Daubert v. The Biomechanist

WDC Journal Edition: Winter 2015
By: Joseph M. Ryan & James M. Ryan, Ryan Law Firm LLC

Wisconsin adopted the Daubert standard with the passage of 2011 Wis. Act 2, the “Tort Reform Bill.” All experts used in cases filed after February 1, 2011 must meet the Daubert standard. This Article will not reiterate the standards of Daubert and its progeny.1 Rather, it will focus on the application of Daubert to biomechanical testimony, and specifically ,how to avoid and defeat Daubert challenges.

Since the adoption of the Daubert standard, the plaintiffs’ bar has been attempting to exclude biomechanical testimony.2 Although there has not yet been a Wisconsin appellate decision on the matter, a review of various circuit court orders suggests that such motions have largely been unsuccessful.3 That is not to say that biomechanists’ opinions have been freely admitted. There are, of course, traps to avoid when using such an expert to ensure that her opinions are admissible. This Article will explore those potential pitfalls. It will begin by explaining the analysis employed by a biomechanist in a typical low-velocity impact case.

The Biomechanist’s Method

The field of biomechanics provides information about the forces generated in an accident, how the body moves in response to those forces, and what types of injuries would result from those forces.4

Simply put, the science of biomechanics involves applying the principles of mechanical engineering to the human body. The human body is no different than any other physical structure, such as a bridge. A bridge is capable of handling certain loads, and when the load capacity is exceeded, the structure fails. In order for the structural failure to occur, there needs to be: 1) a manner of loading known to cause failure (i.e., mechanism); and 2) a load magnitude greater than the capacity of the structure (i.e., tolerance).

To determine whether the plaintiff’s body experienced loading conditions known to cause injury (i.e., whether there was a mechanism of injury), the biomechanist needs to first analyze the plaintiff’s kinematic response to the impact, i.e., how the plaintiff’s body moved relative to the vehicle. Then, if there is a manner of loading consistent with the plaintiff’s claimed injury, the biomechanist will determine whether the plaintiff experienced a load greater than his or her capacity to resist it. In order to determine whether the load was greater than the plaintiff’s capacity, the biomechanist must calculate the forces involved in the accident and compare those forces to the forces the plaintiff’s body was capable of tolerating.

Manner of Loading Known to Cause Injury— The Kinematic Response

The biomechanist will use the laws of physics, occupant restraint system data, and multiple collision scenarios from crash and sled tests to determine whether the plaintiff’s movements during an accident were consistent with the injuries claimed by the plaintiff (i.e., whether there was a mechanism of injury).

The laws of physics play an important role in analyzing the plaintiff’s body movement in response to a collision. In a rear end accident, for example, the movement of the occupant in the target vehicle willalways be rearward relative to the vehicle (the seatback actually goes forward and hits the back of the occupant).5 Any rearward movement of the plaintiff in a “Low Velocity Impact,” or “LVI,” should be well supported by the seatback and headrest. Any forward rebound will likewise have been well controlled by the seat belt and occupant restraint system. The practitioner should be sure to ask at the plaintiff’s deposition whether she or he was belted, and whether the head restraint was properly adjusted.

The practitioner should also take note of the plaintiff’s height, weight, seating position, and awareness of the impending impact. These characteristics may help determine whether an injury could have occurred.6For example, the plaintiff’s head position may change the potential for her or him to experience whiplash injuries, so it is important to ask whether she or he was looking left, right, checking her or his blind spot, etc. In addition, the plaintiff’s hand location could influence the probability of other claimed injuries. Finally, awareness of the impending impact significantly reduces the risk of whiplash injury.

Asking the right questions during the plaintiff’s deposition will ensure both that the biomechanist has the information she needs to properly evaluate the plaintiff’s kinematic response to the accident and decrease the risk of exclusion under Daubert.

Personal Tolerance of the Plaintiff

If, during the kinematic analysis, the biomechanist finds that there was a mechanism of injury for theplaintiff’s claimed injuries, the biomechanist will then determine whether the mechanism of injury exceeded the personal tolerance of the plaintiff.

Because every person’s body is capable of withstanding different load applications, the biomechanist musttailor the load tolerance analysis to the specific individual or risk exclusion under Daubert.7 Even if not excluded, failure to tailor the load tolerance analysis to the individual plaintiff will subject the biomechanist to some unpleasant and, perhaps, damaging cross-examination.8 In order to determine the plaintiff’s personal load tolerance, the biomechanist must first know the plaintiff’s pre-incident physical condition.

