The authors have no acknowledgements.

The following procedures are in accordance with the standards of the Brigham Young University Institutional review board (IRB).
1. Prepare the Contraction Protocols
NOTE: The following protocol instructions are based on the Biodex Advantage software. Navigating the software and operating the dynamometer will be different if different systems are used.
<ol>
	<li>Isokinetic Strength Test Protocol
	<ol>
		<li>To make the isokinetic protocol, open dynamometer control software on the computer and select the &#34;Protocol&#34; tab and then select the &#34;Record&#34; tab on the toolbar on the top of the screen. Select &#34;New Protocol&#34; from the dropdown list.</li>
		<li>In the &#34;Study Type&#34; box, select the &#34;Test&#34; option.</li>
		<li>Select the following parameters from the dropdown menus: Under the &#34;Mode&#34; menu select Isokinetic. Under the &#34;Joint&#34; menu select knee. Under the &#34;Pattern&#34; menu select extension/flexion. Select concentric contractions for both extension and flexion movements. Select &#34;reps&#34; under the &#34;End By&#34; dropdown menu.</li>
		<li>On the &#34;Unilateral&#34; tab program 1 set of 3 repetitions at a speed of 60&#176;/sec for both the away and toward contractions. To do this, enter &#34;1&#34; into the &#34;# sets&#34; field and type &#34;3&#34; in the &#34;End By Reps&#34; row. Then type 60 in both the &#34;Speed Away&#34; and &#34;Speed Toward&#34; rows.</li>
		<li>Use 90&#176; as the anatomical reference point and set range of motion limits to approximately 10&#176; away and 110&#176; towards (0&#176; = full extension, 135&#176; = full flexion).To do this, select the &#34;set ROM&#34; button on the left side of the screen. Calibrate the lever arm so that 90&#176; is parallel to the floor (as indicated using the lever arm angle indicator provided on the computer screen). Then using 90&#176; as the anatomical reference point, set the range of motion limits to approximately 10&#176; away and 110&#176; towards (0&#176; = full extension, 135&#176; = full flexion). 
		NOTE: The joint angle settings given here are preferred, however these settings should be modified on a case-by-case basis especially when working with subjects with a fixed flexion deformity or other limitation.</li>
		<li>Name the protocol in the &#34;Description&#34; field on the bottom left of the screen and select the save button on the top menu bar.</li>
	</ol>
	</li>
	<li>Isometric Strength Test Protocol
	<ol>
		<li>Repeat steps 1.1.1 to begin making the isometric protocol.</li>
		<li>Select the &#34;Test&#34; option from the &#34;Study Type&#34; box.</li>
		<li>Select the following parameters from the dropdown menus: Under the &#34;Mode&#34; menu select &#34;isometric&#34;. Under the &#34;Joint&#34; menu select &#34;knee&#34;. Under the &#34;Pattern&#34; menu select &#34;extension/flexion&#34;. Under the &#34;Contraction Direction&#34; menu select &#34;away&#34;. In the &#34;End By&#34; menu select &#34;reps&#34;.</li>
		<li>Program a test with 1 set of 3 isometric contractions lasting 5 sec each at a joint angle of 70&#176;. To do this, type &#34;1&#34; into the &#34;Positions&#34; field on the &#34;Unilateral&#34; tab. Under the position #1 column, type &#34;3&#34;in the &#34;End by Reps&#34; row. In the row labeled &#34;Angle&#34; select &#34;70&#34;.</li>
		<li>Select 90&#176; as the anatomical reference point and an away limit to 70&#176;.</li>
		<li>Name the protocol in the &#34;Description&#34; field on the bottom left of the screen and select the save button on the top menu bar.</li>
	</ol>
	</li>
	<li>Muscle Damaging Eccentric Exercise Protocol
	<ol>
		<li>To make the eccentric exercise protocol, open dynamometer control software on the computer and select the &#34;Protocol&#34; tab. Then select the &#34;Record&#34; tab on the toolbar on the top of the screen. Now click on &#34;New Protocol&#34; from the dropdown list.</li>
		<li>Select the &#34;Exercise&#34; option from the &#34;Study Type&#34; box.</li>
		<li>Select the following parameters from the dropdown menus: Under the &#34;Mode&#34; menu select &#34;isokinetic&#34;. Under the &#34;Joint&#34; menu select &#34;knee&#34;. Under the &#34;Pattern&#34; menu select &#34;Extension/Flexion&#34;. Under the &#34;Contraction&#34; menu select &#34;Con/ECC&#34;.</li>
		<li>On the &#34;Unilateral&#34; tab, program 10 sets of 10 repetitions at speeds of 180&#176;/sec away and 120&#176;/sec towards with 60 sec rest between sets.
		<ol>
			<li>Type &#34;10&#34; into the &#34;# Sets&#34; field.</li>
			<li>In the first column (labeled #1), type &#34;10&#34; in the row labeled &#34;End by Reps&#34;. Then type &#34;180&#34; in the next row labeled &#34;Speed Away&#34;. In the next row labeled &#34;Speed Toward&#34;, type &#34;120&#34;. In the row labeled &#34;Torque&#34;, type 200 to 600 depending on the anticipated strength of the subject.</li>
			<li>Repeat step 1.3.4.2 for sets #2 through #10.</li>
			<li>Type 60 in the &#34;Rest Time in secs&#34; field.</li>
		</ol>
		</li>
		<li>Type 90&#176; into the &#34;Anatomical Reference&#34; field.</li>
		<li>Select the &#34;Set ROM&#34; button on the left side of the screen and set range of motion limits to 40&#176; away and 110&#176; towards (0&#176; = full extension, 135&#176; = full flexion). These settings provide the range of motion through which the subject must provide resistance against the arm of the dynamometer. As a safety precaution, the dynamometer will stop moving if the subject stops providing resistance within this specified range of motion.
