In terms of energy used/calories burned, is it the same result when walking a mile as when running it? I ask because it would use more force to drive the legs and body when running, but it would take a shorter period of time than a walking pace, even though you would actually be moving the body through space for a longer period of time when walking. So do we go for the more time efficient running or less strenuous walking (not thinking about fitness benefits or goals of an individual, purely for comparison)?
Great question! There are many views about this topic, and it can be quite confusing to say the least. I will provide answers based on the fact that we will simply compare the two without associating cardiovascular benefits or fitness goals of a client.
There are many factors involved with this question, so let me start with basic physiology. The metabolic equivalent of intensity (MET) is a widely used physiological concept that expresses the energy cost of physical activities as a multiple of resting metabolic rate (RMR). It is defined as the ratio of work metabolic rate to a standard RMR of 1 kcal•kg-1•h-1 or 3.5 ml O2•kg-1•min-1. The MET value of many physical activities has been described in a compendium (see reference #2 below) ranging from sleeping to high intensity running. All activities are assigned an intensity level in METs, and the energy cost is calculated as the MET level multiplied by the standard RMR value. Interestingly, the author of the study, Ainsworth, indicated that it was developed to classify activities to standardize MET intensities in survey research and not to determine the exact cost of activity a person does. Among physiologists, however, the MET system is accepted to express energy expenditure in relation to body weight. The American College of Sports Medicine has defined light, moderate and heavy activity to associate with specific MET levels, and tables have been developed based on this system for exercise prescription.
In theory, the absolute distance of one mile should elicit the same energy expenditure, typically expressed as 100 calories. However, many have argued that this is not the case due to body weight and efficiency / economy / biomechanic differences. It is not likely that a 150 pound male will burn the same amount of calories that a 200 pound male will while covering a distance of one mile at the same absolute intensity. When relative intensity is applied, possibly based as a percentage of heart rate, then the two may be more similar in energy expenditure. However, notwithstanding to intensity, a larger mass expends more energy than a smaller mass. Analysis of the biomechanics associated with running and walking suggest that walking is more efficient at lower speed due to gait. At a lower speed, running is thought to be less efficient because of the energy loss due to the impact of the ground and bent knees. To further complicate the matter, ground force impact could be analyzed as well as ground terrain itself. This concept would certainly be better answered by an expert in biomechanics, physics and/or engineering.
According to the Compendium of Physical Activities, MET values are assigned to the following activities:
*mph: miles per hour
Based on this data, it would be justifiable to conclude that simply from an energy expenditure standpoint, running would elicit more calories burned than walking. This, of course, does not account for any biomechanical / economical or body weight variables, but it accounts for the physiology of energy expenditure as a whole.
- Byrne, NM et al. (2005). Metabolic equivalent: one size does not fit all. J Appl Physiol 99: 1112-1119.
- Ainsworth BE et al. (2000). Compendium of Physical Activities: an update of activity codes and MET intensities. Med Sci Sports Exerc 32: 498-516.