have found, however, that the cross-sectional area of
all fibre types were larger in the loin of Duroc than in the loin of
Pietrain although the percentage of lean meat was higher in Pietrain
pigs (61.1%) compared to Duroc pigs (59.4%). This indicates that the
loin of Pietrain pigs contains a higher number of muscle fibres than
the loin of Duroc pigs. According to Werner et al. (2010) the cross-
sectional area of muscle fibre types in Duroc–Pietrain cross was closer
to that of Pietrain than that of Duroc although the lean content of
Duroc–Pietrain cross was the lowest, 57.9%. According to the above
mentioned papers, Lefaucheur (2010) has also reviewed the relation-
ship between the lean content and the muscle fibre cross-sectional
area to be contradictory in the literature. According to Lefaucheur
(2010), the carcass lean content and muscle growth potential would
be primarily dependent on total fibre number. Therefore, one should
first take into account total fibre number before studying any rela-
tionships between muscle development and muscle fibre cross-
sectional area. Lefaucheur (2010) also reports, a strong positive corre-
lation between the cross-sectional area of muscle fibres and muscle
development which can be expected by a constant total fibre number.
In the present study, however, the thinnest fibres were in NL not in
NDL. Growth in muscle fibre length is also important when explaining
muscle growth. Muscle fibre length is difficult to measure, and there-
fore, increase of length of muscle fibres is poorly known.