Aerobic fitness was measured using a maximal oxygen
consumption (V˙ O2max) test on a TrackMaster TMX425C
motor-driven treadmill (Full Vision, Newton, KS). Expired
gases were analyzed using a TrueOne2400 Metabolic Measurement
System (ParMedics, Sandy, UT). Children performed
a modified Balke treadmill protocol. The test began
with a 3-min warm-up, during which the speed and grade
were gradually increased. During the test, the beginning
speed and grade were based on the participant’s estimated
aerobic fitness level, in accordance with the recommendations
of the American College of Sports Medicine (1).
Lower-fit participants began the test at a speed of 3.2 mph
and a grade of 6-, and higher-fit participants began the test at
a speed of 5 mph and a grade of 0-. The treadmill speed
remained constant during the test, and the grade changed
every 2 min, with a 2- increase for lower-fit participants
and a 2.5- increase for higher-fit participants. Relative peak
oxygen consumption (mLIkgj1Iminj1) was based on a maximal
effort when participants exhibited three of the following
four criteria: (a) plateau in oxygen consumption, (b) HR
within 10 bpm of age-predicted maximum, (c) RER Q 1.10,
or (d) RPE on the Children’s OMNI Scale Q 9 (36).