49 CFR § 399.209
Test procedures
November 18, 2020
(a) The force exerted on a handhold will be measured using a handheld spring scale or force transducer which can be attached to the vehicle and is free to rotate into alignment with a person's hand position.
(b) Hand grasp will be evaluated by observing the handgrip of any individual who conforms with the definition of “person” appearing in §399.205 of this subpart.