Handgrip strength, pulmonary function tests, and pulmonary muscle strength in fibromyalgia syndrome: is there any relationship?

Objective: It has been reported that patients with fibromyalgia syndrome (FMS) have lower maximal respiratory pressures than healthy subjects, indicating reduced pulmonary muscle strength. It has also been reported that patients with FMS have reduced grip strength. In this study, we aimed to examine the possible relationship between handgrip strength as a determinant of peripheral muscle strength and pulmonary muscle strength in patients with FMS by comparing them with healthy controls.

Methods: Forty-one consecutive women with FMS (diagnosed according to the American College of Rheumatology 1990 criteria) were compared with 40 age- and body mass index-matched healthy female controls. Pulmonary function tests were assessed by spirometry. Maximal pulmonary pressures were evaluated using an oral pressure meter. A dyspnea score was obtained. Pain was scored according to visual analogue scale and chest pain was classified (0-9) in fibromyalgia patients. Chest expansion was also measured in the two groups. Tender points were also evaluated in FMS patients. Grip strength (Jamar handheld dynamometer) was also measured in the two groups.

Results: The difference in pulmonary function tests was not statistically significant between groups. Maximal respiratory pressures (maximum inspiratory pressure and maximum expiratory pressure) and endurance (maximum ventilatory volume) were significantly lower in patients with FMS than in controls. There was also a statistically significant difference between groups regarding grip strength. There was also significant correlation between maximal inspiratory pressure and maximal expiratory pressure values and handgrip strength in patients with FMS.

Conclusion: These data indicate that handgrip strength may be a determinant of pulmonary muscle strength in fibromyalgia patients.

Key Words: fibromyalgia, grip strength, maximal respiratory pressures

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Fibromyalgia syndrome (FMS) is a chronic form of non-articular rheumatism characterized by widespread pain, stiffness, and multiple tender points. It is regarded as part of a spectrum of chronic widespread pain. The etiopathogenesis remains unknown. It is associated with a variety of symptoms such as fatigue, poor sleep, anxiety, depression, headaches, dizziness, irritable bowel syndrome, and dyspnea. (1)

Despite normal pulmonary spirometric values, patients with FMS have lower maximal respiratory pressures, which indicate reduced respiratory muscle strength. (2) Lurie et al (2) reported that maximum inspiratory and expiratory muscle strength values were low in patients with FMS. They indicated that there was an isometric type muscle dysfunction in this syndrome. Caidahl et al (3) also suggested that effort dyspnea is related to reduced maximum inspiratory pressure in FMS patients. It has also been reported that not only the presence of dyspnea but also other factors such as reflex inhibition due to a fear of pain together with chest wall discomfort and markedly decreased voluntary muscle strength due to supraspinal factors may result in lower maximum respiratory pressures. (3)

It was also shown that handgrip strength is reduced in FMS patients. (4) In the present study, we examined the possible relationship between handgrip strength and maximal respiratory pressures (maximum inspiratory pressure [MIP] and maximum expiratory pressure [MEP]) and endurance (maximum voluntary ventilation [MVV]) in patients with FMS. We assessed whether handgrip strength may be a determinant of pulmonary muscle strength in these patients.

Patients and Methods

Forty-one consecutive women who fulfilled the 1990 American College of Rheumatology criteria (1) for FMS were included in the study and compared with 40 age- and BMI-matched female healthy controls. All FMS patients were newly diagnosed. All of them were nonsmoking premenopausal women. Patients and controls had no history of any respiratory or cardiac disease; were not on current therapy (pharmacologic or physical training); and had no history of any systemic or rheumatic disease, malignant or infective disease, or trauma.

All of the individuals were at the same physical activity level and had no history of a regular exercise regimen. All patients were examined for spinal deformities or other disease that may have resulted in pain. All patients underwent a physical examination that included inspection for thoracic scoliosis, kyphosis, and pectus carinatum or excavatum; inspection of the cervical spine and shoulder movements; and palpation of the sternomastoid, trapezius, and pectoralis muscles. A chest wall examination included palpation of the posterior, lateral, and anterior chest wall.

Electrocardiograms and chest films of all subjects were obtained. Blood was tested for erythrocyte sedimentation rate, blood count, thyroid hormone levels, rheumatoid factor, antinuclear antibodies, creatine kinase, calcium, and hepatic enzymes.

Tender points were examined using the protocol described by Wolfe et al. (1) A score for the number of tender points was obtained ranging from 11 to 18. All patients had pain bilaterally in the neck-shoulder region and in the lumbosacral-hip region, with radiation of pain to the extremities. In all cases, the pain was perceived as more severe in one-half of the body.

