Whip Cracking Mystery Explained
The snapping of a whip occurs in part because the tip of the whip reaches the speed of sound and creates a sonic boom.
“Although the loop travels at one speed, some parts of the whip, including the tip in the final stages of motion, travel twice as fast.”
Professor Alain Goriely
University of Arizona Department of Mathematics
Physical Review Letters published by the American Physical Society
May 23, 2002
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“g” is the acceleration due to earth’s gravity, typically 9.81 m/s2 (32.2 ft/s2)
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A typical rear-end collision at 8 mph “produced a 2 g acceleration of the [struck] vehicle and a 5 g acceleration of the [occupant’s] head.”
This is a “magnification of acceleration for the head.”
The head reaches an acceleration of 2.5 times the vehicle acceleration.
Clinical Biomechanics of the Spine
Augustus A. White, MD, D Med Sci
Professor of Orthopedic Surgery at Harvard Medical School
Orthopedic Surgeon-in-Chief at Beth Israel Hospital in Boston
Manohar M. Panjabi, PhD
Professor of Orthopedics and Rehabilitation and Mechanical Engineering
Director of Biomechanics Research
Yale University School of Medicine
J.B. Lippincott Company
1990
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[Caution: DO NOT TRY THIS!! This discussion is provided for historical reference and biomechanical understanding only]
An internet search suggests that historically, and in some present-day locations, snakes can be killed by subjecting them to a whipping mechanism. The snake is grabbed by its tail and the grabber subjects the snake to a whipping motion, similar to the motion that one could use to snap a wet towel. The internet posts many comments on this technique, and there are a handful of gruesome videos showing it being performed.
Some of the internet descriptions or visualizations of these practices report or show the involved snake deceased, with a fractured neck. Others report or show a complete dislocation and inertial decapitation of the snake’s head. The commentary notes that the degree of injury is dependent upon the diameter of the snake’s neck. [This point pertaining to neck diameter and injury is relevant to this discussion].
Rumor suggests that writer Mark Twain described the technique, its application employed to venomous snakes caught on the banks of the Mississippi River by adolescents. Rumor also claims that Mark Twain labeled the practice as the “whip-snap.”
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Prior to the advent of the automobile, whiplash-type neck injuries were reported in the medical journals of the day (1). These injuries were primarily noted to occur following collisions involving trains and were known as “railway spine.”
The first full-length medical study of “railway spine” was by John Eric Erichsen in 1864. Dr. Erichsen was a Professor of Surgery at University College in London. Erichsen took the view that minor injuries of the head and spine could result in severe disability due to ‘molecular disarrangement’ or anemia of the spinal cord.
Dr. Erichsen’s first book on the topic was titled Railway and Other Injuries of the Nervous System. The book was considered to be authoritative and was frequently cited in court cases. Erichsen’s second book on the subject was published in 1882, titled On Concussion of the Spine: Nerve Shock and Other Obscure Injuries of the Nervous System in the Clinical and Medico-Legal Aspects.
In 1883 (2) and 1885 (3), the understanding of “railway spine” advanced with the publication of Injuries of the Spine and Spinal Cord without apparent Mechanical Lesion, and Nervous Shock in their Surgical and Medico-Legal Aspects. The author, Herbert W. Page, MD, was a London surgeon (1845-1925).
During World War I (1914-1918), a whiplash mechanism injury was recognized in test pilots for the US Navy. Military airplanes were launched from the decks of battleships and cruisers using the catapult method (1):
“The violent force on the cervical spine in catapulting was great enough to cause a blackout for a few seconds and accidents occurred that were undoubtedly due to the whiplash effect.”
In their 1982 text The Spine, orthopedic surgeon Richard Rothman and neurosurgeon Frederick Simeone note (5):
“Acceleration extension injuries of the spine were first recognized as a clinical entity with the introduction of catapult-assisted takeoffs from aircraft. Many pilots developed persisting neck pain of sufficient severity to warrant medical discharge from the service. Some even lost consciousness on takeoff and crashed. It became apparent that the lesion was due to hyperextension of the neck, produced by sudden acceleration.”
