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.

Watch this Scientific Journal Video about Muscle Imbalances: Testing and Training Functional Eccentric Hamstring Strength in Athletic Populations at JoVE.com

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 ...

muscle-imbalances-testing-training-functional-eccentric-hamstring

Nanyang Technological University

Research

JoVE Journal

Medicine

15.2K Views.  Charles University. 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.

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

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.

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, ...

A Murine Model of Muscle Training by Neuromuscular Electrical Stimulation

Neuromuscular electrical stimulation (NMES) is a common clinical modality that is widely used to restore1, maintain2 or enhance3-5 muscle functional capacity. Transcutaneous surface stimulation of skeletal muscle involves a current flow between a cathode and an anode, thereby inducing excitement of the motor unit and the surrounding muscle fibers. 
NMES is an attractive modality to evaluate skeletal muscle adaptive responses for several reasons. First, it provides a reproducible experimental model in which physiological adaptations, such as myofiber hypertophy and muscle strengthening6, angiogenesis7-9, growth factor secretion9-11, and muscle precursor cell activation12 are well documented. Such physiological responses may be carefully titrated using different parameters of stimulation (for Cochrane review, see 13). In addition, NMES recruits motor units non-selectively, and in a spatially fixed and temporally synchronous manner14, offering the advantage of exerting a treatment effect on all fibers, regardless of fiber type. Although there are specified contraindications to NMES in clinical populations, including peripheral venous disorders or malignancy, for example, NMES is safe and feasible, even for those who are ill and/or bedridden and for populations in which rigorous exercise may be challenging. 
Here, we demonstrate the protocol for adapting commercially available electrodes and performing a NMES protocol using a murine model. This animal model has the advantage of utilizing a clinically available device and providing instant feedback regarding positioning of the electrode to elicit the desired muscle contractile effect. For the purpose of this manuscript, we will describe the protocol for muscle stimulation of the anterior compartment muscles of a mouse hindlimb.

A murine model of neuromuscular electrical stimulation (NMES), a safe and inexpensive clinical modality, to the anterior compartment muscles is described. This model has the advantage of modifying a readily available clinical device for the purpose of eliciting targeted and specific muscle contractions in mice.

Neuromuscular electrical stimulation (NMES) is a common clinical modality that is widely used to restore1, maintain2 or enhance3-5 muscle functional ...

Single-stage Dynamic Reanimation of the Smile in Irreversible Facial Paralysis by Free Functional Muscle Transfer

Unilateral facial paralysis is a common disease that is associated with significant functional, aesthetic and psychological issues. Though idiopathic facial paralysis (Bell&#8217;s palsy) is the most common diagnosis, patients can also present with a history of physical trauma, infectious disease, tumor, or iatrogenic facial paralysis. Early repair within one year of injury can be achieved by direct nerve repair, cross-face nerve grafting or regional nerve transfer. It is due to muscle atrophy that in long lasting facial paralysis complex reconstructive methods have to be applied. Instead of one single procedure, different surgical approaches have to be considered to alleviate the various components of the paralysis.
The reconstruction of a spontaneous dynamic smile with a symmetric resting tone is a crucial factor to overcome the functional deficits and the social handicap that are associated with facial paralysis. Although numerous surgical techniques have been described, a two-stage approach with an initial cross-facial nerve grafting followed by a free functional muscle transfer is most frequently applied. In selected patients however, a single-stage reconstruction using the motor nerve to the masseter as donor nerve is superior to a two-stage repair. The gracilis muscle is most commonly used for reconstruction, as it presents with a constant anatomy, a simple dissection and minimal donor site morbidity.
Here we demonstrate the pre-operative work-up, the post-operative management, and precisely describe the surgical procedure of single-stage microsurgical reconstruction of the smile by free functional gracilis muscle transfer in a step by step protocol. We further illustrate common pitfalls and provide useful tips which should enable the reader to truly comprehend the procedure. We further discuss indications and limitations of the technique and demonstrate representative results.

The use of the masseteric nerve as donor nerve represents a single-stage alternative to the criterion standard two-stage procedure of cross-facial nerve grafting and free muscle transfer in facial paralysis. We provide a detailed description to safely perform this technique with a gracilis muscle transfer and discuss indications and limitations.

Unilateral facial paralysis is a common disease that is associated with significant functional, aesthetic and psychological issues. Though idiopathic ...

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 ...

Proximal Cadaveric Femur Preparation for Fracture Strength Testing and Quantitative CT-based Finite Element Analysis

Cadaveric fracture testing is routinely used to understand factors that affect proximal femur strength. Because ex vivo biological tissues are prone to lose their mechanical properties over time, specimen preparation for experimental testing must be performed carefully to obtain reliable results that represent in vivo conditions. For that reason, we designed a protocol and a set of fixtures to prepare the femoral specimens such that their mechanical properties experienced minimal changes. The femora were kept in a frozen state except during preparation steps and mechanical testing. The relevant clinical measures of total hip and femoral neck bone mineral density (BMD) were obtained with a clinical dual X-ray absorptiometry (DXA) bone densitometer, and the 3D geometry and distribution of bone mineral were obtained using CT with a calibration phantom for quantitative estimations based on the greyscale values. Any possible bone disease, fracture, or the presence of implants or artifacts affecting the bone structure, was ruled out with X-ray scans. For preparation, all bones were carefully cleaned of excess soft tissue, and were cut and potted at the internal rotation angle of interest. A cutting fixture allowed the distal end of the bone to be cut off leaving the proximal femur at a desired length. To allow positioning of the femoral neck at prescribed angles during later CT scanning and mechanical testing, the proximal femoral shafts were potted in polymethylmethacrylate (PMMA) using a fixture designed specifically for desired orientations. The data collected from our experiments were then used for validation of quantitative computed tomography (QCT)-based finite element analysis (FEA), as described in a different protocol. In this manuscript, we present the protocol for the precise bone preparation for mechanical testing and subsequent QCT/FEA modeling. The current protocol was successfully applied to prepare about 200 cadaveric femora over a 6-year time period.