Musculoskeletal pain was scored according to a visual analogue scale (VAS) in FMS patients. Chest pain was classified from 0 to 9 on a point-graded scale (0, no pain; 9, severe pain) in FMS patients. (3)

All subjects passed pulmonary function tests. Pulmonary function tests were evaluated by means of the dry spirometer (Vmax 22; SensorMedics, Yorba Linda, CA) with the subjects seated. Forced vital capacity, forced expiratory volume during the first second (FE[V.sub.1]), FE[V.sub.1]/forced vital capacity ratio, forced expiratory flow at 25 to 75% of vital capacity, and MVV were recorded. The standard value of MVV was calculated as FE[V.sub.1] X 40. The values were expressed as a percentage of the predicted normal values according to European Respiratory Society criteria. (5) (6) The acceptable recordings were obtained from each maneuver, and the highest values were used for further analysis. (7), (8)

The maximum respiratory pressures were obtained by using a digital mouth pressure meter (Sensor Medics MPM). The MIP was measured with the subjects sitting and breathing through a mouthpiece connected to the digital mouth pressure meter, just after clamping the nose. The MEP was measured after end-inspiration by the same procedure. Values were calculated as MIP and MEP in centimeters of water. (9) Respiratory muscle strength was assessed by measuring maximal inspiratory and expiratory mouth pressures generated voluntarily with maximal effort against a mouthpiece valve system that was occluded at residual volume and total lung capacity, respectively. The best of three attempts was selected, with enough recuperation being provided between attempts to avoid short-term fatigability of the respiratory muscles. Patients not able to avoid leaks around the mouthpiece were excluded from the study. (9) All pulmonary tests were performed by an experienced technician. All subjects were naive to the measurement of maximal respiratory pressures.

All participants provided their informed consent before the measurements. Height and weight were measured, and BMI was calculated as an index of body fat in all subjects.

Grip strength was tested by the Jamar handheld dynamometer (Alimed, Inc., Dedham, MA). The dominant hand was tested. The test was performed in a sitting position, with the upper arm parallel to the trunk, the elbow at 90-degree flexion, and the forearm and hand in the zero position. The test was performed three times, and the highest value was noted. Results were expressed as kilograms of force. (10) A history of effort dyspnea was obtained and classified as proposed by Mahler et al (11) in patients and controls.

The chest expansion was measured with the subjects standing with the hands on the hips; the tape measure was placed at the inframammary line in young female subjects and at the fourth intercostal space in women with pendulous breasts. Chest expansion was taken as the difference (to the nearest 0.1 cm) between full expiration and inspiration. The score for three attempts was recorded, and the best of these three was taken as the index of chest expansion. (12)

All statistical tests were analyzed by SPSS version 9.0 (SPSS, Inc., Chicago, IL). An independent t test was used for group comparisons. Pearson's correlation test was used for some correlations. Linear regression test for grip strength was used. Multivariate analysis was also performed for MIP and MEP. A value of P [less than or equal to] 0.05 was considered statistically significant.

Results

Baseline data for the patients and controls are shown in Table 1. Blood tests, electrocardiograms, and chest films were normal in all subjects. The mean duration of symptoms was 6.2 [+ or -] 4.9 years in FMS patients before diagnosis. In FMS patients, the mean number of tender points was 13.3 [+ or -] 1.9 (range, 11-17), the mean VAS score was 6.2 [+ or -] 4.9 cm, and the mean chest pain score was 1.4 [+ or -] 2.4. The total dyspnea scores of the patients and controls were 9.6 [+ or -] 10.0 and 7.4 [+ or -] 7.3, respectively, and these were insignificant.

There were no significant differences between groups concerning pulmonary spirometric values, age, BMI, and chest expansion, as shown in Table 1. FMS patients had lower MIP, MEP, and MVV values than did healthy controls. Handgrip strength was also lower in FMS patients than in controls. These values were statistically significant.

In patients with FMS, handgrip strength was inversely correlated with VAS score (r = -0.315; P = 0.04). On multivariate analysis, MIP and MEP values were related to handgrip strength (P = 0.037). On linear regression analysis, MVV, age, VAS score, MIP, and MEP had an effect on handgrip strength (P = 0.006, P = 0.012, P = 0.03, P = 0.02, and P = 0.04, respectively).

