Muscle activity in para archery: Gianikellis 2000

This conference contribution, presented at the 2000 ISBS symposium, reports no measurements on archers: it describes a measuring system built at the University of Extremadura to study the shooting of archers with physical disabilities. The system records surface electromyography of the main muscles, joint posture from electrogoniometers and the flexing of the bow during the draw, read by a sensor of the same kind mounted on the bow, all at the same time.

The authors show examples of raw signals, their spectra and a curve of bow deformation during the draw, and list the parameters the system can calculate. They argue that, besides the study of technique, the system could give the archer real-time feedback on how they load the bow. They do not say how many athletes it was tried on, or what their disabilities were.

The measuring chain combines an electromyography system with a Biometrics electrogoniometer system. The electrodes are active silver/silver chloride surface electrodes, 0.5 cm in diameter; the signal passes through a differential amplifier with gain from 10 to 10,000, filtering that removes content below 10 or 100 Hz and above 300, 1,000 or 2,000 Hz, a 50 Hz notch filter for mains noise, then into a 12-bit acquisition card with a combined sampling rate of 50 kHz across 16 channels, eight for electromyography and four for the goniometers. The goniometers and torsiometers are light, flexible strain-gauge sensors with a stated accuracy of 1.5 degrees over 90 degrees from neutral and a precision better than one degree.

Processing is done in MATLAB. From the rectified electromyographic signal the system derives the mean rectified value, the root mean square, a moving average and the integral, which can be normalised to maximal contraction or to the bow's draw weight; from the power spectrum it derives the median frequency, the mean frequency and the bandwidth. From the bow's deformation it calculates indices of the draw such as the force gradient.

This is a technical description, with no stated participants, no data and no test of the system's reliability or validity. In particular, it is not shown that the flexing read by the goniometer on the bow corresponds to the force applied to the string. The claim that, at full draw, the gap between draw weight and muscle tension could cause injury over time is presented as obvious but is not backed by measurements. The work is more than twenty years old and the equipment is that of its time.

For an archer today nothing changes, because there are no findings to apply. The contribution is of historical interest to anyone who follows para archery: it shows that as early as 2000 researchers were planning to study the technique of archers with disabilities by measuring muscles, joints and bow load together, and to use the draw curve as immediate feedback. In the registry it counts as the description of a method, not as evidence on how archers with disabilities shoot.