Table 2. – Classifications of physical exercise.

Classification		Features
By predominant metabolic pathway	Alactic anaerobic	High intensity, very short duration
	Lactic anaerobic	High intensity, short duration
	Aerobic	Low or medium intensity, prolonged duration
By pace	Fixed, constant, or continuous	No change of pace over time
	Variable, intermittent, or interval	Pace changes over time
By relative intensity*	Low or light	Easy to breathe, barely short of breath (Borg < 4)
	Medium or moderate	Breathing faster and labored, but still controlled. Can speak a sentence (Borg 4–7)
	High or heavy	Breathing very rapid and labored; short or out of breath. Barely able to speak (Borg > 7)
By muscle mechanics	Static	There is no movement; mechanical work is zero
	Dynamic	Involves movement; mechanical work is positive or negative

*A Borg scale of 0 to 10 was considered.