This project was funded by, in part, by start-up funds from Wayne State University to M.H. Malek.

All procedures were approved by the University Institutional Review Board for Human Subjects.
1. Preparation of the Participant&#8217;s Leg
<ol>
	<li>Have the participant neatly roll up their shorts for the desired leg. Then tape the shorts so that the quadriceps femoris muscle group is exposed and draw a line around the area the participant needs to shave.</li>
	<li>IMPORTANT: Have the participant shave their leg before the test rather than the previous day as this ensures that there are no stubbles which may interfere with the EMG signal.</li>
	<li>Once the participant has finished shaving the desired area of the leg, clean the shaved area with rubbing alcohol to ensure there are no remnants of the shaving gel (or cream) which can interfere with the EMG signal.</li>
</ol>
2. Measurement of Leg for Electrode Placement
<ol>
	<li>In order to place the EMG electrode on the vastus lateralis muscle, make the following measurements
	<ol>
		<li>Have the participant stand straight facing the researcher.</li>
		<li>Locate the anterior spina iliaca superior (ASIS) and the lateral side of the patella. The ASIS is the hip bone; palpate it by placing the hand on either side of the abdomen below the umbilicus.</li>
		<li>With a tape measure, measure the distance between the two locations identified above and take 2/3 of that value on the line from the ASIS to the lateral side of the patella. Note: Further information regarding placement of EMG electrodes can be found on the SENIAM (Surface Electromyography for the Non-Invasive Assessment of Muscles) URL: http://www.seniam.org/</li>
	</ol>
	</li>
</ol>
3. Placement of the EMG Electrodes
<ol>
	<li>After the location of the vastus lateralis has been identified, take the EMG electrodes (most researchers use commercially available disposable Ag-Ag Cl electrodes) and place over the vastus lateralis without removing the adhesive shield. Then with a pen mark the area where the gel portion of the electrode makes contact with the muscle. Ensure that the interelectrode distance is 20 mm center-to-center.</li>
	<li>Use a piece of sandpaper (60 coarse) to gently abrade these two areas to remove the superficial layer of the skin. During this time, ask the participant their level of discomfort. Stop abrading when the participant indicates the area is warm.</li>
	<li>Clean the abraded areas with a towel that is dampened with rubbing alcohol or an alcohol swab. Allow the area on the leg to dry before placing the EMG electrodes.</li>
	<li>Place the EMG electrodes on the sites that were abraded (Figure 2). Take care not to place the electrodes on the iliotibial band (IT band). Ask the participant to contract the quadriceps femoris muscles in order to palpate the vastus lateralis. Place the electrodes on the muscle to ensure it is not on the IT band. Note: If the electrodes on the IT band, the EMG signal would be dampened when the participant is asked to maximally contract.</li>
	<li>Place the reference electrode (3rd electrode) on a boney attachment site such as the ASIS thus not interfering with movement of the lower limbs during the exercise bout.</li>
</ol>
4. Checking the EMG Signal
<ol>
	<li>Prior to starting the exercise test, check the interelectrode impedance. 
	Note: This step is critical because if the signal has too much noise then the EMG data collected during the exercise test will be invalid.
	<ol>
		<li>Have the participant sit in a chair and connect the EMG leads to their respective electrodes attached to the participant&#8217;s leg.</li>
		<li>At this point, have the participant relax their leg, having no tension in the muscle. Then after about 30 sec of relaxation, have the participant maximally contract their quadriceps femoris muscles for 5 sec and then go back to being completely relaxed.</li>
		<li>When performing the task above (step 4.1.2), record the participants EMG signal on the computer.</li>
		<li>Ensure that the interelectrode impedance is &#60;2,000 ohms. Moreover, if a voltmeter is available in the laboratory, then check the baseline noise and keep below 5 &#181;V. In addition, set the sampling frequency at 1,000 Hz.</li>
	</ol>
	</li>
</ol>
5. Setting-up the Cycle Ergometer
<ol>
	<li>After checking the interelectrode impedance, have the participant move from the chair to the cycle ergometer.</li>
