The authors would like to thankfully acknowledge all of the subjects in the study. Funding sources A research grant from the Czech Science Foundation GACR NO. 16-13750S, PRIMUS/17/MED/5 and UNCE 032 project.

The presented protocol follows the guidelines of human research ethics committee at Charles University, Faculty of Physical Education in Sport and has been previously approved as part of research.
1. Familiarize All Subjects Before Isokinetic Testing by Following Steps
<ol>
	<li>Ensure that the subjects have not had any recent musculoskeletal injuries or pain in the lower limbs in the previous 6 months. If a subject reports recent knee pain, or has knee pain during testing, exclude the subject.</li>
	<li>As eccentric isokinetic testing is likely a novel stimulus for many individuals, familiarize the subject with the protocols on a valid isokinetic dynamometer19,20 (steps 1.3 to 1.7.6, below) at least twice before participating in official testing. Instruct the subjects to not perform any lower body resistance training, or other strenuous exercises, 72 h before testing.</li>
	<li>To begin, guide the subjects through a general warm up.
	<ol>
		<li>Instruct the subjects to jog for 5-10 min or cycle for 5-10 min on an ergometer with a resistance of 1.5-2 W/kg of body mass with a cadence between 60-90 rpm.</li>
		<li>After cycling, instruct the subjects to perform two sets of 8-10 body weight lunges and 8-10 hamstring curls on a Swiss ball with each leg with 1 min of rest between sets.</li>
		<li>Next, guide the subjects through dynamic stretching of the lower limbs including the quadriceps and hamstrings21.</li>
	</ol>
	</li>
	<li>Show the subject an example of the isokinetic torque-angle curve and explain that live visual feedback will be provided during the test.</li>
	<li>Explain that the subject should &#34;kick out as hard and fast as possible&#34; for concentric knee extension and &#34;pull back as hard as fast as possible&#34; for concentric knee flexion. Also explain that the machine will move on its own during eccentric actions, but that the subject should try to &#34;push as hard as possible&#34; during eccentric knee flexion (eccentric action of the quadriceps) and &#34;pull as hard as possible&#34; during eccentric knee extension (eccentric actions of the hamstrings).</li>
	<li>Allow the subject to ask any questions and make sure they understand what will happen during the test. Clearly state that if the subject experiences any pain or discomfort during the test that makes the subject wish to terminate the test at any time, the subject should inform the researcher immediately, and the test can be safely aborted.</li>
	<li>Start the pre-set protocol listed in Table 1, and continually guide the subject through the protocol.
	<ol>
		<li>Using the recommendations of Brown22, position the subject on the dynamometer in a sitting position with a hip angle of 100&#176; of extension. Adjust the settings of the dynamometer to ensure that the subject&#39;s hips are all the way back and in contact with the chair and the dynamometer&#39;s axis of rotation axis is in-line with the axis of rotation of the subject&#39;s tested knee.</li>
		<li>Instruct the subject to hold a deep breath while fixing the shoulders, pelvis, and thigh of the tested leg using the pads and straps on the dynamometer. Fix the lever arm of the dynamometer to the distal part of the shin with the pad placed 2.5 cm over the apex of the medial malleolus, but do not support the non-exercised lower limb.</li>
		<li>Allow the subject to passively and actively go through the full extension and flexion range of motion while readjusting the straps, dynamometer settings, or both if needed.</li>
		<li>Ensure that the subjects can see a screen that shows the torque-angle curve and provide a verbal countdown to begin the test. Instruct the subjects to hold the handgrips located at the side of the seat during all testing efforts.</li>
		<li>Start the test and verbally encourage the subject by using phrases such as &#34;go&#34;, &#34;push harder&#34;, &#34;pull, pull, pull&#34;, etc. During the rest intervals, provide the subject with short instructions about the upcoming task.</li>
		<li>After completing the protocol, allow the subject to get out of the dynamometer chair, and adjust the dynamometer to test the other limb.</li>
		<li>After repositioning the subject and adjusting the machine accordingly, perform the gravity correction measurement again and start the test for the untested lower limb.</li>
	</ol>
	</li>
	<li>Open the test results that show the angle-torque curve and check whether the subject achieved the selected speed of contraction for the whole movement.
