Effect of bow drawing technique on skilled archer postural stability: a case study

Keywords:

• Archery
• center of pressure
• force plate
• bow draw

1. Introduction

At the Olympic games, archers use a recurve bow to shoot arrows at a 122 centimeters diameter target set 70 meters away. Postural stability and consistency are therefore determinant in the archer’s performance.

A shot is generally decomposed in two main phases. The aiming phase, mostly static, is followed by the string release phase, which is much more dynamic. To optimize bow draw length consistency, a small metallic device called ‘clicker’ is mounted on the bow riser. When the clicker falls, the metallic sound emitted signals the correct draw length is reached. Then the archer releases the arrow with a reaction time latency.

Previous studies showed the importance of postural stability on archery performance (Keast and Elliott 1990), particularly during the last second preceding string release (Mason and Pelgrim 1986) and during the release (Tinazci 2011). Moreover limited postural sway (Simsek et al. 2019) and postural consistency across shootings (Stuart and Atha 1990) are crucial indicators of an archery performance.

Bow drawing action directly challenges the archer upper body stability, which is reflected in the ground reaction forces.

The current study aims to characterise the effects of different bow drawing techniques on the archer’s postural stability.

2. Methods

One skilled archer participated. He was asked to shoot at a target set 12 meters away from him, with each foot resting on each of two 6-axis force plates (Sensix, Poitiers, France). An ADXL354 analog accelerometer was mounted on the bow riser to monitor the clicker fall and the bowstring release. Both devices were synchronized and sampled at a 1000 Hz frequency. Analog signals from the force plates were filtered using a 3rd order Butterworth low-pass filter with a 6 Hz cutoff frequency (Spratford and Campbell 2017). The centre of pressure (COP) was computed in the anteroposterior (AP) and mediolateral (ML) directions. The ML direction was the shooting direction.

The archer shot 3 arrows using one of three different bow draw techniques for a total of 9 shots: upper-draw (preferred technique), lower-draw and direct draw.

Based on accelerometer data, two phases were identified (Figure 1): a pre-release phase (i.e. the one second period preceding Tclicker plus the reaction time) and a post-release phase (i.e. the 0.5 seconds period following Trelease). The reaction time to the clicker fall was computed as the difference between Trelease and Tclicker.$\overline{{\mathit{COP}}_{AP}}$ and $\overline{{\mathit{COP}}_{ML}}$ were defined as the mean position of the COP in AP and ML directions respectively. Several postural stability indicators were computed during the two phases (Prieto et al. 1996): the mean and RMS distance around the mean COP position, mean and maximum velocity of the COP, and the 95% confidence ellipse area of the COP path.

Figure 1. Top: events detection based on accelerometer data: pre-release phase before Trelease (vertical green line) and post-release phase after. Bottom: COP trajectory in the ML (shooting) direction.

A Kruskal-Wallis test was performed on each postural parameter in both the pre-release and the post release phases to assess whether the postural stability indicators were different between the three drawing techniques. Reaction time duration was also compared between the three drawing techniques. A Wilcoxon-Mann-Whitney test was used as post-hoc. For all tests, given the low number of shots performed, a p < 0.1 was set for significance.

3. Results and discussion

All recorded shots hit the target centre, therefore performance was maximal. The average reaction time was 209 ± 105 ms but was significantly longer and more variable when using the direct draw (304 ± 149 ms) compared to both the upper (161 ± 34 ms) and lower draw techniques (163 ± 22 ms). Upper and lower draw techniques reaction time were similar to elite archers performances (Spratford and Campbell 2017).

No statistical differences were observed in the post-release phase between the three drawing techniques in the postural stability indicators. Thus, only postural stability indicators computed in the pre-release phase were analysed and presented in Table 1.

Table 1. Indicators of pre-release postural stability, significant differences are presented in bold (p < 0.1).

		Pre-release
	Upper	Direct	Lower
$\overline{{\mathit{COP}}_{AP}}$ (mm)	61.7 ± 2.8	72.1 ± 6.3	72.7 ± 4.6
$\overline{{\mathit{COP}}_{ML}}$ (mm)	−50.0 ± 7.7	−49.4 ± 6.0	−48.0 ± 1.2
Mean dist (mm)	1.2 ± 0.7	1.5 ± 0.3	1.3 ± 0.5
Mean dist AP (mm)	0.9 ± 0.8	1.0 ± 0.4	1.1 ± 0.6
Mean dist ML (mm)	0.4 ± 0.2	0.8 ± 0.1	0.5 ± 0.2
RMS dist (mm)	1.4 ± 0.7	1.7 ± 0.4	1.5 ± 0.5
RMS dist AP (mm)	1.1 ± 0.8	1.3 ± 0.6	1.2 ± 0.7
RMS dist ML (mm)	0.6 ± 0.3	1.0 ± 0.1	0.6 ± 0.2
Mean v (mm/s)	9.2 ± 3.2	11.9 ± 3.0	9.6 ± 0.7
Mean v AP (mm/s)	6.1 ± 1.5	8.3 ± 3.0	6.8 ± 1.8
Mean v ML (mm/s)	5.8 ± 2.4	6.6 ± 0.7	5.5 ± 1.1
Max v (mm/s)	55.9 ± 25.1	39.1 ± 15.7	40.8 ± 15.9
Max v AP (mm/s)	15.8 ± 6.9	19.0 ± 4.0	15.5 ± 4.1
Max v ML (mm/s)	47.3 ± 34.3	31.7 ± 18.5	36.0 ± 16.3
95% area (mm²)	10.5 ± 10.3	21.8 ± 9.7	10.9 ± 5.2

During the pre-release phase, the mean distance, the RMS distance to the mean COP and the 95% ellipse area were all smaller than in regular quiet standing, but the mean velocity was higher (Prieto et al. 1996). Reducing postural sway amplitude while increasing COP velocity pre-release suggests that the archer increases his own stiffness to reduce postural oscillation and facilitate the aiming task. These results are comparable to elite archers postural sway amplitude (Simsek et al. 2019) and post-release sway ellipse area (Keast and Elliott 1990).

$\overline{{\mathit{COP}}_{\mathrm{A}P}}$ and RMS distance ML pre-release were the only parameters significantly reduced in the upper draw compared to the direct draw technique (both p = 0.09). Additionally, despite not significant, a reduction of the mean distance of the COP in the ML direction by a factor of 2 between the direct and the upper draw techniques (0.8 versus 0.4 on average) was noted. These results suggest that bow drawing technique mostly challenges postural stability in the shooting direction (ML) pre-release.

This case study, presents several limitations. For technical reasons, the target could not be set further away. Hence, it was not possible to correlate any of the postural indicators with shooting performance. The number of shots analysed is also very low which prevented the analysis for drawing consistency. Further experimentations including more archers and a higher number of shots are needed to better assess the effects of bow drawing techniques on postural stability and shooting performance.

4. Conclusions

The skilled archer tested increases postural stability to facilitate aiming prior to bowstring release. Bow drawing techniques have limited influence on pre-release postural stability, but differences are found only in the shooting direction. Since archers need to minimize the postural oscillation to increase shooting performance, the upper draw technique seems more appropriate for this archer than the direct draw.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work is supported by the French National Institute of Sport and Physical Education, the French Archery Federation, the French National Research Technology Association and the French Ministry of Sports.