E qui un fantastico articolo per comprendere perché il grip è fondamentale! Prometto che non scriverò "lo avevo detto io... hahhahahaha"
Another interesting result Hatze showed was that although the time the
ball is in contact with the racquet's strings is in the 3-7 millisecond
(ms) range, the vibration of the racquet continues for typically another
40 ms afterwards.
Dr. Duane V. Knudson has conducted a great deal of research into forces
induced in the arm by the tennis racquet. Knudson and White (1989)
reported on experiments using "pressure pad" type sensors on the grip of
a tennis racquet to measure the forces between the hand and the racquet
during a stroke, and vibration sensors on the racquet. The racquet was
used by seven expert players on forehand drives from balls fired from a
machine.
Using the same instrumentation as above, including three-dimensional
cinematography, Knudson (1991a) investigated the variability of the hand
forces. He found that the hand forces were somewhat correlated with
both pre-impact grip tightness and off-center impacts; and recommended
that tennis elbow sufferers grip the racquet lightly, and use a racquet
with high polar moment of inertia (more on this next month).
Knudson (1991b) then evaluated the
Forces on the hand in the tennis one-handed backhand,
considered to be the key stroke for tennis elbow. Using two pressure
pad type sensors in the grip he noted there was less variation between
players and strokes than for the forehand case, and also higher forces
at one point on the grip.
Tomosue et al (1991) measured vibrations in the racquet handle and in
the player's wrist during forehand drives. No significant differences
between 7 Dunlop racquets were found. They also found that off-center
ball impacts gave 1.9-3.1 times greater vibrations in the wrist -- and
that the wrist vibrations were about one tenth of the racquet handle
vibrations.
Hatze (1991) investigated
The effectiveness of grip bands in reducing racquet vibration transfer and slipping.
Tennis balls were fired at a racquet gripped in an artificial arm.
The 'arm' was fitted with a range of pressure and acceleration sensors.
He tested 26 band grips (commercially available damping material
designed to be wrapped around the racquet grip in order to reduce
slippage and vibration transfer). Only small vibration reductions were
found (maximum vibration reduction of 5% compared with a control leather
grip) which suggested that relaxing the grip is much more effective than using these bands.
Hennig et al. (1992) performed experiments to address
the
Transfer of tennis racquet vibrations onto the human forearm Using accelerometers at the wrist and elbow on 24 players vibrations induced in the arm
during simulated backhand strokes were measured. Each player tested 23
different racquets. They found (in contrast to Tomosue et
al. 1991) some difference between racquets.
In agreement with Tomosue et al. they observed greater vibrations, by a factor
of 3, when the ball strikes the racquet off-center. They also find vibration levels at the elbow to
be approximately a third those at the wrist.
Roetert et al. (1995) reviewed some previous work on muscular activity
during tennis strokes in
The biomechanics of tennis elbow,
an integrated approach and in particular electromyographic (EMG) analysis.
(EMG is a method of determining muscle activation.)
Using indwelling wire electrodes (which penetrate the skin
and actually go into the muscles), Morris et al. (1989) observed high
levels of wrist extensor muscle activity (especially the extensor carpi
radialis brevis --
[Devi essere iscritto e connesso per vedere questo link])
during the acceleration and follow-through phases
of the backhand and the cocking phase of the serve and
suggested that this may be one reason for the predisposition of
these muscles to injury. Giangarra et al. (1993) also using indwelling
wire electrodes to obtain EMG data from five forehand muscles presented
evidence explaining why a two-handed backhand was much safer.
Adelsburg (1986) using surface electrodes (a noninvasive method, doesn't penetrate the skin)
tried to relate forces in the muscles to changes in grip size and
although they found some significant differences between different sized
grips, they did not find differences during backhand strokes.
Yet with all of this research one key question still hasn't been
answered: how the injury arises physically; what combination of
mechanical stresses causes the inflammation, strain, or tears to the
tendon at its attachment to the bone.
We'll conclude this segment at this point. As I mentioned there
will be a third article on this subject to tie things all together.
Again I'd like to thank my good friend Dr. Alison Cooke for her assistance in preparing this column.
References:Adelsberg, S., "The tennis stroke: an EMG of selected muscles with
rackets of increasing grip size", American Journal of Sports Medicine
vol. 14 (2), 139-142, 1986.
Brody, H., "Physics of the tennis racket", American Journal of Physics vol. 47 (6), 482-487, 1979.
Brody, H., "Physics of tennis II: the 'sweet spot'", American Journal of Physics vol. 49 (9), 816-891, 1981.
Brody, H, "The physics of tennis III: the ball-racket interaction", American Journal of Physics vol. 65 (10), 981-987, 1997.
Cooke, A.J., Roussopoulos, K., Pallis, J. M., Haake, S.,
"Correlation between racquet design and arm injuries,"
4th International Conference of the Engineering of Sport, September, 2002.
Giangarra, C.E. et al., "Electromyagraphic and cinematographic
analysis of elbow function in tennis players using single- and
double-handed backhand drives", American Journal of Sports Medicine vol.
21, 394-399, 1993.
Hatze, H., "The effectiveness of grip bands in reducing racquet
vibration transfer and slipping", Medicine and Science in Sports and
Exercise vol. 24 (2), 226-230, 1991.
Hatze, H., "Forces and duration of impact, and grip tightness during the
tennis stroke", Medicine and Science in Sports vol. 8 (2), 88-95, 1976.
Hennig, E.M., Rosenbaum, D. and Milani, T.L., "Transfer of tennis racket
vibrations onto the human forearm", Medicine and Science in Sports and
Exercise vol. 24 (10), 1134-1140, 1992.
Knudson, D.V. and White, S.C., "Forces on the hand in the tennis
forehand drive: application of force sensing resistors", International
Journal of Sport Biomechanics vol. 5, 324-331, 1989.
Knudson, D.V., "Hand forces and impact effectiveness in the
tennis backhand", Journal of Human Movement Studies vol. 17, 1-7, 1989.
Knudson, D.V., "Forces on the hand in the tennis one-handed
backhand", International Journal of Sports Biomechanics vol. 7, 282-292,
1991.
Knudson, D.V., "Factors affecting force loading on the hand in the tennis forehand", vol. 31 (4), 527-531, 1991.
Morris, M. et al., "Electromyographic analysis of elbow function
in tennis players", American Journal of Sports Medicine vol. 17,
241-247, 1989.
Roetert, E.P., Brody, H., Dillman, C.J., Groppel, J.L., and
Schultheis, J.M., "The biomechanics of tennis elbow: an integrated
approach," Clinics in Sports Medicine vol. 14 (1), 47-57, 1995.
Roussopoulos, K., and Cooke, A.J., "Correlation between racket design
and arm injuries: A feasibility study report," Technical report prepared
for the International Tennis Federation, 2000.
Tomosue, R., Mutoh, Y., Yoshinari, K., and Kawazoe, Y.,
"Measuring the vibrations of a racket handle and the wrist joint in the
tennis forearm drive", Abstracts from International Society of
Biomechanics XIII, 1991.