Ph.D. A.M. Pukhov
Ph.D. S.A. Moiseyev
S.M. Ivanov
Dr.Biol., Professor R.M. Gorodnichev
Velikie Luki State Academy of Physical Culture and Sport, Velikie Luki

Keywords: archery, shooting accuracy, precision movements, movement control, electromyography.

Introduction. Success of aiming procedure in archery largely depends on how harmonic is the athlete’s musculoskeletal system performance. Elite archers improve and perfect their technical skills for many years of training. It is the precise inter-muscular coordination that makes the shooting action sequence of an elite archer look so fluent and easy. Motor skills of elite archers provide an excellent subject for studies of the aiming and shooting movements. The study focused on the contraction patterns of the relevant muscles provides sets of parametric data on the muscular activity in correlation with the shooting accuracy rates.

The purpose of the study was to explore the specifics of muscular control by elite archers

Materials and methods. Subject for our study were 8 elite archers (Masters of Sport and International Class Masters of Sports) selected among the competitors of the training camp of the Russian Youth National Archery Team in the town of Orel in May 2014. The subject archers shot 10 series of 3 shots from classic recurve bows on the 18-meter distance indoors. Simultaneous electrical activity records for the leading muscles supported by video-captures of the shooting process with accounts of the shooting accuracy rates were made. The 16-channel ME 6000 electromyograph was used to measure bio-potentials of the relevant key skeletal muscles and the data records were processed by MegaWin Software (provided by Mega Electronics, Findland). Electromyograms (EMG) were made using skin-fixed 0.9mm electrodes, with the active electrode and reference electrode being placed 2cm apart from one another on the motor point of the subject muscle and along fibers of the same muscle, respectively. Video captures of the archer’s movements in the shooting process were made by Qualisys (Qualisys Track Manager, Sweden) Video System equipped with 8 high-speed video cameras. Light-reflecting markers were fixed on the archer’s body and shooting equipment, including the joint rotation axes, risers and limbs of the bow etc.

Results and discussion. Sport movements in general and the archery shooting technique in particular may be classified into the movement performance phases with indication of the boundary points. In our previous studies we offered 6 phases in the archery shooting process with precise boundary points, namely: (1) preparatory stance and set-up; (2) expansion (drawing); (3) loading; (4) release; 5) follow-through (completion); and 6) relaxation [1, 2]. The preparatory postural phase and relaxation phase have never been subject to serious analysis as they are deemed to fall beyond the standard archery shooting sequence.

In our preliminary studies [3] we used electromyographic data and analyses to explore 32 bilateral body muscles and the upper and lower limb muscles apparently involved in the classic archery shooting process and highlighted the 12 leading muscles showing the highest EMG amplitudes and dynamics in various phases of the shooting process, including the radial flexor and ulnar extensor muscles of the right and left wrists; triceps of the right and left arms; back bundles of the right deltoid muscle and front bundles of the left deltoid muscle; and the upper and lower trapezius muscles (Figure 1).

Figure 1. Key muscles involved in archery shooting sequence

The summarized EMG amplitudes of the above key muscles were found to achieve their peak values in the release phase (231.5±39.6 mkV) and loading phase (224.7±40.1 mkV). The muscular activity values in the expansion and completion phases were not that high making up 168.3±24.4 mkV and 123.5±20.7 mkV, respectively. In the expansion phase the athlete performs high-amplitude and fast “overcoming” drawing movement that requires no maximum or sub-maximum force from the muscles, whilst isometric slow movements normally claim the maximum or sub-maximum efforts. Following the expansion phase and entering the loading action phase, the dynamic contraction action is transformed into the static action that means that the athletes shift loads from one muscle group to the other [4]. In the completion phase, the muscles are released of the bowstring drawing load, and the test data showed drastic falls of the relevant EMG amplitudes.

Based on the specific aspects of bioelectrical activity in different shooting sequence phases, the subject muscles were broken down into a few groups for the purposes of the study. Classified with the first group were the left-hand muscles including ulnar extensor muscle of the wrist, triceps muscle of the arm, front bundles of the deltoid muscle and the upper trapezius muscles as their electrical activity amplitudes in the expansion phase to the loading phase showed insignificant growths varying within 1% to 14% followed by fast drops by 23% in the shot completion phase. These muscles were found responsible for the mostly isometric postural actions including the stretched arm fixing action to secure fixed position of the bow and the shoulder girdle and thereby help the archer maintain the optimal stance throughout the shooting process.