Our modern understanding of these events questions the shortsightedness of using a catapult launch of airplanes that were not equipped with head restraints to protect the pilots from hyperextension injuries.
In 1919, the Boston Medical and Surgical Journal published an early report on motor vehicle collision injuries, calling them “Neck Injuries.” The author, Herman W. Marshall, MD, presented the most detailed description of the mechanics, pathoanatomy, diagnostics, and management of motor vehicle collision neck injuries of the time. Many of his concepts remain valid today. His article included the necessity of x-rays and he advocated the use of spinal manipulation in treatment (4).
The term “whiplash” was first used in 1928 to “describe the effects of sudden acceleration-deceleration forces in motor vehicle accidents which resulted in injuries to the cervical spine,” at the symposium of the Western Orthopaedic Association in San Francisco by physician Harold Crowe, MD (1, 6, 7). At this conference, Dr. Crowe presented a report on eight cases of neck injuries resulting from traffic accidents (7).
The first recorded published use of the word “whip lash” occurred seventeen years later when physician Arthur Davis, MD, used the term in an article titled Injuries of the Cervical Spine (8). [Dr. Davis did not use the word “whiplash” but rather used two words “whip lash”].
•••••
The understanding of whiplash injuries advanced during the COVID-19 pandemic. Public fear, government lockdowns, and businesses mandating remote work resulted in far fewer vehicles on the roads and highways. Fewer vehicles on the road allowed for increased speeds, and speeds increased, dramatically. An article from USA Today headlines read (9):
Rate of Traffic Deaths Rises During Pandemic:
Drivers, Tempted by Open Roads, Increase Speed
The article notes that there was “widespread reports of excessive speeding during the pandemic,” stating:
“The rate of traffic deaths jumped in the first half of 2020, and safety experts blame drivers who sped up on roads left open when COVID-19 pandemic shut down businesses and limited commuting.”
“Small changes in speed when you’re involved in a crash can readily increase your chances of getting a severe injury.”
A similar article from the Associated Press headlines was (10):
Pandemic Set Off Deadly Rise in Speeding that Hasn’t Stopped
The article states:
“The number of highway deaths in 2020 was the greatest in more than a decade, even though vehicles were driven fewer miles during the pandemic.”
“People are flying down the roads.”
“Tickets issued by the California Highway Patrol for speeding in excess of 100 mph from January to June [2021] were nearly double pre-pandemic levels.”
The message is clear. Increased speed increases the number of collisions, and these collisions increase rates of both injury and death. Of course, these findings are logical.
Another interesting finding was presented by researchers from the Insurance Institute for Highway Safety and reviewed in USA Today (11):
Smaller Cars Means More Injuries for Women
“The smaller, lighter vehicles that women often drive, and the type of crashes they get into, may explain why they are much more likely to suffer a serious injury in a collision than men.”
“Women are three times as likely to experience a broken bone, concussion or other moderate injury, and twice as likely to suffer a serious injury.”
The message here is two-fold:
- Pertaining to vehicle collisions resulting in injury and/or death, larger vehicles are more protective, and smaller vehicles are more dangerous for its occupants.
- In similar collisions, injury rates are different for men v. women.
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The incidence of whiplash injuries increased significantly in the 1940s. Ian Macnab states (5):
“Acceleration injuries of the neck were not commonly seen again until the massive invasion by motor vehicles of the urban areas in the late 1940s.”
By 1968, data began to show that the majority of injuries from motor collisions were in women (12). This was quantified in a study published in the Journal of the American Medical Association, by physicians Charles Schutt, MD and F Curtis Dohan, MD, in an article titled (12):
Neck Injury to Women in Auto Accidents:
A Metropolitan Plague
The primary purpose of this article was to demonstrate the high rate of neck injury incurred in auto accidents by women in metropolitan regions. The authors note that the neck-injury rate for women was 70% higher than that for men. Injuries to other areas, other than the neck, were also higher in women. Their explanation for these findings included:
- “The higher frequency of acceleration injuries of the neck in women in contrast to men suggests that muscle strength may play a role.” They noted that that slender [necked] women tended to have longer disability.