	<li>Have the participant stand next to the cycle ergometer and raise their knee until the thigh is parallel with the ground. Then have the participant hold this position and adjust the seat height to match the same height as the participant&#8217;s thigh.</li>
	<li>Thereafter, have the participant sit on the cycle ergometer seat and then pedal a couple times while asking them if they are comfortable with the seat height. If needed, adjust the seat height.</li>
	<li>Ensure that the participant&#8217;s legs are near full extension with a slight bend (~5&#176;) in the knees during each pedal revolution.</li>
	<li>Before starting the test, have the participant wear a polar heart rate monitor so that heart rate can be documented throughout the exercise test.</li>
</ol>
6. Performing the EMG Fatigue Threshold Protocol
<ol>
	<li>Have the participant start cycling and gradually increase their cadence to 70 revolutions/min. Then increase the power output on the cycle ergometer to 50 W.</li>
	<li>Have the participant cycle at this power output for approximately 2-3 min. 
	Note: This is a low intensity exercise and will serve as the warm-up.</li>
	<li>After the warm-up period, increase the power output by 25 W every 2 min until the participant is no longer able to maintain the 70 revolutions/min cadence or requests that the test be stopped. 
	Note: It should be noted that during the exercise test, the EMG signal is recorded for 10 sec epochs during each 2 min stage for sec 10&#8211;20, 30&#8211;40, 50&#8211;60, 70&#8211;80, 90&#8211;100, and 110-12021. Most EMG systems will have an option to set the automatic recording at the desired interval. Thus, for each stage there should be 6 data files.</li>
	<li>Once the incremental test has concluded, have the participant perform a cool down at 50 W. Check that the length of the cool down corresponds with having the participant&#8217;s heart rate return to the value during the warm-up phase. Monitor this by checking the participant&#8217;s heart rate using the polar heart rate monitor.</li>
	<li>Once the cool down is completed, remove the EMG leads and have the participant step off the cycle ergometer and return to the chair. Then carefully remove the EMG electrodes and wipe the areas with a clean towel dampened with rubbing alcohol or an alcohol swab.</li>
</ol>
7. Processing the EMG Signal
<ol>
	<li>After the test is completed, process the raw EMG data files that were collected during the exercise test so that the data can be used to determine the EMG fatigue threshold.
	<ol>
		<li>Perform processing of the EMG signal with either the software used to collect the EMG signal or custom written software using various platforms such as MATLAB or LabVIEW.</li>
		<li>Filter the collected EMG signals using a band-pass filter. Use a setting of 10 to 500 Hz. Note: This alters the frequency of the signal so that low frequency artifacts due to movement of the EMG leads (&#60;10 Hz), and high frequency artifacts from the environment (&#62;500 Hz), are removed. Use a notch filter of 60 Hz if there is any interference from the power supply of the computer or EMG system.</li>
		<li>Once the signal has been filtered, determine the signal amplitude by calculating the root mean square value of the signal: Square each of the data points, sum them, divide by the number of data points, then take the square root of the resulting value. Perform these calculations using the aforementioned software.</li>
	</ol>
	</li>
</ol>
8. Determining the EMG Fatigue Threshold for Each Participant
<ol>
	<li>Perform the following steps for each participant.
	<ol>
		<li>After the EMG signal has been processed; use a statistical program (e.g.: GraphPad Prism) and label the first column &#8220;Time&#8221; and the subsequent columns with the power outputs used for the test.</li>
		<li>For each power output, fill-in the corresponding EMG amplitude value for each 20 sec interval.</li>
		<li>For each power output, analyze the time (x-axis) vs EMG amplitude (y-axis) relationship with linear regression to determine if the slope of the regression line is significantly (p &#60;0.05) different from zero.</li>
		<li>After performing the linear regression analyses for all power outputs, identify the highest power output with a non-significant (p &#62;0.05) slope.</li>
		<li>Then identify the lowest power output with a significant (p &#60;0.05) slope.</li>
		<li>Once these two power outputs have been identified, add them and divide by 2; the resultant power output is the estimated EMG fatigue threshold.</li>
	</ol>
	</li>
</ol>

