Relationships among measures of physical fitness in adults with heart failure
DISCUSSION
This study explored the relationships among 3 diffe-
rent measures of physical fitness in adult patients with
HF: exercise capacity, muscle function, and functional
capacity. These measures were assessed with 3 valid
and reliable instruments: the 6MWT, the MFT, and the
DASI. Analysis revealed low-to-moderate correlations
among these 3 variables. Principal component analysis
grouped them into 2 factors: one related to lower limbs
capacity and another related to upper limbs capacity.
To our knowledge this is the first study to explore re-
lationships among exercise capacity, muscle function,
and functional capacity, and to explain the role of these
measures in the assessment of physical fitness.
Measurement of the 6MWT in the current study was
similar to that in previous studies on patients with HF
(36, 37). Some studies have reported better perfor-
mance, but the patients in those studies were younger
and had fewer comorbidities (14, 20, 24, 38, 39).
Regarding muscle function, the scores were lower
than those in other studies, mainly for isotonic shoulder
flexion and shoulder abduction (12, 14, 40). This might
be explained by the in-hospital recruitment for this
study. The patients might have been more clinically
compromised than outpatients. Heel-lift performance
was similar or slightly lower compared with the fin-
dings of previous studies (12, 28, 40). As in the study
by Cider et al. (12), the current study demonstrated a
strong correlation between the results for the right and
left limbs. It is possible that the patients might have
remembered the number of contractions performed
the first time; thus, they performed the same number
the second time. The patient’s choice to consider the
number of completed contractions on the first attempt
a goal to be achieved on the second attempt is beyond
the clinician’s control (12).
The mean DASI score in this study was similar to
(17, 32), or higher than (4, 30, 41), those in other stu-
dies. The median score for dichotomizing the patients
into high and low was significantly higher than the
cut-off reported by Mantziari et al. (30), who used the
sum of the 4 items of the DASI that were lower than 3
METs. The cut-off, 9.95 METs, reported for the study
of Mantziari et al. represented empirically the mini-
mum level of patient personal autonomy (taking care
of himself or herself, walking 100 m, moving inside
the home and performing light housework).
For exercise capacity, the correlation analysis sho-
wed a low-to-moderate positive correlation with all of
the evaluations of the muscle function and functional
capacity. This was in accordance with previous findings
(14, 20). Borland et al. reported a low-to-moderate
positive correlation between exercise capacity and
muscle function (not for shoulder abduction evalua-
613
tion) (14), and Myers et al. reported a moderate positive
correlation between exercise capacity and functional
capacity (0.44; p < 0.01) (20). Moreover, a low positive
correlation was found between functional capacity and
muscle function. This confirmed, for the first time, that
functional capacity was related to exercise capacity
and muscle function.
NYHA class was found to be correlated with exer-
cise capacity, muscle function, and functional capacity.
This further confirmed the strong relationship between
physical fitness measured in its multidimensiona-
lity and the functional classification assessed by the
NYHA. Previous studies have reported that the NYHA
class was related to functional capacity (4) and muscle
function (27). According to another study (20), age was
correlated with 6MWT, MFT and DASI, thus showing
that older patients with HF had lower physical fitness.
Moreover, movement impairment was correlated
with lower exercise capacity, muscle function and func
tional capacity (Table IV). Thus, as expected, physical
fitness assessment could be influenced by movement
impairment. It must be emphasized, therefore, that in
patients with impairment of the lower limbs, physical
fitness could be assessed if the patients were still able
to perform tests with their upper limbs. For clinicians,
this suggests that there are alternative ways to assess
physical fitness in patients with HF.
As was reported by Dziubek et al., movement im-
pairment can be the result of multiple factors, and it
can reduce exercise capacity (42). Patients with HF
who have movement impairment and comorbidities
might have poorer performance in exercise capacity
and muscle function for reasons other than HF (3, 4).
This would be an interesting question for exploration
in future studies.
In this study, exercise capacity, muscle function
and functional capacity were measured by different,
but correlated, aspects of physical fitness. The re-
sults show that there are commonalities among these
measures even if the correlation coefficients were only
low-to-moderate. This inconsistency in the results of
the 6MWT, MFT and DASI was seen in 44% of par-
ticipants. A possible explanation is the DASI, which
uses self-reported data, unlike other more objective
instruments used for assessment of exercise capacity
and muscle function. Coutinho-Myrrha et al. reported
a lower correlation between DASI and peak VO 2 , if
DASI is self-administered (43).
To detect the structure in the relationships between
measures, principal component analysis was performed,
and 2 factors were found. The first factor was based on
the tests that involved mainly the lower limbs (6MWT,
right heel-lifts and left heel-lifts in the MFT and DASI
scores). The second factor was based on the tests that
J Rehabil Med 51, 2019