The effect of a modified one-plane golf swing upon the lumbar spine “crunch factor”

Abstract

Background: The full, modern one-plane golf swing is associated with large rotational velocities and resultant stress to the lumbar spine. The “crunch factor” (CF) has been previously defined as the instantaneous product of lateral flexion and axial rotation velocity, and has been hypothesized as a potential mechanism for golf-related low back pain (LBP). Shortening the backswing ameliorates compressive forces, but there is no data to substantiate a reduction of the CF. Purpose:The purpose of this paperwas to compare theCF during the full and shortened modern one-plane golf swings in low handicap players. Methods: Thirteen healthy subjects participated in the study after providing written informed consent. Subjects ranged from 19 to 66 years of age (38± 15 yr), and did not currently have low back or shoulder pain. The mean handicap was 7± 2 according to USGA handicapping standards. Data were collected in a motion analysis laboratory using Vicon MX Cameras (Denver, CO) capturing data at 240Hz andBertec (Columbus,OH) force plates sampling at 1000Hz. Subjects utilized their own 7-iron for all swings. Subjects reported to the lab on two occasions to perform five full and five shortened swings in a counter-balanced order. A full swing was defined as the club reaching ±10◦ of horizontal position in the top of the backswing, which is an arc of motion equivalent to approximately 270◦. This arc begins at address (0◦) and ends at the final club position prior to the initiation of downswing. Conversely, a shortened swing was defined as attaining an arc of 225± 10◦. Dependent variables included were club-head velocity (CHV), peak CF, and the timing of CF (TCF). Swings between the two sessions were compared with paired t-tests with SPSS 21.0 (IBM, Armonk, New York). There were no differences (p> 0.05) between the two sessions, therefore the data from the two sessions were pooled for data analysis yielding 10 swings for each condition. Data was analyzed with repeated measures ANOVA with an apriori alpha of 0.05. SPSS software (Chicago, IL) was used to analyze the data. Data are reported as means± SEM. All force data is expressed in Newtons (N) normalized to body mass. Results: The backswing club angles were 231± 7.4◦ and 268± 8.2◦ for the shortened and full swings, respectively (p 0.05) and this occurred 0.08± 0.01s after impact. Conclusion(s): These results corroborate earlier papers purporting peak lateral flexion angles and rotational velocities immediately after impact. Furthermore, the current data shows that the CF is significantly reduced with a shortened swing. It is currently unknownwhether this significant reduction is clinically meaningful. More research is needed to examine the shortened swing in golfers with LBP. Implications: Shortening the back swing is associated with reduced lumbar spine stress, which may have implications for patients with chronic low back pain.