<ol>
	<li>Hendrix, C. R., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Comparison+of+critical+force+to+EMG+fatigue+thresholds+during+isometric+leg+extension.">Comparison of critical force to EMG fatigue thresholds during isometric leg extension.</a> Medicine and science in sports and exercise. 41, 956-964 (2009).</li><li>Herda, T. J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Quantifying+the+effects+of+electrode+distance+from+the+innervation+zone+on+the+electromyographic+amplitude+versus+torque+relationships.">Quantifying the effects of electrode distance from the innervation zone on the electromyographic amplitude versus torque relationships.</a> Physiological measurement. 34, 315-324 (2013).</li><li>Ryan, E. D., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Inter-individual+variability+among+the+mechanomyographic+and+electromyographic+amplitude+and+mean+power+frequency+responses+during+isometric+ramp+muscle+actions.">Inter-individual variability among the mechanomyographic and electromyographic amplitude and mean power frequency responses during isometric ramp muscle actions.</a> Electromyography and clinical neurophysiology. 47, 161-173 (2007).</li><li>Beck, T. W., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+influence+of+electrode+placement+over+the+innervation+zone+on+electromyographic+amplitude+and+mean+power+frequency+versus+isokinetic+torque+relationships.">The influence of electrode placement over the innervation zone on electromyographic amplitude and mean power frequency versus isokinetic torque relationships.</a> Journal of neuroscience. 162, 72-83 (2007).</li><li>Beck, T. W., Stock, M. S., DeFreitas, J. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Time-frequency+analysis+of+surface+electromyographic+signals+during+fatiguing+isokinetic+muscle+actions.">Time-frequency analysis of surface electromyographic signals during fatiguing isokinetic muscle actions.</a> Journal of strength and conditioning research / National Strength, &amp; Conditioning Association. 26, 1904-1914 (2012).</li><li>Evetovich, T. K., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mean+power+frequency+and+amplitude+of+the+mechanomyographic+signal+during+maximal+eccentric+isokinetic+muscle+actions.">Mean power frequency and amplitude of the mechanomyographic signal during maximal eccentric isokinetic muscle actions.</a> Electromyography and clinical neurophysiology. 39, 123-127 (1999).</li><li>Blaesser, R. J., Couls, L. M., Lee, C. F., Zuniga, J. M., Malek, M. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Comparing+EMG+amplitude+patterns+of+responses+during+dynamic+exercise:+polynomial+versus+log-transformed+regression.">Comparing EMG amplitude patterns of responses during dynamic exercise: polynomial versus log-transformed regression.</a> Scandinavian journal of medicine, &amp; science in sports. In press, (2015).</li><li>Briscoe, M. J., Forgach, M. S., Trifan, E., Malek, M. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Validating+the+EMGFT+from+a+single+incremental+cycling+testing.">Validating the EMGFT from a single incremental cycling testing.</a> International journal of sports medicine. 35, 566-570 (2014).</li><li>Zuniga, J. M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Neuromuscular+and+metabolic+comparisons+between+ramp+and+step+incremental+cycle+ergometer+tests.">Neuromuscular and metabolic comparisons between ramp and step incremental cycle ergometer tests.</a> Muscle. 47, 555-560 (2013).</li><li>Mastalerz, A., Gwarek, L., Sadowski, J., Szczepanski, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+influence+of+the+run+intensity+on+bioelectrical+activity+of+selected+human+leg+muscles.">The influence of the run intensity on bioelectrical activity of selected human leg muscles.</a> Acta of bioengineering and biomechanics / Wroclaw University of Technology. 14, 101-107 (2012).</li><li>Basmajian, J. V., De Luca, C. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Muscles alive, their functions revealed by electromyography. , (1985).</li><li>Vries, H. A., Moritani, T., Nagata, A., Magnussen, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+relation+between+critical+power+and+neuromuscular+fatigue+as+estimated+from+electromyographic+data.">The relation between critical power and neuromuscular fatigue as estimated from electromyographic data.</a> Ergonomics. 25, 783-791 (1982).</li><li>Vries, H. A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+method+for+estimating+physical+working+capacity+at+the+fatigue+threshold+(PWCFT).">A method for estimating physical working capacity at the fatigue threshold (PWCFT).</a> Ergonomics. 30, 1195-1204 (1987).</li><li>Vries, H. A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Factors+affecting+the+estimation+of+physical+working+capacity+at+the+fatigue+threshold.">Factors affecting the estimation of physical working capacity at the fatigue threshold.</a> Ergonomics. 33, 25-33 (1990).</li><li>Astrand, I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+physical+work+capacity+of+workers+50-64+years+old.">The physical work capacity of workers 50-64 years old.</a> Acta physiologica Scandinavica. 42, 73-86 (1958).</li><li>Hettinger, T., Birkhead, N. C., Horvath, S. M., Issekutz, B., Rodahl, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Assessment+of+physical+work+capacity.">Assessment of physical work capacity.</a> Journal of Applied Physiology. 16, 153-156 (1961).</li><li>Smith, J. L., Karwowsk, W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> International encyclopedia of ergonomics and human factors. , (2006).</li><li>Kenny, G. P., Yardley, J. E., Martineau, L., Jay, O. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Physical+work+capacity+in+older+adults:+implications+for+the+aging+worker.">Physical work capacity in older adults: implications for the aging worker.</a> American journal of industrial medicine. 51, 610-625 (2008).</li><li>Matsumoto, T., Ito, K., Moritani, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+relationship+between+anaerobic+threshold+and+electromyographic+fatigue+threshold+in+college+women.">The relationship between anaerobic threshold and electromyographic fatigue threshold in college women.</a> European journal of applied physiology. 63, 1-5 (1991).</li><li>Guffey, D. R., Gervasi, B. J., Maes, A. A., Malek, M. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Estimating+electromygraphic+and+heart+rate+fatigue+threshold+from+a+single+treadmill+test.">Estimating electromygraphic and heart rate fatigue threshold from a single treadmill test.</a> Muscle. 46, 577-581 (2012).</li><li>Camic, C. L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+influence+of+the+muscle+fiber+pennation+angle+and+innervation+zone+on+the+identification+of+neuromuscular+fatigue+during+cycle+ergometry.">The influence of the muscle fiber pennation angle and innervation zone on the identification of neuromuscular fatigue during cycle ergometry.</a> Journal of electromyography and kinesiology : official journal of the International Society of Electrophysiological Kinesiology. 21, 33-40 (2011).</li></ol>

