1.2. Energy expenditure

The initial Compendium of Physical Activities (developed in 1989 and published in 1993) presented intensities in physical activities based on the rate of energy expenditure expressed in METs and estimated from similar activities with a known MET value. The energy cost of an activity is normally measured through direct and indirect calorimetry methods such as the respiratory calorimetry (Bray, Wong, Morrow, Butte and Pivarnik, 1994) or the doubly labelled water measure (Davidson, McNeil, Haggarty, Smith and Franklin, 1997). Other methods include using accelerometers (Jakicic, Winters, Lagally, Ho, Robertson and Wing, 1999) or through heart rate monitoring (Kirsten, Hennings, Mitchell and Wareham, 2001). ACSM guidelines for Exercise Testing and Prescription (1995) express energy expenditure for the various gaits in horseback riding of galloping = 8.2 METs, trotting = 6.6 METs and walking = 2.4 METs.