Caloric Expenditure on Road Bike

By Bob Seebohar

Date Released :
10 May 2006


Question:
How would I figure out caloric expenditure for someone who did outdoor cycling on a road bike if they only gave me miles per hour average and distance in miles? The leg ergometry metabolic equations usually need a power output in watts, and I do not believe I can get that from just this information.
Answer:
Caloric or energy expenditure is commonly measured in exercise physiology laboratories using the method of indirect calorimetry. Indirect calorimetry is a measurement of oxygen uptake, which can determine energy expenditure. There is a direct relationship between calories burned and oxygen consumed; therefore, it is an easy measurement to complete in a lab environment.
However, conducting indirect calorimetry tests using a metabolic cart with clients is not always the most convenient method for determining energy expenditure. Metabolic equations published in the American College of Sports Medicine Guidelines for Exercise Testing and Prescription require a power measurement to determine energy expenditure; therefore, these equations cannot be used based on the information provided by the client. However, there is another method for determining energy expenditure when power measurements are not known.
By obtaining the metabolic equivalent (MET) value for a given intensity of exercise, it is possible to further calculate energy expenditure. The Compendium of Physical Activities, an update of activity codes and MET intensities provides a detailed list of various activities and their corresponding MET value. Specifically, there are five bicycling examples presented that would apply to this client:
 1011.9 mph, leisure, slow effort, 6 METs
 1213.9 mph, leisure, moderate effort, 8 METs
 1415.9 mph, racing or leisure, fast, vigorous effort, 10 METs
 1619 mph, racing/not drafting or <19 mph drafting, very fast, racing, 12 METs
 >20 mph, racing, not drafting, 16 METs
Evaluation steps include the following:
 Determine MET value for client
 Calculate VO2 in mL/kg/min
 MET x 3.5 ml/kg/min = VO2 ml/kg/min
 Express VO2 in L/min
 VO2 ml/kg/min x kg (body weight)/1000 = VO2 L/min
 Calculate energy expenditure
 VO2 L/min x 5 = calories expended per minute
 Multiply this number by 60 to determine calories expended per hour.
Example
A client weighs 80 kilograms and bicycles at an average speed of 19 miles per hour.
 Determine MET value for client
 Calculate VO2 in mL/kg/min
 MET x 3.5 ml/kg/min = VO2 ml/kg/min
 12 x 3.5 ml/kg/min = 42 ml/kg/min
 Express VO2 in L/min
 VO2 ml/kg/min x kg (body weight)/1000 = VO2 L/min
 42 x 80/1000 = 3.4 L/min
 Calculate energy expenditure
 VO2 L/min x 5 = calories expended per minute
 3.4 L/min x 5 = 17 calories expended per minute
 Multiply this number by 60 to determine calories expended per hour: 17 x 60 minutes = 1020 calories expended per hour.
Remember, equations used to predict energy expenditure are most appropriate for steady state submaximal aerobic exercise. Variables that can change the mechanical efficiency of the person exercising (wind, terrain) can result in a loss of accuracy. Obtaining power measurement data would provide a more accurate determination of energy expenditure as the ACSM equations could then be utilized, but the aforementioned method of calculating energy expenditure from speed (miles per hour) can be used as a guide.
References:
 Ainsworth, B et al. (2000). Compendium of Physical Activities: an update of activity codes and MET intensities. Medicine and Science in Sports and Exercise, Vol. 32, No. 9, Suppl., pp S498S516.
 Lippincott, Williams and Wilkins. ACSM’s Guidelines for Exercise Testing and Prescription, Sixth Edition. 2000.