It has been hypothesized that a maturational threshold exists whereby prepubescent children are unable to elicit physiological changes in response to training (Gilliam and Freedson, 1980). It has been proposed by Katch (1983) that there is a critical period in a child’s life, a “trigger point”, below which the effects of training will be minimal, or will not occur. It is believed that this trigger point is influenced by the modulating effects of hormones that initiate puberty and influence functional development and subsequent organic adaptations (Katch, 1983).

One study that supports this hypothesis followed a group of seven Japanese boys from the age of 9.7 – 15.8 years and determined their peak VO₂ annually (Kobayashi et al., 1978). The boys trained for 1 – 1.5 h per day, 4 or 5 times a week and engaged in various school based activities including endurance running, football and swimming. Peak VO₂ increased slowly in the boys until 1 year prior to peak height velocity after which peak VO₂ was found to increase above the normal increase attributable to age and growth (i.e. a greater increase was seen in the training group than in the control group). A major limitation of this study, however, was that measurements of peak VO₂ for the control group were not started until after the age of peak height velocity. Indirect supporting evidence for the “trigger point” hypothesis is provided by a study conducted by Mirwald and colleagues (1981) who measured peak VO₂ twice yearly in 25 boys from 7 – 17 years of age. From the beginning of the study peak VO₂ was found to be higher in the “active” boys compared with the “inactive” boys but this difference only reached statistical significance at peak height velocity.

In contrast with the findings of these studies, in an often cited report Weber and colleagues (1976), studied twelve pairs of identical twin boys where one twin trained and the other acted as his control. There were four sets of twins at each of 10, 13 and 16 years and the training twins followed the same 10-week programme. Percentage changes in the peak VO₂ of the trained boys were 23.5%, 14.2% and 20.5% at ages 10, 13 and 16 years respectively suggesting that the pre and post-pubertal periods were more amenable to training than circumpuberty. In a similar study, Danis and colleagues (2003) studied nine pairs of identical twin boys where one twin trained and the other acted as his control. An influence of training in the prepubertal but not in the pubertal twins was found. The findings of these two studies are in conflict with the view that more mature young people are more likely to improve aerobic fitness following training than those who have yet to reach puberty (Katch, 1983).

To address this issue, studies meeting the criteria for inclusion in this review were categorised into participants of either 8-10 years of age (Table 1) or 11-18 years of age (Table 2). Analysis of the studies in Tables 1 and 2 reveals that 6 of the 11 studies (55%) in Table 1 (participants <11 years) and 4 of the 7 studies (57%) in Table 2 (participants ≥ 11 years) reported significant increases in peak VO₂ with training. The average increase in mass-related peak VO₂ in studies in Table 1 was 6.5% (compared with an average control group change of – 0.4%) and in Table 2, 5.5% (control group 0.14%). These figures represent a very crude overview of studies including different training programmes but they are in accord with the changes reported in reviews by Payne and Morrow (1993) and Le Mura and colleagues (1999).

There is therefore no evidence to indicate a greater effect of training on the peak VO₂ of those 11 years and above than those under 11 years of age. Similarly, of the eight studies which verified the prepubertal status of participants, five (63%) showed a significant increase in peak VO₂ and three reported no significant change. Therefore, despite suggestions of a “maturation threshold” (Gilliam and Freedson, 1980) or a “critical or trigger point” (Katch, 1983) underpinning trainability, the influence of age and maturation on increasing the peak VO₂ of 8-18 year-olds through training remains to be proven.

A variety of exercise modes have been used in training studies undertaken with young people. Studies involving continuous exercise (Massicotte and Macnab, 1974; Lussier and Buskirk, 1977; McManus et al., 1997), interval training (Savage et al., 1986; McManus et al., 1997; Baquet et al., 2002) and a mix of the two (Burkett et al., 1985; Mahon and Vaccaro, 1989; Mandigout, et al., 2001; Obert et al., 2003) have resulted in significant increases in peak VO₂. Similarly, both cycling and running training have produced increases in peak VO₂. It can be concluded that, exercise using large muscle groups, regardless of mode, has the potential to increase peak VO₂. However, studies incorporating both interval and continuous exercise appear to have been the most successful, possibly because the variation retained the participants’ interest and attention and facilitated sessions of longer duration. Resistance exercise has also been observed to significantly increase peak VO₂ in two studies following 4 (Docherty et al., 1987) and 14 (Weltman et al., 1986) weeks of training.

With two exceptions the frequency of training in all studies was 3 to 4 sessions per week. In a study performed by Burkett and colleagues (1985) 5 sessions per week were employed and only 2 sessions per week in a study conducted by Baquet and colleagues (2002). Both of these studies demonstrated significant increases in peak VO₂ (i.e. 9.3% and 8.2% respectively).

The duration of sessions varied from 12 to 90 min with most studies in the range 20 to 40 min per session. Interestingly, the study employing a session duration of 12 min reported a significant increase in peak VO₂ only in the group training at high intensity (Massicotte and Macnab, 1974). This indicates the potential importance of training volume (interaction between intensity and duration). In general, training sessions of 40 to 60 min have been the most successful in increasing peak VO₂.

The intensity of exercise appears to be crucial and of the 9 studies which have used a training stimulus of 85% to 90% of maximum heart rate (HR max), 7 induced significant increases in peak VO₂. Two studies have specifically addressed training intensity. Savage and colleagues (1986) reported a significant increase in peak VO₂ in boys who trained at 85% of HR max but no increase in peak VO₂ in boys who trained at 70% of HR max. Similarly, Massicotte and Macnab (1974) compared boys who trained for 12 min, 3 times per week for 6 weeks at 66 to 72%, 75 to 80% or 88 to 93% of HR max. Only the group who trained at the highest intensity significantly improved peak VO₂. It is important to note that in both these studies the training groups were not matched for total exercise volume. The duration and frequency of the exercise sessions and the length of the training period were identical for each group. This would result in the boys in the higher intensity exercise groups expending more energy than those in the lower intensity exercise groups and consequently experiencing a greater exercise volume.

The length of training programmes ranged from 6 to 20 weeks but no clear inferences of length of programme on increase in peak VO₂ can be drawn from the available data. For example, Stoedefalke and colleagues (2000) trained postmenarcheal girls for 20 weeks without inducing an increase in peak VO₂ whereas Massicotte and Macnab (1974) demonstrated a 10.8% increase in peak VO₂ in boys after only 6 weeks of training.

A study conducted by Obert and colleagues (1996) is worthy of note because of the high frequency (10 per week) and long duration (60 to 90 min) of sessions and the programme length (52 weeks). The study is, however, limited by the small sample size (5 girls in the experimental group). To maintain consistency between training and assessment mode the pre-test and post-test assessments were carried out using a swim bench ergometer. This limits the ability to compare the results of this study with those that determined peak VO₂ using treadmill or cycle ergometer protocols. Nonetheless, the 29% increase in mass-related peak VO₂ seen as a result of training in the girls who participated in this study is striking. This study highlights the potential importance of long-term, specific training programmes. Given the inconsistency of significant improvements in peak VO₂ identified in studies lasting 7-8 weeks and the failure of some 12-week programmes to enhance peak VO₂ it seems prudent to recommend minimum programme duration of 12 weeks.