View Full Version : Summary on Human Tolerance to Blunt Impact

03-19-2001, 08:18 AM
Hi All,

Two weeks ago, I posted a question pertaining to the injury threshold of
human body extremities when subjected to blunt impact (see the tail of this
message for the original post). I have been provided information and
literature search from some members on the following topics:

- Quasi static loading condition
- Classical “metallurgical” type of test such as Charpy impact tests
- Automobile safety related tests

Unfortunately, I have not yet been able to lay my hand on an extensive list
of papers dealing with the above topic list. However, I have already at
least a comment on each topic that I would like to share with you. Your
further feedbacks and suggestions on this matter will remain greatly

First, it is a known fact that bones have a viscoelastic material behavior.
Therefore, I do not think that their failure under quasi-static bending
force can be a reliable indication of how they would respond to a force of
the same magnitude applied dynamically. Second, in my view, the Charpy
impact test of cortical bone does not suffice to predict the bone fracture
since it does not take into account the structural properties of the bone as
a whole anatomical unit. Third, the data on the bone failure simulated for
the automobile industry appears to be the closest to what happens during
the blunt impact. Nonetheless, this still may not address the
particularities of blunt impact injury. The reason for that is the latter
involves low mass (20 kg) but low velocity (4-10 m/s).
Also, in addition to the different rates at which the striking energy is
delivered to the viscoelastic bone and the overlying soft tissues, the shape
of the threat (e.g. baseball bat vs car bumper) has to be considered, since
the energy distribution may account for the nature of the sustained injury.

In conclusion, evaluating the threshold injury of human beings is a
challenging task and the bone strength depends on various factors such as
age, gender, material density, etc. However, unlike automobile users who
form a very heterogeneous group, professional sport players, prison guards
and anti-riot officers represent a much more homogeneous sampling of
individuals and their tolerance to injury is higher due to their general
good physical condition. Therefore, one may wonder if bone failure
evaluation for automobile safety is still applicable to blunt impact injury,
despite the clear differences between the two contexts and environments?

Finally, I thank the few but very helpful members who contributed
thoughtfully to orient my line of thinking in regard to this subject. The
list of the responses is pasted next.

Ismael El Maach

************************* Message 1 of 9 *******************
I think that their is a deeper question to your loading
conditions. You need to answer exactly what bone types Cortical or
trabecluar and is it a long bone at mid shaft, deminsions, mineral
density? If you get the modulus in the primary directions and the
dimensions of the bone you wish to test,it is fairly easy to solve for the
quazi static condition of a beam with the loading that you desire for a
minimum. Lots of intro orthopedic biomechanics can help you step through
this. There have been hundreds of material studies done on the anisotropic
behavior of bone and I would definatley look at those to get the material
one that I have seen used several times for the different stress strain
curves for longitudinal, 30 deg, 60 deg and transverse loading was
Frankel and Nordin, 1980 ( I have seen this reference in a chart several
Good Luck,
T. Withrow

************************** 2/9 **************************************
Hi, Hope all is well! Don't have any answer for you, but remember
impactor geometry has as much affects as energy, i.e. a 90 degree
anvil will fracture a forearm with orders of magnitude less energy
than a flat board will.

Cheers, Trey
Joseph Crisco

************************** 3/9 *******************************
Dear Sir:

At The University of Tennessee Engineering Institute for Trauma & Injury
Prevention we have conducted numerous tests of the nature that you have
described. I could mail copies of some of our published papers if you are
interested. For now, the following numbers may help you:

Some results of our tests indicate failure forces for the femur ranged 1.31
8.37 kN. Bending moments averaged from approximately 100 to 500 Nm. These
values varied depending on the speed of impact, impactor geometry, direction
of impact, gender of specimen, etc. Several tests were performed from
perpendicular (transverse) impacts to the mid-thigh. Intact leg specimens
inverted and suspended against a large steel elbow plate in the test zone by
rod passing through the tibial plateau such that impact occurred on the
anterior or lateral surface.

Good luck!
-Tyler Kress

****************************** 4/9 *******************************

Sport Discus had this study which compared cadaver tibia fractures. I
remember talking to one of the authors at the ACSM meeting, and they may
have had additional data on other bones.

TI: Comparison of soccer shin guards in preventing tibia fracture
AU: Francisco,-A.-C; Nightingale,-R.-W; Guilak,-F; Glisson,-R.-R;
JN: American-journal-of-sports-medicine-(Waltham, Mass.) 28(2), Mar/Apr
2000, 227-233 Refs:18, Total Pages: 7.
CN: American College of Sports Medicine. Meeting (1999: Orlando, Fla.)
PY: 1999
AB: The goal of this study was to evaluate the effectiveness of a number of
shin guards in protecting against tibia fracture in soccer players. A
secondary purpose was to determine the relationship between the material and
structural differences in shin guard design and the protection provided.
Twenty-three commercially available shin guards were tested on a model leg
containing a synthetic tibia that had been calibrated against human cadaver
specimens. Each guard was categorized into one of four material types:
plastic (N = 9), fiberglass (N = 6), compressed air (N = 4), and Kevlar (N =
4). The maximum combined force at the ends of the tibia, the principal
strain on the posterior side of the tibia, and the contact time of the
impact were measured using a drop track impact simulation. Shin guards
provided significant protection from tibia fracture at all drop heights. The
average guard reduced force by 11 % to 17 % and strain by 45 % to 51 %
compared with the unguarded leg. At the higher drop heights, material
composition and structural characteristics of the shin guards showed
significant differences in protective abilities. These findings indicate
that all shin guards provide some measure of protection against tibia
fracture, although the level of protection may vary significantly among the
different guards.