		<ol>
			<li>To set the range of motion, select the &#34;set ROM&#34; button on the left side of the screen. Calibrate the lever arm so that 90&#176; is parallel to the floor (as indicated using the lever arm angle indicator provided on the computer screen). Then using 90&#176; as the anatomical reference point, set the range of motion limits to 40&#176; away and 110&#176; towards (0&#176; = full extension, 135&#176; = full flexion). 
			NOTE: These joint angle settings are suggestions for a typical healthy subject. These should be modified to fit the abilities from one individual to another.</li>
		</ol>
		</li>
		<li>Name the protocol in the &#34;Description&#34; field and select the &#34;Save&#34; button at the top tool bar.</li>
	</ol>
	</li>
</ol>
2. Baseline Measurements
<ol>
	<li>Soreness Measurements
	<ol>
		<li>Make a visual analog scale by drawing a 100 mm line horizontally across a page.</li>
		<li>On the left-hand side of the line indicate &#34;No soreness&#34; and on the right-hand side of the line indicate &#34;Extreme soreness&#34; (Figure 1). This method is commonly used to assess delayed-onset muscle soreness1,10,11.</li>
		<li>Instruct the subject to do two body-weight squats. Perform both squats with arms held straight out in front of the shoulders and feet shoulder-width apart. Proper depth is reached when the upper legs are parallel to the floor before returning to the start position.</li>
		<li>Ask the subject to indicate the intensity of the soreness he or she felt in the quadriceps femoris muscles during the squats by drawing a vertical line at the appropriate spot on the visual analog scale.</li>
		<li>Quantify the subject&#39;s level of soreness by measuring the distance in millimeters from the no-soreness end of the visual analog scale to subject&#39;s mark.</li>
	</ol>
	</li>
	<li>Serum Creatine Kinase 
	CAUTION: Wear protective gloves before handling blood and dispose of needles immediately after use in a sharps container as per hospital or university policy.
	<ol>
		<li>Follow standardized phlebotomy procedures to withdraw blood from the antecubital region of the subject&#39;s arm under fasting conditions to obtain 5 to 6 ml of blood12.</li>
		<li>Centrifuge the blood sample at 15 x g for 15 min at 3 &#176;C to separate serum from blood cells.</li>
		<li>Using a transfer pipette, transfer the serum sample into a microcentrifuge tube labeled appropriately for subject and time point.</li>
		<li>Store the sample at -80 &#176;C for later use.</li>
		<li>Assay the serum samples for creatine kinase activity using a commercially available kit according to manufacturer&#39;s protocol. Alternatively, the serum samples can be transported to a local medical diagnostic laboratory for analysis.</li>
	</ol>
	</li>
	<li>Subject Preparation
	<ol>
		<li>Forty-eight hours prior to the subject&#39;s visit, instruct them to avoid strenuous or unaccustomed exercise, non-steroidal anti-inflammatory drugs and alcohol.</li>
		<li>When the subject arrives, collect weight, height, sex, and leg dominance information prior to setup. Leg dominance can be determined by asking the subject with which leg they would choose to kick a ball.</li>
		<li>Have the subject warm up at 50 to 150 W for 10 min on a bicycle ergometer before performing the strength tests.</li>
		<li>After the warm-up ask the subject to sit in the chair of the dynamometer. Adjust the tilt, height, depth, recline, and rotation of the seat and shaft arm to fit the subject. Use the lateral femoral condyle as a reference and align rotational axis of the knee with that of the dynamometer shaft arm. Adjust the shaft arm length so that it is just proximal to the medial malleolus, and secure with strap. Subject should be able to plantar flex comfortably with full range of motion.</li>
		<li>Leave sufficient space (25 mm) between the front edge of the seat and the back of the leg to allow maximal flexion of the knee joint without pinching or discomfort.</li>
		<li>Stabilize subject with shoulder, hip, ankle and thigh straps. To isolate the knee extensors and avoid ancillary muscle involvement, it is essential that the subject be securely stabilized.</li>
		<li>Have the subject perform 3-5 practice extension/flexion maneuvers of the knee, monitor range of motion and signs of discomfort that may exist prior to beginning the contraction protocol, and adjust as needed.</li>
		<li>Now that the adjustable components of the dynamometer are properly fitted to the subject, record the seat position settings and shaft arm position for repeatable setup on subsequent visits. 
		NOTE: It is important that the subject is safe and comfortable. The dynamometer is equipped with an emergency stop button for both the subject and operator in the case of an emergency.</li>
	</ol>
	</li>
	<li>Force Measurement
	<ol>
		<li>After the subject is properly oriented in the seat and the isometric strength test protocol is loaded, instruct the subject on how to perform the test.
		<ol>
			<li>Tell the subject that he or she will be contracting against the lever arm that will stay stationary. Tell the subject to follow the prompts of the computer screen doing 3 contractions lasting 5 sec each.</li>
