Here is a detailed explanation of the pelvis and thorax kinematic sequence curves from TPI 3D, focused around transition.  They display how transition occurs and there is a lot of information that can be gleaned from them.  They relate directly to the spine rotation graph also.  So for TPI 3D techies here we go.

The two above graphs have time in seconds along the X-axis and the specific parameter along the Y-axis, hence they show last part of backswing, top of backswing, downswing and impact.  The red line in the kinematic sequence graph is the rotation velocity of the pelvis around its superior-inferior (up-down) axis. The green line is the same but for the thorax (ribcage). The red line in the second graph is the spine rotation angle in degrees (a.k.a. X-Factor).  The first vertical black line indicates top of backswing (Top). The second vertical black line indicates impact (Imp). The vertical blue lines show other critical events during the swing and will be discussed:

Pelvis Transition: This vertical line indicates when the pelvis rotational velocity is zero. To its left both the pelvis and thorax segments have a negative value which means they are in the backswing. So for the pelvis this line indicates the exact point at which the pelvis is transitioning from backswing to downswing. Notice on the spine rotation graph that this is labeled as -45°; this means that when the pelvis transitioned there was 45°of “coil” between the pelvis and thorax, or the X-Factor was 45°. Also notice however that the green line, the thorax, is still negative; it is still in its backswing. So for the short period of time between the pelvis transition line and the thorax transition line the pelvis is in the downswing and the thorax is still in the backswing; they are moving opposite directions so the spine rotation angle keeps increasing (in the negative direction).

Thorax Transition: This vertical line indicates when the thorax rotational velocity is zero. At this point the thorax is now changing from backswing to downswing. The value for spine rotation at this point is -48°; so now there is 48° of spine coil (X-Factor). The spine coil has increased from 45° to 48°; so there is 3° of spine rotational stretch or X-Factor Stretch; but wait we are not finished yet; X-Factor is still stretching! This portion of the stretch so far is called the contra-directional stretch since “contra” means “opposite” and the pelvis and thorax were (until now) moving in the opposite directions. Notice at this point the thorax rotational velocity is zero and pelvis rotational velocity is positive; this means that the spine is still coiling and the X-Factor is still stretching. Notice that between thorax transition and the next critical point, the equal velocity line, the pelvis is moving faster than the thorax, so the X-Factor keeps stretching until the equal velocity point is reached. We call this portion of the stretch, ipsi-directional stretch, because “ipsi” means “the same” and in this phase the pelvis and thorax are moving in the same direction; they are both now turning in the downswing. At the equal velocity point the value of spine rotation is -51° in this example, so the spine coil has increased in this phase from 48° to 51°, so there is another 3° of X-Factor Stretch.

Equal Velocity: This vertical line indicates when both the pelvis and thorax are rotating in the downswing with the same rotational velocity. From this point on the thorax will be turning faster than the pelvis and the X-Factor will begin closing; X-Factor Stretch is done. This is shown by the spine rotation curve; it is now going up towards zero. So the total X-Factor Stretch is from pelvis transition to the equal velocity point and is the sum of both the contra and ipsi stretch values; in this case 3° + 3° = 6°.

Pelvis Peak Velocity: This vertical line indicates where the pelvis reaches its maximum turning speed during the downswing. Notice it is before the thorax peak and lower than the thorax peak. After this point it should rapidly decrease (decelerate) as it transfers speed to the thorax segment.

Thorax Peak Velocity: This vertical line indicates the point at which the thorax reaches its maximum turning speed during the downswing. In an efficient swing it should be larger than the pelvis peak and later than the pelvis peak, because it has received its “boost” from the pelvis segment and the “rotating” muscles of the spine and the abdomen. It also should then decelerate rapidly transferring its energy to the arm and eventually the club.

I recently attended the annual track and field summit that included sessions on sprints, hurdles, throws and jumps. I especially enjoyed the seminars by Dr. Ralph Mann on sprint mechanics. Here are some of the main points that I picked up.

Ralph emphasizes “front side” mechanics rather than “back side” mechanics. It is a mistake to think that you should push vigorously behind you to make you go fast forward once you are at full speed; rather you should concentrate on popping your feet of the ground as fast as you can in front of you and pop them back down also as quickly as you can. There is not enough time or benefit in thinking about pushing behind you.

Ground time is the key to speedy sprinting, the shorter the better. According to Ralph’s model the best male sprinters spend no more than about .087 seconds on the ground on each step. Lesser sprinters spend more time on the ground. Time in the air on the other hand is much the same for the full range of sprint abilities. So a major distinguishing factor is how quickly you can punch off the ground on every step.

