Exercise efficiency, or economy of motion describes the bodies’ ability to translate chemical energy into locomotion. In this post, the best practices for measuring economy/efficiency are described. One of the main benefits of measuring exercise economy is that it can be accomplished at low work-rates. This allows less taxing testing environments, with minimal devices making these very accessible measurements.
Measuring Efficiency and Economy
While exercise efficiency/economy are generally used synonymously, their experimental determination is slightly different. Measurements of efficiency are the ratio of chemical energy required for a given power/speed output while measurements of economy describe the oxygen requirement for a speed/power output.
Efficiency – power output/energy required to maintain a speed or power
Economy – power output/oxygen required to maintain a speed or power
Given these differentiations, four major measures of efficiency and economy have been tested and established. The four different measures are given below:
*Gross efficiency (%) – Work rate (W)/energy expenditure (J/s).
*Delta efficiency (%) – Change in work rate/change in energy expenditure
Cycling Economy (kJ/L) – Power output (J/s) * 60 (s/min) /oxygen consumption (L/s) * 1000 (J/kJ)
Running Economy (ml O2/kg/km) – VO2 * 60 min/hr * Body Mass (kg)-1 * Running Speed (km/h)
In order to calculate efficiency, caloric energy expenditure must be estimated. The estimation of energy expenditure if dependent on both oxygen consumption and carbon dioxide production and can be determined by the following equation:
Energy Expenditure (J/s) – [(3.869 x VO2) + (1.195 x VCO2)] x (4.1896/60) x 1000
Required Testing Apparatus
- Treadmill, cycle or rowing ergometer.
- Metabolic device with an Oxygen sensor (No CO2 sensor necessary). *Denotes Variables that require CO2 Sensor
- Cadence control (when comparing between participant populations) such as a metronome.
Measuring efficiency/economy is highly dependent on the speed/power output and cadence. Therefore careful selection of both load and cadence is important to be able to compare individuals within a study or an individual at different times. For cycling, cadence should be between 80-100 bpm, while running should be somewhere around 180 bpm. When selecting speed/power output make sure that the intensity of the load selected is well below the athletes’ threshold. This allows steady-state oxygen consumption to be reached. If you are testing a wide range of training capacities try to make the load low enough but not so low that athlete’s cycling or running gait is changed. Typically, power outputs of 75, 125, and 175w should suffice. When testing an individual have the athlete select their most natural/comfortable cadence and test them at three submaximal stages. Note these and any cadence differences between tests.
Example Experimental Protocol
In order to determine efficiency and economy variables for cycling or running at least two submaximal steady-state exercise stages must be completed especially when trying to measure Delta Efficiency. Typically, it takes the body 3-6 minutes of continuous load exercise to reach steady-state oxygen consumption thus stage duration should be greater than 5 minutes. When calculating these values it is advisable to use an average of THE LAST 30s to 2 minutes of the stage to ensure steady state was attained. An example economy measurement protocol could be as follows:
- On a cycle ergometer, set the load to 75w and have the athlete maintain a cadence of 90rpm for 7 minutes,
- Maintaining 90rpm have the athlete cycle at 125w for 7 minutes,
- Increase the wattage to 175w and have the athlete maintain 90rpms for another 7 minutes.
- Total Time: 21 minutes
- Repeat test after each mesocycle (4-8 weeks)
Calculating economy/efficiency values for an athlete or group of participants can allow for comparison of how well each individual is able to translate chemical energy into mechanical energy for movement. Testing these values requires very little testing equipment and does not require an athlete to dig too deep, in fact, this test could be used as a warm-up before an all-out session. In the next blog post I will walk through an example of how to calculate Gross and Delta Efficiency as well as Cycling Economy.