	<ol>
		<li>To determine if the desired speed was accomplished, ensure that the angle-torque curve does not appear to be interrupted (Figure 1).</li>
		<li>If the curve looks interrupted (Figure 2), it is likely that the subject did not push or pull against the lever arm fast enough for the dynamometer to register torque. If the subject was not able to reach the required angular velocity and register torque, continue with additional familiarization or exclude the subject from the study and check the possibility of an articular knee lesion23.</li>
	</ol>
	</li>
</ol>
2. Isokinetic Strength Measurement After Two Familiarization Visits
<ol>
	<li>Set up the dynamometer&#39;s software to perform the tests according to Table 1, and complete the protocol as described in steps 1.3 to 1.7.6.</li>
	<li>After the end of the protocol, allow the subject out of the chair and begin analyzing the data.</li>
</ol>
3. Hamstrings to Quadriceps Functional Ratio Calculation
<ol>
	<li>Use the best peak torque values from all three trials at each given speed and type of muscle action. Insert the peak torque data and resultant ratios into a data organizing software that can graphically depict data such as Microsoft Excel.</li>
	<li>Calculate the H/QFUNC60 ratio by dividing the hamstring eccentric peak torque at 60&#176;&#183;s-1 by the quadriceps concentric peak torque at 60&#176;&#183;s-1.</li>
	<li>Calculate the H/QFUNC180 ratio by dividing the hamstring eccentric peak torque at 180&#176;&#183;s-1 by the quadriceps concentric peak torque at 180&#176;&#183;s-1.</li>
	<li>Calculate the H/QFUNC240 ratio by dividing the hamstring eccentric peak torque at 240&#176;&#183;s-1 by the quadriceps concentric peak torque at 240&#176;&#183;s-1.</li>
	<li>After creating a table similar to Table 2, compare the H/QFUNC ratios across different speeds and between the right and left limbs.
	<ol>
		<li>Compare the measured peak values with normative data of a similar athletic group of the same age and gender.</li>
		<li>Determine if bilateral imbalances are present by comparing the right and left limbs at each tested speed.</li>
		<li>Determine if the ipsilateral H/Qconv ratio at the same speed is above or below 0.624. If the values are below 0.6, the ipsilateral hamstring weakness is present compared to the quadriceps; design a specific hamstring strengthening intervention (Section 4).</li>
		<li>Determine if the ipsilateral H/Qfunc ratio increases along with increased speed and reaches the desired value of 1.012,18, preferably in the speed of 180&#176;&#183;s-1. If the HQfunc does not increase with the increased speed, implement hamstring training to resolve the reciprocal function of the hamstrings (Section 4).</li>
	</ol>
	</li>
</ol>
4. Eccentric Hamstring Strength Training Examples
<ol>
	<li>Consult with a trained exercise professional25, such as Certified Strength and Conditioning Specialist, to select various exercises that target the hamstrings across a variety of muscle lengths, speeds, and movement patterns.
	<ol>
		<li>Consult the exercise professional for advice regarding exercises that improve neuromuscular control during landing and jumping in addition to exercises reported to decrease hamstring injury risk.</li>
		<li>Under the professional&#39;s guidance, use the Nordic curl (Russian curl) exercise which can strengthen the hamstrings and reduce the risk of injury26,27, as this exercise focuses on eccentric hamstring strengthening.</li>
		<li>Under the professional&#39;s guidance, use unilateral knee flexions on a Swiss ball to strengthen the hamstrings and possibly reduce a bilateral strength deficit28,29.</li>
		<li>Under the professional&#39;s guidance, use unilateral or bilateral Romanian deadlifts, the good morning exercise, or both to strengthen the hip extension function of hamstrings28,30,31.</li>
		<li>Under the professional&#39;s guidance, use complex exercises to strengthen both the hamstrings and quadriceps during &#34;triple extension&#34; exercises where the hips, knees, and ankle simultaneously flex and extend such as the squat, deadlift, and lunge.</li>
		<li>Under the professional&#39;s guidance, use exercises such as drop jumps or other repeated jumps to train proprioception in the lower limbs.</li>
	</ol>
	</li>
	<li>Under the professional&#39;s guidance, progressively increase the number of sets and repetitions in bodyweight exercises such as the Nordic curl and unilateral hamstring curl on the Swiss ball32, while also progressively increasing the external resistance and decreasing the number of repetitions in complex exercises (for an example, see Table 3).</li>
</ol>

