Fine-wire, isometric contraction. Mathieu PA, Univ Montreal, CA.

Two pairs of fine wire electrodes (Chalgren, USA) were inserted by a physician in the right biceps brachii (BB) muscle in accordance with medical practice and ethical rules. Insertion was approximately 10 mm deep below the BB belly. Each pair separated by 10 to 15 mm, with trajectories perpendicularly oriented to the skin surface and pointing toward each other. The reference electrode was placed over the ulna bone close to the wrist and unipolar signals were collected. Analog signals were amplified (gain: 5000 V/V) and band-pass filtered (3 Hz to 3 kHz, second order filters) prior to being sampled at 8 kHz. A handcuff placed over the wrist was connected to a dynamometer (Intertechnology Inc., Don Mills, Ontario, Canada). This was used to measure the contraction level and provide feedback to the subject in order to maintain an isotonic contraction of the biceps over a 10 s period. The mean of two 5 s maximal voluntary contractions were taken as the maximum voluntary contraction (100% MVC). Contraction levels ranged from 5 to 30 % MVC with 5 contractions conducted per level. A cue was given to the subject to initiate the contraction and the data acquisition was started only after the required level was reached and kept constant for 2-3 s. The trial was discarded if the contraction level presented on a display was not considered constant during the 10 s of data acquisition. To minimize the effects of fatigue, a 15 s rest was allowed between each contraction, a 2 minute break was taken between contraction levels and the contractions were realized in the following order: 30%, 20%, 10% followed by 25%, 15% and 5% MVC. When a full set of acquisitions was over, a 15 min rest was given to the subject before the entire protocol was repeated to collect a second data set. Two maximum voluntary contractions were also done at the end of the first data set as well as at the end of the second one to check that the experimental conditions were constant. The experiments were repeated 5 times at a minimum interval of 2 days within a two- week period. At the end of the first experiment, pen marks were made very near the insertion points of the wire electrodes. The same points were used in the four following experiments. The angles between the two needles used to insert the electrodes were approximately the same during each experiment but could not be controlled precisely. Neither could the depth of penetration be controlled precisely. Following their removal at the end of each experiment, the wires were examined to identify the presence of a kink that could reveal the depth of penetration and to ascertain that the full tip of the electrodes were intact.

The signals are stored in three channels, with channels 2 and 3 being the monopolar wire signals and channel 1 being the difference between the two. EMGlab gives a warning message when the files are loaded because the sampling rate ( 8 kHz) is less than twice the default Nyquist rate (5 kHz). This message can be safely ignored for these signals.

* Please cite this data as:
Mathieu PA. [Online dataset R007, available at http://www.emglab.net]

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