The authors have nothing to disclose.

We here present a method for determining neuromuscular fatigue in the quadriceps femoris muscles for dynamic exercise. This method provides a straightforward and non-invasive approach to using surface EMG. Moreover, the versatility of this method is that researchers can adapt it to other modes of exercise such as the treadmill20.
Theoretically, for intensities at or below the EMG fatigue threshold the participant should be able to sustain the exercise workbout indefinitely12,13. Briscoe et al.8 validated the EMG fatigue threshold for cycle ergometry. On separate occasions each participant exercised at 70%, 100%, and 130% of their EMG fatigue threshold. The authors found that for 70% and 100% of the EMG fatigue threshold participants did not have increased EMG amplitude during the exercise workload8. For the workload at 130% of EMG fatigue threshold, however, participants exhibited a significant increase in EMG amplitude8. Briscoe et al.8 concluded that the EMG fatigue threshold for cycle ergometry was a valid protocol to determine neuromuscular fatigue during continuous exercise.
With regard to critical steps in the protocol and troubleshooting consider the following. If there is too much noise in the EMG signal when performing step 4.1.2 then first check the connection between the EMG electrodes and the device recording the signal. Oftentimes, the EMG leads may not be connected properly to the EMG electrode. Second, the areas where the electrodes are placed need to be free of any hair and feel smooth to the touch rather than rough (i.e., shaving stubbles). Therefore, ensure that all hair is thoroughly removed in locations where the EMG electrode will be placed. Also, it is important to clean the area once the abrading is completed. Again, the goal is to have a clean and smooth surface. Third, the center area of the EMG electrode should not be dry and if so use conductance gel (such as those used for ultrasound) as a supplement. Make sure to use the gel sparingly, because excess gel may interfere with the adhesiveness of the EMG electrode. Taken together, these items are common culprits which increase the noise in the EMG signal and thus contaminating the data.
Although the EMGFT protocol is versatile there are potential limitations to its application in a clinical setting. For example, certain clinical populations may not tolerate the testing protocol. That is, while the increase in workload can be modified (i.e., 5 W instead of 25 W per stage) patients with severe respiratory and/or cardiac illnesses may prematurely fatigue during the initial stages of the test. Another potential limitation is that the quadriceps femoris muscles are all activated during cycle ergometry; however, the EMG signal is being recorded from only one of these muscles. To date, no studies have determined the EMGFT across the three superficial quadriceps femoris muscles for cycle ergometry to identify whether there are differences between muscles.
In summary, the method of estimating the EMG fatigue threshold from a single incremental exercise test is a useful tool for assessing neuromuscular fatigue during dynamic exercise. Moreover, this test provides an objective method of determine of the efficacy of various interventions that attenuate muscle fatigue.

Surface electromyography (EMG) is a noninvasive approach of studying motor unit recruitment during isometric1-3, isokinetic4-6, or continuous7-10 muscle action. The amplitude of the EMG signal represents muscle activation which consists of the number of motor units activated, the firing rate of the motor units, or both11. The concept of the EMG fatigue threshold is used to indicate the highest workload in which an individual can exercise indefinitely without an increase in EMG amplitude8.
It is important to briefly discussion the origin of the EMG fatigue threshold. The original study by deVries et al.12 involved a protocol that consisted of multiple (usually 3 to 4) discontinuous work bouts, where the EMG amplitude was plotted versus time for each work bout. The power output was then plotted versus the slope coefficients from the EMG amplitude versus time relationship, and then extrapolated to zero slope (the y-intercept)12. The authors12 originally termed that protocol the physical working capacity at the fatigue threshold (PWCFT). In a another study, deVries et al.13 used discontinuous work bouts, but used linear regression to find the first power output that resulted in a significant slope for the EMG amplitude versus time relationship. The authors13 also termed that protocol the PWCFT, creating some confusion in the literature. In a subsequent article, deVries et al.14 modified their earlier protocol13 and developed a continuous incremental protocol. The EMG amplitude was plotted against time for each power output and the PWCFT was defined as the average of the highest power output that resulted in no change in EMG amplitude over time and the lowest power output that resulted in an increase in EMG amplitude over time14.
It should be noted that the term PWC was originally introduced in the late 1950s15,16 and is synonymous with a plethora of literature (past, present, and across different countries) examining aerobic capacity at a given workload17. Moreover, the term is used in the ergonomic and industrial literature which focus on day-to-day productivity of workers performing repetitive action during 8 hour work days such as individuals in an assembly plant18.
The term EMG fatigue threshold was initially used by Matsumoto and colleagues19 after they modified the deVries12 protocol where the power output versus slope coefficients of the EMG amplitude versus time relationship are plotted and extrapolated to the point of zero slope. More recently, Guffey et al.20 and Briscoe et al.8 used the method of deVries et al.14 and the terminology of Matsumoto et al.19 to operationally define the EMG fatigue threshold. Moving forward, we recommend that the term EMG fatigue threshold be used. Thus, the EMG amplitude versus time relationship is plotted for each power output and then analyzed using linear regression analyses (Figure 1). To estimate the EMG fatigue threshold, the highest power output with a non-significant (p &#62;0.05) slope and the lowest power output with a significant (p &#60;0.05) slope is identified and then the average is calculated14. This protocol is simple, convenient, and completed within 15-20 min. Moreover, the incremental rate can be modulated based on the individual&#8217;s level of habitual physical activity, and therefore has potential applications in clinical settings.

