Aim: Muscle strength is an excellent indicator of general health when based on reliable measurements. Muscle strength data for a healthy population are rare or non-existent. The aim of the present study was to measure a set of normal values for isometric and isokinetic muscle strength for all the major joint movements of the body and, from these data, to create a basis for comparison of the muscle strength of an individual with the expected value in a normal population. Methods: A randomly selected group, aged 20-80 years, from the Copenhagen City Heart Study were studied. The group was subgrouped according to age and gender. Isometric and isokinetic muscle strength was measured in each subject across the main joints in the body. A statistical model was developed that encompassed the three main muscle groups: upper limbs, trunk and lower limbs. Results: Muscle strength in healthy men decreases in a linear fashion from the age of 25 years down to between 54% and 89% at the age of 75 years, and seems not highly dependent on any other parameter than age. For women, the muscle strength is dependent on weight and is only related to age from around 40 years of age. The decrease in muscle strength from the age around 40 to 75 years is 48-92%. For most muscle groups, men are 1.5-2 times stronger than women, with the oldest men having strength similar to that observed among the youngest women. Conclusion: We developed a model to compare the isometric and isokinetic muscle strength of all the major joint movements of an individual with values for a healthy man or woman at any age in the range of 20-80 years. In all age groups, women have lower muscle strength than men. Men's muscle strength declines with age, while women's muscle strength declines from the age of 41 years.

Men and women demonstrate impressive levels of muscular strength in the flexors and extensors of the cervical spine and can maintain these values until the seventh decade of life. Successful rehabilitation of the cervical musculature will require considerable resistance for sufficient stimulation of the cervical musculature.

The aim of this study was to examine the learning effect during a set of isokinetic measurements, to evaluate the reliability of the Biodex System 3 PRO dynamometer, and to compare the Biodex System 3 PRO and the Lido Active dynamometers on both extension and flexion over the elbow and the knee at 60 degrees s(-1). Thirteen (nine women, four men) healthy participants were measured five times using the Biodex and once using the Lido dynamometer. The intervals between the first four tests were 20 min, and 1 week between tests 4 and 5. Between Biodex and Lido measurements there was a 20 min time interval. When comparing the first five measurements (Biodex), no systematic effect over time and an excellent reliability were found with respect to elbow and knee flexion and extension. No difference in muscle strength (Nm) between the Biodex and Lido was observed for knee flexion (P = 0.59), knee extension (P = 0.18) and elbow extension (P = 0.63). However, elbow flexion showed a 14.8% (95% CI: 11.2-18.4%; P = 0.0001) higher peak torque on Biodex. In conclusion, no learning effect was observed and the Biodex proved to be a highly reliable isokinetic dynamometer. A difference was observed when comparing Biodex and Lido on elbow flexion, but the difference did not outrange the expected variation found with a typical isokinetic measurement, which is why both sets of equipment seem applicable in clinical practice.

The objectives were to determine whether the low muscle strength in fibromyalgia is due to lack of exertion and to determine the relation between strength and muscle area. Secondarily we examined the voluntary muscle strength of the different muscles of the leg. The twitch interpolation technique was used to estimate the degree of central activation and the 'true' quadriceps muscle strength. Muscle cross-sectional area was determined with magnetic resonance imaging (MRI). The estimated 'true' muscle strength was 91 Nm (S.D. = 34 Nm) in 15 fibromyalgia patients compared with 125 Nm (28 Nm) in 14 healthy controls (P < 0.02). The 'true' strength divided by the sum of the maximal areas of the four bellies of the quadriceps muscle was lower, being 1.56 Nm/cm2 (0.32 Nm/cm2) in fibromyalgia patients compared with 2.11 Nm/cm2 (0.39 Nm/cm2) in the controls (P < 0.001). The voluntary muscle strength of the flexor muscles of the knee and of the plantar flexors of the ankle was markedly reduced in patients, but no significant differences could be observed in the strength of the dorsal flexors of the ankle. In conclusion, a reduction of the estimated 'true' quadriceps muscle strength per unit area of about 35% was found in fibromyalgia patients.

Previous studies have shown decreased voluntary muscle strength and endurance in patients with fibromyalgia. The aim of this study was to determine to what extent this is due to lack of exertion. The twitch interpolation technique was used to determine the degree of central activation and estimate the "true" quadriceps muscle strength in patients with fibromyalgia and age and sex matched controls. Subjects hereafter performed an endurance test consisting of repetitive contractions at 50% of estimated "true" muscle strength of four seconds duration followed by a six second rest until exhaustion, or maximally for 40 minutes. Twitch decline and increases in mean rectified EMG were used as objective markers of fatigue. The estimated "true" muscle strength was 82 (SD 26) Nm in 20 patients with fibromyalgia compared with 133 Nm (SD 28) Nm in the 21 controls (p < 0.001). The "true" muscle strength per cm2 midthigh cross sectional area was lower 0.50 (SD 0.15) Nm/cm2 in the patients compared with 0.74 (SD 0.15) Nm/cm2 in the controls (p < 0.001). The decline over time in twitch sizes was similar in the two groups. The mean rectified EMG signal at a fixed force level of 50% of "true" muscle strength increased similarly in the two groups. Relaxation rates and contraction rates also increased equally in the two groups. In conclusion, a reduction of the estimated muscle strength per area unit of about 35% was found in the patients with fibromyalgia. This might be secondary to physical inactivity or neuroendocrine factors. No differences in changes in the neurophysiological indices associated with fatigue were found between the two groups.