Table 2.

Cardiovascular and Metabolic Data

	Incline	Level	Decline	Age Effect
Heart rate, beats per minute
Young	103.7 ± 4.5	90.6 ± 4.1	85.2 ± 4.3	93.2 ± 4.3
Old	119.4 ± 4.6	105.8 ± 4.1	99.6 ± 4.3	108.3 ± 4.2*
RER, unitless
Young	0.88 ± 0.02	0.87 ± 0.01	0.91 ± 0.02	0.88 ± 0.02
Old	0.86 ± 0.02	0.81 ± 0.02	0.83 ± 0.02	0.83 ± 0.02*
VO2, mL·kg−1·min−1
Young	16.9 ± 0.4	12.0 ± 0.4	9.3 ± 0.5	12.7 ± 0.3
Old	17.2 ± 0.4	12.9 ± 0.4	11.1 ± 0.5	13.8 ± 0.4*
Cw, J·kg−1·m−1
Young	4.28 ± 0.15	2.61 ± 0.14	1.67 ± 0.19	2.86 ± 0.16
Old	4.58 ± 0.13	3.09 ± 0.12	2.46 ± 0.14	3.38 ± 0.13†
M. activation, %
Young	45.8 ± 4.4	37.2 ± 3.6	37.3 ± 4.9	40.1 ± 4.3
Old	45.8 ± 1.2	80.2 ± 5.1	75.1 ± 5.2	67.1 ± 3.9†
M. coactivation, %
Young	20.6 ± 2.1	20.8 ± 2.6	18.3 ± 1.4	19.9 ± 2.1
Old	50.9 ± 3.0	52.9 ± 6.4	46.9 ± 4.0	50.3 ± 4.5*

Notes: Values are mean ± SD. C_w = metabolic cost of walking; M. activation, summed electromyographic muscle activation in percent of maximum voluntary contraction for the vastus lateralis, biceps femoris, tibialis anterior, and lateral gastrocnemius acting as agonist muscles during the gait cycle; M. coactivation, summed electromyographic muscle activation in percent of maximum voluntary contraction for the vastus lateralis, biceps femoris, tibialis anterior, and lateral gastrocnemius acting as antagonist muscles during the gait cycle; RER = respiratory exchange ratio.

^*Age main effect.

^†Age by condition interaction effect.