Despite increases take-off thrust, acceleration slowed significantly, which may be explained by the appearance of additional braking force.
My emphasis.
11:59:47 F/O: What are you doing
Presumably said to Captain.
RECOMMENDATION: Conduct classes with flight crews YAK-42 TO CORRECT Position of the feet on the pedals at various stages of flight, and THE
PROCEDURE ADJUSTMENT pilot SEATS.
Other than a failed rollout and rotation what other 'stages of flight' are relevant to this accident?
Toxicology may reveal a lot.