Biomechanical and modelling analysis of shaft length effects on golf driving performance

The purpose of this thesis was to determine how shaft length affects golf driving performance. Shaft length effects on the golf swing have been of interest to several researchers (including Egret et al., 2003; Reyes and Mittendorf, 1999 and Mitzoguchi and Hashiba, 2002). A range of drivers with lengths between 46" and 52", representing lengths close to the 48" limit imposed by the R&A Rules Limited (2004), were assembled and evaluated. A 5-camera three dimensional motion analysis system tracked skin markers attached to 9 low-medium handicapped (5.4 ± 2.8) golfers. Clubhead and ball launch conditions and drive distance and accuracy were determined for 5 lowmedium handicapped golfers (5.1 ± 2.0) and 7 elite golfers (0.21 ± 2.41) who performed shots on a purpose-built practice hole. Finally, motion analysis was conducted for an elite golfer (+1 handicap) and experimentally obtained marker data was used to drive a large-scale musculoskeletal model. Low-medium handicapped golfers demonstrated more significant variation in performance due to shaft length than elite golfers. Postural kinematics remained largely unaffected, as were ball spin, launch angle and swing tempo. As shaft length increased from 46" to 52", initial ball velocity (+ 1.90 ms-1, p < 0.05) and ball carry (+ 14 yds, p < 0.001) increased significantly for low-medium handicapped golfers. As shaft length increased from 46" to 50" initial ball velocity (+ 1.79 ms-1, p < 0.01) increased significantly for elite golfers. Ball carry (+ 4.73 yds, p = 0.152) also showed NS increases for elite golfers. Furthermore, as shaft length increased, for all club comparisons there were NS decreases (p = 0.063) in shot accuracy for low-medium handicapped golfers, but no decrease in accuracy for elite golfers. Model simulated results, including posture, timing and predicted muscle force compared well with experimental results (r > 0.98, p < 0.05). Simulations showed that for the range of clubs modelled (46" to 50") hip/shoulder differential angle at the top of the backswing increased significantly (+ 6.13º, p < 0.001) as shaft length increased, and each 2" increase in shaft length required a NS additional 4.5 N force (p = 0.117) to maintain normal swing kinematics. The results from this thesis indicate that modest improvements in shot performance brought about by increasing driver length are the result of increased hip/shoulder differential angle at the top of the backswing and increased predicted muscle force.