There are no conflicts of interest to report.

The first critical step in the aforementioned protocol is the athlete&#39;s familiarization, especially for the eccentric tests. Subjects may have to be familiarized two or three times to ensure reliable data during such isokinetic testing. Furthermore, it may be a good idea to re-familiarize subjects if testing sessions are more than two months apart. The second critical step is properly setting up the athlete in the dynamometer, ensuring that the knee axis is in-line with the axis of the dynamometer; it is also important to note that stronger individuals may push or pull so hard against the lever arm that the seat pad becomes depressed or the knee joint may move slightly forward or backward. These possibilities should be considered during positioning the athlete and during testing. Another critical point is the ability of the athlete to produce maximal torque production at all tested speed conditions and load range data reduction across increasing velocities. The maximal attainable torque is highly dependent on the speed of contraction, meaning that it is crucial to check whether an athlete can generate torque against the lever arm throughout the whole range of motion (ROM) during high-speed protocols (240&#176;&#183;s-1). Along these lines, the load range data should be reduced by eliminating the first and last 10&#176; of measured range of motion22 to avoid artificial spikes in the torque output signal that may occur at the beginning and end of the ROM.
After completing a successful test, it is also important to interpret the data correctly. If the H/Qconv values (e.g., at 60&#176; m&#8729;s-1) are below 0.6, ipsilateral hamstring weakness is present compared to the quadriceps. However, assessing this ratio alone is not enough for predicting a possible hamstring strain or anterior cruciate ligament injury33,34. More important is to assess whether the H/Qfunc ratio increases along with the tested speed. The minimal recommended H/Qfunc increase between different tested speeds is not sufficiently established. However, we are suggesting optimal H/Qfunc increase between the speed of 60&#176;, 180&#176;, and 240&#176;&#183;s-1 from above 0.6, to above 0.8, to above 0.113,18. The H/QFUNC should be also evaluated in relation to specific athlete groups, where uninjured elite sprinters tested at 60&#176;&#8729;s-1 were reported for H/QFUNC 0. 83 &#177; 0.17 and injured sprinters 0.73 &#177; 0.1235. Between-leg comparisons may be valuable information as well. For example, a bilateral strength difference greater than 15% (measured in the same speed) is considered to increase an athlete&#39;s risk of knee injury36 and a difference over 20% indicates that an athlete is predisposed to injury37. On the other hand, a bilateral deficit less than 10% is not considered a significant imbalance and is interpreted as a target for athletes with previous imbalances or athletes reconditioning after injury2.
Although the presented protocol can be used in many athletic populations, it is possible to adjust the speed and contraction mode for testing untrained or extremely trained subjects. In the event that maximal strength tests are warranted, isometric tests can be performed on a dynamometer as well and can be used in conjunction with dynamic testing38. If the athletes are highly trained or participate in high velocity sports, speeds nearer to 300&#176;&#183;s-1 39 or more may be appropriate. Regardless of the speeds used, the presented method is limited to isokinetic contractions and single joint movements, neither of which happen during sport. However, in a laboratory setting, isokinetic measurements likely provide the most valid and reliable data for assessing concentric and eccentric strength of the knee flexors and extensors22. One alternative method for assessing muscle net force is by calculating it from reactive force40; however, this method is unable to isolate force or torque generated by a specific group of muscles.
If coaches or practitioners are in search of additional data to create global strength measures for different muscle groups, additional measurements can be performed on the muscles of the lower body35,41,42,43,44,45. Together, the H/QFUNC ratio combined with strength measurements of the hip adductors, abductors, and extensors can provide a wealth of data that can be used to monitor the effectiveness of a resistance training program. The future application of this method might be in its combination to other isolated strength measures, specification of compared knee joint angles for specific purposes13, and combination with multijoint movements such as the leg press46 or squat47.