Rated with the second group were the right-hand muscles and the lower trapezius muscles which biopotential values rapidly increased in the loading phase by 60±10% and the release phase by 71±10% compared to the expansion phase (p<0,05). The significant growth of activity in these muscles was indicative of the redistribution of the muscular loads at the moment when the bowstring is drawn to the maximum and the isotonic-type muscular contraction transforms to the static-type tension. The main load in this phase is held by the lower trapezius muscles that enable the athlete to bring together the shoulder blades and expand the chest till the arrow shaft passes the clicker, and by the back bundles of the right deltoid muscle that draws and holds the bowstring.

The radial flexor muscle of the left wrist was rated with the third group. Its activity was found to drastically increase in the shot completion phase compared to the previous phases to help hold the bow after the arrow is released.

In the loading phase, there was detected a stochastic sequence of high- and low-intensity electrical activity surges in the trapeziu muscle that is indicative of corrective actions by the muscle control mechanism. This control mechanism apparently triggers the corrective actions by afferent impulses coming from proprioceptors of the active muscles to help perform the motor program on the peak of the aiming process that normally occurs in the loading phase and manifests itself by such jumps in amplitude and timing of the shot performance process. Bio-potentials of the left-wrist radial flexor muscle of the wrist showed the highest concentrations in the first 0.2-0.4 seconds of the shot completion phase as their amplitudes were 4 to 5 times higher than in the earlier stages. Such bioelectrical activity is indicative of the programmatic control mechanism acting on the muscle.

As far as the shooting accuracy is concerned, we rated every shot with the following three classes: “10 center”, “10 points” and “9 points and less”. Every shot hitting the central ten was rated as accurate, and all other shots hitting aside from the 10 point round were treated as inaccurate. Our analyses of the electrical activity of muscles in the accurate and inaccurate shooting processes showed relatively higher tensions of every muscle when the arrow hit the 10 center round, with the only exclusion for the right trapezius muscle. Inaccurate shots triggered reliably higher EMG amplitude responses in this muscle (193.5±8.1 mkV) than the precise shots in the center of the target round (172.6±10.2 mkV) (p<0.05).

It is not unusual that the archer makes some technical mistake in the aiming process and naturally tries to respond by compensatory adjustments to correct it. These compensatory movements are not always successful in correcting the mistake and may even further and considerably worsen the process. Inaccurate shots in this case with deviations of arrow in different sectors of the target may be caused by the same technical mistake. It is traditional in the shooting sports to name different arrow deviations from the center round with reference to an hour circle, with the strict top point of the target being called “12.00 o’clock”, strict right-hand point “3.00 o’clock” etc. Having sorted out the inaccurate shots by the deviations in our analysis, we found that most of the non-precise arrows hit the 7.00-8.00 o’clock (20%) and 9.00 o’clock fields (17%) and no one of these shots came to the two o’clock sector (Figure 2).

Figure 2. Inaccurate shots: numbers and sectors of deviation, %

Proceeding from our comparative analysis of the inaccurate shot electrical activity and deflections compared to the precise 10-center shots, the EMG patterns were similar for the following sector groups: 1.00- and 7.00-8.00-o’clock arrows; 3.00- and 9.00- o’clock arrows; 4.00-5.00- and 11.00-o’clock arrows; and the group of 6.00-, 12.00- and 10.00- o’clock arrows.

It was further found that the inaccurate shots to the 1.00- and 7.00-8.00-o’clock sectors were associated with the high activity of the ulnar extensor muscle of the left wrist that was 22.3% and 13.4% higher, respectively (p<0.05). The EMG amplitudes for the triceps muscle of left arm in the cases of the inaccurate 1.00-o’clock and 7.00-8.00-o’clock shots were 11.8% and 18.00% lower, respectively (p<0.05). The electrical activity of the lower left trapezius was found to be reliably lower in these cases than that for the accurate shots to the center. Furthermore, the 1.00-o’clock arrows were associated with significant activity of the left deltoid muscle (16% higher), low activity of the radial flexor muscle of the left wrist (31% lower), and the upper right (8% lower) and the lower left (32% lower) trapezius muscles. The inaccurate 7.00-8.00-o’clock shots showed high EMG amplitudes for the right deltoid (20% higher) and upper right trapezius (31% higher) muscles.

