September 2003 -- Question: In your work in biomechanics, have you ever put together a template for how to qualitatively analyze a tennis stroke? I am aware of all the research that quantifies stroke mechanics but, for a teacher in the field, what do you recommend on how to use this biomechanical information?
Answer: Several years ago, I organized a flow chart to qualitatively evaluate a tennis stroke. I arranged this generally for several different strokes, and then I did it specifically for each of the strokes. I will give you the guidelines for the general approach and, if there is interest, I can provide the specific examples in later columns. Please bear in mind that this should only serve as a guideline.
There are 10 areas with which you must concern yourself. This general list will work for the forehand and backhand groundstrokes, volley and return of serve. I will list them and the factors you should examine for each.
Preparation phase
- Overall starting position:
* Balance (static) between the base of support (feet position) and line of gravity
* Knees bent slightly (which lowers the center of gravity)
* Body weight evenly distributed on the balls of the feet
* Relaxed stance, yet alert and ready to react
* Grip one that is not extreme or unduly limiting
* Parallel shoulder and hip alignment
- Movement/placement of the feet:
* Balance (dynamic and static) between the feet positions (base of support and line of gravity)
* Feet placement should facilitate the smooth and natural execution of the unit turn
- Backswing:
* Relaxed, yet deliberate
* Presence of the unit turn: The racquet should not be taken back with the arm/hand alone, but rather, by the legs, hips, and shoulders moving/rotating together as one single, well-coordinated unit.
- When this happens rhythm is created and maintained between the backswing and leg action.
- Any hitches (pronounced interruptions of this rhythm) seriously undermine the effectiveness of the shot.
Acceleration phase
- Feet through the legs:
* A position that is controlled/balanced and has the potential for power from the leg drive (knees slightly flexed unweighting as if starting to sit down on the edge of a chair)
* This is the initial impulse the point at which the feet push against the ground with a certain force, the ground pushes back with an equal (and opposite) force, and this force begins to move up from the feet into the lower and upper legs.
* This is the first link in the acceleration phase of the stroke and, as such, is perhaps the most important one.
* In this initial impulse link, most of the force of the stroke is created in the form of linear momentum as the body begins to move.
* When an adequate amount of force is not created at this point, the result is a relatively weak and ineffective shot (relative to what it could be). As is often the case, the player may try to get additional power from other body parts, thus passing up his best chance for power and control while running the risk of muscle strain and/or injury.
* Again, the linked system is based on the successive integration of body segments to generate optimal force. When one biomechanical link is either incomplete or nonexistent, this shortcoming is compounded by the fact that successive links are generally negatively affected also. For instance, it may actually be the result of ineffective preparation (poor overall starting position and/or poor movement/placement of the feet).
* The linked system is very useful and effective in separating causes from effects. In any event, all components should be evaluated numerically as distinct and separate links.
- Legs through the hips/trunk:
* Flexed legs becoming extended legs just as the player moves into the initial hip/trunk rotation.
* Again, the force generated/transmitted from the legs to the hips/trunk is primarily the result of linear momentum force resulting from upward and outward movement.
* This force that is generated and transmitted from the legs actually leads the hips and trunk and initiates their rotation (angular momentum).
- Hips/trunk through shoulders:
* General body control
* Rotation of the hips/trunk. This rotation of the hips/trunk should lead the shoulders into their own rotation. At this point in the acceleration phase, the force is ideally transmitted from the hips/trunk to the shoulders in a powerful, yet rhythmical manner.
* This particular movement is critical to the overall effectiveness of the stroke since it is the greatest opportunity to achieve force through the realization of angular (or rotational) momentum. When executed properly, the hips/trunk uncoil as the force is generated and transmitted to the shoulders.
- Shoulders through arm(s):
* As the body continues to rotate, the rotation of the shoulders should lead the arm.
* Again, the force (from both angular and linear momentums) should be transmitted from the shoulders to the swinging arm(s) in a powerful, yet rhythmical way.
- Arm(s) to hand(s):
* Position of the racquet head The hand should be used to guide and control the racquet head.
* Speed of the racquet head The entire body should be used to generate racquet head speed.
Overall finishing position
- What to look for:
* Dynamic balance and general body control (e.g., position of feet vs. line of gravity)
* Potential for quick recovery with little effort
Overall stroke effectiveness
- What to look for:
* Control and placement of shot
* Depth of shot into the court
* Consistency of shot
* Power of shot
Send questions to jgroppel@LGEPerformance.com.