<table><tbody><tr><td>839 E Monark cycle ergometer&amp;nbsp;</td><td>Monark Exercise AB</td><td>839 E</td><td></td></tr><tr><td>Heart rate monitor</td><td>Polar</td><td>Polar H1</td><td></td></tr><tr><td>Laptop</td><td>Dell Inspiron</td><td>varies</td><td>any laptop computer with USB slots should work.</td></tr><tr><td>EMG amplifiers</td><td>BioPac Systems, Inc.</td><td>100B</td><td>100C are the latest version</td></tr><tr><td>Disposable EMG electrodes</td><td>BioPac Systems, Inc.</td><td>EL-500</td><td></td></tr><tr><td>Sandpaper</td><td>Home Depot</td><td>9 inch x 11 inch 60 Grit course no-slip grip Advanced Sandpaper (3-Pack)</td><td></td></tr></tbody></table>

determining the electromyographic fatigue threshold following a single visit exercise test

Theoretically, the electromyographic (EMG) fatigue threshold is the exercise intensity an individual can maintain indefinitely without the need to recruit more motor units which is associated with an increase in the EMG amplitude. Although different protocols have been used to estimate the EMG fatigue threshold they require multiple visits which are impractical for a clinical setting. Here, we present a protocol for estimating the EMG fatigue threshold for cycle ergometry which requires a single visit. This protocol is simple, convenient, and completed within 15-20 min, therefore, has the potential to be translated into a tool that clinicians can use in exercise prescription.

As shown in Figure 1, for a single participant, each power output that is completed has six data points that represent the EMG amplitude for the vastus lateralis muscle. Therefore, in this example, the highest power output with a non-significant (p &#62;0.05) slope is 200 watts, whereas the lowest power output with a significant (p &#60;0.05) slope is 225 W. Therefore, for this participant the EMG fatigue threshold is 213 W. Once the EMG fatigue threshold is determined for each participant then inferential statistics can be performed.

<img alt="Figure 1" src="/files/ftp_upload/52729/52729fig1.jpg" /> 
Figure 1: Representative results for a single participant. Linear regression was performed for the EMG amplitude versus time relationship for each power output. The power output indicated by the red arrow (200 W) is the highest power output with a non-significant (p &#62;0.05) slope, whereas the power output indicated by the green arrow (225 W) is the lowest power output with a significant (p &#60;0.05) slope. The average of these two power outputs equal 213 W, which is the EMGFT.
<img alt="Figure 1" src="/files/ftp_upload/52729/52729fig2.jpg" /> 
Figure 2: Depiction of the electrode arrangement for the vastus lateralis muscle. In addition, we have provided a visual of where the EMG electrodes are placed for the rectus femoris and vastus medialis muscles. Specific directions for EMG electrode placed can be found on the following website: http://www.seniam.org.

Watch this Scientific Journal Video about Determining The Electromyographic Fatigue Threshold Following a Single Visit Exercise Test at JoVE.com

Determining The Electromyographic Fatigue Threshold Following a Single Visit Exercise Test

This protocol describes the electromyographic fatigue threshold which demarcates between nonfatiguing and fatiguing exercise workloads. This information could be used to develop a more individualized training program.

Theoretically, the electromyographic (EMG) fatigue threshold is the exercise intensity an individual can maintain indefinitely without the need to recruit ...

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12.5K Views.  Wayne State University. This protocol describes the electromyographic fatigue threshold which demarcates between nonfatiguing and fatiguing exercise workloads. This information could be used to develop a more individualized training program.

Video: Determining The Electromyographic Fatigue Threshold Following a Single Visit Exercise Test

Utilizing Transcranial Magnetic Stimulation to Study the Human Neuromuscular System

Transcranial magnetic stimulation (TMS) has been in use for more than 20 years 1, and has grown exponentially in popularity over the past decade. While the use of TMS has expanded to the study of many systems and processes during this time, the original application and perhaps one of the most common uses of TMS involves studying the physiology, plasticity and function of the human neuromuscular system. Single pulse TMS applied to the motor cortex excites pyramidal neurons transsynaptically 2 (Figure 1) and results in a measurable electromyographic response that can be used to study and evaluate the integrity and excitability of the corticospinal tract in humans 3. Additionally, recent advances in magnetic stimulation now allows for partitioning of cortical versus spinal excitability 4,5. For example, paired-pulse TMS can be used to assess intracortical facilitatory and inhibitory properties by combining a conditioning stimulus and a test stimulus at different interstimulus intervals 3,4,6-8. In this video article we will demonstrate the methodological and technical aspects of these techniques. Specifically, we will demonstrate single-pulse and paired-pulse TMS techniques as applied to the flexor carpi radialis (FCR) muscle as well as the erector spinae (ES) musculature. Our laboratory studies the FCR muscle as it is of interest to our research on the effects of wrist-hand cast immobilization on reduced muscle performance6,9, and we study the ES muscles due to these muscles clinical relevance as it relates to low back pain8. With this stated, we should note that TMS has been used to study many muscles of the hand, arm and legs, and should iterate that our demonstrations in the FCR and ES muscle groups are only selected examples of TMS being used to study the human neuromuscular system.

Transcranial magnetic stimulation (TMS) is a non-invasive tool to gain insight on the physiology and function of the human nervous system. Here, we present our TMS techniques to study cortical excitability of the upper limb and lumbar musculature.

Transcranial magnetic stimulation (TMS) has been in use for more than 20 years 1, and has grown exponentially in popularity over the past decade.  While ...