The plaintiff’s pre-incident physical condition is established by reviewing the plaintiff’s activities, which is usually done via the plaintiff’s deposition. The practitioner who intends to use a biomechanist should focus some portion of the deposition on the plaintiff’s pre-incident activities, as the typical loads experienced by the human body during daily activities are well documented.9 Questions about the deponent’s exercise habits, recreational activities, and household duties are often useful. Using the plaintiff’s pre-incident daily activities, the biomechanist can determine the forces the plaintiff was able to withstand prior to the accident.

The biomechanist will then need to determine the force of the accident in order to see whether that force was within the plaintiff’s pre-injury tolerance. The force of the accident will be within the plaintiff’s pre-injury tolerance if the forces from the accident are less than the forces involved in the plaintiff’s everyday activities.

In order to determine the force generated in an accident, the biomechanist will need crash test data supplied by the Insurance Institute for Highway Safety (IIHS) for exemplar vehicles, police reports, vehicular repair estimates, photographs of the damage, data from peer reviewed scientific literature, as well as VinLink and Expert Auto Sales data from the subject vehicles (in addition to the plaintiff’s medical records and deposition testimony, which are needed for the injury causation analysis). Failure to use exemplar vehicles—such as by using vehicles of makes and models that are different than the vehicles in the subject accident—has been grounds for testimony exclusion under Daubert.10

The force involved in an accident will come in two measurements: Delta-V and units of gravity. Delta-V is the change in velocity of the target vehicle. A change in velocity of less than 10 mph is generally considered a “low velocity impact.” However, the practitioner should consider avoiding use of a biomechanist where the Delta-V is greater than 7.5 mph because human volunteer test subjects are typically not exposed to speeds greater than that. The obvious cross-examination tact is to point out the incongruity of claiming the plaintiff could not be injured at 15 mph Delta-V yet human volunteers’ exposure is limited to a 7.5 mph Delta-V, because beyond that speed they could be injured.

There are two exceptions to this rule: 1) the accident takes place over an elongated change in time, or Delta-T; and 2) the plaintiff complains of chronic pain, such as a disc herniation.

The first exception is when the Delta-T, or change in time, is elongated, for example, by the bullet vehicle’s override/underride of the target vehicle’s bumper. When the length of time during which an impact takes place is stretched out, injury potential is reduced. For example, an occupant of a car traveling 60 mph that takes 10 seconds to slow down to 0 mph will not be injured at all, whereas an occupant who goes from 60 mph to 0 mph in less than half a second can be seriously injured. In an underride situation, the length of time over which the occupant experiences the change in velocity is greater because the direction of force is down and forward, causing a longer impact duration. For the same reason, an underride will also push the target vehicle a shorter distance than a direct bumper-to- bumper impact because some of the forward energy will be displaced downward.

The second exception involves the type of injury about which the plaintiff complains. Human volunteer studies generally only look at acute outcomes immediately following the crash test. The threshold for acute injuries resulting in transient pain is much lower than the threshold for injuries producing chronic pain. According to epidemiological literature, the threshold for significant risk of chronic pain and disc herniation is closer to a Delta-V of 12-15 mph. Therefore, any plaintiff claiming chronic pain due to disc herniation as the result of a low velocity impact can be proved wrong, as the science does not allow for such injuries, and, consequently, a biomechanist would be useful to refute this type of injury, even at a Delta-V of greater than 7.5 mph.11

Pitfalls and Practice Pointers

Choose a biomechanist who has personally conducted crash tests and published peer-reviewed articles on crash testing, injury causation, and injury tolerance. If, for instance, the biomechanist has done nothing but design running shoes for the last ten years and is now making a living testifying about car accidents and injury potential, a judge will be skeptical of the integrity of the opinions being proffered.12 A Wisconsin circuit court judge echoed these sentiments when he stated that the reconstructionist’s research “isn’t that of a scientist simply in the quest of knowledge or truth, but it’s part of his desire to promote his business as consulting, and to testify as an expert witness in these kinds of cases.” 13

Do not use a biomechanist or reconstruction engineer who will use only vehicle repair bill amounts to determine the amount of damage caused by the accident. In Clemente v. Blumberg,14 a New York appellate case, the expert engineer used the monetary value of repair bills to “calculate” change in velocity. His theory was that if the repair bill amounts were close, the forces involved in the accident would be similar. The obvious flaw here is that there is no uniformity among mechanic repair bills, and therefore, the application of the engineer’s methods to the facts was unreliable.