			<li>Tell the subject to maintain maximal effort for each contraction. Tell the subject to breathe during the contractions. Ask the subject to cross their arms across the chest during the test.</li>
			<li>Start the isometric protocol and allow the subject to practice the test with submaximal effort. This practice trial will familiarize the subject to the test as well as provide a test-specific warm-up. Allow the subject to practice the test 2 to 3 times.</li>
		</ol>
		</li>
		<li>Once the subject is ready, start the test and verbally encourage the subject to provide maximal effort for each contraction.</li>
		<li>Record torque, power, and work. The software also calculates the coefficient of variance (a statistical representation of test validity based on reproducibility of performance, lower values indicate higher reproducibility). If the coefficient of variance exceeds 15%, repeat the test. Repeat the test up to 4 times. If the subject is unable to produce a coefficient of variance less than 15% after 4 attempts use the data from the set that yielded the lowest coefficient of variance value.</li>
		<li>Allow the subject two to three minutes to rest, and then load the isokinetic protocol to obtain isokinetic strength data.</li>
		<li>After the subject is secured in the seat, instruct on how to perform the isokinetic test.
		<ol>
			<li>Tell the subject that they will be doing three extension and flexion contractions against the lever arm that will move at a fixed rate. Tell the subject the goal is to contract as forcefully as possible throughout the entire range of motion for each contraction.</li>
			<li>Tell them that the lever arm will stop when they reach the end of the range of motion. Ask the subject to cross his arms across the chest during the test. Remind the subject not to hold their breath during the contractions 
			NOTE: While the data gathered from the flexion component of the contraction may not be of interest to the researcher, subjects who provide maximal effort for both the flexion and extension maneuvers tend to yield better force consistency during the extension maneuver.</li>
		</ol>
		</li>
		<li>Start the test and verbally encourage the subject to provide maximal effort.</li>
		<li>Record torque, power, and work. The software also calculates the coefficient of variance (a statistical representation of test validity based on reproducibility of performance, lower values indicate higher reproducibility). If the coefficient of variance exceeds 15%, repeat the test.
		<ol>
			<li>Repeat the test up to 4 times. If the subject is unable to produce a coefficient of variance less than 15% after 4 attempts, use the data from the set that yielded the lowest coefficient of variance value.</li>
		</ol>
		</li>
	</ol>
	</li>
</ol>
3. Damage Induction
<ol>
	<li>One to three days after the baseline measurements of Part 2, have the subject return to the lab for the damage induction portion of the protocol</li>
	<li>Have the subject warm-up on a cycle ergometer for 10 min at 50 to 150 W.</li>
	<li>After the warm-up, orient and secure the subject in the dynamometer using the adjustment settings recorded in step 2.3.7, load the muscle damaging eccentric exercise protocol and instruct the subject on how to properly perform the exercise.
	<ol>
		<li>Tell the subject that they will contract against the lever arm to initiate the movement of the shaft arm for each contraction. Tell the subject that as the shaft arm moves toward them at a fixed rate, their goal is to contract against it as forcefully as possible.</li>
		<li>Allow the subject to grasp the handgrips located on either side of the seat.</li>
		<li>Tell the subject to breathe during the contractions; exhale during the eccentric phase.</li>
	</ol>
	</li>
	<li>When the subject is ready, start the first set of contractions by pushing the start button on the screen.</li>
	<li>Verbally encourage the subject to maintain maximal effort for each contraction.</li>
	<li>Follow the prompts on the screen that will guide the subject through 10 sets of 10 repetitions with a 1 min rest period between sets.</li>
	<li>Once 10 sets are completed allow the subject 1 to 5 min to rest before repeating the protocol. 
	NOTE: The maximum number of sets available under the eccentric protocol is 10 however this may vary depending on the dynamometer and software used. The rest provides time for the operator to reload the protocol if necessary.</li>
	<li>Repeat the procedure two more times for a total of 300 predominantly eccentric contractions.</li>
</ol>
4. Muscle Damage Assessment
<ol>
	<li>Repeat both Isokinetic and isometric strength tests as described in 2.4 immediately after the damaging exercise and at 24, 48, 72, and 96 hr after.</li>
	<li>Repeat the soreness measurement as described in part 2.1 at 24, 48, 72, and 96 hr after damaging exercise. Be sure to use a new visual analog scale for each assessment so that the subject cannot see their previous responses.</li>
	<li>Repeat the blood draw as described in part 2.2 for the creatine kinase assay at 48 and 120 hr after damaging exercise, or at time points dictated by the experimental protocol.</li>
	<li>Plot the creatine kinase, strength and soreness data on the y-axis of a graph against time on the x-axis.</li>
	<li>Observe how these variables deviate from and return toward baseline values in the days following exercise, indicating damage and repair, respectively.</li>
</ol>