Force and Position Control in Humans - The Role of Augmented Feedback

During motor behaviour, humans interact with the environment by for example manipulating objects and this is only possible because sensory feedback is constantly integrated into the central nervous system and these sensory inputs need to be weighted in order meet the task specific goals. Additional feedback presented as augmented feedback was shown to have an impact on motor control and motor learning. A number of studies investigated whether force or position feedback has an influence on motor control and neural activation. However, as in the previous studies the presentation of the force and position feedback was always identical, a recent study assessed whether not only the content but also the interpretation of the feedback has an influence on the time to fatigue of a sustained submaximal contraction and the (inhibitory) activity of the primary motor cortex using subthreshold transcranial magnetic stimulation. This paper describes one possible way to investigate the influence of the interpretation of feedback on motor behaviour by investigating the time to fatigue of submaximal sustained contractions together with the neuromuscular adaptations that can be investigated using surface EMG. Furthermore, the current protocol also describes how motor cortical (inhibitory) activity can be investigated using subthreshold TMS, a method known to act solely on the cortical level. The results show that when participants interpret the feedback as position feedback, they display a significantly shorter time to fatigue of a submaximal sustained contraction. Furthermore, subjects also displayed an increased inhibitory activity of the primary cortex when they believed to receive position feedback compared when they believed to receive force feedback. Accordingly, the results show that interpretation of feedback results in differences on a behavioural level (time to fatigue) that is also reflected in interpretation-specific differences in the amount of inhibitory M1 activity.

Controlling an identical movement with position or force feedback results in different neural activation and motor behavior. This protocol describes how to investigate behavioral changes by looking at neuromuscular fatigue and how to evaluate motor cortical (inhibitory) activity using subthreshold TMS with respect to the interpretation of augmented feedback.

During motor behaviour, humans interact with the environment by for example manipulating objects and this is only possible because sensory feedback is ...

Behavior

Measuring the Motor Aspect of Cancer-Related Fatigue using a Handheld Dynamometer

Cancer-related fatigue (CRF) is commonly reported by patients both during and after receiving treatment for cancer. Current CRF diagnoses rely on self-report questionnaires which are subject to report and recall biases. Objective measurements using a handheld dynamometer, or handgrip device, have been shown in recent studies to correlate significantly with subjective self-reported fatigue scores. However, variations of both the handgrip fatigue test and fatigue index calculations exist in the literature. The lack of standardized methods limits the utilization of the handgrip fatigue test in the clinical and research settings. In this study, we provide detailed methods for administering the physical fatigue test and calculating the fatigue index. These methods should supplement existing self-reported fatigue questionnaires and help clinicians assess fatigue symptom severity in an objective and quantitative manner.

Simple and accessible methods were developed to measure the motor aspect of cancer-related fatigue objectively and quantitatively. We describe, in detail, ways to administer the physical fatigue test using a simple handgrip device as well as methods to calculate fatigue indices.

Cancer-related fatigue (CRF) is commonly reported by patients both during and after receiving treatment for cancer. Current CRF diagnoses rely on ...

Cancer Research

Standing Neurophysiological Assessment of Lower Extremity Muscles Post-Stroke

Transcranial magnetic stimulation (TMS) is a common tool used to measure the behavior of motor circuits in healthy and neurologically impaired populations. TMS is used extensively to study motor control and the response to neurorehabilitation of the upper extremities. However, TMS has been less utilized in the study of lower extremity postural and walking-specific motor control. The limited use and the additional methodological challenges of lower extremity TMS assessments have contributed to the lack of consistency in lower extremity TMS procedures within the literature. Inspired by the decreased ability to record lower extremity TMS motor evoked potentials (MEP), this methodological report details steps to enable post-stroke TMS assessments in a standing posture. The standing posture allows for the activation of the neuromuscular system, reflecting a state more akin to the system's state during postural and walking tasks. Using dual-top force plates, we instructed participants to equally distribute their weight between their paretic and non-paretic legs. Visual feedback of the participants' weight distribution was provided. Using image guidance software, we delivered single TMS pulses via a double-cone coil to the participants' lesioned and non-lesioned hemispheres and measured the corticomotor response of the paretic and non-paretic tibialis anterior and soleus muscles. Performing assessments in the standing position increased the TMS response rate and allowed for the use of the lower stimulation intensities compared to the standard sitting/resting position. Utilization of this TMS protocol can provide a common approach to assess the lower extremity corticomotor response post-stroke when the neurorehabilitation of postural and gait impairments are of interest.

This protocol describes the process for performing a neurophysiological assessment of the lower extremity muscles, tibialis anterior and soleus, in a standing position using TMS in people post-stroke. This position provides a greater probability of eliciting a post-stroke TMS response and allows for the use of reduced stimulator power during neurophysiological assessments.

Transcranial magnetic stimulation (TMS) is a common tool used to measure the behavior of motor circuits in healthy and neurologically impaired ...

