TABLE 4.

Descriptive examination of the correlations and differences between other indirect methods and the measured VO_2max.

Methods	Reference	Predicted VO2max	CE	t	r	ICC	MAE	MAPE (%)
		(mL⋅kg–1⋅min–1)	(mL⋅kg–1⋅min–1)				(mL⋅kg–1⋅min–1)
Equation 1	Klusiewicz et al., 2016
	Male (n = 23)	65.7 ± 6.1	5.0 ± 5.6	4.310*	0.568*	0.427*	6.0 ± 4.5	10.3
	Female (n = 22)	59.5 ± 5.9	2.8 ± 3.5	3.701*	0.807*	0.723*	3.9 ± 2.3	6.9
	All (n = 45)	62.7 ± 6.7	3.9 ± 4.8	5.513*	0.721*	0.604*	5.0 ± 3.8	8.6
Equation 2	Marsh, 2012
	Male (n = 29)	62.1 ± 2.8	-0.2 ± 2.8	-0.333	0.602*	0.600*	2.2 ± 1.7	3.5
	Female (n = 16)	57.8 ± 2.6	2.2 ± 4.5	1.954	0.125	0.099	3.6 ± 3.8	6.9
	All (n = 45)	60.6 ± 3.4	0.7 ± 3.7	1.238	0.655*	0.615*	2.7 ± 2.5	4.8
Equation 3	Marsh, 2012
	Male (n = 29)	64.0 ± 3.5	1.7 ± 2.3	4.116*	0.787*	0.704*	2.3 ± 1.7	3.6
	Female (n = 16)	59.2 ± 3.4	3.6 ± 5.2	2.728*	0.008	0.006	4.8 ± 4.2	9.0
	All (n = 45)	62.3 ± 4.2	2.4 ± 3.7	4.352*	0.671*	0.586*	3.1 ± 3.0	5.6

CE, constant error, arithmetic mean of the difference between estimated and measured VO_2max; t, t value from paried sample t-test; r, pearson correlation coefficient; ICC, intraclass correlation coefficient; MAE, mean absolute error; and MAPE, mean absolute percentage error. *Statistically significant (P ≤ 0.05). Equation 1: VO_2max (mL⋅kg^–1⋅min^–1) in males = (3.2131 + 0.0076 × PWC170) / body mass, VO_2max (mL⋅kg^–1⋅min^–1) in females = (2.4138 + 0. × PWC170) / body mass. Equation 2: VO₂ (mL⋅kg^–1⋅min^–1) = (speed (m⋅min^–1) × 0.2) + (gradient × speed (m⋅min^–1) × 0.9) + 3.5, where the estimated maximal speed was calculated as following steps, (1) linear regression was used based on steady-state heart rate values and running speed were obtained for each stage of the submaximal running test, (2) the linear line was then extrapolated to estimated maximal heart rate (220 – age) to determine the value of estimated maximal speed. Equation 3: VO_2max (mL⋅kg^–1⋅min^–1) = VO₂-stage 4 + b (HRmax – HR-stage 4), where the VO₂-stage 4 was calculated based on the steady-state HR in stage 4 of the submaximal running test as the Eq. (2), HRmax refers to estimated maximal heart rate (220 – age), and the additional coefficient b is calculated from b = (VO2-stage 4 – VO2-stage 3) / (HR-stage 4 – HR-stage 3), which is the ratio of the difference between the estimated VO2 of last two stages of submaximal running test and corresponding change of steady-state heart rate.