Paul Jarle Mork

Association between physical exercise, body mass index, and risk of fibromyalgia: longitudinal data from the Norwegian Nord-Trøndelag Health Study.

To examine the association between leisure time physical exercise, body mass index (BMI), and risk of fibromyalgia (FM).

Sleep problems and risk of fibromyalgia: Longitudinal data on an adult female population in Norway

OBJECTIVE Sleep problems are common among patients with fibromyalgia (FM). However, it is not known whether poor sleep is a contributing factor in FM or a consequence of the illness. The aim of the current study was to prospectively investigate the association between self-reported sleep problems and risk of FM among adult women. METHODS We longitudinally studied 12,350 women who did not have FM, musculoskeletal pain, or physical impairments at baseline (1984-1986). A generalized linear model was used to calculate the adjusted relative risk (RR) of FM at followup in 1995-1997. RESULTS Incident FM was reported by 327 women at followup. A dose-dependent association was found between sleep problems and risk of FM (P for trend<0.001), with an adjusted RR of 3.43 (95% confidence interval [95% CI] 2.26-5.19) among women who reported having sleep problems often or always, compared to women who never experienced sleep problems. Age-stratified analysis showed that women age≥45 years who reported having sleep problems often or always had an adjusted RR of 5.41 (95% CI 2.65-11.05), whereas the corresponding RR for women ages 20-44 years who reported having sleep problems often or always was 2.98 (95% CI 1.76-5.05). CONCLUSION These prospective data indicate a strong dose-dependent association between sleep problems and risk of FM. The association is somewhat, although not significantly, stronger in middle-aged and older women than in younger women.

Back posture and low back muscle activity in female computer workers: a field study.

BACKGROUND Few studies have investigated sitting posture and low back muscle activity in occupational settings. This study aims to determine back posture and its influence on low back muscle activity in computer workers, and to investigate whether the work situation is associated with exacerbation of low back pain. METHODS Twenty-one female computer workers participated. Surface electromyographic activity was recorded from lumbar multifidus, longissimus, and iliocostalis throughout the workday. Simultaneous inclinometer recordings from pelvis, upper trunk, and left thigh were used to determine back posture and identify periods with sitting, standing, and walking. Low back pain intensity was recorded by visual analogue scale every hour throughout the work and leisure periods. FINDINGS All subjects adopted a markedly flexed back posture while seated at work. Surface electromyographic activity was very low for all muscles during sitting (group median <1.4% of root-mean-square-detected response at maximal voluntary contraction). Back posture moderately influenced electromyographic activity, accounting for 19% (sitting) to 38% (standing) of intra-individual variation in muscle activity. Subjects reporting aggravating low back pain (n=10) during the workday were not distinguished by duration of sitting, sitting posture, or low back muscle activity. Low back pain was markedly reduced from the last hour of work to the first hour of leisure, accompanied by an increase in low back muscle activity. INTERPRETATION Low back muscle activity was very low during seated posture, presumably due to the flexion-relaxation phenomenon. Sustained stretch of passive lumbar structures in combination with essentially silent muscles may exacerbate low back pain in sedentary workers.

Data mining of motor patterns recorded with wearable technology

Discusses utilizing self-organizing maps to manage large data sets gathered in the field. Dramatic advances in wearable technology suggest that wearable sensors and systems are close to deployment in the clinical field environment. Miniature, wireless sensors are becoming readily available due to the tremendous research efforts focused on this area as well as the great interest demonstrated by the private sector for the associated potential market of these devices. Wearable systems, including base stations and hand-held units, are becoming less cumbersome, with an ever-increasing capacity to receive and store vast amounts of data for extensive periods of time. Further, the growing availability of wireless LANs makes it possible to envision wearable systems from which data can be continuously uploaded, while hand-held units provide a means to communicate with the patient when needed.

The use of EMG biofeedback for learning of selective activation of intra-muscular parts within the serratus anterior muscle: a novel approach for rehabilitation of scapular muscle imbalance.

