Introduction
It is known that peripheral muscle atrophy and dysfunction occur in Cystic Fibrosis (CF)1. It is thought that this muscle atrophy may in part contribute to exercise limitation. However, to date no study has assessed the adult CF population using isokinetic strength testing with Biodex® .
Isokinetic strength testing is considered the gold standard and demonstrates improved repeatability and validity when compared to other methods. In addition, isokinetic strength testing provides information on muscle strength throughout joint range as well as muscle power, which may more accurately reflect day-to-day muscle function for the patient. Methods
Adult subjects diagnosed by quantitative iontophoretic sweat tests, appropriate clinical features and CFTR genotyping and with clinically stable CF were recruited from the national adult CF centre.
The group was divided into mild, moderate and severe disease severity based on forced expiratory volume (FEV1).
Peak quadriceps torque (normalized to body weight) and average power were assessed using the Biodex ® Isokinetic System. Appropriate test protocol was rigidly applied to control for fatigue.
Differences between the mild, moderate and severe groups were assessed using one factor ANOVA with tukey post hoc tests. CF data was also compared to published age matched normal data.
Results
42 subjects (25 Males, 17 Females) were recruited, from the day care centre of the national referral centre.
Both peak quadriceps torque and average quadriceps power were below reported normal values regardless of disease severity.
Significant differences were found between mild and severe groups for both peak quadriceps torque and average quadriceps power (p≤0.05) in both males and females.
FEV1% accounted for 43% of the variance in peak quadriceps torque in males and 46% of the variance in females.
Similarly, FEV1 accounted for 38% of the variance in average quadriceps power in males and 57% of the variance in females.
Discussion
This study confirms muscle atrophy in adult CF using isokinetic strength testing. Both torque and power were reduced compared to normal values regardless of disease severity but there was a statistically significant reduction in both variables with increasing disease severity.
Our data suggests that FEV1 is a significant predictor of muscle function in adult CF. Isokinetic testing is not widely available but our data suggest that a lower FEV1 score corresponds to a reduction in both peak torque and power. In turn this may compromise social functioning and quality of life.
Conclusion
Strength training should form an important part of exercise prescription in CF and should incorporate specific power training.