<ol>
	<li>Deyhle, M. 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=Skeletal+Muscle+Inflammation+Following+Repeated+Bouts+of+Lengthening+Contractions+in+Humans.">Skeletal Muscle Inflammation Following Repeated Bouts of Lengthening Contractions in Humans.</a> Front. Physiol. 6, 424 (2015).</li><li>Hyldahl, R. 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=Extracellular+matrix+remodeling+and+its+contribution+to+protective+adaptation+following+lengthening+contractions+in+human+muscle.">Extracellular matrix remodeling and its contribution to protective adaptation following lengthening contractions in human muscle.</a> FASEB J. 29 (7), 2894-2904 (2015).</li><li>Hyldahl, R. D., Olson, T., Welling, T., Groscost, L., Parcell, A. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Satellite+cell+activity+is+differentially+affected+by+contraction+mode+in+human+muscle+following+a+work-matched+bout+of+exercise.">Satellite cell activity is differentially affected by contraction mode in human muscle following a work-matched bout of exercise.</a> Front. Physiol. 5, 485 (2014).</li><li>Clarkson, P. M., Kearns, A. K., Rouzier, P., Rubin, R., Thompson, P. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Serum+creatine+kinase+levels+and+renal+function+measures+in+exertional+muscle+damage.">Serum creatine kinase levels and renal function measures in exertional muscle damage.</a> Med. Sci. Sports Exerc. 38 (4), 623-627 (2006).</li><li>Clarkson, P. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Exertional+rhabdomyolysis+and+acute+renal+failure+in+marathon+runners.">Exertional rhabdomyolysis and acute renal failure in marathon runners.</a> Sports Med. 37 (4-5), 361-363 (2007).</li><li>Seedat, Y. K., Aboo, N., Naicker, S., Parsoo, I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Acute+renal+failure+in+the+&amp;#34;Comrades+Marathon&amp;#34+runners.">Acute renal failure in the &amp;#34;Comrades Marathon&amp;#34 runners.</a> Ren. Fail. 11 (4), 209-212 (1989).</li><li>Landau, M. E., Kenney, K., Deuster, P., Campbell, W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Exertional+rhabdomyolysis:+a+clinical+review+with+a+focus+on+genetic+influences.">Exertional rhabdomyolysis: a clinical review with a focus on genetic influences.</a> J. Clin. Neuromuscul. Dis. 13 (3), 122-136 (2012).</li><li>Warren, G. 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=Role+of+CC+chemokines+in+skeletal+muscle+functional+restoration+after+injury.">Role of CC chemokines in skeletal muscle functional restoration after injury.</a> Am. J. Physiol. Cell Physiol. 286 (5), C1031-C1036 (2004).</li><li>Zhang, 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=CD8+T+cells+are+involved+in+skeletal+muscle+regeneration+through+facilitating+MCP-1+secretion+and+Gr1(high)+macrophage+infiltration.">CD8 T cells are involved in skeletal muscle regeneration through facilitating MCP-1 secretion and Gr1(high) macrophage infiltration.</a> J. Immunol. 193 (10), 5149-5160 (2014).</li><li>Cermak, N. M., Noseworthy, M. D., Bourgeois, J. M., Tarnopolsky, M. A., Gibala, M. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Diffusion+tensor+MRI+to+assess+skeletal+muscle+disruption+following+eccentric+exercise.">Diffusion tensor MRI to assess skeletal muscle disruption following eccentric exercise.</a> Muscle Nerve. 46 (1), 42-50 (2012).</li><li>Chen, Y. W., Hubal, M. J., Hoffman, E. P., Thompson, P. D., Clarkson, P. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Molecular+responses+of+human+muscle+to+eccentric+exercise.">Molecular responses of human muscle to eccentric exercise.</a> J. Appl. Physiol. 95 (6), 2485-2494 (2003).</li><li>Stasinger, S. K., Di Lorenzo, M. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Phlebotomy Textbook. , 188-203 (2011).</li><li>Hubal, M. J., Chen, T. C., Thompson, P. D., Clarkson, P. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Inflammatory+gene+changes+associated+with+the+repeated-bout+effect.">Inflammatory gene changes associated with the repeated-bout effect.</a> Am. J. Physiol. Regul. Integr. Comp. Physiol. 294 (5), R1628-R1637 (2008).</li><li>Stupka, N., Tarnopolsky, M. A., Yardley, N. J., Phillips, S. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cellular+adaptation+to+repeated+eccentric+exercise-induced+muscle+damage.">Cellular adaptation to repeated eccentric exercise-induced muscle damage.</a> J. Appl. Physiol. 91 (4), 1669-1678 (2001).</li><li>Smith, L. 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=Changes+in+serum+cytokines+after+repeated+bouts+of+downhill+running.">Changes in serum cytokines after repeated bouts of downhill running.</a> Appl. Physiol. Nutr. Metab. 32 (2), 233-240 (2007).</li><li>Marqueste, T., Giannesini, B., Fur, Y. L., Cozzone, P. J., Bendahan, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Comparative+MRI+analysis+of+T2+changes+associated+with+single+and+repeated+bouts+of+downhill+running+leading+to+eccentric-induced+muscle+damage.">Comparative MRI analysis of T2 changes associated with single and repeated bouts of downhill running leading to eccentric-induced muscle damage.</a> J. Appl. Physiol. 105 (1), 299-307 (2008).</li><li>Crameri, R. 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=Myofibre+damage+in+human+skeletal+muscle:+effects+of+electrical+stimulation+versus+voluntary+contraction.">Myofibre damage in human skeletal muscle: effects of electrical stimulation versus voluntary contraction.</a> J. Physiol. 583 (Pt 1), 365-380 (2007).</li><li>Yu, J. G., Malm, C., Thornell, L. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Eccentric+contractions+leading+to+DOMS+do+not+cause+loss+of+desmin+nor+fibre+necrosis+in+human+muscle.">Eccentric contractions leading to DOMS do not cause loss of desmin nor fibre necrosis in human muscle.</a> Histochem. Cell Biol. 118 (1), 29-34 (2002).</li><li>Jamurtas, A. Z., 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+between+leg+and+arm+eccentric+exercises+of+the+same+relative+intensity+on+indices+of+muscle+damage.">Comparison between leg and arm eccentric exercises of the same relative intensity on indices of muscle damage.</a> Eur. J. Appl. Physiol. 95 (2-3), 179-185 (2005).</li></ol>