Motor control and learning possibilities of scapular muscles are of clinical interest for restoring scapular muscle balance in patients with neck and shoulder disorders. The aim of the study was to investigate whether selective voluntary activation of intra-muscular parts within the serratus anterior can be learned with electromyographical (EMG) biofeedback, and whether the lower serratus anterior and the lower trapezius muscle comprise the lower scapula rotation force couple by synergistic activation. Nine healthy males practiced selective activation of intra-muscular parts within the serratus anterior with visual EMG biofeedback, while the activity of four parts of the serratus anterior and four parts of the trapezius muscle was recorded. One subject was able to selectively activate both the upper and the lower serratus anterior respectively. Moreover, three subjects managed to selectively activate the lower serratus anterior, and two subjects learned to selectively activate the upper serratus anterior. During selective activation of the lower serratus anterior, the activity of this muscle part was 14.4+/-10.3 times higher than the upper serratus anterior activity (P<0.05). The corresponding ratio for selective upper serratus vs. lower serratus anterior activity was 6.4+/-1.7 (P<0.05). Moreover, selective activation of the lower parts of the serratus anterior evoked 7.7+/-8.5 times higher synergistic activity of the lower trapezius compared with the upper trapezius (P<0.05). The learning of complete selective activation of both the lower and the upper serratus anterior of one subject, and selective activation of either the upper or lower serratus anterior by five subjects designates the promising clinical application of EMG biofeedback for restoring scapular muscle balance. The synergistic activation between the lower serratus anterior and the lower trapezius muscle was observed in only a few subjects, and future studies including more subjects are required before conclusions of a lower scapula rotation couple can be drawn.

Effect of body mass index and physical exercise on risk of knee and hip osteoarthritis: longitudinal data from the Norwegian HUNT Study

Background Mechanical joint stress imposed by high body mass index (BMI) is associated with increased risk of knee and hip osteoarthritis. This prospective study investigated the independent and joint association of BMI and physical exercise on risk of knee and hip osteoarthritis. Methods The study includes 15 191 women and 14 766 men in the Norwegian HUNT Study without pain or physical impairment at baseline. Occurrence of self-reported physician-diagnosed osteoarthritis was assessed at 11 years of follow-up. Results BMI was positively related to risk of knee osteoarthritis (Ptrend<0.001), with an RR of 4.37 (95% CI 3.01 to 6.33) in women and 2.78 (95% CI 1.59 to 4.84) in men, comparing obese and normal weight persons. No clear association was observed for hip osteoarthritis. Obesity increased the risk of severe activity-limiting osteoarthritis, with an RR of 2.30 (95% CI 1.68 to 3.15) and 2.50 (95% CI 1.56 to 4.03) in women and men, respectively. Physical exercise did not modify the above associations (Pinteraction>0.34). Exercise intensity was not associated with risk of osteoarthritis in any BMI category; that is, obese persons reporting high-intensity exercise had an RR of 1.28 (95% CI 0.59 to 2.79) for severe osteoarthritis compared with inactive persons. Conclusion High BMI increases the risk of knee osteoarthritis and severe osteoarthritis. Physical exercise does not increase the risk of osteoarthritis at any level of BMI, suggesting that exercise could be encouraged also among individuals with excessive body mass, without concern for an increased risk of osteoarthritis.

Comparison of the cortisol awakening response in women with shoulder and neck pain and women with fibromyalgia

Shoulder and neck pain (SNP) and fibromyalgia syndrome (FMS), two musculoskeletal conditions of unknown pathogenesis, share some common features in terms of altered neuroendocrine responses, pain and stress perception. However, the pain distribution in SNP is localized, whereas in FMS is more widespread. Because regional musculoskeletal pain may represent an intermediate stage along a continuum towards widespread musculoskeletal pain we compared the cortisol awakening response (CAR) in women with SNP with the CAR in FMS patients and healthy controls (HC) in a controlled hospital-hotel setting. The aim of the study was to investigate whether SNP is related to a deviant regulation of the hypothalamic-pituitary-adrenal (HPA) axis. Eighteen women with SNP, 29 female FMS patients, and 27 female HC participated in the study. Cortisol samples were collected upon awakening, 30 and 60 min later. Questionnaires measuring pain levels, sleeping problems, perceived stress, and psychological characteristics were administered to the participants. Compared with HC, women with SNP had a tendency towards higher cortisol levels, whereas FMS had lower cortisol levels. Adjustment for potential confounders did not influence the results. Women with SNP and FMS patients reported more health complaints, pain, and perceived stress than the HC, but women with SNP were less affected than the FMS patients. Women with SNP showed a tendency towards an elevated HPA axis activity compared with HC. The current findings may indicate that the hypercortisolism in regional musculoskeletal pain represent an intermediate stage towards the development of a hypocortisolism in widespread musculoskeletal pain.