The relationship between knee flexor and extensor strength has been identified as an important parameter in assessing a person&#39;s risk of incurring a lower limb injury1. Specifically, there is an increased probability of hamstring injury when ipsilateral or bilateral imbalances in hamstring strength are present when compared to quadricep strength2. Therefore, many sport scientists and practitioners test knee flexor and extensor strength to determine whether an athlete is at risk of incurring a hamstring injury. However, various testing methods are used that do not allow for direct comparisons to be made between methods (e.g., different contraction speeds, different muscle actions, and field testing vs. laboratory testing)3,4,5,6,7,8,9. Although different testing methods provide different bits of valuable information regarding strength levels, the methodological approach for thigh muscle isokinetic strength testing should be unified to enable comparisons across individuals, populations, and time.
Although the evaluation of ipsilateral imbalances between knee flexors and extensors have been often described using the conventional concentric hamstring to concentric quadriceps ratio (H/QCONV)10,11, co-activation of the knee flexors and extensors is known to occur during all movements and takes place through opposing contraction modes. To explain, the knee extensors are primarily involved in propulsion during jumping and running, whereas the knee flexors primarily stabilize the knee during landing and running by decelerating the lower limb and counteracting the rapid and forceful concentric contractions of the extensors. As most movements in sports require simultaneous concentric knee extension and eccentric knee flexion, a relative strength comparison between the two would be appropriate. Therefore, eccentric knee flexor strength relative to concentric knee extensor strength is commonly tested and is known as the &#34;functional ratio&#34; (H/QFUNC)12.
Compared to the H/QCONV ratio where values can range from 0.43 to 0.9012, the H/QFUNC ratio can range from 0.4 to 1.413, indicating that data from different protocols should not be compared to each other. Although maximal concentric torque decreases as concentric speed increases14,15,16, eccentric torque is greater than concentric torque as speed increases16,17. As such, the H/QFUNC ratio can approach a value of 1.0 as the speed of testing contraction increases13,18. Since most sport movements occur at high velocities, knee extensor and flexor strength testing are likely more ecologically valid at higher speeds. Therefore, such strength testing protocols should include progressively increased speeds in a stepwise progression.
If isokinetic testing reveals a large discrepancy between eccentric hamstring and concentric quadricep strength, the discrepancy should be narrowed through training. For this purpose, decreasing knee extensor strength should never compensate for weak knee flexors at the expense of a more favorable H/QFUNC ratios, especially in sporting environments. The other option would be to progressively and intensively increase knee flexor strength so that the hamstrings become stronger, especially in relation to the quadriceps, at higher speeds. Therefore, if isokinetic testing reveals some degree of hamstring weakness, a training intervention will likely be necessary to increase hamstring strength, especially during eccentric muscle actions. As with all training interventions, follow-up testing should be performed to determine the efficacy of the eccentrically-focused hamstring strength training program, and further adjustments may need to be made. The objective of this paper is to describe how to test isokinetic functional eccentric hamstring strength, reveal potential hamstring weakness, and suggest how to resolve a functional hamstring weakness.

<table><tbody><tr><td>HumacNorm</td><td>CSMI, Stoughton, MA, USA</td><td>021-54412236 (model 502140)</td><td>Standard Dynamometr</td></tr><tr><td>SoftwareHumac 2015</td><td>Computer Sports Medicine Inc. Stoughton, MA, USA</td><td>Version155</td><td>Software for dynamometr</td></tr></tbody></table>

muscle imbalances: testing and training functional eccentric hamstring strength in athletic populations

Many hamstring injuries that occur during physical activity occur while the muscles are lengthening, during eccentric hamstring muscle actions. Opposite of these eccentric hamstring actions are concentric quadriceps actions, where the larger and likely stronger quadriceps straighten the knee. Therefore, to stabilize the lower limbs during movement, the hamstrings must eccentrically combat against the strong knee-straightening torque of the quadriceps. As such, eccentric hamstring strength expressed relative to concentric quadricep strength is commonly referred to as the &#34;functional ratio&#34; as most movements in sports require simultaneous concentric knee extension and eccentric knee flexion. To increase the strength, resiliency, and functional performance of the hamstrings, it is necessary to test and train the hamstrings at different eccentric speeds. The main purpose of this work is to provide instructions for measuring and interpreting eccentric hamstring strength. Techniques for measuring the functional ratio using isokinetic dynamometry are provided and sample data will be compared. Additionally, we briefly describe how to address hamstring strength deficiencies or unilateral strength differences using exercises that specifically focus on increasing eccentric hamstring strength.

