Forty women (range 25-75 years), with a class I and II RA diagnosis according to the American Rheumatism Association's 1987 revised criteria, were recruited from a university hospital's rheumatology clinic. Exclusion criteria included the presence of any cardiovascular, neuromuscular and metabolic diseases or severe limitations in mobility. Five patients were excluded for not attending the inclusion criteria, leading to a final number of 35 RA patients.

Thirty-five healthy women, age- and body size-matched to the RA patients, were recruited as controls (CG).

The Timed Up and Go test; Maximal knee-extensor muscle strength (isometric and concentric tests) was measured with a Biodex System 3 dynamometer; A B-mode ultrasonography system with a linear-array probe (60 mm, 7.5 MHz) was used to determine VL and RF muscle thickness, pennation angle, fascicle length and tendon CSA. Measurements were obtained with the volunteer seated in the dynamometer, during isometric contraction at 90° of knee flexion.

An 8-channel EMG system was synchronized with the dynamometer through a Windaq data acquisition system and used to evaluate the vastus lateralis and rectus femoris electrical activity during isometric knee-extensor tests.

Maximal knee-extensor muscle strength (isometric and concentric tests), in different angles and velocities were measured with a Biodex System 3 dynamometer (Biodex Medical Systems, Shirley, NY, USA). A 2-min interval was observed between contractions. We used the peak torque of each maximal test to analysis.

An ultrasonography system was used to determine VL and RF muscle thickness, pennation angle and fascicle length. Muscle architecture measurements were obtained with the volunteer seated in the dynamometer, during isometric contraction at 90° of knee flexion. Muscle thickness was considered the distance between deep and superficial aponeuroses. The best fascicle in each image was used for pennation angle and fascicle length analysis. Pennation angle was calculated as the angle between the muscle fascicle and the deep aponeurosis, whereas fascicle length was measured as the length of the fascicular path between the two aponeuroses. Furthermore, patellar tendon cross-section area was measured with probe perpendicular to tendon during isometric contractions.

Timed Up and Go test

Vastus Lateralis and Rectus Femoris muscle activation during strength tests