In the manufacturing of cooked ham, tumbling is applied to the muscles before moulding and cooking in rotating drums equipped with baffles. This promotes a mechanical action on meat pieces due to hundreds of successive falls and is known to determine cooking yield and ham quality. However little information is available on the effect of this mechanical action on the basic phenomena like salt migration, protein solubilisation and denaturation... It is, however, too complicated to study the mechanical behavior of the muscles in industrial tumblers. Both the dynamic and rate of muscle deformation were estimated from high-speed films (1000 frames/s) during the end of a fall against a rigid surface. The fall height was varied from 25 cm to 1 m and two types of pork muscles were used: Semimembranosus (SM) and Rectus femoris (RF). Image analysis of about 50 films shows that the duration of muscle deformation and the maximum muscle strain varied from 20 to 120 ms and from a few % to 40%.