The examples below show the differences between young elite soccer athletes (age 15.4 &#177; 0.5 years, body mass 62.7 &#177; 8.2 kg, height 175 &#177; 9.1, training experience more than 8 years) performing eccentric hamstring training (EHT, n = 18) and without EHT (n = 15) for 12 weeks (Figure 3). The group performing EHT included this exercise two times per week, while the group without EHT performed core training and a general lower limb program instead. Both groups participated in their program for four months.
Before the training program, neither group increased their H/Qfunc as the tested speed increased (Figure 3). After 12 weeks of training, EHT players had significantly greater H/Qfunc at each tested speed. Moreover, the EHT group showed increased H/Qfunc between the speeds 60&#176;&#183;s-1, 180&#176;&#183;s-1, and 240&#176;&#183;s-1, while the core training group (without EHT) showed H/Qfunc increase only between the speed 60&#176;&#183;s-1 and 240&#176;&#183;s-1.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/57508/57508fig1.jpg" /> 
Figure 1: Apropriate knee flexors and extensor torque during 10-90&#176; knee flexion range of motion. (A) Torque/angle strength curve for knee extension, (B) torque/angle strength curve for knee flexion. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/57508/57508fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/57508/57508fig2.jpg" /> 
Figure 2:. Interrupted knee flexors and extensor torque during 10-90&#176; knee flexion range of motion. (A) Torque/angle strength curve for knee extension, (B) torque/angle strength curve for knee flexion. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/57508/57508fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/57508/57508fig3.jpg" /> 
Figure 3: The representative results of H/Qfunc with and without specific hamstring training. H: hamstrings, Q: quadriceps, EHT: eccentric hamstrings training, PRE: test before specific training, POST: test after 12 weeks specific training. Data are presented as the mean &#177; standard deviation. The error bars represent the standard deviation.
<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Test phase</td>
			<td>Task</td>
			<td>Rest</td>
		</tr>
		<tr>
			<td>Pre-test</td>
			<td>Gravity correction, set knee flexion to 90&#176;, set range of motion from 90&#176; to 10&#176; (where 0&#176; = full extension)</td>
			<td></td>
		</tr>
		<tr>
			<td>Trial at 60&#176;&#183;s-1</td>
			<td>Concentric knee extension/flexion 1 repetition</td>
			<td>15 s</td>
		</tr>
		<tr>
			<td>Test at 60&#176;&#183;s-1</td>
			<td>Concentric knee extension/flexion 3 repetitions</td>
			<td>60 s</td>
		</tr>
		<tr>
			<td>Trial at 60&#176;&#183;s-1</td>
			<td>Eccentric knee extension/flexion 1 repetition</td>
			<td>15 s</td>
		</tr>
		<tr>
			<td>Test at 60&#176;&#183;s-1</td>
			<td>Eccentric knee extension/flexion 3 repetitions</td>
			<td>60 s</td>
		</tr>
		<tr>
			<td>Trial at 180&#176;&#183;s-1</td>
			<td>Concentric knee extension/flexion 1 repetition</td>
			<td>15 s</td>
		</tr>
		<tr>
			<td>Test at 180&#176;&#183;s-1</td>
			<td>Concentric knee extension/flexion 3 repetitions</td>
			<td>60 s</td>
		</tr>
		<tr>
			<td>Trial at 180&#176;&#183;s-1</td>
			<td>Eccentric knee extension/flexion 1 repetition</td>
			<td>15 s</td>
		</tr>
		<tr>
			<td>Test at 180&#176;&#183;s-1</td>
			<td>Eccentric knee extension/flexion 3 repetitions</td>
			<td>60 s</td>
		</tr>
		<tr>
			<td>Trial at 240&#176;&#183;s-1</td>
			<td>Concentric knee extension/flexion 1 repetition</td>
			<td>15 s</td>
		</tr>
		<tr>
			<td>Test at 240&#176;&#183;s-1</td>
			<td>Concentric knee extension/flexion 3 repetitions</td>
			<td>60 s</td>
		</tr>
		<tr>
			<td>Trial at 240&#176;&#183;s-1</td>
			<td>Eccentric knee extension/flexion 1 repetition</td>
			<td>15 s</td>
		</tr>
		<tr>
			<td>Test at 240&#176;&#183;s-1</td>
			<td>Eccentric knee extension/flexion 3 repetitions</td>
			<td>60 s</td>
		</tr>
	</tbody>
</table>
Table 1: Isokinetic testing protocol.
<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Right lower limb</td>
			<td>Hamstrings peak torque (N&#8729;m)</td>
			<td>Quadriceps peak torque (N&#8729;m)</td>
			<td>H/Q conventional</td>
			<td>H/Q functional</td>
		</tr>
		<tr>
			<td>60&#176;&#183;s-1 concentric</td>
			<td>117</td>
			<td>243</td>
			<td>0.48</td>
			<td rowspan="2">0.7</td>
		</tr>
		<tr>
			<td>60&#176;&#183;s-1 eccentric</td>
			<td>171</td>
			<td>327</td>
			<td>0.52</td>
		</tr>
		<tr>
			<td>180&#176;&#183;s-1 concentric</td>
			<td>123</td>
			<td>168</td>
			<td>0.73</td>
			<td rowspan="2">0.95</td>
		</tr>
		<tr>
			<td>180&#176;&#183;s-1 eccentric</td>
			<td>159</td>
			<td>327</td>
			<td>0.59</td>
		</tr>
		<tr>
			<td>240&#176;&#183;s-1 concentric</td>
			<td>98</td>
			<td>137</td>
			<td>0.71</td>
			<td rowspan="2">1.21</td>
		</tr>
		<tr>
			<td>240&#176;&#183;s-1 eccentric</td>
			<td>167</td>
			<td>297</td>
			<td>0.56</td>
		</tr>
		<tr>
			<td>Left lower limb</td>
			<td></td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>60&#176;&#183;s-1 concentric</td>
			<td>118</td>
			<td>245</td>
			<td>0.48</td>
			<td rowspan="2">0.62</td>
		</tr>
		<tr>
			<td>60&#176;&#183;s-1 eccentric</td>
			<td>152</td>
			<td>282</td>
			<td>0.54</td>
		</tr>
		<tr>
			<td>180&#176;&#183;s-1 concentric</td>
			<td>113</td>
			<td>151</td>
			<td>0.75</td>
			<td rowspan="2">0.99</td>
		</tr>
		<tr>
			<td>180&#176;&#183;s-1 eccentric</td>
			<td>149</td>
			<td>286</td>
			<td>0.52</td>
		</tr>
		<tr>
			<td>240&#176;&#183;s-1 concentric</td>
			<td>114</td>
			<td>134</td>
			<td>0.85</td>
			<td rowspan="2">1.14</td>
		</tr>
		<tr>
			<td>240&#176;&#183;s-1 eccentric</td>
			<td>153</td>
			<td>298</td>
			<td>0.51</td>
		</tr>
	</tbody>
</table>
Table 2: Organized table with test outcome values. H: hamstrings, Q: quadriceps.
<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Week</td>
			<td>Sessions per week</td>
			<td>Sets</td>
			<td>Repetitions</td>
		</tr>
		<tr>
			<td>1</td>
			<td>1</td>
			<td>1</td>
			<td>5</td>
		</tr>
		<tr>
			<td>2</td>
			<td>2</td>
			<td>2</td>
			<td>6</td>
		</tr>
		<tr>
			<td>3</td>
			<td>2</td>
			<td>3</td>
			<td>6-8</td>
		</tr>
		<tr>
			<td>4</td>
			<td>2</td>
			<td>3</td>
			<td>8-10</td>
		</tr>
		<tr>
			<td>5</td>
			<td>3</td>
			<td>3</td>
			<td>8-10</td>
		</tr>
		<tr>
			<td>6-12</td>
			<td>3</td>
			<td>3</td>
			<td>12,10,8</td>
		</tr>
	</tbody>
</table>
Table 3: Nordic curl exercise volume progression according to Mj&#248;lsnes32.

