able. A similar pattern has been found in the
deltoid muscle, where there is an even greater
variation. Young elite skiers have been found to
have a lower percentage of slow-twitch fibres
than older skiers (Rusko 1976), which can be an
effect either of training or further selection. The
predominance of slow-twitch fibres is logical,
since the metabolism in cross-country skiing is
predominantly aerobic and slow-twitch fibres
have a high oxidative capacity. Furthermore, the
number of capillaries is greater around a slow-
twitch than a fast-twitch fibre. This enhances the
transportation of gases and nutrients between
blood and muscle cells, allowing for an effective
aerobic metabolism. All these findings are consis-
tent with the hypothesis that physical training
for many years increases local aerobic metabolic
capacity (Saltin & Gollnick 1983).
However, the physiological variable that most
evidently distinguishes elite cross-country skiers
from the average person as well as less successful
cross-country skiers is the maximum oxygen
uptake, expressed as litres per minute as well as
in relation to body size (ml · min–1·kg–1body
mass). Over the decades, reports have confirmed
that elite cross-country skiers have, without
exceptions, very high values (Table 51.1). World-
class skiers have displayed a higher maximum
oxygen uptake than less successful skiers (Bergh
1987; Ingjer 1991). Skiers of junior age display
lower values than adults (Rusko 1976; Bergh
& Forsberg 1992). These differences are also
reflected in differences in racing speed and, thus,
racing success.
The power facilitated by the metabolism is
necessary for moving the body mass, and more
power increases speed. On the other hand, a
higher body mass demands more power at a
given speed. Thus, there is a need to compensate
for differences in body mass, otherwise it is not
possible to compare the values obtained in differ-
ent skiers. Traditionally, such compensations
have been made by means of dividing maximum
oxygen uptake by body mass. However, it has
been demonstrated that the power needed to ski
at a given speed on level terrain increases less
than proportional to body mass. Thus, it is not
logical to divide oxygen uptake by body mass in
order to equate heavy and light skiers. Therefore,
dimensional analysis and empirical findings
suggest that a division by body mass raised to
the second or third power may be more valid for
cross-country skiing (Bergh 1987). This is sup-
ported by a study of Ingjer (1991), which dem-
onstrated that world-class skiers differed
significantly from medium-class and less suc-
cessful skiers if the maximum oxygen uptake
was divided by body mass raised to the second
or third power, whereas a division by body mass
did not reveal any significant difference. Thus, it
seems logical to relate maximum oxygen uptake
body mass raised to the second or third power if
the purpose is to predict the capacity for cross-
county skiing.cross-country skiing 657
Table 51.1Different measurements of maximum oxygen uptake in elite cross-country male skiers.
O2max.uptake O2max.uptake
(l · min-^1 ) (ml·kg-^1 · min-^1 )Mean SD Mean SD Reference5.5 0.2 80.1 1.4 Åstrand (1955)
5.6 0.3 82.5 1.5 Saltin & Åstrand (1967)
5.5 0.2 75 2.7 Hanson (1973)
6.5 0.5 83.8 6.4 Bergh (1987)
6.7 0.6 87.0 6.9 Bergh & Forsberg (1992)Although all groups can be characterized as elite skiers, there were differences in the performance level both within
and between groups.