The ability to separate the lower body from the upper body during the backswing in addition to creating what is often referred to as a "X factor stretch" during the initiation of the downswing are key factors in the development of power in the golf swing. These two fundamental components of the swing commonly referred to as the "X" factor allow for the sequencing of the swing to occur correctly in addition to speed generation to be maximized into the impact position.

Unfortunately for many golfers the ability to achieve separation between the lower and upper body is quite difficult. The reasons behind the inability to create an "X" factor can be linked to improper execution of swing mechanics but in many cases it is the result of physical limitations (i.e. a lack of flexibility, poor stability, limited core strength, etc.) not allowing the golfer to perform an "X" factor in the swing.
When we take a look at the "physical side" of the equation relative to developing separation between the lower and upper body certain physical components must be present in the body. To best explain the physical requirements required in the execution of the golf swing we can direct our attention to the principle of the body-swing connection.
This principle simply states that in order to execute a biomechanically correct golf swing certain physical components (i.e. flexibility, strength, power...) must be present in the body. If the body is lacking in the required levels of flexibility, mobility, stability, strength, and power, the ability to execute an efficient golf swing where an "X" factor is achieved will potentially be limited; resulting in the development of swing faults and compensations to overcome these physical limitations.
In order to understand what muscles require strength and what joints require mobility to execute an efficient golf swing we can turn our attention to the Mobility/Stability Pattern of Human Movement. This principle states in order to create efficient movement or athletic actions, the body must operate in an alternating pattern of mobile joints and stable body segments. If this pattern of mobile joints and stable body segments is altered, dysfunction in movement patterns or athletic actions will occur. Relative to the golf swing this principle indicates the ability to execute each phase of the golf swing, generate speed, and transfer this speed to the golf club will be impeded if dysfunction exists within the mobility/stability pattern of human movement.
A joint-by-joint review of the mobility/stability pattern of human movement indicates the following: Ankle -- mobile, knee -- stable, hip -- mobile, sacral/lumbar/pelvic complex -- stable, thoracic spine -- mobile, scapular/thoracic spine -- stable, gleno-humeral joint -- mobile, elbow -- stable, wrist -- mobile as it pertains to efficient human movement and the golf swing.
Taking the information learned from the Mobility/ Stability Pattern of Human Movement and applying it the ability to create an "X" factor we can see certain segments of the body must be stable and specific joints mobile to allow for separation to occur between the lower and upper body. Specifically the hip joint must be mobile and the body segments (i.e. muscles) above and below the hips require stability. Mobility in the hips provides the needed ranges of motion for an "X" factor to occur whereas stability in the core and musculature of the lower body allow for stable platforms for separation to occur.
Simplifying this information indicates in order to create an "X" factor in the golf swing from a physical standpoint requires the development of mobility in the hips and strength in the core and lower body. To develop these physical requirements of the "X" factor we can implement a series of golf fitness exercises to develop strength and mobility.
A very effective and simple golf fitness exercise to develop strength in the lower body is the Jefferson squat. The Jefferson squat develops strength in the majority of the musculature of the lower body allowing for a stable lower half which is required for separation to occur in the swing.
To perform the Jefferson squat grasp a dumbbell with both hands in front of the hips. Extend the arms straight, place the feet slightly wider than shoulder width apart, toes pointed outward at 45 degrees, and heels on the floor. Maintain an upright torso with the eyes looking forward, and arms extended straight.
Slowly lower the hips while keeping the torso upright by bending both knees. Continue to squat downward until the thighs are parallel to the floor. Pause for one second, return to the starting position of the exercise, and repeat for 8-15 repetitions.
Remember the ability to create separation between the upper and lower body and achieve an "X" factor does require certain physical characteristics in terms of flexibility, mobility, stability, strength, and power to be present in the kinetic chain of the body. If these physical components are limited or non-existent, the ability to execute an efficient golf swing will most likely be limited. To learn more about Sean Cochran and his golf fitness training exercises and golf fitness programs go to http://www.seancochran.com.