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Muscle Imbalances: Testing and Training Functional Eccentric Hamstring Strength in Athletic Populations

The hamstrings are a group of muscles that are sometimes problematic for athletes, resulting in soft tissue injury in the lower limbs. To prevent such injuries, functional training of the hamstrings requires intensive eccentric contractions. Additionally, hamstring function should be tested in relation to quadricep function at different contraction speeds.

Many hamstring injuries that occur during physical activity occur while the muscles are lengthening, during eccentric hamstring muscle actions. Opposite ...

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15.2K Views.  Charles University. De hamstrings zijn een groep van spieren die soms problematisch voor atleten zijn, wat resulteert in zachte weefsel schade in de onderste ledematen. Om te voorkomen dat dergelijke verwondingen, vereist functionele training van de hamstrings intensieve excentrische contracties. Bovendien, moet hamstring functie worden getest in verband met de quadricep functie bij samentrekking van de verschillende snelheden.

Video: Muscle Imbalances: Testing and Training Functional Eccentric Hamstring Strength in Athletic Populations

An Inertial Measurement Unit Based Method to Estimate Hip and Knee Joint Kinematics in Team Sport Athletes on the Field

Current athlete monitoring practice in team sports is mainly based on positional data measured by global positioning or local positioning systems. The disadvantage of these measurement systems is that they do not register lower extremity kinematics, which could be a useful measure for identifying injury-risk factors. Rapid development in sensor technology may overcome the limitations of the current measurement systems. With inertial measurement units (IMUs) securely fixed to body segments, sensor fusion algorithms and a biomechanical model, joint kinematics could be estimated. The main purpose of this article is to demonstrate a sensor setup for estimating hip and knee joint kinematics of team sport athletes in the field. Five male subjects (age 22.5 &#177; 2.1 years; body mass 77.0 &#177; 3.8 kg; height 184.3 &#177; 5.2 cm; training experience 15.3 &#177; 4.8 years) performed a maximal 30-meter linear sprint. Hip and knee joint angles and angular velocities were obtained by five IMUs placed on the pelvis, both thighs and both shanks. Hip angles ranged from 195&#176; (&#177; 8&#176;) extension to 100.5&#176; (&#177; 8&#176;) flexion and knee angles ranged from 168.6&#176; (&#177; 12&#176;) minimal flexion and 62.8&#176; (&#177; 12&#176;) maximal flexion. Furthermore, hip angular velocity ranged between 802.6 &#176;&#183;s-1 (&#177; 192 &#176;&#183;s-1) and -674.9 &#176;&#183;s-1 (&#177; 130 &#176;&#183;s-1). Knee angular velocity ranged between 1155.9 &#176;&#183;s-1 (&#177; 200 &#176;&#183;s-1) and -1208.2 &#176;&#183;s-1 (&#177; 264 &#176;&#183;s-1). The sensor setup has been validated and could provide additional information with regard to athlete monitoring in the field.&#160;This may help professionals in a daily sports setting to evaluate their training programs, aiming to reduce injury and optimize performance.