Randall Jensen, Ph.D, FACSM

*********************** 5/9 *******************************
Dr. Maach,

Actually, there is a wealth of research in the literature (particularly the
automobile safety literature) dealing with the failure strength of long
in bending. A quick search should yield dozens of results. Here is a very
short and incomplete list of references:

H. Yamada, Strength of Biological Materials, Williams and Wilkins Co.,
Baltimore, Md. 1970.

G. W.Nyquist, "Injury Tolerance Characteristics of the Adult Human Lower
Extremities Under Static and Dynamic Loading," Biomechanics and Medical
Aspects of Lower Limb Injuries, SAE #861925, 1986.

P. Schreiber, J. R. Crandall, T. Micek, S. Hurwitz, "Static and Dynamic
Strength of the Leg," Proc. 1997 IRCOBI conference, Hannover, Germany;
September 24-26, 1997.

S. Duma, P. Schreiber, J. McMaster, J. R. Crandall, C. R. Bass, W. D.
"Dynamic injury tolerances for long bones of the female upper extremity,"
Journal of Anatomy, 194(3): 463-471, 1999.

Good luck,

Jim Funk

************************* 6/9 ***************************
Dear sir,
I would be interested in your replies. Please forward them to me at your
earliest convenience. Thank you in advance for your attention to this


Mr. Adelino Yung

************************* 7/9 *************************

The auto safety industry may yet contain the answers to your questions

shear loading of lower limb - pedestrian studies
bending of leg - numerous studies for occupants and pedestrians
bending/shear of upper extremity - studies of frontal airbag/forearm
interaction, studies of side airbag/arm interaction
I suggest searching the impact biomechanics literature related to auto
more thoroughly.

************************* 8/9 ***************************
Mr. Doug Moore forwarded the following posting to me.

From: Alex DePaula
>Subject: Replies: Impact testing of cortical bone
>Date: Fri, 26 Jan 2001 14:35:00 -0500
>Dear Biomechanics list:
>I am looking for information about falling-mass impact testing of cortical
>bone or people with knowledge of impact testing of bone. Any type of
>testing information could also be helpful (Izod, Charpy or other).

Here are the 3 replies:

Dear Dr. DePaula:

We have been impact testing bare bones and intact specimens for 15 years in
our laboratories. However, we do not do the classical "metallurgical" types
of test (Izod, Charpy, Rockwell, etc.). Our primary interest has been to
study failure thresholds (e.g. force, energy, etc.) for various bones and
intact specimens in order to understand mechanisms of injury and
design criteria. We have used accelerator-cart/guiderail systems and
drop towers in our research. Is there some specific information that you
need? I would write more, but I am not sure what kind of information you
looking for... Do you want data? Are you interested in experimental
methodolgy? Let me know, and I will see if I can help more.


Tyler Kress, Ph.D.
Associate Director
Engineering Institute for Trauma & Injury Prevention
The University of Tennessee

Tyler A. Kress, Ph.D.
The University of Tennessee

Yamada in Evans (Ed) Strength of Biological Materials, Williams and Williams
pub. 1970 lists the impact snapping strength of femoral cortical bone for
adult human, horse, bovine in the radial and tangential directions. These
data were collected using an Izod impact machine. Values are in lbf/in^2
(mean +- SD):
Human radial (12.13 +- 1.35)
Human tangential (8.87 +- 0.98)
Horse radial (10.27 +- 0.89)
Horse tangential (10.73 +- 0.93)
Bovine radial (9.80 +- 0.65)
Bovine tangential (11.20 +- 0.84)

Hope this helps.

Richard Kent
University of Virginia


We have been interested in more rigorously discriminating comminution
patterns in high-energy injuries, based on fracture energy absorption. To
create fractures in cortical bone segments, we use a drop tower apparatus
that was constructed in our lab. We have also conducted tests of energy
absorption in cortical bone beam specimens using a Balanced Hounsfield
Impact Tester. (Some of this data is published in Beardsley et al, The Iowa
Orthopaedic Journal, 20:24-30, 2000). I am also aware of an early paper by
Bonfield and Datta (Journal of Applied Physics, 37:869, 1966) that reports
on the fracture behavior of short beam compact bone specimens in a
traditional Charpy test.

I would be interested in reading other responses that you receive regarding
this matter.


Christina Beardsley

********************** 9/9 *********************************
Mr. Dany Lafontaine suggested the following reference
FUNG, y. c. biomechanical Oroperties of living tissues. New York: Spingler
Verlag, 1981. 443 p

**************** My original Posting *********************

From: Ismael El Maach
Subject: Human tolerance to blunt impact
Date: Mon, 5 Mar 2001 13:49:19 -0500

Dear Biomech-L members,

Dynamic fracture forces of most body parts, as related to motor vehicle, is
well documented in the literature (e.g. SAE reports). For instance, the
force necessary to fracture the femur is generally determined from
biomechanical testing where impact is delivered longitudinally through a
flexed knee.

*** Here is now my request:

As opposed to the experiments carried out in the automobile industry, where
long bones are loaded longitudinally, I am interested in knowing how much
force (or energy) is needed to fracture the long bones of the limbs as a
result of blunt impact delivered in a transversal manner (perpendicular to
the bone shaft). Malicious kicks to the tibia and bat blows on the forearm
during violent assaults are two examples among others where such forces may
be applied.

Any information would be much appreciated and, of course, I will post a
summary of the responses.


Ismael El Maach

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