The authors have nothing to disclose.

Several steps are critical to obtaining the desired results of this protocol. First, subjects must be adequately familiarized to the contraction protocols, particularly the force measurements. Be sure that the subject understands exactly what they are expected to do and give them an opportunity to practice the strength tests prior to data collection. Subjects who are not adequately familiarized with these procedures may show a learning curve over the days following the damage induction. This can be a confounding variable...

The overall goal of this procedure is to induce exertional damage to the quadriceps femoris muscles using voluntary lengthening (eccentric) contractions in human subjects.
Contraction-induced skeletal muscle damage is a common consequence of exercise that is marked by delayed onset muscle soreness1, transient strength loss, and elevated muscle-specific enzymes in the blood2. Exertional muscle damage is most pronounced following exercise to which the subject is unaccustomed, particularly when eccentric contractions are involved3. Exertional muscle damage is typically benign. Soreness subsides, and both serum proteins and strength typically return to pre-damage levels within a few days to weeks after the damaging insult. In extreme cases, exertional muscle damage can lead to a life-threatening syndrome know as rhabdomyolysis. However, exertional muscle damage is usually insufficient to cause clinical rhabdomyolysis in healthy individuals4 in the absence of compounding factors including heat stress, dehydration5, infection6 or rare genetic predispositions7. 
Contraction-induced muscle damage is typically less severe than toxin-induced or freezing-induced injury, methods often used in rodent studies8,9. Yet, contraction-induced injury provides a useful method to study the muscle damage response with notable advantages. First, it is a safe and ethical method for use with human subjects1-3. Thus, interspecies translation of the results is not needed as data can be obtained directly from human subjects. Moreover, translating data obtained from rodent studies is very difficult given that the severity of injury seen in the rodent injury models exceeds the level of damage that would be ethical to induce in human subjects. Second, contraction-induced damage is commonly experienced and a natural process of exercise. Therefore, this mode of damage induction is useful for studying muscle damage in the context of exercise, adaptation to exercise as well as overt muscle injury. Here we describe a safe and reliable method to induce and evaluate skeletal muscle damage using lengthening contractions in humans.

<table><tbody><tr><td>Biodex Dynomometer</td><td>Biodex Medical Systems</td><td>850-000</td><td>Other models are available and should produce similar results</td></tr><tr><td>Creatine Kinase kit</td><td>Sigma-Aldrich&amp;nbsp;</td><td>MAK116</td><td></td></tr><tr><td>Serum Vacutainers</td><td>BD Bioscience</td><td>367812</td><td></td></tr><tr><td>Winged safety push button blood collection set</td><td>BD Bioscience</td><td>367338</td><td></td></tr><tr><td>Cryogenic vials</td><td>Sigma-Aldrich</td><td>V5007</td><td>We use the 2&amp;nbsp;ml vials to store serum aliquots</td></tr></tbody></table>

induction and assessment of exertional skeletal muscle damage in humans

Contraction-induced muscle damage via voluntary eccentric (lengthening) contractions offers an excellent model for studying muscle adaptation and recovery in humans. Herein we discuss the design of an eccentric exercise protocol to induce damage in the quadriceps muscles, marked by changes in strength, soreness, and plasma creatine kinase levels. This method is simple, ethical, and widely applicable since it is performed in human participants and eliminates the interspecies translation of the results. Subjects perform 300 maximal eccentric contractions of the knee extensor muscles at a speed of 120&#176;/sec on an isokinetic dynamometer. The extent of the damage is measurable using relatively non-invasive isokinetic and isometric measures of strength loss, soreness, and plasma creatine kinase levels over several days following the exercise. Therefore, its application can be directed to specific populations in an attempt to identify mechanisms for muscle adaptation and regeneration.

Using the methods presented here, baseline soreness, serum creatine kinase activity, and strength (isometric and isokinetic) measurements were taken in 7 untrained young men. The following day, the subjects underwent the muscle damaging eccentric contraction protocol described above. To provide indices of muscle damage, follow up assessments of strength, soreness and serum creatine kinase activity were made. Strength was measured immediately after as well as 24, 48, 72, and 96 hr after ex...

Watch this Scientific Journal Video about Induction and Assessment of Exertional Skeletal Muscle Damage in Humans at JoVE.com

Induction and Assessment of Exertional Skeletal Muscle Damage in Humans

This article describes a safe and reliable method to induce and quantify exertional skeletal muscle damage in human subjects.

Contraction-induced muscle damage via voluntary eccentric (lengthening) contractions offers an excellent model for studying muscle adaptation and recovery ...

induction-assessment-exertional-skeletal-muscle-damage

Universidad de Cartagena UDEC

Research

JoVE Journal

Medicine

7.4K Views.  Brigham Young University. This article describes a safe and reliable method to induce and quantify exertional skeletal muscle damage in human subjects.

