthma (31). This difference probably occurs because airway
obstruction leads to static hyperinflation and places the respiratory
muscle at a mechanical disadvantage (32). Interestingly, we observed
that adolescents with FAO exhibit a higher maximal expiratory pressure
(MEP) than do non-FAO adolescents. This finding can be explained by the
fact that the lower the airway caliber is, the greater the respiratory
requirement for exhaling air from the lungs (32).
Several studies have evaluated upper and lower peripheral muscle
strength in children and adolescents with asthma (22, 33, 34), and most
of them did not observe differences between subjects with asthma and
their nonasthmatic peers (22, 33). Our results showed that the upper and
lower limb muscle strength values were similar between the FAO and
non-FAO groups. In contrast, Lattorre-Romám et al. (2013) demonstrated
different handgrip strength results in subjects with asthma. The authors
reported that subjects with a lower FEV1 also had poorer
handgrip strength (34). The discrepancy between the results presented by
Lattorre-Romám et al. (2013) and our results may have occurred because
Lattorre-Romám et al. (2013) evaluated adolescents with asthma of steps
1 to 5, while we assessed adolescents with asthma of steps 3 to 5
(mostly severe asthma). Interestingly, in our study, both groups
exhibited reduced muscle strength in the upper and lower limbs
(approximately 50% of predicted), suggesting that both the FAO and
non-FAO groups have muscle weakness. Muscle weakness might be explained
by the fact that subjects with moderate-to-severe asthma are more
sedentary and present a greater number of exacerbations, leading to an
increase in the dose of oral corticosteroids needed (26, 35, 36).
The HRQoL scores were similar
between the FAO and non-FAO groups in all the questionnaire domains
(physical activity, emotions, and symptoms). Amaral et al. (2014)
evaluated HRQoL in adolescents with a lower or normal peak expiratory
flow, and the authors did not observe any significant differences
between them (37). Our results are supported by those in previous
studies demonstrating that adolescents with controlled and partially
controlled asthma have a better HRQoL (38, 39). In addition, a worse
HRQoL in subjects with uncontrolled asthma is associated with fewer
symptom-free days (40). Taken together, these results suggest that HRQoL
in adolescents is more strongly related to asthma control than is
airflow obstruction.
Our study has limitations. First, because the incidence of FAO in
adolescents is low, we had to recruit a large number of adolescents for
the FAO group; however, the number of adolescents reached the sample
size calculation. Second, we did not include a group of adolescents
without asthma; however, the most recent systematic review demonstrated
no differences in physical fitness between adolescents with and without
asthma (25). Finally, adolescents were selected based on their
spirometry results, and complete lung function (volumes and capacities)
was not evaluated. However, the LLN, assessed by spirometry, has been
reported to be a good index for detecting FAO (3).