Quantifying Arms and Legs Contributions during Repetitive Electrically-Assisted Sit-To-Stand Exercise in Paraplegics: A Pilot Study

Execution of Sit-to-Stand (SitTS) in incomplete spinal cord injury (SCI) patients involves motor function in both upper and lower extremities. The use of arm support, in particular, is a significant assistive factor while executing SitTS movement in SCI population. In addition, the application of functional electrical stimulation (FES) onto quadriceps and gluteus maximus muscles is one of the prescribed management for incomplete SCI to improve muscle action for simple lower limb movements. However, the relative contribution of upper and lower extremities during SitTS has not been thoroughly investigated. Two motor incomplete SCI paraplegics performed repetitive SitTS to fatigue exercise challenge. Their performance was investigated as a mixed-method case-control study comparing SitTS with and without the assistance of FES. Three sets of SitTS tests were completed with 5-min resting period allocated in between sets, with mechanomyography (MMG) sensors attached over the rectus femoris muscles bilaterally. The exercise was separated into 2 sessions; Day 1 for voluntary SitTS and Day 2 for FES-assisted SitTS. Questionnaires were conducted after every session to gather the participants&#39; input about their repetitive SitTS experience. The analysis confirmed that a SitTS cycle could be divided into three phases; Phase 1 (Preparation to stand), Phase 2 (Seat-off), and Phase 3 (Initiation of hip extension), which contributed to 23% &#177; 7%, 16% &#177; 4% and 61% &#177; 6% of the SitTS cycle, respectively. The contribution of arms and legs during SitTS movement varied in different participants based on their legs&#39; Medical Research Council (MRC) muscle grade. In particular, the applied arm forces start to increase clearly when the leg forces start to decline during standing. This finding is supported by the significantly reduced MMG signal indicating leg muscle fatigue and their reported feeling of tiredness.

Arms contribution in Sit-To-Stand (SitTS) is determined by the legs' muscle condition. Several compensating strategies were discovered in efforts to achieve complete SitTS cycles. These findings triangulate the spinal cord injury (SCI) persons' biomechanical measures with their subjective feeling of load borne by both their limbs throughout the SitTS approaches.

Execution of Sit-to-Stand (SitTS) in incomplete spinal cord injury (SCI) patients involves motor function in both upper and lower extremities. The use of ...

Engineering

Assessment of Neuromuscular Function Using Percutaneous Electrical Nerve Stimulation

Percutaneous electrical nerve stimulation is a non-invasive method commonly used to evaluate neuromuscular function from brain to muscle (supra-spinal, spinal and peripheral levels). The present protocol describes how this method can be used to stimulate the posterior tibial nerve that activates plantar flexor muscles. Percutaneous electrical nerve stimulation consists of inducing an electrical stimulus to a motor nerve to evoke a muscular response. Direct (M-wave) and/or indirect (H-reflex) electrophysiological responses can be recorded at rest using surface electromyography. Mechanical (twitch torque) responses can be quantified with a force/torque ergometer. M-wave and twitch torque reflect neuromuscular transmission and excitation-contraction coupling, whereas H-reflex provides an index of spinal excitability. EMG activity and mechanical (superimposed twitch) responses can also be recorded during maximal voluntary contractions to evaluate voluntary activation level. Percutaneous nerve stimulation provides an assessment of neuromuscular function in humans, and is highly beneficial especially for studies evaluating neuromuscular plasticity following acute (fatigue) or chronic (training/detraining) exercise.

We present a protocol to assess changes in neuromuscular function. Percutaneous electrical nerve stimulation is a non-invasive method that evokes muscular responses. Electrophysiological and mechanical properties of these responses permit the evaluation of neuromuscular function from brain to muscle (supra-spinal, spinal and peripheral levels).

Percutaneous electrical nerve stimulation is a non-invasive method commonly used to evaluate neuromuscular function from brain to muscle (supra-spinal, ...

Neuroscience

Measuring Neuromuscular Junction Functionality

Neuromuscular junction (NMJ) functionality plays a pivotal role when studying diseases in which the communication between motor neuron and muscle is impaired, such as aging and amyotrophic lateral sclerosis (ALS). Here we describe an experimental protocol that can be used to measure NMJ functionality by combining two types of electrical stimulation: direct muscle membrane stimulation and the stimulation through the nerve. The comparison of the muscle response to these two different stimulations can help to define, at the functional level, potential alterations in the NMJ that lead to functional decline in muscle.
Ex vivo preparations are suited to well-controlled studies. Here we describe an intensive protocol to measure several parameters of muscle and NMJ functionality for the soleus-sciatic nerve preparation and for the diaphragm-phrenic nerve preparation. The protocol lasts approximately 60 min and is conducted uninterruptedly by means of a custom-made software that measures the twitch kinetics properties, the force-frequency relationship for both muscle and nerve stimulations, and two parameters specific to NMJ functionality, i.e. neurotransmission failure and intratetanic fatigue. This methodology was used to detect damages in soleus and diaphragm muscle-nerve preparations by using SOD1G93A transgenic mouse, an experimental model of ALS that ubiquitously overexpresses the mutant antioxidant enzyme superoxide dismutase 1 (SOD1).

A functional assessment of the neuromuscular junction (NMJ) can provide essential information on the communication between muscle and nerve. Here we describe a protocol to comprehensively evaluate both the NMJ and muscle functionality using two different muscle-nerve preparations, i.e. soleus-sciatic and diaphragm-phrenic.

Neuromuscular junction (NMJ) functionality plays a pivotal role when studying diseases in which the communication between motor neuron and muscle is ...