Discussion

The present study shows that handgrip strength may be a part of pulmonary muscle strength or may reflect the status of pulmonary muscle strength (MIP and MEP) and serve as a peripheral determinant of it in FMS patients as a simple, noninvasive method. Furthermore, the results may confirm the hypothesis that grip strength is related to physical performance in these patients in the presence of normal pulmonary function tests. (10) Only female patients were eligible for the study, because of the low incidence of FMS in men.

Measurement of maximum respiratory pressures is a non-invasive method for assessing the strength of inspiratory and expiratory muscles, even though it has some limitations (motivation and cooperation of subjects, learning effects, and degree of fatigue). (9) Therefore, the normal range for these maneuvers is wide and varies between laboratories. (9) However, ours was a controlled study, and the pulmonary functions of patients were also verified with spirometric values. However, these data are worth following up with ancillary tests (electrical stimulation of the respiratory muscles during maneuvers) to ensure that the results are at maximal levels. (9), (13)

Patients with moderate or severe pain are likely to reduce their physical activity and thus display a deconditioned muscular state. (14), (15) In some studies, it has been reported that patients with FMS had a low exercise capacity and low physical fitness. (16) Although the exact mechanism in these patients is not known, (2), (3) reduced pulmonary muscle strength may be related to reduced muscle performance together with central nervous system dysfunction or an impaired control mechanism at a supraspinal level. (2), (3) The reduced muscle performance can also partly be explained by an altered neurohumoral reactivity in these patients. (17) In addition to impaired central drive for activation, motivational factors and reflex inhibition due to pain or fear of pain may contribute to its etiopathogenesis. (18)

When pulmonary muscle strength is reduced, prominent dyspnea related to severity and progression of disease may result. (2), (3) Caidahl et al (3) reported that patients with FMS have dyspnea, which may result from respiratory muscle weakness together with central nervous system dysfunction. They studied a selected group of patients who had been unresponsive to treatment and who were disabled and had a more refractory type of FMS than the average patient with this syndrome. By contrast, Ozgocmen et al (13) found reduced MIP and MEP values in their patients, even though they did not report dyspnea. In the present study, we found no significant difference in dyspnea scores between patients and controls. However, our patients were newly diagnosed, and further follow-up is necessary to evaluate the difference or any changes in effort dyspnea.

Weiss et al (14) indicated that chest wall discomfort appeared to be the etiologic factor causing reduced pulmonary muscle strength (MIP and MEP) and that the diagnosis can only be made by characteristic clinical findings of FMS. Ozgocmen et al (13) reported that reduced chest expansion as a result of reflex inhibition caused by the fear of pain may be related to reduced MIP and MEP values. In our study, we found lower MIP and MEP values in patients than in healthy controls, although we found insignificant differences in dyspnea scores and chest expansion between groups. Therefore, we suggest that reduced endurance in these patients may result in reduced pulmonary muscle strength, together with impaired central drive for activation. (2), (3)

Handgrip strength is a simple, noninvasive method for evaluating a patient's upper extremity muscle strength, and has been reported to be related not only to muscular strength but also to bone mass, despite its limitations. (4) It has been shown that handgrip strength is reduced in FMS patients in comparison with healthy controls. (4) Nordeskiold and Grimby (4) suggested that fatigue, pain, and other factors of central origin could play a role in reduced grip strength in FMS, which may also be in accordance with the explanation of reduced respiratory muscle strength in these patients. Sinaki (19) also showed a positive correlation between back extensor muscle strength and handgrip strength. Carter et al (20) showed that peripheral muscle strength assessed by handgrip strength is the most important determinant of exercise intolerance in ankylosing spondylitis, suggesting that deconditioning is the main factor in the reduced aerobic capacity in these patients. Mannerkorpi et al (21) also found significant differences between fibromyalgia patients and controls regarding physical function, handgrip strength, pain severity, and quality of life. Mannerkorpi et al (22) also showed that women with FMS are markedly below average in physical performance abilities when measured by clinical tests, such as handgrip strength, back flexibility, 6-minute walk distance, leg strength, and isometric shoulder endurance. Jentoft et al (10) reported improved grip strength in the land-based exercise group compared with the pool-based exercise group in patients with FMS. Jacobsen and Danneskiold (23) reported that isometric and isokinetic muscle strength were found to be lower in the FMS group than in the controls. Norregaard et al (17) suggested that lower voluntary muscle strength is partly attributable to lower central activation. Other studies have shown lower aerobic capacity and lower maximal heart rates in FMS patients. (22), (23) Muscle strength, morphology, and metabolism seem to be abnormal in FMS, although more recent studies have demonstrated these to be nonspecific for FMS. (3) It is well known that patients with FMS easily become fatigued. This may be related to poor sleep, which may be accounted for by reduced muscle strength. (24) Vincken et al (25) reported that proximal muscle weakness was associated with more reduced maximal respiratory pressures, indicating respiratory muscle strength. Therefore, reduced MIP and MEP values together with reduced MVV (endurance) values may be related to low physical performance and reduced exercise capacity in FMS patients, and low grip strength may be a simple peripheral indicator of this process. (3)

