Download One of the most important types of stress, in terms of its

One of the most important types of stress, in terms of its effect on the human body, is impact
force. Impact force has been defined as a force resulting from the collision of two bodies over a
relatively short time period (29).
(845)
Impact forces during running vary in magnitude from approximately 1.5 to 5 body weights and
last from about 10-30 ms (31).
(845)
A number of variables have an effect on impact forces including the foot and center of mass
velocity at contact, the effective mass of the body at contact, the area of contact, and the material
properties of the damping elements such as soft tissue, shoes, and the surface of contact (30).
(846)
Impact and Overuse Injuries in Runners
Med. Sci. Sports Exerc., Vol. 36, No. 5, pp. 845-849, 2004.
ALAN HRELJAC
Kinesiology and Health Science Department, California State University, Sacramento, Sacramento, CA
Pronation indeed forms an integral part of the normal foot unroll. It seems wise to "correct" these
variables in a gentle, individualized way. The correcting strategies could consist of tape, inserts,
or orthotics in the shoe or specially designed, adequate, antipronation shoes.
(338)
Gait-Related Risk Factors for Exercise-Related
Lower-Leg Pain during Shod Running
Vol. 39, No. 2, pp. 330-339, 2007
TINE MARIEKE WILLEMS', ERIK WITVROUWl, ANNELEEN DE COCK 2, and DIRK DE
CLERCQ 2
'Departments of Rehabilitation Sciences and Physiotherapy and 2Movement and Sport Sciences, Ghent University,
Ghent, BELGIUM
Risk Factors and Mechanisms of Knee Injury in Runners
Med. Sci. Sporis Exerc., Vol. 40, No. 11, pp. 1873-1879, 2008.
STEPHEN P. MESSIER', CLAUDINE LEGAULT2, CASEY R. SCHOENLANK', JOVITA
JOLLA NEWMAN',
DAVID F. MARTIN3, and PAUL DEVITA4
J.JB. Snow Biomechanics Laboratory, Department of Health and Exercise Science, Wake Forest University,
Winston-
Studies on lower extremity loads and overuse injury have shown that impact forces at commonly
injured sites are extremely high (41),
(1874)
Although these data do not provide unequivocal support, it appears that high forces applied to the
lower extremity tissues during running are associated with running-related injuries and therefore
may be mechanisms of knee injuries.
(1874)
Mercer et al. (27) found that overstriding by 15% of freely chosen stride length increased
peak leg accelerations compared with normal stride length and understriding by 15%. Over
thousands of strides, the increased shock to the lower extremity may result in overuse
injury.
(1874)
Increased muscle strength should increase the shock absorbing capabilities of the muscles
surrounding the knee joint, resulting in lower knee joint loads.
(1877)
poor flexibility could affect changes in joint angle and the knee extensor moment, increasing
joint stiffness and knee joint forces. Consequently, poor hamstring flexibility would be
detrimental to joint function by increasing joint stiffness and reducing the contribution of the
knee to shock attenuation after heel strike.
(1878)
We found that larger knee joint loads were related to poor hamstring flexibility, higher BW,
greater weekly mileage, and greater muscular strength. Most of these risk factors could
potentially be modified to reduce knee joint loads to lower the risk of injury.
(1878)
A well-designed shoe can assist in reducing the number of lower limb injuries arising from sport
and training activities.
(584)
… properly made footwear may attenuate the heel strike-initiated shock waves and reduce the
degree of injuries.
(584)
The magnitude of a shock wave initiated at the heel strike is activity dependent, subject to the
particular characteristics and mechanical properties of the footwear and the ground surface.
(583)
Since grass surface is intrinsically more uneven . . . one may hypothesize that this unevenness
may be a reason for overall increase in dynamic loading.
(583)
Injury Prevention in Distance Running
Distance running involves racing over distances from 1500 meters to marathon, even
ultra-marathons. While suggestions for injury prevention in this paper can be applied to all of
these distances, it will be focused on the application to races of 1600 meters, 3200 meters, and 3
miles. Distance running, like all sports requires great physical strain on the body, and
overstepping the limits of the human machine often results in injury.
Injury is damage sustained by tissues of the body (Zernicke et al, 514). While injuries
during running may have a variety of causes, the most important factor (Zernicke et al, 509), and
the one that will be the main focus of this paper, is force applied to the body upon impact by the
foot on the ground. Force is the mechanical action applied to an object that tends to produce
acceleration (Zernicke et all, 509). Running movement is produced and controlled by both
internal forces from the muscles and external forces such as gravity and impact (Zernicke et al,
509). These forces act on tissues in the body of the runner, and when they exceed the tissues
ability to withstand the lad, an injury occurs (Zernicke et al, 509).
The force that results when a runner’s foot collides with the ground is an example impact
force, which is the most important factor when discussing injuries (Hreljac, 845). When a
runner’s foot strikes the ground in stride, force is applied to the body. This impact force can be
more than five body weights in magnitude (Hreljac, 845). High impact forces and loads on the
legs cause many overuse injuries (Messier et al, 1874).
To avoid injury, this force needs to be balanced with the ability of musculoskeletal
structures to respond to stress (Mcnitt-Gray, 523). The impact force in running depends on
several variables, including the area of contact as well as the properties of damping elements
such as tissue, shoes, and the running surface (Hreljac, 846). The force can be lessened or
balanced through simple improvements such as stretching, weight lifting, correct gait and foot
pronation, cushioning shoes, and careful choice of running surface. These improvements focus
on the physics principles of elasticity and most importantly, force.
I do not think that Ms. Riddle will know much more about the physics of muscles (in
relation to cross country) than I already know or have learned from my sources. I think she will
reinforce the importance of stretching in order to increase elasticity of muscles and range of
motion. The common adage “bend, don’t break” will apply. Obviously, the longer a muscle can
stretch or the more force it can take before tearing, the less chance of an injury. I know that the
calves are the “shock absorbers” of the body and that force goes through them, and then the
knees, quadriceps, and hamstrings.
Bibliography
A. HRELJAC, Med. Sci. Sports Exerc. 36, 845 (2004).
S. P. MESSIER, C. LEGAULT, C. R. SCHOENLANK, J. J. NEWMAN, D. F. MARTIN, and P.
DEVITA, Med. Sci. Sports Exerc. 40, 1873 (2008).
J.L. MCNITT-GRAY, in in Biomechanics of Sport, edited by Vladimir M. Zatsiorsky (Blackwell
Science, Osney Mead, Oxford, 200), pp. 523-549.
A.S. VOLOSHIN, in Biomechanics of Sport, edited by Vladimir M. Zatsiorsky (Blackwell
Science, Osney Mead, Oxford, 200), pp. 577-587.
T. M. WILLEMS, E WITVROUWl, A. DE COCK , and D. DE CLERCQ, Med. Sci. Sports
Exerc. 39, 330 (2007).
R.F. ZERNICKE and W.C. WHITING, in Biomechanics of Sport, edited by Vladimir M.
Zatsiorsky (Blackwell Science, Osney Mead, Oxford, 200), pp. 507-522.