Discussion
The main findings of the present study indicate that fitness testing is a powerful tool to discriminate between presence and absence of fibromyalgia in women regardless of the age range of the women. These results support our previous findings and highlight the importance of implementing fitness testing as a complementary tool for the diagnosis and monitoring of fibromyalgia. The arm curl, 30-s chair stand, and handgrip strength tests were those that more potently discriminated women with fibromyalgia from healthy women. An arm curl test score of <20 repetitions was associated with 36 times greater odds of having fibromyalgia in women age 35–44 yr. An arm curl test score <16 repetitions was associated with 24 times greater odds of having fibromyalgia in women age 45–54 yr. In the group of women age 55–65 yr, the highest OR values were observed for the handgrip strength test. The odds of having fibromyalgia was 17 times greater in those patients who performed <19 kg. In agreement with previous studies from our group, we recommend the use of fitness testing in clinical setting as a quick and complementary tool for fibromyalgia diagnosis.
As expected, we observed patients with fibromyalgia to have lower functional capacity than healthy women in all the studied physical fitness tests. Therefore, we confirm that physical fitness is clearly decreased in people with fibromyalgia compared with that in their age-matched healthy peers and is similar to that in healthy older adults. Hence, patients with fibromyalgia have impaired functional capacity with high risk of disability and difficulties on doing tasks associated with staying physically independent. Patients with chronic pain reduce their physical activity and thus display a deconditioned fitness status. Indeed, in the recent study by Bjornsdottir et al., the authors studied the consequences of chronic pain in 5906 Icelanders age 18–79 yr reporting chronic low back pain, chronic neck symptoms, and/or fibromyalgia, with the aim of analyzing the global burden imposed by chronic pain conditions. Several symptoms and functional limitations in daily life were strongly associated with chronic pain, including deficient energy and muscular discomfort, physical mobility limitations, lifting groceries, climbing stairs, and stooping. The authors also found that women, but not men, with chronic pain tended to refrain from physical activity.
Pain is the more predominant symptom in fibromyalgia and can be on the basis of the lower functional capacity observed. Our group previously examined the association between pain and functional capacity levels in a smaller sample of similar age and region. We observed inverse association of tender point count with the 30-s chair stand and the distance covered in the 6-min walk tests and positive association of the algometer score with the 30-s chair stand, the 6-min walk, and the back scratch tests. However, we did not assess the arm curl test and we found that weight status seems to play a role in these associations. This is the reason why all the analysis performed in the present study related to fitness were adjusted for BMI. Our results concur with these studies, suggesting that the higher the muscle strength, the lower the pain and symptomatology reported. Hooten et al. found that higher knee extensor isometric and isokinetic strength was associated with lower pressure pain threshold. Similarly, Assumpção et al. observed that muscle strength (knee and elbow extension) was related to pain threshold and pain on a visual analog scale. However, the association of aerobic fitness with pain and symptomatology in women with fibromyalgia is not clear, with some studies reporting a certain degree of association, while others reporting lack of relation.
Our first study analyzing the use of physical fitness testing for the diagnosis and monitoring of fibromyalgia was solely performed, assessing the handgrip strength test in 81 female patients with fibromyalgia and 44 control women. We observed that a score lower than 23 kg was associated with 34 times higher odds of having fibromyalgia after adjustment for age. In the present study, this association was lower but we have included higher sample size and further adjusted for age, BMI, and medication and, thus, gained in accuracy. In our subsequent study, the sample comprised 94 female patients with fibromyalgia and 66 healthy controls. That time, we assessed the same physical fitness tests battery than in the present study, except for the inclusion of the arm curl test and the exclusion of the 30-s blind flamingo test (static balance) this time. We observed that all fitness tests, except the back scratch test, were able to discriminate between presence and absence of fibromyalgia. We found that the 30-s chair stand test showed the highest ability to discriminate presence and absence of fibromyalgia (we did not assess the arm curl test). A chair stand test lower than 10 repetitions was then associated with 52 times higher odds of having fibromyalgia, whereas in the present study, we have modified the cutoff up to <12 repetitions for the entire sample size. This time, we have also proposed a cutoff point <13 for women age 35–44 yr and <11 for women age 55–65 yr. Therefore, the 30-s chair stands test showed remarkable discriminative capacity to identify fibromyalgia presence (now being the second proposed test). Indeed, the arm curl, the 30-s chair stand, and the handgrip strength tests, which measure muscle strength, seem to be the most discriminative fitness tests to establish fibromyalgia presence or absence.
