Comparative Analysis of Body Sway Characteristics in Para-Archers with Above-knee Amputation and Non-Disabled Archers under Windy Conditions: A Case Study

This case study explored the body sway characteristics of two para-archers with above-knee amputation (AKA) under windy conditions and compared their performance with two non-disabled counterparts. We expected that relative to non-disabled individuals, archers with AKA would exhibit a more significant increase in center of pressure (CoP) sway area, sway path, and sway velocity, and a more pronounced decline in performance when shooting under windy compared to no wind conditions.

Four experienced archers, two with AKA (Archer_A1 and Archer_A2), including a Paralympian, and two non-disabled (Archer_N1 and Archer_N2), were recruited in this study. All subjects had at least 15 years of archery experience. Each subject shot 15 arrows on a 40cm target face located 18m away under two conditions: calm (C_calm) and windy (C_wind), where an industrial blower fan was placed in front of the subjects and generated wind at a speed of 8.3m/sec. Changes in CoP were captured using two force platforms (FP4060-05-PT, Bertec Corp.) from the instant of bow-raising to the end of follow-through. Parameters including sway area, sway path, and sway velocity were recorded. Shooting performance, which is defined as the distance between the centre of the target (‘X’) and the arrow, was measured. Percentage changes in these parameters were computed with [(C_wind – C_calm)/C_calm]. 

When comparing with C_calm, archers with AKA demonstrated a larger CoP sway area (Archer_A1: 97.5%; Archer_A2: 49.6%) in C_wind. This pattern was seen in Archer_N1 (31.6%). On the contrary, Archer_N2 showed a 27.7% decrease in sway area under C_wind. Furthermore, all archers demonstrated a longer CoP sway path (Archer_A1: 103.9%; Archer_A2: 27.9%; Archer_N1: 25.4%; Archer_N2: 1.2%) and higher sway velocity (Archer_A1: 26.9%; Archer_A2: 6.6%; Archer_N1: 35.1%; Archer_N2: 14.7%) under windy conditions. All archers performed poorer in C_wind, with the changes being more significant among non-disabled archers than those with AKA (Archer_A1: 92.8%; Archer_A2: 72.8%; Archer_N1: 222.5%; Archer_N2: 136.6%).

The findings suggest that experienced archers with AKA would demonstrate a larger CoP sway area and a longer path under windy conditions compared to non-disabled archers. Such differences in CoP sway velocity were not consistent among the four archers. Contrary to our expectations, the impact of wind on archery performance was less pronounced among archers with AKA than the non-disabled archers. 

These preliminary results suggest that further studies using this protocol could reveal how individuals with AKA sway during archery shooting. Understanding the biomechanical changes of para-archers to windy conditions is an integral part of ensuring athletes’ safety, especially novice archers, during training and competition. This case study can inform a robust study design with a larger sample size. The relationship between CoP sway characteristics and archery performance also warrants further investigation.