The transition phase of a golf swing is considered to be a decisive instant required for a powerful swing. However, at the same time, the low back torsional loads during this phase can have a considerable effect on golf-related low back pain (LBP). Previous efforts to quantify the transition phase were hampered by problems with accuracy due to methodological limitations. In this study, vector-coding technique (VCT) method was proposed as a comprehensive methodology to quantify the precise transition phase and examine low back torsional load. Towards this end, transition phases were assessed using three different methods (VCT, lead hand speed and X-factor stretch) and compared; then, low back torsional load during the transition phase was examined. As a result, the importance of accurate transition phase quantification has been documented. The largest torsional loads were observed in healthy professional golfers (10.23 ± 1.69 N · kg⁻¹), followed by professional golfers with a history of LBP (7.93 ± 1.79 N · kg⁻¹), healthy amateur golfers (1.79 ± 1.05 N · kg⁻¹) and amateur golfers with a history of LBP (0.99 ± 0.87 N · kg⁻¹), which order was equal to that of the transition phase magnitudes of each group. These results indicate the relationship between the transition phase and LBP history and the dependency of the torsional load magnitude on the transition phase.