Monitoring athletes is essential for improving performance and reducing injury risk in team sports. Current methods to monitor athletes do not include the lower extremities. Attaching multiple inertial measurement units to the lower extremities could improve monitoring athletes in the field.

Current athlete monitoring practice in team sports is mainly based on positional data measured by global positioning or local positioning systems. The ...

Behavior

Applications of In Vivo Functional Testing of the Rat Tibialis Anterior for Evaluating Tissue Engineered Skeletal Muscle Repair

Despite the regenerative capacity of skeletal muscle, permanent functional and/or cosmetic deficits (e.g., volumetric muscle loss (VML) resulting from traumatic injury, disease and various congenital, genetic and acquired conditions are quite common. Tissue engineering and regenerative medicine technologies have enormous potential to provide a therapeutic solution. However, utilization of biologically relevant animal models in combination with longitudinal assessments of pertinent functional measures are critical to the development of improved regenerative therapeutics for treatment of VML-like injuries. In that regard, a commercial muscle lever system can be used to measure length, tension, force and velocity parameters in skeletal muscle. We used this system, in conjunction with a high power, bi-phase stimulator, to measure in vivo force production in response to activation of the anterior crural compartment of the rat hindlimb. We have previously used this equipment to assess the functional impact of VML injury on the tibialis anterior (TA) muscle, as well as the extent of functional recovery following treatment of the injured TA muscle with our tissue engineered muscle repair (TEMR) technology. For such studies, the left foot of an anaesthetized rat is securely anchored to a footplate linked to a servomotor, and the common peroneal nerve is stimulated by two percutaneous needle electrodes to elicit muscle contraction and dorsiflexion of the foot. The peroneal nerve stimulation-induced muscle contraction is measured over a range of stimulation frequencies (1-200 Hz), to ensure an eventual plateau in force production that allows for an accurate determination of peak tetanic force. In addition to evaluation of the extent of VML injury as well as the degree of functional recovery following treatment, this methodology can be easily applied to study diverse aspects of muscle physiology and pathophysiology. Such an approach should assist with the more rational development of improved therapeutics for muscle repair and regeneration.

Applications of In Vivo Functional Testing of the Rat Tibialis Anterior for Evaluating Tissue Engineered Skeletal Muscle Repair

We describe an in vivo protocol to measure dorsiflexion of the foot following stimulation of the peroneal nerve and contraction of the anterior crural compartment of the rat hindlimb. Such measurements are an indispensable translational tool for evaluating skeletal muscle pathology and tissue engineering approaches to muscle repair and regeneration.

Despite the regenerative capacity of skeletal muscle, permanent functional and/or cosmetic deficits (e.g., volumetric muscle loss (VML) resulting from ...

Bioengineering

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.

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 ...

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

Adapted Resistance Training Improves Strength in Eight Weeks in Individuals with Multiple Sclerosis

Hip weakness is a common symptom affecting walking ability in people with multiple sclerosis (MS). It is known that resistance strength training (RST) can improve strength in individuals with MS, however; it remains unclear the duration of RST that is needed to make strength gains and how to adapt hip strengthening exercises for individuals of varying strength using only resistance bands. This paper describes the methodology to set up and implement an adapted resistance strength training program, using resistance bands, for individuals with MS. Directions for pre- and post-strength tests to evaluate efficacy of the strength-training program are included. Safety features and detailed instructions outline the weekly program content and progression. Current evidence is presented showing that significant strength gains can be made within 8 weeks of starting a RST program. Evidence is also presented showing that resistance strength training can be successfully adapted for individuals with MS of varying strength with little equipment.

Hip weakness is a common symptom affecting walking ability in people with multiple sclerosis. Isolated muscle strengthening is a useful method to target specific weaknesses. This protocol describes a progressive resistance-training program using exercise bands to increase hip muscle strength.