- Also, women often occupied the right front passenger seat more frequently, and therefore, they may be less likely to be alerted to an impending collision, through use of the rearview mirror. They concluded that this “awareness factor was an important factor in subsequent injury.”
In addition, the authors noted that work disability averaged 8 weeks, and that 75% continued to have symptoms more than 6 months after being injured. Yet, neither work disability nor continuing symptoms were related to pending litigation. The authors noted:
“These and other data do not support the opinion that prolonged symptoms are commonly due to litigation neurosis or malingering.”
“Our findings do not support the apparently popular opinion that the symptoms of whiplash injury are often due to malingering and usually to subconscious psychoneurotic mechanisms in people seeking the secondary gain of a large payment from the company insuring the owner of the other car.”
“It seems probable that many of the patients with whiplash-type injuries may have an organic basis for their supposedly psychoneurotic symptoms.”
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In 1972, John States and colleagues from the University of Rochester published a pertinent study for the Society of Automotive Engineers (13). The authors showed that women have a greater ratio of head mass to neck cross-sectional area. This is determined by measuring the head circumference (H), then measuring the neck circumference (N). The authors noted that the head/neck ratio (H/N) might explain the increased incidence of whiplash injuries in women. Women have a higher head/neck ratio, indicating a larger head relative to neck size and thus an increased susceptibility to injury in rear-end automobile collisions.
•••
In 1975, Richard Snyder and colleagues from the University of Michigan, published a pertinent study for the Highway Safety Research Institute (14). Using mathematical modeling based on anthropometric data, the authors concluded that decreased cervical strength in women may be responsible for their increased incidence of cervical injuries when exposed to rear-end collisions.
•••
In the following decades, a number of published studies would note that women are more likely to be injured in a motor vehicle collision than a man, and/or women are more likely to have persistent (long-lasting) neck complaints after a collision:
February 1995 (15)
Injuries to the Cervical Spine in Automobile Accidents
Versicherungsmedizin
The authors investigated a data pool of 15,000 vehicle-vehicle collisions, noting that “acceleration injuries to the cervical spine occur especially during rear-end collisions.”
The authors note that acceleration injuries of the cervical spine from rear-end collisions remains significant, despite improvement of protective properties in vehicles. Ironically, the authors claim that there is an increase in the incidence of injuries to the cervical spine that they attribute to the high use of seatbelts. [Shoulder harness seat belts increase the “whip” influence to the cervical spine by restricting the motion of the trunk without restricting the motion of the head]. The authors state:
“It can be shown that women, front seat occupants and occupants of lighter vehicles have a higher risk of suffering from such injuries.”
April 1995 (16)
Scientific Monograph of the Quebec Task Force on Whiplash-Associated Disorders: Redefining “Whiplash” and its Management
Spine
In this comprehensive review of the literature, initially evaluating more than 10,000 articles, the authors noted that women are more injured than men in similar motor vehicle collisions.
1996 (17)
Gender Patterns in Minor Head and Neck Injuries: An Analysis of Casualty Register Data
Accident Analysis and Prevention
These authors note that the “incidence of minor and moderate head and neck injuries was higher among women than men,” noting that women have greater vulnerability to whiplash in injuries. They state:
“As compared to men, women more often sustained their head and neck injuries as pedestrians and as car passengers, and in rear-end and side collisions.”
1998 (18)
Clinical Response of Human Subjects to Rear-End Automobile Collisions
Archives of Physical Medicine and Rehabilitation
Most motor vehicle collision research involves only male subjects. This study is different. The authors exposed 42 persons, half were women (twenty-one), to two controlled low-speed rear-end automobile collisions to assess the relation between both gender and impact severity and the presence, severity, and duration of whiplash-associated disorders (WAD). The subjects were young, between 20 to 40 years old (male mean, 26 yrs., female mean, 27 yrs.). Subjects had no medical conditions or history of soft-tissue disease or related syndromes.