It turns out that the back leg doesn’t (or shouldn’t) push off the ground to full extension; it should be slightly bent at the knee, with the ankle actively attempting to dorsi-flex. This is counter intuitive since you would think that you should push off as hard as you can, and extend off the ground, to get the most push. But it turn out that the amount of time it takes to push that last little bit into full extension is better spent quickly pulling the knee forward and upward in recovery ready for the next step.

Also the “recovery leg” doesn’t bend at the knee so much that your heel kicks your butt, i.e. full knee flexion shouldn’t occur. In the past the theory was that the more you bend the knee the faster you could bring it through since it has a lower moment of inertial and can hence rotate through quicker. Well this is probably true but it is not needed; there is time enough for the leg to swing through correctly even when it is only partially bent. In fact poor sprinters recover too quickly and reach full thigh flexion too early after rear foot toe off. Full flexion of the thigh (i.e. highest knee lift at the front) should occur more than a quarter of the way into the air phase (about .033 seconds after toe off) and not earlier. Ralph believes this is the best overall single descriptor of good sprint mechanics. It allows the foot to come straight down touching the ground just slightly in front of the center of gravity. If the knee comes through too fast it will either hit the ground from an “up to down” path (not good) or the knee will cast out the shin causing the sprinter to over stride. Over striding is bad because your touchdown point is too far in front of your center of gravity, causing you to slow down. High heels at the back is a sign of poor technique, whereas high knees and an upright posture is a sign of good technique. Remember we are after front side mechanics not back side mechanics.

Good touch down position is reached with the swing through knee even with the knee of the leg touching down. If the swing knee is behind the lead knee at touch down this is a sign of poor technique, back side mechanics and over striding.

Here are some critical values from Ralph Mann’s elite sprinter model for male sprinters.

• Horizontal Velocity 12.55 m/s
• Stride Rate 4.63 steps/second (will alter with leg length)
• Stride Length 2.7 m (will alter with leg length)
• Ground Time 0.087 sec (will alter with leg length)
• Air Time 0.123 sec
• Upper Leg Recovery Time 0.033 sec

Ralph summarizes:

“Success in the short sprint is determined by the ability of the athlete to generate great amounts of explosive strength at the proper time. Generally the proper mechanical application of this strength results in an elite performance that is characterized by a high stride rate and moderate stride length.”

For an in deeper insight, I recommend you buy his book

The Mechanics of Sprinting and Hurdling
Dr. Ralph V. Mann
2011 Edition

This work can be purchased at https://www.createspace.com/3604805

Back in 2000 my colleagues and I wrote a paper where we showed that an increase in the X-Factor at the beginning of the downswing seemed to be more important that the X-Factor itself.  We called this the “X-Factor Stretch”.

Jim McLean is well known for his teaching of the X-Factor and has also mentioned in several articles that the hips should turn into the downswing before the shoulders, but he hadn’t quantified how much and hadn’t given it a name, so I coined the term “X-Factor Stretch” to describe this increase in X-Factor.

The X-Factor is the difference in the amount of turn between the hips and the shoulders at the top of backswing.  The X-Factor Stretch is something different and here’s an explanation.  If you measure the X-Factor at the time the hips transition from backswing to downswing and then again at its maximum, which  should be a little later in the downswing, when the shoulder turning speed has reached the same speed as the turning speed of the hips, then find the difference between the two, that is the X-Factor Stretch. 

X-Factor Example:

If the shoulders are turned to 90 degrees at the top of backswing and the hips to 45 degrees then the X-Factor is 90 – 45 = 45 degrees.

X-Factor Stretch Example:

If the X-Factor is 45 degrees at the transition of the hips and if the hips are leading the shoulders in the downswing the X-Factor will continue to increase until the hips no longer outpace the shoulders.  If the X-Factor increases to say 50 degrees, then the X-Factor Stretch is 50 – 45 = 5 degrees, that is, the X-Factor has stretched an additional 5 degrees.  This extra stretch provides for extra power in the downswing.

