Determining The Electromyographic Fatigue Threshold Following a Single Visit Exercise Test

The overall goal of this procedure is to describe the electromyographic fatigue threshold, which demarcates between non fatiguing and fatiguing exercise workloads. This is accomplished by first preparing the participant's leg for the placement of the EMG electrodes. The second step is to place the EMG electrodes on the desired superficial quadriceps femoral muscles.

Next, the EMG signal is checked to determine the signal to noise ratio and improve electrode placement if necessary. The final step is to have the participant perform an incremental cycle ergometry test to voluntary exhaustion. Ultimately, the EMG fatigue threshold mathematical model is used to estimate the power output at which theoretically, the participant can cycle indefinitely without an increase in EMG amplitude.

The main advantage of this technique over existing methods is that we use surface EMG in a single incremental exercise test. This method can provide insight into identifying the highest exercise intensity that demarcates between non fatiguing and fatiguing exercise. Demonstrating the procedure will be Charlie Anderson and Jacob Blackmore.

Second year students in the doctorate in physical therapy program Begin by preparing the participant's leg and accurately locating the vastus laterals muscle as described in the accompanying text protocol. Then place gel coated silver, silver chloride electrodes over the vastus laterals without removing the adhesive shield. Mark the location where the gel portion of the electrode makes contact with the muscle and ensure the inter electrode distance is 20 millimeters from center to center.

Next, use a piece of 60 grit sandpaper to gently abraid these two areas, removing the superficial layer of the skin. Be sure to ask the participant their level of discomfort during the abrasion and stop when the participant indicates the area is warm. Clean the abbra areas with an alcohol swab and allow the area to air dry for a few seconds.

Then ask the participant to contract the quadriceps femoral muscles so that it is possible to palpate the vastus laterals. Place the EMG electrodes on the abbra sites taking care not to place the electrodes on the ileal tidal band. Place the reference electrode on a bony attachment site such as the asis, so as not to interfere with movement of the lower limbs during exercise, adjust the cycle ergometer specifically for each participant as described in the accompanying text protocol.

Then have the participant put on a heart monitor in order to document their heart rate throughout the exercise test. Set up the EMG system to take recordings at ten second intervals every 20 seconds. Also, begin monitoring the heart rate by recording the values on a data collection sheet.

During each stage, have the participants start cycling and gradually increase their cadence to 70 revolutions per minute after they reach 70 revolutions per minute, increase the power output on the cycle ergometer to 50 watts. Have the participants cycle at this power output for approximately two to three minutes as a warmup, and begin taking EMG signal recordings after the warmup period. Increase the power output by 25 watts every two minutes until the participant is no longer able to maintain 70 revolutions per minute cadence or requests that the test be stopped.

Open the E-M-G-F-T data file using a commercial statistical program. The first column is labeled time, whereas the subsequent columns are labeled for each power output. For each power output, there is the corresponding EMG amplitude for each 22nd interval for each power output, the time versus EMG amplitude is plotted.

The x axis is labeled as time, and the Y axis is labeled EMG amplitude. Perform linear regression for the time versus EMG amplitude relationship. For each power output.

Identify the highest power output without a statistically significant slope and the lowest power output with a statistically significant slope. The EMG fatigue threshold, therefore is the average of these two power outputs. Shown here is the combined power output for a single participant of the fatigue test.

This particular participant made it through 11 two minute test periods where the power was increased by 25 watts every two minutes. The power output at 200 watts is the highest power output with a non-significant slope, whereas the power output at 225 watts is the lowest power output with a significant slope. The average of these two power outputs equals 213 watts, which is the EMG fatigue threshold for this particular participant.

Once mastered, this testing procedure can be completed within one hour. After watching this video, you should have a good understanding of how to assess neuromuscular fatigue using a non-invasive method such as surface EMG.