This study had a twofold purpose: i) to develop a regression equation to estimate metabolic equivalent (MET) in walk/run by heart rate increment above rest (NetHR), and; ii) to determine NetHR thresholds for light, moderate, and vigorous physical activity (PA), from middle aged to elderly. Sample 1 (prediction sample) comprised 39 subjects (19 male and 20 female), with 58.2 ± 11.0 years old. Sample 2 (validation sample) comprised 40 subjects (18 male and 22 female) with 63.3 ± 7.0 years old. Each participant did the following activities in sequence, a 15min rest period in supine position, walk at 3km/h, walk at 4.5km/h, and walk at 6km/h, for 6 min at each walk velocity interval. The oxygen up-take (VO₂) and heart rate (HR) were continuously and simultaneously assessed. A hierarchical linear model was used to analyze the relationship between metabolic equivalent (MET) and NetHR. The regression equation for MET prediction was: MET = 1.265780 + 0.109479 NetHR. The NetHR thresholds (upper limit) for light, moderate and vigorous PA were 16 and 35 and 70 bpm, respectively. NetHR is a practical, valid and non-invasive method to prescribe physical activity, taking in account individual characteristics (HR at rest combined with NetHR) in middle-aged to older adults.