Peak
V
·
O
2
limits the child’s capacity to perform aerobic exercise but it does not
describe fully all aspects of aerobic fitness. Exercise of the intensity and duration
required to elicit peak
V
·
O
2
is rarely experienced by many young people.17,18 The vast
majority ofhabitual physical activity is submaximal and of short duration and, under
these circumstances, it is the transient kinetics of
V
·
O
2
which reflect the integrated response of the oxygen delivery system and the
metabolic requirements of the exercising muscle.19–21 Furthermore, peak
V
·
O
2
is neither the best measure of a child’s ability to sustain submaximal
aerobic exercise nor the most sensitive means to detect improvements in aerobic
fitness after a training programme. Despite its origins in anaerobic metabolism, blood
lactate accumulation is a valuable indicator of aerobic fitness and it can be used to
monitor improvements in muscle oxidative capacity with exercise training in the
absence of changes in peak
V
·
O
2
.16,22 However, as
V
·
O
2
kinetics is comprehensively reviewed in Chapter 22 and blood lactate
accumulation during exercise is analysed in Chapter 8, we will focus herein on aerobic
fitness as described by peak
V
·
O
2
.