“Given the greater frequency of WAD reported in women, a specific goal of this study was to expose an equal number of male and female volunteer human subjects of a specific age group to two controlled low-speed rear-end automotive collisions (change in velocity of [2.5 m/h and 5 m/h]) to assess the relation of gender and impact severity with the presence, severity, and duration of WAD.”
“Epidemiologic studies have concluded that women sustain WAD more frequently than do men.”
Similar to the 1972 study for the Society of Automotive Engineers (13), this study included the anthropometric measures of head and neck circumference to calculate the ratio of head to neck cross-sectional area (using H/N). Again, the authors note:
“A higher female H/N ratio suggested a larger head relative to neck size and thus an increased susceptibility to WAD in rear- end automobile collisions.”
The authors found that 29% of those exposed to speed change of 2.5 m/h experienced whiplash symptoms, and 38% of those exposed to speed change of 5 m/h experienced whiplash symptoms. They concluded:
“The duration of symptoms experienced by women was significantly longer when compared with that in men” at 2.5 m/h.
2001(19)
Whiplash: Epidemiology, Diagnosis and Treatment
Ugeskrift for Laeger [Danish]
These authors note:
“The association between cause (whiplash mechanism) and effect (symptoms) is poor.”
“Recent years have seen an increasing number of car occupants with neck complaints following a car collision and a declining number of persons involved in car crashes–a relationship that is not well understood.”
“Although mostly men are involved in motor vehicle accidents, an equal number of men and women seek emergency care, but it is mostly women who have persistent (long-lasting) neck complaints after a car collision.”
2003 (20)
Seat Influences on Female Neck Responses in Rear Crashes: A Reason Why Women Have Higher Whiplash Rates
Traffic Injury Prevention
This study addresses seat properties that may explain a reason for the higher injury rates in women. The authors discovered that seat stiffness increases the forward acceleration of the female mass (which is less) in comparison to males (which is greater). As a consequence, they showed that neck displacements are greater in the female than male. The authors state:
“Since the earliest crash investigations, whiplash has been found to occur more often in women than men.”
“Neck displacements are greater in women because of a higher ratio of seat stiffness to torso mass.”
2008 (21)
Head and Neck Anthropometry, Vertebral Geometry and Neck Strength in Height-matched Men and Women
Journal of Biomechanics
The goal of this study was to quantify differences in head and neck geometry and neck strength in male and female subjects. The authors found:
“Based on 14 matched pairs of men and women, we found that most head and neck anthropometric parameters were significantly smaller in females compared to males.”
“Female vertebrae between C3 and C7 were significantly smaller than male vertebrae in the anterior-posterior dimension.”
“Female necks were also significantly weaker than male necks (32% weaker in flexion and 20% weaker in extension).”
“These results demonstrate that male and female necks are not geometrically similar.”
“Women have an increased incidence of whiplash injury and neck pain compared to men.”
2010 (22)
What Factors Influence Persistent Neck Pain after Whiplash?
Spine
The objective of this study was to identify factors that predict a patient’s risk of developing chronic symptoms and disabilities after a whiplash injury. It is a prospective study involving 557 patients who suffered whiplash injury after vehicle collision.
The authors note that the energy transferred in vehicle collisions “results in bone or soft tissue injuries, which could invariably lead to a variety of clinical symptoms.” In this unselected 557-subject prospective group, 67% of these injuries were to female subjects. The authors state:
“To be [a] woman is a poor recovery prognostic factor.”
“Attention must be drawn to the high prevalence (67%) of women who ask for medical assistance after whiplash injury.”
2014 (23)
Symptoms, Disabilities, and Life Satisfaction Five Years After Whiplash Injuries
Scandinavian Journal of Pain
The primary objective of this investigation was to study neck pain and other symptoms, disability, and life satisfaction five years after whiplash injury. Five years after the emergency department visit, 186 persons aged 18-64 were evaluated.