Avoid any testimony wherein the expert opines that the occupant cannot be injured below a certain Delta-V. These “threshold of injury” opinions have been rejected time and again. The Ohio Court of Appeals inAzzano v. O’Malley-Clements rejected the opinion that the plaintiff “experienced a velocity change which ‘is below the threshold for symptomology.’”15 In Schlict v. American Nat’l Property and Cas. Co., et al., a La Crosse County Circuit Court case, the judge determined that there has not been general consensus in the scientific community with respect to the claim that low-speed collisions never cause injury, assuming normal seating conditions.16 The “threshold of injury” theory was also rejected in Schultz v. Wells, a Colorado Court of Appeals case.17

The biomechanist or reconstruction engineer should not correlate vehicle damage with injury potential. The opinion should not be that, “because there was no damage to the vehicle, no one was injured.” The expert must bridge the gap between the vehicle damage and the injury. The expert must use the vehicle damage to determine the force involved and compare that force to the plaintiff’s personal tolerance. Without the bridge, the testimony will likely be excluded as the plaintiff will argue that property damage is neither a valid predictor of acute injury risk nor of symptom duration.18

It is beneficial to have an expert physician rely on the biomechanist’s report. The best practice is to get the biomechanist’s report to the IME doctor before the IME doctor issues her report.19 In Rizzi v. Mason,20 a Delaware case, the defense sought to admit testimony of a biomechanist and the court disallowed the testimony because there was no medical expert “establishing a correlation between the force (or lack of force) generated upon impact and plaintiff’s injuries.”21 In contrast, the court in Kelly v. McHaddon,22 another Delaware case applying the same standard, allowed the biomechanist’s testimony because the “medical expert relied on the biomechanical expert’s report in rendering his opinion that plaintiff’s injury was not caused by the collision.”23 Considering the biomechanist’s report in conjunction with the IME doctor’s report is especially critical when there are preexisting neck and back problems—it’s like splitting aces.

The Reference Manual on Scientific Evidence

As should be apparent at this point, biomechanical testimony can be very useful in a low velocity

impactcase,particularlygivenitscross-disciplinary foundation. Indeed, such testimony is expressly favored by the Federal Guidelines on Scientific Evidence for this very reason:

[O]ne cross-disciplinary domain deals with the study of injury mechanics, which spans the interface between mechanics and biology. The traditional role of the physician is the diagnosis (identification) of injuries and their treatment, not necessarily a detailed assessment of the physical forces and motions that created injuries during a specific event. The field of biomechanics (alternatively called biomechanical engineering) involves the application of mechanical principles to biological systems, and is well suited to answering questions pertaining to injury mechanics.... A practitioner whose experience spans the interface between mechanics (i.e., engineering) and biology (i.e., science), considered in the context of the facts of a particular case, can be of significant assistance inanswering questions pertaining to injury mechanism and causation.24


If presented correctly, there should be no exclusion of any biomechanical opinions in the face of a Daubert challenge. After all, if a lay juror is able to reasonably conclude that a person is not injured based only on the lack of damage to the plaintiff’s vehicle, as happened in the Wisconsin Supreme Court case of Bartell v. Luedtke,25 then certainly that conclusion can be bolstered and explained by proper scientific testimony.

Joseph Ryan graduated from UW-Madison with a B.A. in political science and received his J.D. from Marquette University Law School. He opened Ryan Law Firm with his father, James Ryan, in 2014, focusing on civil litigation with an emphasis on insurance defense. Joseph is admitted to the Eastern and Western Districts of Wisconsin and is a Member of the Wisconsin Defense Counsel.

James Ryan has been involved in civil litigation since graduating from Marquette Law School in 1985. He has tried well over 100 jury trials to verdict since that time, and argued several cases to the appellate courts. He is a pioneer in defending low velocity impact cases, having tried his first LVI case in 1996. Since that time he has spoken at various seminars on this topic as well as a variety of others in the field of civil trial law. He has practiced with his son Joseph in Brookfield since 2014.


1 The Daubert factors, a non-exhaustive list, are as follows:

  1. Whether the theories employed by the expert have been tested;
  2. Whether the theories have been subject to peer review and publication;
  3. Whether the theories employed by the expert have a known error rate;
  4. Whether the theories are subject to standards governing their application;
  5. Whether the theories employed by the expert enjoy widespread acceptance;
  6. Whether the theory flows out of research the expert conducted independent of litigation or whether it was developed for purposes of testifying;
  7. Whether the expert extrapolated an accepted premise to an unfounded conclusion;
  8. Whether the expert has adequately accounted for obvious alternative explanations;
  9. Whether the expert is being as careful as he would be in his regular profession outside his paid consulting;
  10. Whether the field of expertise is known to reach reliable results for the opinion given.