Firing patterns of low-threshold trapezius motor units in feedback-controlled contractions and vocational motor activities

The study aimed to examine firing patterns of low-threshold trapezius motor units, with attention given to motor unit recruitment threshold. Different motor tasks were explored: shoulder elevation, arm movement in typing, and the motor response to mental stress. Contraction amplitudes in the range from 1 to 10% of the surface electromyographic (SEMG) signal at maximal voluntary contraction (1–10% EMGmax) were studied, representing the range of trapezius muscle activity commonly observed in daily living. Single motor unit activity was recorded by a quadrifilar fine-wire electrode. A surface electrode simultaneously recorded the SEMG signal. Low-threshold motor units showed a small increase in mean firing rate, from 10.5 to 12.5 pulses per second (p<0.01), in constant-amplitude contractions when SEMG amplitude increased from <2% to >4% EMGmax. After the first few minutes, firing rates were similar for all motor units in a contraction, despite different recruitment thresholds. Firing rates of motor units with threshold <2% EMGmax were the same in constant-amplitude contractions, contractions with vocational arm movement, and contractions with imposed stress for SEMG amplitude at the same level. High-frequency firing patterns were observed in dynamic contractions, limited to bursts of up to a second duration. We conclude that low-threshold trapezius motor units have similar, stable firing rates in sustained contractions, independent of task and recruitment threshold, but with a small increase for increasing contraction amplitude.

Catecholamines and heart rate in female fibromyalgia patients.

BACKGROUND Fibromyalgia syndrome is a disease of unknown pathogenesis characterised by widespread chronic musculoskeletal pain. Fibromyalgia has been associated with dysregulation of the stress systems, but results are inconsistent. PURPOSE To investigate autonomic nervous system activity (urinary noradrenaline, adrenaline, dopamine, and heart rate) of fibromyalgia patients and healthy controls. METHODS Urinary catecholamines and heart rate were assessed for a 24-hour period in a controlled hospital setting (including relaxation, a test with prolonged mental stress, and sleep), and during daily activity in 29 female fibromyalgia patients and 29 age-matched female healthy controls. RESULTS With repeated measures ANOVAs, catecholamine levels were lower in patients than controls (P=.035 for noradrenaline; P=.005 for adrenaline; P=.001 for dopamine). One-way ANOVAs for the single periods showed that patients compared to controls had significantly lower adrenaline levels during the night (P=.010) and the second day (P=.010), significantly lower dopamine levels during the first day (P=.008), the night (P=.001), and the second day (P=.004). However, single time point noradrenaline levels were not significantly different between the groups. Overall, heart rate was significantly higher in patients than controls (P=.014). Specifically, significant differences emerged during relaxation (P=.016) and sleep (P=.011), but not during stress provocation or daily activities. CONCLUSIONS The results indicate an altered regulation of the autonomic nervous system in fibromyalgia patients, with attenuated activity of both the sympathetic (adrenal medulla component) and the parasympathetic branch.

Heart rate variability in fibromyalgia patients and healthy controls during non-REM and REM sleep: a case–control study

Objectives: To investigate heart rate variability (HRV) in fibromyalgia (FM) patients and healthy controls (HCs) during different sleep stages, and to examine the association of HRV with pain and sleep quality. Method: Polysomnography was recorded from 23 female FM patients and 22 age- and sex-matched HCs. HRV was recorded from bedtime until awakening including the standard deviation of normal-to-normal intervals (SDNN), the root mean square successive difference (RMSSD), and the low (LF; 0.04–0.15 Hz) and high (HF; 0.15–0.4 Hz) frequency power. Subjective scores of neck/shoulder pain and sleep quality were obtained at bedtime and awakening. Results: Both patients and HCs showed high incidence of arousals per hour (FM: 16 ± 9.7; HCs: 17 ± 11). RMSSD was lower in patients than HCs during non-rapid eye movement (non-REM) stage 2 (N2) sleep (mean ± SD; 30 ± 12 ms vs. 42 ± 13 ms, p < 0.002) and during REM sleep (23 ± 11 ms vs. 37 ± 16 ms, p < 0.003). HRV did not differ between groups during N3 sleep (p > 0.19 for all comparisons). In patients, SDNN, RMSSD, and HF power showed modest positive correlations with sleep quality (HF power during N3 sleep showed the highest correlation; Spearman’s ρ = 0.54) and modest negative correlations with neck/shoulder pain (RMSSD during N3 sleep showed the highest correlation with pain at bedtime; Spearman’s ρ = –0.51). Conclusions: RMSSD, indicative of parasympathetic predominance, is attenuated in FM patients compared to HCs during N2 sleep and REM sleep. This difference was not present for the HF component. HRV during sleep in FM patients is moderately and positively associated with sleep quality and moderately and negatively associated with neck/shoulder pain.