The most common symptoms five years after whiplash injury were fatigue (41%), poor memory (39%), and headache (37%). Inability to sustain previous workload (44%) and fatigue at work (43%) were frequently reported disabilities. Only 39% were satisfied with their somatic health and 60% with their psychological health. Compared with healthy controls, the whiplash injured exhibited more symptoms and had lower life satisfaction.
“Women reported significantly higher pain intensity than men.”
2015 (24)
Gender, Age and Ethnicity Influence on Pain levels and Analgesic Use in the Acute Whiplash Injury
European Journal of Trauma and Emergency Surgery
The authors evaluated whether gender, age or ethnicity comprise a risk factor for those initial pain levels following whiplash injury. They reviewed 2,538 patients with acute whiplash injury that were treated at the emergency department.
The initial pain level in acute whiplash injury is the most consistent predictor of transformation to a chronic pain syndrome, and women had significantly higher initial pain levels. Age and ethnicity did not influence pain levels.
2018 (25)
Sex-based Differences in Pain Distribution in a Cohort of Patients with Persistent Post-traumatic Neck Pain
Disability Rehabilitation
These authors analyzed a cohort of 745 consecutive patients suffering from post-traumatic neck pain. The cohort contained nearly twice as many females as males (64% versus 36%). The authors concluded that being female was a “risk factor for the development of persistent pain after neck trauma.”
SUMMARY
The “whiplash” mechanical phenomenon has been observed for centuries, long before the first automobiles appeared on our roads. An early and persistent observation is that when exposed to the same or similar collision forces, females are more greatly injured and more likely to suffer prolonged symptoms than males. A handful of researchers have attempted to discover the explanation for this observation. Proposed mechanisms include:
- Women, on average, have a smaller neck circumference compared to the circumference of their head as compared to men. This anthropometric difference would subject the female neck to a greater inertial load and result in greater injury.
- Women, on average, have smaller neck diameter and weaker cervical muscles, ligaments, bones, etc., compared to men. In a given collision, these factors would also subject the female neck to a greater inertial load and result in greater injury.
- Women, on average, weigh less than men. The forward phase of a rear-end whiplash collision is magnified by the springiness of the seat, which adds to the inertial load to the cervical spine structures. Lighter women are flung forward more greatly than men, increasing their risk for injury.
- Awareness of an impending collision is an important factor in whiplash injury. Joints are injured when muscles do not adequately protect them. When a collision is not anticipated, forces are fully applied to the joints, bypassing any protection for the muscles. On average, when men and women are in the same vehicle, the man drives and the woman is the front seat passenger. This front seat passenger position often reduces awareness of an impending collision, increasing injury.
Providers who treat whiplash injuries should be aware of the unique characteristics of injuries to women.
REFERENCES
- Todman D; Whiplash Injuries: A Historical Review; The Internet Journal of Neurology; 2006; Vol. 8; No. 2.
- Page HW; Injuries of the Spine and Spinal Cord without apparent Mechanical Lesion, and Nervous Shock in their Surgical and Medico-Legal Aspects; J & A Churchill; 1883.
- Page HW; Injuries of the Spine and Spinal Cord without apparent Mechanical Lesion, and Nervous Shock in their Surgical and Medico-Legal Aspects; Second Edition; J & A Churchill; 1885.
- Marshall HW; Neck Injuries; Boston Medical and Surgical Journal; January 23, 1919; Vol. 180; No. 4; pp. 93-98
- Rothman RH, Simeone FA; The Spine; Second Edition; Vol. 2; Macnab I; Acceleration Extension Injuries of the Cervical Spine; Chapter 10; WB Saunders Company; 1982.
- Crowe HE; Injuries to the Cervical Spine; Paper presented at the meeting of the Western Orthopedic Association; San Francisco; 1928.
- Crowe H; A New Diagnostic Sign in Neck Injuries; California Medicine; January 1964; Vol. 100; No. 1; pp. 12-13.
- Davis AG; Injuries of the Cervical Spine; Journal of the American Medical Association; January 20, 1945; Vol. 127; No. 3; pp. 149-156.
- Bomey S; Rate of Traffic Deaths Rises During Pandemic; USA Today; January 29, 2021; pp. 1B-2B.