Daubert v. Merrell Dow Pharmaceuticals, 509 U.S. 579, 593- 596 (1993); Lyman v. St. Jude Medical S.C., 580 F. Supp. 2d 719 (E.D. Wis. 2008).
2 Daubert actually liberalizes and favors admission of expert testimony. Admission under Daubert is more fluid than the rigid Frye test. Under Frye, expert opinion, even if founded on good science and related to the facts of the case, could not be admitted unless the science was generally accepted. Under Daubert, general acceptance is only one factor to consider, among many.
3 The Authors of this Article were able to locate four Wisconsin circuit court decisions and one 7th Circuit decision admitting biomechanist testimony and argued two with the same results.
4 See Smelser v. Norfolk Southern Railway Company, 105 F.3d 299, 305 (6th Cir. 1997).
5 For whatever reason, every plaintiff says their first movement is forward. Some Daubert motions may go so far as to say that the biomechanist fails to apply the principles and methods reliably to the facts because he or she did not take into account the plaintiff’s testimony that they first moved forward, despite the physical impossibility of such a claim.
6 Azzano v. O’Malley-Clements, 710 N.E.2d 373, 376 (Ohio App. 1998).
7 Wis. Stat. § 907.02 (2011). The testimony is the product of reliable principles and methods and the witness has applied the principles and methods reliably to the facts of the case. See Lewis v? Citgo Petroleum Corp?, 561 F.3d 698, 705 (7th Cir. 2009).
8 The argument will be that, although an “average person” from a crash test study was not injured in any crash tests using the same force as this accident, this plaintiff has pre- existing problems which make her more susceptible to injury, and, therefore, those crash tests do not apply to the facts of this case. That is, just because one person was not injured at these forces does not mean that this plaintiff could not have been injured.
9 T.P. Ng, W.R. Bussone, et al., “Thoracic and Lumbar Spine Accelerations in Everyday Activities,” Biomedical Sciences Instrumentation 42:410-5 (2006); J.R. Funk, J.M. Cormier, et al., “The Effect of Gender and Body Size on Linear Accelerations of the Head Observed During Daily Activities,” Biomedical Sciences Instrumentation 42:25- 30 (2007); J.R. Funk, J.M. Cormier, et al., “An Evaluation of Various Neck Injury Criteria in Vigorous Activities,” Proceedings of IRCOBI (International Research Council on the Biomechanics of Injury) Conference 2007, at 233-248 (2007). The practitioner should focus on daily activities: exercise, grocery shopping, cleaning, taking out the garbage, and objects the person was able to lift prior to the accident. Often times, these small tasks will result in greater force than the LVI in which the plaintiff claims to have been injured.
10 See Azzano, 710 N.E.2d 373. There were additional reasons the reconstructionist in Azzano was barred, including failure to account for occupant seating position. The reconstructionist was also barred from offering injury threshold testimony because he was not a biomechanist.
11 The Authors acknowledge the contribution to this paragraph from biomechanist Brian Stemper, Ph.D.
12 Under Daubert, one of the factors to consider when admitting or excluding expert testimony is whether the theory flows out of research the expert conducted independent of litigation or whether it was developed for purposes of testifying. See also Suanez v? Egeland, 801 A.2d 1186 (N.J. App. 2002). It should also be noted that, when testifying about injury potential, only hire a biomechanical expert with a Ph.D.
13 Schlict v? American Nat’l Property and Cas? Co?, et al?, La Crosse County Case No. 13-CV-463.
14 705 N.Y.S.2d 792 (N.Y. App. 1999).
15 Azzano, 710 N.E.2d at 372.
16 See Schlict, supra note 14, transcript of oral argument.
17 13 P.3d 846 (Colo. App. 2000).
18 Arthur C. Croft & Michael Freeman, Correlating Crash Severity with Injury Risk, Injury Severity, and Long-Term Symptoms in Low Velocity Motor Vehicle Collisions, Med. Sci. Monit., at 11(10), p. RA320 (2005). See also Clemente, 705 N.Y.S.2d 792.
19 Rizzi v. Mason, 799 A.2d 1178 (S. Ct. Del. 2002); Kelly v. McHaddon, 2002 WL 388120 (S. Ct. Del. 2004) (unpublished decision); Eskin v? Carden, 842 A.2d 1222 (S. Ct. Del. 2004). In Eskin, the expert biomechanical testimony was disallowed in part because it was not “tied in with the medical people.”
20 Rizzi, 799 A.2d 1178.
21 Id.
22 Kelly, 2002 WL 388120.
23 Id.
24 Nat’l Research Council of the Nat’l Academies, Fed. Judicial Ctr., Reference Manual on Scientific Evidence, at 901-902 (The Nat’l Academies Press 3d ed. 2011)
25 52 Wis. 2d 372, 378, 190 N.W.2d 145 (1971).