Chest
Volume 101, Issue 2, February 1992, Pages 485-489
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Clinical Investigations
Oxygen Uptake Plateau during Maximal Treadmill Exercise in Children

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The leveling of oxygen uptake at high work loads has been utilized to define maximal Vo2 during progressive exercise testing. Exercise studies in children have indicated, however, that a Vo2 plateau can commonly be demonstrated in less than one half of subjects. To examine the potential contributions of subject effort, aerobic fitness, and nonaerobic performance to this variability, 15 children ages 7 to 10 years performed progressive treadmill walking to exhaustion with a ramp protocol. The Vo2 plateau was defined as a change in Vo2 during the final minute of exercise less than 2 SD below the mean of increases between the previous 4 to 5 submaximal minutes. Five subjects (33.3 percent) demonstrated a plateau. No significant differences in mean peak Vo2, heart rate, or respiratory exchange ratio were observed between plateau and nonplateau groups. Testing results of speed (50-yard sprint) and leg power (vertical jump) were also similar. These findings suggest the following: (1) subject effort, aerobic fitness, and nonaerobic factors do not explain the presence or absence of a Vo2 plateau during exercise testing of children; and (2) a Vo2 plateau should not be used as a requirement for defining Vo2max during treadmill testing in this age group.

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METHODS

Twenty-one healthy children volunteered for treadmill testing. All were active, nonobese, and not participating in endurance training programs. None was taking medications which would influence exercise performance.

Exercise to exhaustion was performed with a continuous, progressive treadmill walking protocol in an air-conditioned laboratory (temperature 20 to 22° C). After receiving testing instructions, each subject was acclimated to the treadmill with a 2-min walk at 0 percent grade, 3.0 mph.

RESULTS

The average age of the subjects was 9.4 years (range 7.9 to 10.6), with a mean weight of 33.4 kg (SD 7.8) and height 139 cm (SD 7). Nine were boys and six were girls. Average peak Vo2 for the boys was 52.1 ml kg−1 min−1 (SD 5.7) and 49.0 ml kg−1 min−1 (SD 4.5) for the girls. It was the opinion of the testing staff that all subjects achieved at least a near-maximal exercise effort as indicated by unsteady gait, sweating, and breathlessness. All demonstrated an RER over 1.01 and/or heart rate

DISCUSSION

Previous studies have indicated that from 21 to 60 percent of children will demonstrate a Vo2 plateau during a progressive continuous treadmill exercise test (Table 2). The finding of a plateau in 33 percent of subjects in the present study utilizing a ramp protocol is therefore consistent with earlier reports, which have all involved multistage steady-state protocols. It should be noted that while the appearance of a Vo2 plateau has been considered less common in children than adults, a

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