Introduction
For this week’s article we look at X-factor stretch in the golf swing. X-factor is the name given to the difference in rotation between your pelvis and shoulders somewhere near the top of the backswing prior to the pelvis rotation changing direction to start your downswing. X-factor stretch is when the pelvis changes direction in relation to the shoulders (which are either static or still rotating away from the target) and the connective and/or muscle tissue is placed under a momentary “stretch”. Given this is a method for storing energy in the backswing, it can lead to greater distance and has often been considered a biomechanical performance measure. But it can also increase the likelihood of lower back pain. This recent study by Kenny et al with collegiate golfers investigated how golf specific exercises could help with golf performance and the use of x-factor stretch.
Article Title
Kenny D-M, Presnall J, Cosio-Lima L, and Greska E. The effects of a 5-week golf specific strength and conditioning intervention on swing performance factors. British Journal of Sports Medicine 51: 339-339, 2017.

Background
The effects of golf specific strength and conditioning interventions on performance are scarcely researched. However, a multitude of research exists relative to golf related injuries. From those studies, it has been postulated that an increase in the X-Factor Stretch (XFS) variable increases the probability of a lower back injury. As the XF has been identified as a performance variable, it is of interest to determine how it is influenced by a golf specific intervention. Objective To examine the effects of a 5-week strength and conditioning intervention on golf swing performance factors. Design Quasi-experimental. Setting Laboratory and gym. Participants Nine female NCAA Division II collegiate golfers (age 20.7±2.7 yrs; height 175 ±9.81 cm; body mass 76.5 ±9.2 kg), maintaining a handicap of ≤3. Intervention:
The 5-week strength and conditioning intervention was implemented to improve the subject’s golf swing. The majority of the exercises were lower body orientated, and included rotational aspects.

Main Outcome Measurements:
The pre- and post-testing procedures included a biomechanical analysis using 3D motion analysis. The dependent variables were clubhead velocity (CV; m/s), hip velocity (HV; °/s), XFS angle (°), and ball speed (BS; m/s). It was hypothesized that CV, HV, and BS would increase without an increase in the XFS. T-tests were used to define statistical significance (p<0.05).

Results:
From pre- to post-intervention, subjects significantly increased HV (8.2±0.5°/s to 8.8±0.7°/s; p<0.001), and CV (35.8±0.9 m/s to 36.8±2.5 m/s; p=0.018) and significantly decreased XFS (−54.9±10.2° to −47.9±4.2°; p<0.001). We did not detect a significant change in BS from pre- to post-intervention (52.7±2.8 m/s to 53.2±5.1 m/s).
Conclusion
It was demonstrated that the intervention increased CV, HV, and BS; but decreased the XFS. Thus, it can be suggested that a golf specific strength and conditioning program can increase golf swing performance factors, without increasing the risk of lower back injury.
So the take home message is that once again we see that increasing the strength of the golf specific muscles gives the golfer more options to create greater club-head speeds without having to over-utilise the potentially injury inducing stretch-shorten cycle in the golf swing. It’s also possible that increasing golf-specific muscle strength also provides protective support to the structures of the lower back during the golf swing.

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