Biomechanical engineer
Expert class library · Personal injury · Defense side
Analyzes the forces generated in an accident and whether they were sufficient to cause the claimed injury. Frequently retained by the defense in low-speed collision and slip-and-fall cases.
What this expert is retained to answer
- What accelerations and forces did the occupant or pedestrian experience in this event?
- Were those forces within the range that people tolerate in everyday activities?
- Could forces of this magnitude cause the type of injury the plaintiff claims?
- Is the claimed injury mechanism consistent with how the body moved during the event?
Methods
- Injury mechanism analysis
- Force and acceleration estimation
- Occupant kinematics
- Comparison to tolerance data
How the testimony is attacked
- Specific causation beyond biomechanics. The leading attack is that a biomechanical engineer may describe forces and the general types of injury they can produce but cannot say what caused this person's injury. The Sixth Circuit in Smelser held a biomechanical engineer's opinion on the cause of the plaintiff's specific injuries went beyond his expertise and should have been excluded.
- Bridging engineering and medicine without a validated method. Even a witness trained in both fields may be challenged for using force calculations to reach a medical conclusion. In Maines v. Fox the trial court barred a biomechanical engineer who was also a physician from giving a specific causation opinion for that reason, though the appellate court found that ruling an abuse of discretion.
- Untested methodology. Opponents argue that tests or calculations were not peer reviewed or generally accepted. In Smelser the court also found the expert's seat belt testing unreliable because it was neither published nor shown to be an accepted method.
- Ignoring individual susceptibility. Plaintiffs argue that tolerance data drawn from healthy test subjects says little about a person with preexisting degeneration. Courts often cite the lack of medical training to assess individual tolerance as a reason to confine biomechanical opinions to general causation.
- Failure to object to the scope of testimony. Scope objections must be made specifically and on time. In Mathis v. Huff & Puff Trucking the Tenth Circuit refused to disturb a bench verdict that relied on a defense biomechanical engineer's opinion that the collision forces were insufficient because the plaintiff never made specific objections at trial.
What the public record shows
A deliberately narrow CourtListener search, biomechanical AND "injury causation" AND (Daubert OR "Rule 702"), returned 20 opinions filed since 2015, as of October 2, 2026; broader searches return more. Three that show how courts handle this class of testimony:
| Outcome | Case | Court | Why |
|---|---|---|---|
| Excluded | Smelser v. Norfolk Southern Railway Co.105 F.3d 299 | 6th Cir. 1997 | The Sixth Circuit held that the plaintiff's biomechanical engineer should not have been allowed to testify that a defective shoulder belt caused the plaintiff's specific injuries, because that opinion exceeded his biomechanics expertise and rested on unreliable testing. |
| Admitted | Mathis v. Huff & Puff Trucking, Inc.787 F.3d 1297 | 10th Cir. 2015 | The Tenth Circuit affirmed a judgment that relied on a defense biomechanical engineer's testimony that the collision forces were insufficient to cause the claimed spinal injury, rejecting a scope challenge the plaintiff had not preserved with specific objections. |
| Limited | Maines v. Fox190 So. 3d 1135 | Fla. Dist. Ct. App. 2016 | The trial court allowed a defense biomechanical engineer and physician to testify that the collision forces would not generally cause the injury but barred his specific causation opinion; the appellate court found that limit an abuse of discretion but harmless because his other testimony conveyed the substance. |
Each case links to the free opinion text on CourtListener.
Under amended Rule 702
Since December 1, 2023, Rule 702 says expressly that the party offering an expert must show the court it is more likely than not that the testimony meets each requirement: that it rests on sufficient facts or data, uses reliable methods, and reflects a reliable application of those methods to the case. Questions about the basis of an opinion are no longer automatically matters of weight for the jury. For how the circuits have applied the amendment, see the Rule 702 tracker, which follows each court of appeals; for what that means for preparing or attacking this class of expert, see the guide on amended Rule 702.
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Last reviewed October 2, 2026. How this page is built: rulings are found by searching court opinions on CourtListener, and each one is read in the opinion before it is summarised here; outcomes are labelled by what the court did with the expert's testimony. No individual expert is named. This page summarises public decisions for orientation and is not legal advice; read the opinion before relying on any ruling.