Video: Induction and Assessment of Exertional Skeletal Muscle Damage in Humans

In Vivo Canine Muscle Function Assay

We describe a minimally-invasive and reproducible method to measure canine pelvic limb muscle strength and muscle response to repeated eccentric 
contractions. The pelvic limb of an anesthetized dog is immobilized in a stereotactic frame to align the tibia at a right angle to the femur. Adhesive wrap affixes the 
paw to a pedal mounted on the shaft of a servomotor to measure torque. Percutaneous nerve stimulation activates pelvic limb muscles of the paw to either push (extend) or 
pull (flex) against the pedal to generate isometric torque. Percutaneous tibial nerve stimulation activates tibiotarsal extensor muscles. Repeated eccentric (lengthening) 
contractions are induced in the tibiotarsal flexor muscles by percutaneous peroneal nerve stimulation. The eccentric protocol consists of an initial isometric contraction 
followed by a forced stretch imposed by the servomotor. The rotation effectively lengthens the muscle while it contracts, e.g., an eccentric contraction. During 
stimulation flexor muscles are subjected to an 800 msec isometric and 200 msec eccentric contraction. This procedure is repeated every 5 sec. To avoid fatigue, 4 min rest 
follows every 10 contractions with a total of 30 contractions performed.

In Vivo Canine Muscle Function Assay

We describe a minimally-invasive and painless method to measure canine hindlimb muscle strength and muscle response to repeated eccentric contractions.

We describe a minimally-invasive and reproducible method to measure canine pelvic limb muscle strength and muscle response to repeated eccentric 
...

Manual Muscle Testing:  A Method of Measuring Extremity Muscle Strength Applied to Critically Ill Patients 

Survivors of acute respiratory distress syndrome (ARDS) and other causes of critical illness often have generalized weakness, reduced exercise tolerance, and persistent nerve and muscle impairments after hospital discharge.1-6 Using an explicit protocol with a structured approach to training and quality assurance of research staff, manual muscle testing (MMT) is a highly reliable method for assessing strength, using a standardized clinical examination, for patients following ARDS, and can be completed with mechanically ventilated patients who can tolerate sitting upright in bed and are able to follow two-step commands. 7, 8 
This video demonstrates a protocol for MMT, which has been taught to &ge;43 research staff who have performed &gt;800 assessments on &gt;280 ARDS survivors. Modifications for the bedridden patient are included. Each muscle is tested with specific techniques for positioning, stabilization, resistance, and palpation for each score of the 6-point ordinal Medical Research Council scale.7,9-11 Three upper and three lower extremity muscles are graded in this protocol: shoulder abduction, elbow flexion, wrist extension, hip flexion, knee extension, and ankle dorsiflexion. These muscles were chosen based on the standard approach for evaluating patients for ICU-acquired weakness used in prior publications. 1,2.

Manual Muscle Testing:  A Method of Measuring Extremity Muscle Strength Applied to Critically Ill Patients

Survivors of acute respiratory distress syndrome (ARDS) and critical illness frequently develop long-lasting muscle weakness. Manual muscle testing (MMT) is a standardized clinical examination commonly used to measure strength of peripheral skeletal muscle groups. This video demonstrates MMT using the 6-point Medical Research Council scale.

Survivors of acute respiratory distress syndrome (ARDS) and other causes of critical illness often have generalized weakness, reduced exercise tolerance, ...

An in vivo Rodent Model of Contraction-induced Injury and Non-invasive Monitoring of Recovery

Muscle strains are one of the most common complaints treated by physicians. A muscle injury is typically diagnosed from the patient history and physical exam alone, however the clinical presentation can vary greatly depending on the extent of injury, the patient's pain tolerance, etc. In patients with muscle injury or muscle disease, assessment of muscle damage is typically limited to clinical signs, such as tenderness, strength, range of motion, and more recently, imaging studies. Biological markers, such as serum creatine kinase levels, are typically elevated with muscle injury, but their levels do not always correlate with the loss of force production. This is even true of histological findings from animals, which provide a "direct measure" of damage, but do not account for all the loss of function. Some have argued that the most comprehensive measure of the overall health of the muscle in contractile force. Because muscle injury is a random event that occurs under a variety of biomechanical conditions, it is difficult to study. Here, we describe an in vivo animal model to measure torque and to produce a reliable muscle injury. We also describe our model for measurement of force from an isolated muscle in situ. Furthermore, we describe our small animal MRI procedure.

An in vivo Rodent Model of Contraction-induced Injury and Non-invasive Monitoring of Recovery

An in vivo animal model of injury is described. The method takes advantage of the subcutaneous position of the fibular nerve. Velocity, timing of muscle activation, and arc of motion are all pre-determined and synchronized using commercial software. Post injury changes are monitored in vivo using MR imaging/spectroscopy.

Muscle strains are one of the most  common complaints treated by physicians. A muscle injury is typically diagnosed from the patient history and  physical ...

