Three methods of beginning the downswing kinematic sequence are explained; they are:
- Stretching: Proximal segment precedes the distal segment, stretching the muscles, putting them in eccentric contraction hence providing more force for later in the downswing.
- Riding: Proximal and distal segment turn at the same speed in the downswing, the muscles are in isometric contraction to stabilize the distal segment. Large force is built up between the segments also providing large initial force for later in the downswing.
- Fanning: Distal segment immediately precedes the proximal segment in the downswing with the muscles immediately going into concentric contraction not allowing as much force to build; not as effective at the other two methods.
These relationships can be explained by looking at the force-velocity curve of muscle contraction.
The key to an efficient transfer of energy in the downswing is a good kinematic sequence. Each body segment should accelerate and decelerate in an orderly sequential manner. But there is more to it than simply seeing the curves accelerate and decelerate. Look at the two downswing kinematic sequence graphs below; yes, it is obvious that the golfer on the right is out of sequence, the blue curve (the lead arm) peaks before the red (pelvis) and the green (thorax or upper body); whereas, the peaking order of the golfer on the left is correct; pelvis, thorax, arm then club.
There is another obvious difference between the two graphs and you can see from the captions, one is called “riding” and the other is called “fanning”. Riding is where all the curves track very closely together in the early phase of the downswing and fanning is where they fan apart. What does this mean and how does this effect efficiency? Unfortunately, the fanning method does not transfer energy as well as the riding method.
To simplify the discussion, let’s use graphs of just the pelvis and thorax sequences in the downswing. Remember that the kinematic sequence shows the turning or swinging speed of the segments. Let’s also add a third version called “Stretching”. Focus in on the area in the gray circle; this is the beginning of the downswing.
Examine the middle graph first; if the two curves rise very closely together then these two body segments are turning at about the same speed and accelerating at approximately the same rate (at least for the early portion of the downswing). That means there is no relative speed difference between the two body segments so the thorax is “riding” on the pelvis and the core muscles are in isometric contraction. Let’s look at this from a muscle biomechanics perspective. Check out the Force-Velocity Curve in the graph below.
Notice that when there is isometric contraction, force production in the muscle is very high, that is, the muscle is very capable of generating a large force in an isometric contraction. This is a classic example of energy transfer across a joint, in this case, the “joint” is lumbar and lower thoracic spine. The energy generated by the legs and butt gets the pelvis turning, and in the “riding” example, the core is strong enough to pass this energy (and speed) directly to the thorax. At the appropriate time the core muscles fire explosively, the thorax increases speed but the pelvis is pushed back. This opposite torque causes the pelvis to “peel” off and then decelerate. The riding method is a very efficient method of transferring and adding energy to the thorax.
Now look at the stretching example; here the pelvis is moving slightly faster than the thorax in the early part of downswing. This means that the spine angle is actually widening under eccentric contraction. The muscles are lengthening slightly so the force-velocity curve now shows that the muscle is capable of generating even more force than in the isometric condition. This is one physiological reason why it is beneficial to stretch the core in the downswing; it allows the muscles to produce more force and store energy which is returned and transferred to the thorax as soon as the muscles begin concentrically contracting.
So in summary so far; when the red curve is higher on the graph than the green curve, the pelvis is turning faster than the thorax and the core muscles are eccentrically contracting; this is the “stretching” example. In contrast, when the red and green curves are riding almost exactly on top of each other then the pelvis and thorax are turning at the same rate and the muscles are isometrically contracting; this is the “riding” example. The stretching method in the downswing is more efficient than the riding method provided that the stretch is not too excessive or too slow. This action is known as the stretch-shorten cycle of muscle. Both stretching and riding are better than the fanning method which is now to be discussed.
What happens in the “fanning” method and why is it not as efficient? Again look at the pelvis (red) and the thorax (green) curves in the graph. You see that pretty much immediately after the top of backswing, the thorax curve accelerates faster than the pelvis curve, consequently there quickly becomes a large speed difference between the two body segments and the muscles are immediately contracting concentrically. Looking at the force-velocity graph we see that we have dropped to a lower force on the curve. As speed increases the muscles cannot produce as much force. Certainly as the speed between segments increases even more the force a muscle can produce drops even more.
In short, research has shown that a pre-loaded muscle can contract more forcefully than one that is not pre-loaded. So both the stretching and the riding methods pre-load the muscle. It has also been proven that a quick pre-stretch of the muscle may produce an even more forceful contraction so an appropriately pre-stretched muscle will contract more forcefully than one that is not.
I have used the pelvis and thorax as the example here, but if you look at the first graph presented you can see that similar actions occur at each joint during the downswing. The shoulder and the wrist also undergo a similar eccentric, isometric or concentric contraction at different phases of the downswing. Looking at the shape of the kinematic sequence curves in the early downswing can give us insight in how powerful the downswing is likely to be; moderate stretching and riding are good, but fanning is not. Note that fanning at the wrist joint early in the downswing is also more commonly known as casting; using this analogy you could call fanning at the shoulder; casting the arm, and fanning at the spine as casting the thorax.