Comparisons of the biomechanical characteristics of the swing planes for the driver and 7-iron during the golf swing

Objective To compare swing plane biomechanics between the driver and 7-iron in golf and elucidate the kinematic and dynamic mechanisms underlying swing plane formation. Methods Sixteen male low-handicap golfers were recruited. A 3D motion capture system and two force plates were used to simultaneously record swing data for the driver and 7-iron. Swing plane angle, torso and pelvic angle, center of mass displacement, and ground reaction force (GRF) parameters were calculated. Statistical analyses were performed using paired t-tests, correlation analysis, and SPM {t}. Results The driver showed a significantly smaller tilt angle than the 7-iron across all phases (p < 0.001), and a significantly smaller azimuth angle during the release-acceleration phase (p < 0.001). During the backswing, the 7-iron tilt angle was negatively correlated with torso rotation ROM (r = −0.701) and pelvic rotation ROM (r = −0.730), whereas the driver exhibited greater torso and pelvic rotation ROM than the 7-iron (both p < 0.05). During the release-acceleration phase, the driver tilt angle was positively correlated with pelvic forward tilt ROM (r = 0.850). SPM analysis further showed that the driver had a significantly smaller torso side tilt angle than the 7-iron during 0%–89% swing cycle (p = 0.001). During the downswing to follow through, the driver tilt angle was negatively correlated with AP RGRFmax (r = −0.805), whereas the 7-iron tilt angle was positively correlated with ML LGRFmax (r = 0.633). In addition, the driver exhibited significantly greater AP RGRF during 0%–5%, 37%–62%, and 83%–89% swing cycles, and significantly smaller ML LGRF during 0%–18% and 84%–93% swing cycles, compared with the 7-iron (p < 0.05). Conclusion The driver relies on rotation of the torso and pelvis, combined with power generation from the rear, to create a flat swing plane, while the 7-iron maintains a steep and highly consistent plane through body posture control and front-side braking. Training should focus on strengthening the corresponding biomechanical capabilities to optimize the stability of swing plane.