The Use of Thermal Infra-Red Imaging to Detect Delayed Onset Muscle Soreness

Delayed onset muscle soreness (DOMS), also known as exercise induced muscle damage (EIMD), is commonly experienced in individuals who have been physically inactive for prolonged periods of time, and begin with an unexpected bout of exercise1-4, but can also occur in athletes who exercise beyond their normal limits of training5. The symptoms associated with this painful phenomenon can range from slight muscle tenderness, to severe debilitating pain1,3,5. The intensity of these symptoms and the related discomfort increases within the first 24 hours following the termination of the exercise, and peaks between 24 to 72 hours post exercise1,3. For this reason, DOMS is one of the most common recurrent forms of sports injury that can affect an individual&#x2019;s performance, and become intimidating for many1,4.
For the last 3 decades, the DOMS phenomenon has gained a considerable amount of interest amongst researchers and specialists in exercise physiology, sports, and rehabilitation fields6. There has been a variety of published studies investigating this painful occurrence in regards to its underlying mechanisms, treatment interventions, and preventive strategies1-5,7-12. However, it is evident from the literature that DOMS is not an easy pathology to quantify, as there is a wide amount of variability between the measurement tools and methods used to quantify this condition6. It is obvious that no agreement has been made on one best evaluation measure for DOMS, which makes it difficult to verify whether a specific intervention really helps in decreasing the symptoms associated with this type of soreness or not. Thus, DOMS can be seen as somewhat ambiguous, because many studies depend on measuring soreness using a visual analog scale (VAS)10,13-15, which is a subjective rather than an objective measure. Even though needle biopsies of the muscle, and blood levels of myofibre proteins might be considered a gold standard to some6, large variations in some of these blood proteins have been documented 6,16, in addition to the high risks sometimes associated with invasive techniques. 
Therefore, in the current investigation, we tested a thermal infra-red (IR) imaging technique of the skin above the exercised muscle to detect the associated muscle soreness. Infra-red thermography has been used, and found to be successful in detecting different types of diseases and infections since the 1950&#x2019;s17. But surprisingly, near to nothing has been done on DOMS and changes in skin temperature. The main purpose of this investigation was to examine changes in DOMS using this safe and non-invasive technique.

The purpose of this investigation was to assess whether using an infra-red thermal camera is a valid tool for detecting and quantifying the muscle soreness after exercising.

Delayed onset muscle soreness (DOMS), also known as exercise induced muscle damage (EIMD), is commonly experienced in individuals who have been physically ...

Induction of Acute Skeletal Muscle Regeneration by Cardiotoxin Injection

Skeletal muscle regeneration is a physiological process that occurs in adult skeletal muscles in response to injury or disease. Acute injury-induced skeletal muscle regeneration is a widely used, powerful model system to study the events involved in muscle regeneration as well as the mechanisms and different players. Indeed, a detailed knowledge of this process is essential for a better understanding of the pathological conditions that lead to skeletal muscle degeneration, and it aids in identifying new targeted therapeutic strategies. The present work describes a detailed and reproducible protocol to induce acute skeletal muscle regeneration in mice through a single intramuscular injection of cardiotoxin (CTX). CTX belongs to the family of snake venom toxins and causes myolysis of myofibers, which eventually triggers the regeneration events. The dynamics of skeletal muscle regeneration is evaluated by histological analysis of muscle sections. The protocol also illustrates the experimental procedures for dissecting, freezing, and cutting the Tibialis Anterior muscle, as well as the routine Hematoxylin &#38; Eosin staining that is widely used for subsequent morphological and morphometric analysis.

This manuscript describes a detailed protocol to induce acute skeletal muscle regeneration in adult mice and subsequent manipulations of the muscles, such as dissection, freezing, cutting, routine staining, and myofiber cross-sectional area analysis.

Skeletal muscle regeneration is a physiological process that occurs in adult skeletal muscles in response to injury or disease. Acute injury-induced ...

Developmental Biology

Human Skeletal Muscle Biopsy Procedures Using the Modified Bergstr&#246;m Technique

The percutaneous biopsy technique enables researchers and clinicians to collect skeletal muscle tissue samples. The technique is safe and highly effective. This video describes the percutaneous biopsy technique using a modified Bergstr&#246;m needle to obtain skeletal muscle tissue samples from the vastus lateralis of human subjects. The Bergstr&#246;m needle consists of an outer cannula with a small opening (&#8216;window&#8217;) at the side of the tip and an inner trocar with a cutting blade at the distal end. Under local anesthesia and aseptic conditions, the needle is advanced into the skeletal muscle through an incision in the skin, subcutaneous tissue, and fascia. Next, suction is applied to the inner trocar, the outer trocar is pulled back, skeletal muscle tissue is drawn into the window of the outer cannula by the suction, and the inner trocar is rapidly closed, thus cutting or clipping the skeletal muscle tissue sample. The needle is rotated 90&#176;&#160;and another cut is made. This process may be repeated three more times. This multiple cutting technique typically produces a sample of 100-200 mg or more in healthy subjects and can be done immediately before, during, and after a bout of exercise or other intervention. Following post-biopsy dressing of the incision site, subjects typically resume their activities of daily living right away and can fully participate in vigorous physical activity within 48-72 hr. Subjects should avoid heavy resistance exercise for 48 hr to reduce the risk of herniation of the muscle through the incision in the fascia.

The purpose of this video is to present the modified Bergstr&#246;m skeletal muscle biopsy technique on human subjects.

The percutaneous biopsy technique enables researchers and clinicians to collect skeletal muscle tissue samples. The technique is safe and highly ...