- Sharp D; Pandemic Set Off Deadly Rise in Speeding that Hasn’t Stopped; Associated Press; August 11, 2021.
- Smaller Cars Means More Injuries for Women; USA Today; February 12, 2021.
- Schutt CH, Dohan FC;Neck Injury to Women in Auto Accidents. A Metropolitan Plague; Journal of the American Medical Association; December 16, 1968; Vol. 206; No. 12; pp. 2689-2692.
- States JD, Balcerak JC, Williams JS, Morris AT, Babcock W, Polvino R, Riger P, Dawley RE; Injury frequency and head restraint effectiveness in rear-end impact accidents; Proceedings of the 16th Stapp Car Crash Conference; November 8-10, 1972; Detroit; Warrendale (PA); Society of Automotive Engineers; 1972.
- Snyder RG, Chaffin DB, Foust DR; Bioengineering Study of Basic Physical Measurements Related to Susceptibility to Cervical Hyperextension-Hyperflexion Injury; Report No. UM-HSRI-BI-75-6; Ann Arbor (MI): Highway Safety Research Institute; 1975.
- Munker H, Langwieder K, Chen E, Hell E; Injuries to the Cervical Spine in Automobile Accidents [article in German]; Versicherungsmedizin; February 1995; Vol. 47; No. 1; pp. 26-32.
- Spitzer WO, Skovron ML, Salmi LR, Cassidy JD, Duranceau J, Suissa S, et al.; Scientific Monograph of the Quebec Task Force on Whiplash-Associated Disorders: Redefining “Whiplash” and its Management; Spine; April 15, 1995; Vol. 20; pp. 9S-73S.
- Bring G, Bjornstig U, Westman G; Gender Patterns in Minor Head and Neck Injuries: An Analysis of Casualty Register Data; Accident Analysis and Prevention; May 1996; Vol. 28; No. 2; pp. 359-70.
- Brault JR, Wheeler JB; Clinical response of human subjects to rear-end automobile collisions; Archives of Physical Medicine and Rehabilitation; 1998, Vol. 79; No. 1; pp. 72-80.
- Lonnberg F; Whiplash: Epidemiology, Diagnosis and Treatment [Article in Danish]; April 16, 2001; Ugeskrift for Laeger; Vol. 163; No. 16; pp. 2231-2236.
- Viano DC; Seat Influences on Female Neck Responses in Rear Crashes: A Reason Why Women Have Higher Whiplash Rates; Traffic Injury Prevention; September 2003; Vol. 4; No. 3; pp. 228-239.
- Vasavada AN, Danarai J, Siegmund GP; Head and Neck Anthropometry, Vertebral Geometry and Neck Strength in Height-matched Men and Women; Journal of Biomechanics; 2008; Vol. 41; No. 1; pp. 114-121.
- Cobo EP, and 8 more; What Factors Influence Persistent Neck Pain after Whiplash?; Spine; April 20, 2010; Vol. 35; No. 9; pp. E338-E343.
- Styrke J, Sojka, Bjornstig U, Stalnacke BM; Symptoms, Disabilities, and Life Satisfaction Five Years After Whiplash Injuries; Scandinavian Journal of Pain; October 1, 2014; Vol. 5; No. 4; pp. 229-236.
- Koren L, Peled E, Trogan R, Norman D, Berkovich Y, Isralit S; Gender, Age and Ethnicity Influence on Pain levels and Analgesic Use in the Acute Whiplash Injury; European Journal of Trauma and Emergency Surgery; June 2015; Vol. 41; No. 3; pp. 287-291.
- Westergren H, Larsson J, Freeman M, Carlsson A, Jöud A, Malmström EM; Sex-based differences in pain distribution in a Cohort of Patients with Persistent Post-traumatic Neck Pain; Disability Rehabilitation; May 2018; Vol. 40; No. 9; pp. 1085-1091.
“Authored by Dan Murphy, D.C.. Published by ChiroTrust® – This publication is not meant to offer treatment advice or protocols. Cited material is not necessarily the opinion of the author or publisher.”