Hip weakness is a common symptom affecting walking ability in people with multiple sclerosis (MS). It is known that resistance strength training (RST) can ...

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.

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 ...

Improving Strength, Power, Muscle Aerobic Capacity, and Glucose Tolerance through Short-term Progressive Strength Training Among Elderly People

This protocol describes the simultaneous use of a broad span of methods to examine muscle aerobic capacity, glucose tolerance, strength, and power in elderly people performing short-term resistance training (RET). Supervised progressive resistance training for 1 h three times a week over 8 weeks was performed by RET participants (71&#177;1 years, range 65-80). Compared to a control group without training, the RET showed improvements on the measures used to indicate strength, power, glucose tolerance, and several parameters of muscle aerobic capacity. Strength training was performed in a gym with only robust fitness equipment. An isokinetic dynamometer for knee extensor strength permitted the measurement of concentric, eccentric, and static strength, which increased for the RET group (8-12% post- versus pre-test). The power (rate of force development, RFD) at the initial 0-30 ms also showed an increase for the RET group (52%). A glucose tolerance test with frequent blood glucose measurements showed improvements only for the RET group in terms of blood glucose values after 2 h (14%) and the area under the curve (21%). The blood lipid profile also improved (8%). From muscle biopsy samples prepared using histochemistry, the amount of fiber type IIa increased, and a trend towards a decrease in IIx in the RET group reflected a change to a more oxidative profile in terms of fiber composition. Western blot (to determine the protein content related to the signaling for muscle protein synthesis) showed a rise of 69% in both Akt and mTOR in the RET group; this also showed an increase in mitochondrial proteins for OXPHOS complex II and citrate synthase (both ~30%) and for complex IV (90%), in only the RET group. We demonstrate that this type of progressive resistance training offers various improvements (e.g., strength, power, aerobic capacity, glucose tolerance, and plasma lipid profile).

The effect of short-term resistance training on elderly people was investigated through the simultaneous use of several methods. Compared to a control group, many improvements were seen, including on muscle aerobic capacity, glucose tolerance, strength, power, and muscle quality (i.e., protein involved in cell signaling and muscle fiber type composition).

This protocol describes the simultaneous use of a broad span of methods to examine muscle aerobic capacity, glucose tolerance, strength, and power in ...

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. ...

Biology

Lower Limb Biomechanical Analysis of Healthy Participants

Biomechanical analysis techniques are useful in the study of human movement. The aim of this study was to introduce a technique for the lower limb biomechanical assessment in healthy participants using commercially available systems. Separate protocols were introduced for the gait analysis and muscle strength testing systems. To ensure maximum accuracy for gait assessment, attention should be given to the marker placements and self-paced treadmill acclimatization time. Similarly, participant positioning, a practice trial, and verbal encouragement are three critical stages in muscle strength testing. The current evidence suggests that the methodology outlined in this article may be effective for the assessment of lower limb biomechanics.

This article introduces a comprehensive experimental methodology on two of the latest technologies available to measure the lower limb biomechanics of individuals.

Biomechanical analysis techniques are useful in the study of human movement. The aim of this study was to introduce a technique for the lower limb ...

In vivo Measurement of Knee Extensor Muscle Function in Mice

Skeletal muscle plasticity in response to countless conditions and stimuli mediates concurrent functional adaptation, both negative and positive. In the clinic and the research laboratory, maximal muscular strength is widely measured longitudinally in humans, with knee extensor musculature the most reported functional outcome. Pathology of the knee extensor muscle complex is well documented in aging, orthopedic injury, disease, and disuse; knee extensor strength is closely related to functional capacity and injury risk, underscoring the importance of reliable measurement of knee extensor strength. Repeatable, in vivo assessment of knee extensor strength in pre-clinical rodent studies offers valuable functional endpoints for studies exploring osteoarthritis or knee injury. We report an in vivo and non-invasive protocol to repeatedly measure isometric peak tetanic torque of the knee extensors in mice across time. We demonstrate consistency using this novel method to measure knee extensor strength with repeated assessment in multiple mice producing similar results.

Quantification of knee extensor maximal strength is imperative to understand functional adaptations to aging, disease, injury, and rehabilitation. We present a novel method to repeatedly measure in vivo knee extension isometric peak tetanic torque.

Skeletal muscle plasticity in response to countless conditions and stimuli mediates concurrent functional adaptation, both negative and positive. In the ...

Muscle Imbalances: Testing and Training Functional Eccentric Hamstring Strength in Athletic Populations

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