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

Isometric and Eccentric Force Generation Assessment of Skeletal Muscles Isolated from Murine Models of Muscular Dystrophies

Critical to the evaluation of potential therapeutics for muscular disease are sensitive and reproducible physiological assessments of muscle function. Because many pre-clinical trials rely on mouse models for these diseases, isolated muscle function has become one of the standards for Go/NoGo decisions in moving drug candidates forward into patients. We will demonstrate the preparation of the extensor digitorum longus (EDL) and diaphragm muscles for functional testing, which are the predominant muscles utilized for these studies. The EDL muscle geometry is ideal for isolated muscle preparations, with two easily accessible tendons, and a small size that can be supported by superfusion in a bath. The diaphragm exhibits profound progressive pathology in dystrophic animals, and can serve as a platform for evaluating many potential therapies countering fibrosis, and promoting myofiber stability. Protocols for routine testing, including isometric and eccentric contractions, will be shown. Isometric force provides assessment of strength, and eccentric contractions help to evaluate sarcolemma stability, which is disrupted in many types of muscular dystrophies. Comparisons of the expected results between muscles from wildtype and dystrophic muscles will also be provided. These measures can complement morphological and biochemical measurements of tissue homeostasis, as well as whole animal assessments of muscle function.

Muscle function measurements contribute to the evaluation of potential therapeutics for muscle pathology, as well as to the determination of mechanisms underlying physiology of this tissue. We will demonstrate the preparation of the extensor digitorum longus and diaphragm muscles for functional testing. Protocols for isometric and eccentric contractions will be shown, as well as differences in results between dystrophic muscles, representing a pathological state, and wildtype muscles.

Critical to the evaluation of potential  therapeutics for muscular disease are sensitive and reproducible physiological  assessments of muscle function. ...

Skeletal Muscle Neurovascular Coupling, Oxidative Capacity, and Microvascular Function with 'One Stop Shop' Near-infrared Spectroscopy

Exercise represents a major hemodynamic stress that demands a highly coordinated neurovascular response in order to match oxygen delivery to metabolic demand. Reactive hyperemia (in response to a brief period of tissue ischemia) is an independent predictor of cardiovascular events and provides important insight into vascular health and vasodilatory capacity. Skeletal muscle oxidative capacity is equally important in health and disease, as it determines the energy supply for myocellular processes. Here, we describe a simple, non-invasive approach using near-infrared spectroscopy to assess each of these major clinical endpoints (reactive hyperemia, neurovascular coupling, and muscle oxidative capacity) during a single clinic or laboratory visit. Unlike Doppler ultrasound, magnetic resonance images/spectroscopy, or invasive catheter-based flow measurements or muscle biopsies, our approach is less operator-dependent, low-cost, and completely non-invasive. Representative data from our lab taken together with summary data from previously published literature illustrate the utility of each of these end-points. Once this technique is mastered, application to clinical populations will provide important mechanistic insight into exercise intolerance and cardiovascular dysfunction.

Here, we describe a simple, non-invasive approach using near-infrared spectroscopy to assess reactive hyperemia, neurovascular coupling and skeletal muscle oxidative capacity in a single clinic or laboratory visit.

Exercise represents a major hemodynamic stress that demands a highly coordinated neurovascular response in order to match oxygen delivery to metabolic ...

Non-invasive Assessment of Dorsiflexor Muscle Function in Mice

Assessment of skeletal muscle contractile function is an important measurement for both clinical and research purposes. Numerous conditions can negatively affect skeletal muscle. This can result in a loss of muscle mass (atrophy) and/or loss of muscle quality (reduced force per unit of muscle mass), both of which are prevalent in chronic disease, muscle-specific disease, immobilization, and aging (sarcopenia). Skeletal muscle function in animals can be evaluated by a range of different tests. All tests have limitations related to the physiological testing environment, and the selection of a specific test often depends on the nature of the experiments. Here, we describe an in vivo, non-invasive technique involving a helpful and easy assessment of force frequency-curve (FFC) in mice that can be performed on the same animal over time. This permits monitoring of disease progression and/or efficacy&#160;of a potential therapeutic treatment.

Measurement of rodent skeletal muscle contractile function is a useful tool that can be used to track disease progression as well as efficacy of therapeutic intervention. We describe here the non-invasive, in vivo assessment of the dorsiflexor muscles that can be repeated over time in the same mouse.

Assessment of skeletal muscle contractile function is an important measurement for both clinical and research purposes. Numerous conditions can negatively ...

Induction and Assessment of Exertional Skeletal Muscle Damage in Humans

Summary

Explore More Videos

Chapters in this video

In Vivo Canine Muscle Function Assay

Manual Muscle Testing: A Method of Measuring Extremity Muscle Strength Applied to Critically Ill Patients

An in vivo Rodent Model of Contraction-induced Injury and Non-invasive Monitoring of Recovery

The Use of Thermal Infra-Red Imaging to Detect Delayed Onset Muscle Soreness

Induction of Acute Skeletal Muscle Regeneration by Cardiotoxin Injection

Human Skeletal Muscle Biopsy Procedures Using the Modified Bergström Technique

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

Isometric and Eccentric Force Generation Assessment of Skeletal Muscles Isolated from Murine Models of Muscular Dystrophies

Skeletal Muscle Neurovascular Coupling, Oxidative Capacity, and Microvascular Function with 'One Stop Shop' Near-infrared Spectroscopy

Non-invasive Assessment of Dorsiflexor Muscle Function in Mice