As recently shown, patients with fibromyalgia might not necessarily fulfill the tender point criteria to be diagnosed, which concurs with our proposal of including new clinical tools for the diagnosis of fibromyalgia. In fact, in an attempt to avoid the requirement of the tender point examination, the ACR released new diagnostic criteria in 2010, which is gaining widespread acceptance. Recently, a study displayed that the combination of the 1990 criteria and the modified 2010 ACR criteria showed higher sensitivity and specificity for fibromyalgia diagnosis than the 1990 or the modified 2010 ACR criteria independently. Because of the unknown etiology of fibromyalgia, there is not a gold standard instrument for its diagnosis. Consequently, the study by Segura-Jimenez et al. showed that the use of different validated diagnostic tools together might enhance the accuracy of fibromyalgia diagnosis. This highlights the need for additional diagnostic tools in fibromyalgia. In this context, fitness testing assessment might improve the diagnostic accuracy of fibromyalgia syndrome and supplement current diagnostic tools, which in turn might also help identify more heterogeneous subgroups of patients (e.g., those fulfilling only ACR 1990 or ACR 2010 or both criteria). In the present study, we found positive relation between better fitness tests scores and lower global score of FIQR, FIQR dimensions, and the modified 2010 ACR criteria. Furthermore, most of the studied tests were also correlated with tender point count and algometer score, which reinforces the use of fitness testing instead of the classical, and more complicated, tender point assessment.
Fatigue has been shown as the second most reported symptom in fibromyalgia. We have observed the highest correlations between FIQR energy rating/fatigue and fitness testing thorough the 30-s chair stand test (lower body muscle strength), followed by the arm curl test (upper body muscle strength), which strengthen the idea that the muscle strength tests proposed in the present study are also sensitive to other important fibromyalgia's key symptoms.
Some limitations need to be mentioned. First, the male sample size was too small to perform the present statistical approach and most of the statistical analysis tests would not be powerful to detect significant effects (i.e., partial correlations, AUC and ROC analysis, binary logistic regression analysis, and of course classifications by age groups), so this study was carried out only in women, and future studies should replicate this analysis in larger samples in men with fibromyalgia. Moreover, because physical fitness levels clearly differ between genders, we could not merge both groups. Second, the higher pain observed in the participants with lower fitness levels could have been influenced by the fear of pain phenomena. Third, we have not objectively assessed physical activity levels among the sample. Finally, in the same way that tender points and the new 2010 diagnosis criteria may erroneously classify people with fibromyalgia when they are healthy, fitness testing can also make that error, classifying a healthy person with little fitness as a person with fibromyalgia. Therefore, the proposed tests should be used just as additional tools for the diagnosis and not as the only sources of criteria. On the other hand, compared with previous literature, the present study involved a large and representative sample (almost 500 female patients with fibromyalgia and 250 age-matched control women from the same geographical area). Furthermore, this study examined a complete range of functional capacity parameters in a single report, which allowed us to make comparisons between fitness tests. Finally, because of the high sample size recruited in the present replication study, we could further establish age-specific fitness cutoff points (i.e., for women age 35–44, 45–54, and 55–65 yr old).
Clinical Implications
The present study has several clinical implications to highlight. These results reinforce our previous hypothesis that physical fitness could be set as a complementary tool for the diagnosis and monitoring of fibromyalgia in clinical settings. The high capacity of the proposed fitness tests to discriminate between presence and absence of fibromyalgia and the fact that they are inexpensive and easily accessible facilitate the inclusion of fitness testing as a complementary fibromyalgia diagnostic tool. This, in turn, might also assist the clinician in targeting treatment. Particularly, the arm curl and the 30-s chair stand tests have great potential in a clinical setting for several reasons: First, a dumbbell or a chair and a stopwatch are all the equipment needed to perform them, so they are extremely cheap. Second, the time needed to perform these tests is just 30 s (2–3 min in total), which is a fundamental issue for clinicians who are usually under time constraints. Third, other fitness tests, such as the 6-min walk test, require larger spaces, whereas the arm curl and the 30-s chair stand tests can be performed in any room without any special requirement. Fourth, the procedures for these tests are simple and do not require any particular training. In addition to these tests, we suggest the use of the handgrip strength test for women age 55–65 yr old (but a hand dynamometer is required).