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CONSTRUCTING A COMPUTER MODEL OF THE ARCHER

To construct a baseline computer model of an archer, we film the archer from different angles (Figure 1). Computer software scans the images and determines all skeletal members and alignment angles throughout the shot process.

To create a model of the ‘typical’ archer, we study multiple archers with different body proportions and the computer merges them into a ‘typical archer’ (Figure 2).

To test this computerized ‘typical archer’, we use a standard archer, with typical dimensions, and map his activities against the computer generated archer’s motions. By setting a monitor up as shown in Figure 3, the archer can easily see his actions, in real time, from any angle. The computer overlays the action the archer is trying to duplicate. With this real time feedback, the archer is able to match his activities exactly to the form and position being analyzed.

We then film this archer as he performs multiple techniques, both good and bad, and analyze these actions and angles to determine, empirically, how critical each action and angle is (Figures 4 & 5).

Once we have a fully functional and calibrated model, we add skeletal and muscular details (Figure 6). We can use this detailed standard model to analyze any technique by having the computer model simulate actual archer body movement during a draw and shot. At this stage, we can make any modifications necessary to ensure that the model motion is accurate.

Once fully tested, the analytical model can be used to compare any actions, and the results of any changes. Below (Figures 7) is a simulation to investigate the differences in body loading between the NTS Rotational draw used by the US team, and a Conventional Linear Draw.

Finally, the computer model can analyze the anchor, alignment, and release, to determine the stresses and interaction between the archer and the bow (Figure 8).

The following plots show the comparison between the loads a stresses on the archer using the NTS rotational draw, used by the US team, and a conventional ‘linear’ draw technique. In this study, both methods come to the same anchor point. The primary interest is to determine the efficiency of the draw, and the difference in the body stresses and strength required to execute the two techniques. This analysis uses a 40 lb draw weight bow. A variation in draw weight from this baseline will affect the numerical results proportionately, but the percentage differences will remain the same.

Note how the NTS draw method requires a much higher torque, about the bow shoulder, to make it

through the draw. In the NTS method the torque at the bow shoulder increases to a maximum at the point when the draw hand is about even with the bow shoulder. From this peak point, the torque decreases as the archer comes to full draw and anchor. By comparison, the linear draw shows a constant increase to that same point.

The plots below show that, because the upper arm is in line with the bow shoulder line for both techniques, the compressive and adverse lateral forces are very similar.

The compressive and lateral bow shoulder plots show that the shoulder joint itself is subjected to the same stresses and wear, but, the muscular strength required by the rotational draw is almost 20% greater than that required by the linear draw.

The draw shoulder torque follows a pattern similar to the bow shoulder torque. The rotational draw technique requires 15% more strength than the linear draw, to draw the bow back to anchor. This extreme draw load is at the point where the draw hand is about even with the bow shoulder. After this point, the torque reduces and the final torque required to hold the bow at anchor is identical for both techniques, provided they arrive at the same anchor alignment.