Ex Vivo Assessment of Contractility, Fatigability and Alternans in Isolated Skeletal Muscles

Described here is a method to measure contractility of isolated skeletal muscles. Parameters such as muscle force, muscle power, contractile kinetics, fatigability, and recovery after fatigue can be obtained to assess specific aspects of the excitation-contraction coupling (ECC) process such as excitability, contractile machinery and Ca2+ handling ability. This method removes the nerve and blood supply and focuses on the isolated skeletal muscle itself. We routinely use this method to identify genetic components that alter the contractile property of skeletal muscle though modulating Ca2+ signaling pathways. Here, we describe a newly identified skeletal muscle phenotype, i.e., mechanic alternans, as an example of the various and rich information that can be obtained using the in vitro muscle contractility assay. Combination of this assay with single cell assays, genetic approaches and biochemistry assays can provide important insights into the mechanisms of ECC in skeletal muscle.

Ex Vivo Assessment of Contractility, Fatigability and Alternans in Isolated Skeletal Muscles

We describe a method to directly measure muscle force, muscle power, contractile kinetics and fatigability of isolated skeletal muscles in an in vitro system using field stimulation. Valuable information on Ca2+ handling properties and contractile machinery of the muscle can be obtained using different stimulating protocols.

 
Described here is a method to measure contractility of isolated skeletal muscles. Parameters such as muscle force, muscle power, contractile kinetics, ...

Biology

Conducting Maximal and Submaximal Endurance Exercise Testing to Measure Physiological and Biological Responses to Acute Exercise in Humans

Regular physical activity has a positive effect on human health, but the mechanisms controlling these effects remain unclear. The physiologic and biologic responses to acute exercise are predominantly influenced by the duration and intensity of the exercise regimen. As exercise is increasingly thought of as a therapeutic treatment and/or diagnostic tool, it is important that standardizable methodologies be utilized to understand the variability and to increase the reproducibility of exercise outputs and measurements of responses to such regimens. To that end, we describe two different cycling exercise regimens that yield different physiologic outputs. In a maximal exercise test, exercise intensity is continually increased with a greater workload resulting in an increasing cardiopulmonary and metabolic response (heart rate, stroke volume, ventilation, oxygen consumption and carbon dioxide production). In contrast, during endurance exercise tests, the demand is increased from that at rest, but is raised to a fixed submaximal exercise intensity resulting in a cardiopulmonary and metabolic response that typically plateaus. Along with the protocols, we provide suggestions on measuring physiologic outputs that include, but are not limited to, heart rate, slow and forced vital capacity, gas exchange metrics, and blood pressure to enable the comparison of exercise outputs between studies. Biospecimens can then be sampled to assess cellular, protein, and/or gene expression responses. Overall, this approach can be easily adapted into both short- and long-term effects of two distinct exercise regimens.

To assess the influence of exercise intensity on physiologic and biologic responses, two different exercise testing protocols were utilized. Methods outlining exercise testing on a cycle ergometer as an incremental maximal oxygen consumption test and endurance, steady state submaximal endurance test are described.

Regular physical activity has a positive effect on human health, but the mechanisms controlling these effects remain unclear. The physiologic and biologic ...

Determining the Functional Status of the Corticospinal Tract Within One Week of Stroke

High interindividual variability in the recovery of upper limb (UL) function after stroke means it is difficult to predict an individual&#39;s potential for recovery based on clinical assessments alone. The functional integrity of the corticospinal tract is an important prognostic biomarker for recovery of UL function, particularly for those with severe initial UL impairment. This article presents a protocol for evaluating corticospinal tract function within 1 week of stroke. This protocol can be used to select and stratify patients in trials of interventions designed to improve UL motor recovery and outcomes after stroke. The protocol also forms part of the PREP2 algorithm, which predicts UL function for individual patients 3 months poststroke. The algorithm sequentially combines a UL strength assessment, age, transcranial magnetic stimulation, and stroke severity, within a few days of the stroke. The benefits of using PREP2 in clinical practice are described elsewhere. This article focuses on the use of a UL strength assessment and transcranial magnetic stimulation to evaluate corticospinal tract function.

This protocol is for evaluating corticospinal tract function within 1 week of stroke. It can be used to select and stratify patients in trials of interventions designed to improve upper limb motor recovery and outcomes and in clinical practice for predicting upper limb functional outcomes 3 months after stroke.

High interindividual variability in the recovery of upper limb (UL) function after stroke means it is difficult to predict an individual&#39;s potential ...

Determining The Electromyographic Fatigue Threshold Following a Single Visit Exercise Test

Summary

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Chapters in this video

Utilizing Transcranial Magnetic Stimulation to Study the Human Neuromuscular System

Force and Position Control in Humans - The Role of Augmented Feedback

Measuring the Motor Aspect of Cancer-Related Fatigue using a Handheld Dynamometer

Standing Neurophysiological Assessment of Lower Extremity Muscles Post-Stroke

Quantifying Arms and Legs Contributions during Repetitive Electrically-Assisted Sit-To-Stand Exercise in Paraplegics: A Pilot Study

Assessment of Neuromuscular Function Using Percutaneous Electrical Nerve Stimulation

Measuring Neuromuscular Junction Functionality

Ex Vivo Assessment of Contractility, Fatigability and Alternans in Isolated Skeletal Muscles

Conducting Maximal and Submaximal Endurance Exercise Testing to Measure Physiological and Biological Responses to Acute Exercise in Humans

Determining the Functional Status of the Corticospinal Tract Within One Week of Stroke