Conclusion

We suggest that handgrip strength, as an indicator of nonrespiratory skeletal muscle force, may contribute to the evaluation of the strength of the respiratory muscles, and this finding may also reflect reduced muscle performance together with impaired central drive for activation in FMS patients. In other words, reduced pulmonary muscle strength may be a part of a reduction in peripheral skeletal muscle performance, or vice versa.

Table 1. Baseline data (a)

                         FMS patients           Controls
                           (n = 41)            (n = 40)

Age (yr)               43.7 [+ or -] 6.9    44.2 [+ or -] 6.4
BMI (kg/[m.sup.2]      26.9 [+ or -] 4.6    29.3 [+ or -] 5.7
Chest expansion (cm)    4.2 [+ or -] 0.9     4.0 [+ or -] 0.8
Grip strength (kg)     20.1 [+ or -] 5.9    23.0 [+ or -] 4.8
Dyspnea score           9.6 [+ or -] 10      7.4 [+ or -] 7.3
FVC (c)               108.8 [+ or -] 12.7  102.8 [+ or -] 14.1
FE[V.sub.1] (c)        97.5 [+ or -] 12.7   95.6 [+ or -] 12.7
FE[V.sub.1]/FVC (c)    77.1 [+ or -] 6.3    79.3 [+ or -] 5.6
FE[F.sub.25%-75% (c)   67.8 [+ or -] 20     70.6 [+ or -] 19
MVV (L/min)            85.3 [+ or -] 19     95.3 [+ or -] 19
MIP (cm, [H.sub.2]O)   53.2 [+ or -] 10     62.6 [+ or -] 15
MEP (cm, [H.sub.2]O)   62.6 [+ or -] 15     68.1 [+ or -] 11

                      P value

Age (yr)              0.07
BMI (kg/[m.sup.2]     0.056
Chest expansion (cm)  0.08
Grip strength (kg)    0.01 (b)
Dyspnea score         0.27
FVC (c)               0.053
FE[V.sub.1] (c)       0.496
FE[V.sub.1]/FVC (c)   0.121
FE[F.sub.25%-75% (c)  0.540
MVV (L/min)           0.05 (b)
MIP (cm, [H.sub.2]O)  0.002 (b)
MEP (cm, [H.sub.2]O)  0.05 (b)

(a) BMI, body mass index; MIP, maximum inspiratory pressure; MEP,
maximum expiratory pressure; FVC, forced vital capacity; FE[V.sub.1],
forced expiratory volume in 1 second; FE[F.sub.25%-75%], forced
expiratory flow at 25-75% of vital capacity; MVV, maximum
voluntary ventilation.
(b) Significant (P [less than or equal to] 0.05).
(c) % predicted.

From the Department of Physical Medicine and Rehabilitation and the Department of Chest Diseases, Faculty of Medicine, Mersin University, Mersin, Turkey.

Reprint requests to Gunsah Sahin, MD, Fatih mah. 13 sokak Istanbul Evleri, C-blok, kat:1 no:1, Mezitli-Mersin 33170, Turkey. Email: [e-mail]

Accepted December 11, 2002.

Copyright [C] 2004 by The Southern Medical Association 0038-4348/04/9701/0025

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RELATED ARTICLE: Key Points

* In this study, we aimed to investigate the possible relationship between hand grip strength and pulmonary muscle strength (maximum pulmonary pressures; MIP, MEP) in patients with primer fibromyalgia (PFM).

* Forty-one consecutive women (mean age 43.7 [+ or -] 6.9) with PFM were compared with 40 age and body mass index matched female controls (mean age 44.2 [+ or -] 6.4).

* Maximum respiratory pressures were significantly lower in PFM patients than controls (p [less than or equal to] 0.05).

* Hand grip strength was lower in PFM patients (p < 0.05).

* There was positive correlation between hand grip strength and maximal pulmonary pressures in PFM patients (p < 0.05).

Gunsah Sahin, MD, Bahar Ulubas, MD, Mukadder Calikoglu, MD, and Canan Erdogan, MD