The 3.00-o’clock and 9.00-o’clock shots were associated with the significant activity of the upper right trapezius muscle and lower activity of the radial flexor muscle of the right wrist, back bundles of the right deltoid muscle and the lower right and upper left trapezius muscles. For the inaccurate arrows hitting the 3.00-o’clock sector, the EMG amplitudes of the lower left trapezius muscle were 21% lower than that for the accurate shots (p<0.05). Statistically reliable activity sags for the ulnar extensor muscle of the left wrist by 26% and the front bundles of the left deltoid muscle by 28% were characteristic of the inaccurate shots to the 9.00-o’clock sector.

It were the high activities of virtually every tested muscle compared to that for the accurate shots that were found to result in non-precise hits to the 4.00-5.00-o’clock sector, whilst the lower activities were the reason for the 11.00-o’clock sector shots. The EMG amplitudes for the radial flexor muscle of the left wrist and the ulnar extensor muscle of right wrist and the triceps of the right arm were not much different for the accurate and inaccurate shots.

The EMG amplitudes for the inaccurate 6.00-o’clock and 10.00-o’clock shots vs. those for the accurate shots were statistically notably higher in the right-hand muscles (12% and 15% higher in the ulnar extensor muscle of the wrist; and 12% and 10 % higher in the back bundles of deltoid muscle, respectively); left-hand muscles (42% and 60% higher in the radial flexor muscle of the wrist and 33% and 46% higher in the triceps muscle of the arm, respectively); and the upper right trapezius muscle (18% and 33% higher, respectively) and upper left trapezius muscle (64% and 65% higher, respectively). Reliably lower activity was fixed in the radial extensor muscle of the wrist and front bundles of the deltoid muscle. What is specific for these inaccurate shots is that the 6.00-o’clock shots were correlated with the 12% higher activity of the lower left trapezius muscle; and the 10.00-o’clock shots – with the 6% higher activity of the lower right trapezius muscle.

The muscular activity for the inaccurate 12.00-o’clock shots was much the same as for the 6.00- and 10.00-o’clock shots, but the differences with the accurate 10-center shots were more expressed and reliably different both from the accurate shots and the 6.00- and 10.00-o’clock inaccurate shots. The EMG amplitudes for the back bundles of the right deltoid muscle were 54% lower than that for the accurate arrows hitting the center.

Precision of any deliberate movement is largely dependent on how well the skeletal muscles involved in the process are harmonized, and the latter are controlled by efferent impulses of brain and afferent nervous impulses coming from proprioceptors of the active muscles. It is the precise inter-muscular coordination and optimal amplitude of the muscular tension that enables the archer to make an accurate shot. Any disturbance in this harmonic muscular action sequence will result in some deviation of the arrow from the target round, and every such deviation is associated with the specific electromyographic pattern.

Conclusion. The study breaks down the archery shooting sequence into 6 active phases with indication of the time intervals when the relevant muscular efforts reach their maximums. It is for the first time that the electrical activity of specific muscles was demonstrated to correlate with the shooting accuracy rated by the hit sectors of the target.

The study was performed under the state order pursuant to the Ministry of Transport of the Russian Federation Order #1084 dated December 19, 2013

References

1. Buchatskaya, I.N. Dinamika elektricheskoy aktivnosti myshts strelkov iz luka v khode mnogokratno povtoryayushchikhsya vystrelov (Dynamics of electrical activity of muscles of archers during repetitive shots) / I.N. Buchatskaya, R.M. Gorodnichev // Teoriya i praktika fizicheskoy kul'tury.– 2015. – № 1. – P. 32–35.
2. Pukhov, A.M. Biomekhanicheskie osobennosti vystrelov raznoy rezul'tativnosti strelkov iz luka (Biomechanical features of archers' shots of varying accuracy) / A.M. Pukhov et al. // Mater. XI Vseros. konf. s mezhdunar. uchastiem i shkoly-seminara dlya molodykh uchenykh (Proc. of the XI All-Russia conf. with int. participation and workshop-seminar for young scientists). – Perm: Publ. h-se of Perm SRPU, 2014. – P. 195–199.
3. Pukhov, A.M. Elektromiograficheskie kharakteristiki rezul'tativnosti pritsel'nyh dvizheniy cheloveka (na primere strel'by iz luka i pistoleta): avtoref. dis. … kand. biol. nauk (Electromyographic characteristics of performance of man's precision actions (case study of archery and pistol shooting): abstract of Ph.D. thesis) / A.M. Pukhov. – Velikie Luki, 2013. – 21 P.

Corresponding author: Alexander-m-p@yandex.ru