The Paper

I presented this paper at the Pre-Olympic Congress in Brisbane, Australia in 2000. I also submitted this research to Golf Magazine and it won second place in their first annual Science in Golf Prize. It was also published in 2001 in a book edited by Patrick Thomas called Optimizing Performance in Golf, unfortunately this book had only a limited publication and is no longer available,  Dan Parks republished it with permission in his first edition of the Journal of Golf Research (2011) online, and I am also making it available with a link to the PDF file at the end of this article.  Here is the abstract:

Abstract

The “X-Factor” is a popular term for the relative rotation of shoulders with respect to hips during the golf swing. A relatively large X-Factor at top of backswing is thought to facilitate high club head speed at impact. Little consideration, however, has been given to how the X-Factor changes early in the downswing. We tested the hypotheses that highly skilled golfers have a higher X-Factor at the top of the backswing and a greater increase in the X-Factor early in the downswing (“X-Factor Stretch”) than less skilled golfers. Multiple swings of 10 highly skilled (handicap 0 or better plus one long drive champion) and 9 less-skilled (handicap ≥ 15) golfers were captured with a SkillTec 3D-Golf™ swing analysis system (Skill Technologies Inc., Phoenix AZ). The X-Factor was measured at the top of backswing and at its maximum in the downswing. A contrast of the X-Factor means at the top of backswing showed no significant difference between the highly skilled and less skilled golfers, (t=1.017, p=0.326). Further, the effects of skill level (highly skilled and less skilled) and swing position (top and maximum) on the X-Factor were assessed using a two-factor ANOVA. The X-Factor averaged for both the top and maximum was 11% higher in highly skilled golfers than the less-skilled players, but this difference was not statistically significant (group main effect F1,17=1.93, p=.18). The X-Factor Stretch occurred during the early stages of the downswing for both highly skilled and less skilled golfers (swing position main effect F1,17=131.57, p<.001), but was significantly greater for the highly skilled players (19%) than the less skilled golfers (13%; group x swing position interaction F1,17=6.90, p=.02). This suggests X-Factor Stretch early in the downswing is more important to an effective swing than simply the X-Factor at the top of backswing.

For the full paper please click here.

So this states that the pelvis slows down before impact in order for efficient transfer of energy to be achieved. But where or at what point in the downswing does that occur. It actually surpised me how early in the downswing this peak speed occurs. I reviewed many of the 3D swings in the TPI database and here are the results.

http://www.thecheethams.com/pdfs/Position-of-Peak-Pelvis-Speed-in-Downswing.pdf

http://www.wired.com/playbook/2011/10/us-track-and-field-and-bmw-join-for-olympic-push/

Here’s a technical description: When you start your somersault you have a certain amount of angular momentum gained from the way you take off; once in the air momentum is conserved.  You can however transfer momentum from the somersaulting axis to the twisting axis by causing a slight tilt sideways.  You do this by quickly dropping an arm sideways.  Dropping your right arm tilts you to the left causing some angular momentum to be transferred to the twist axis, resulting in a twist to the left.  If you were able to exactly move your arms back then the twist would instantly stop.  If you carefully look at the two videos you will see that each leans lightly to different sides.  Also you can easily tell the direction of twist; if you see my stomach after take off then I am twisting left, and have dropped my right arm.  And visa-versa on the other side.

Let me know which you think is the one I had never done before that day, (the video was the second one I did), and I didn’t even hurt myself!

I am preparing a similar series of articles and videos for the golf swing.  I will post them, or links to them here on my blog in the near future.  Here is the link to the Olympic Coach magazine; just click on it, then choose the 2011 Summer issue.  My article is the last one.

http://www.teamusa.org/resources/usoc-sport-performance/coaching-education/olympic-coach-e-magazine

Click here to see the article -> Is there a Perfect Swing

My wife Bridget and I have created eye-catching posters using the beautiful patterns of human motion.  We call them “The 3D Motion Art Series”.  I believe these posters are unique, I have not seen anything like them on the Internet.

They come in many different colors and the first release is focused on the golf swing.  We are working on other sports such as baseball and gymnastics.  These dynamic, 20″ x 30″ posters will look stunning on your wall in your home, gym, studio or office.  The initial golf posters include: 

• Kinematic Sequence – Golf,
• 3D Motion – Golf Swing,
• Motion Sequence – Golf,
• AMM3D – Golf Swing.

Click here to see the “3D Motion Art Posters” at the Cheethams store.

I saw this picture in my recently received USA Diving magazine.  What an amazing pike position!  This is interesting biomechanically, for two reasons;

1) Moment of Inertia – I recently discussed how to make a somersault spin rapidly and here is the picture perfect example.  I don’t think a pike could be any tighter and for him, his moment of inertia is as small as he is capable of making it, (while still in a proper pike position).  This will allow him to spin at his maximum rate for the amount of angular momentum that he created off the board.

2)  Hip hinge – notice how he is hinged at the hip.  His chest and stomach are flat on his legs with minimal rounding of the back.  This requires excellent flexibility.