We present a robust protocol on how to carefully preserve and prepare cadaveric femora for fracture testing and quantitative computed tomography imaging. The method provides precise control over input conditions for the purpose of determining relationships between bone mineral density, fracture strength, and defining finite element model geometry and properties.

Cadaveric fracture testing is routinely used to understand factors that affect proximal femur strength.  Because ex vivo biological tissues are prone to ...

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 ...

Ultrasonography of the Adult Male Urinary Tract for Urinary Functional Testing

The incidence of clinical benign prostatic hyperplasia (BPH) and lower urinary tract symptoms (LUTS) is increasing due to the aging population, resulting in a significant economic and quality of life burden. Transgenic and other mouse models have been developed to recreate various aspects of this multifactorial disease; however, methods to accurately quantitate urinary dysfunction and the effectiveness of new therapeutic options are lacking. Here, we describe a method that can be used to measure bladder volume and detrusor wall thickness, urinary velocity, void volume and void duration, and urethral diameter. This would allow for the evaluation of disease progression and treatment efficacy over time. Mice were anesthetized with isoflurane, and the bladder was visualized by ultrasound. For non-contrast imaging, a 3D image was taken of the bladder to calculate volume and evaluate shape; the bladder wall thickness was measured from this image. For contrast-enhanced imaging, a catheter was placed through the dome of the bladder using a 27-gauge needle connected to a syringe by PE50 tubing. A bolus of 0.5 mL of contrast was infused into the bladder until a urination event occurred. Urethral diameter was determined at the point of the Doppler velocity sample window during the first voiding event. Velocity was measured for each subsequent event yielding a flow rate. In conclusion, high frequency ultrasound proved to be an effective method for assessing bladder and urethral measurements during urinary function in mice. This technique may be useful in the assessment of novel therapies for BPH/LUTS in an experimental setting.

We describe the use of high frequency ultrasound with contrast imaging as a method to measure bladder volume, bladder wall thickness, urine velocity, void volume, void duration, and urethral diameter. This strategy can be used to assess voiding dysfunction and treatment efficacy in various mouse models of lower urinary tract dysfunction (LUTD).

The incidence of clinical benign prostatic hyperplasia (BPH) and lower urinary tract symptoms (LUTS) is increasing due to the aging population, resulting ...

A Training and Testing System for Performing Vascular Reconstruction In Vitro

Manual vascular reconstruction training is essential for a beginner surgeon. However, an optimal training system for vascular reconstruction in vitro has yet to be developed. In this study, we introduce an in vitro training and testing system using a magnetic anchoring technique with which a trainee can practice manual vascular reconstruction individually. Additionally, this system can also be used to test the quality of the reconstruction. The described system includes a vascular reconstruction training machine, magnetic tractors, and a magnetic suture puller. In this manuscript, we detail an end-to-end vein anastomosis using porcine right and left iliac veins. To identify the potential damage caused by a magnetic suture puller on the suture, we created three groups with six segments of 4-0 polypropylene sutures each: a control group with no intervention on the polypropylene suture, a group in which the polypropylene suture is manually pulled with sterile gloves 20x, and a magnetic puller group in which the magnetic puller pulled the polypropylene suture 20x. These groups were tested by light microscopy and breaking strength tests, and the effect of reconstruction was assessed. In the light microscopy test, the control group was less likely to be damaged (p &#60; 0.05) and the number of damaged points of the manual group and magnetic puller group were similar (p &#62; 0.05). The results of the breaking strength test were compared across groups and no significant difference was observed (p &#62; 0.05). The end-to-end anastomosis of the porcine iliac veins was successfully performed using this training system, and the reconstructed veins could undergo 2.0 kPa perfusion pressure. Using this training and testing system the trainee can practice manual vascular reconstruction in vitro individually with the aid of magnetic tractors and a magnetic suture puller, and the quality of the reconstruction can be tested.

Here we present a training and testing system where a trainee can complete manual vascular reconstruction in vitro individually using a magnetic anchoring technique. The system can also be used to test the quality of reconstruction.

Manual vascular reconstruction training is essential for a beginner surgeon. However, an optimal training system for vascular reconstruction in vitro has ...

A Computerized Functional Skills Assessment and Training Program Targeting Technology Based Everyday Functional Skills

Today, many functional skills are technology-based, so development of a technology-based training program has broad importance. Here we present a computerized functional skills training program that was paired in half of the participants with a commercially available cognitive training (CCT) program.
Non-impaired older individuals (NC) aged 60+ (n=45) and similarly aged individuals with mild cognitive impairment (MCI; n=50) were randomized to receive 12 weeks of twice-weekly computerized functional skills training (CFST) or 12 weeks of twice-weekly sessions split between CCT and CFST. Skills trained were use of an ATM; internet banking; ticket kiosk; telephone and internet prescription refill; medication management; and internet shopping. As with previous functional capacity assessments, we focus on completion time for each simulation.
51 participants completed the training program, either by mastering all 6 tasks (34) or completing 12 weeks of training. 44 more participants completed 4 or more training sessions so they were also analyzed for improvement up to their last training session. Completion time for all 6 tests significantly improved from the baseline assessment to the final training session in both groups of participants (all p&#60;0.001 with an average improvement in task completion time of 45%). Further, there was no differential improvement in MCI and NC in the 6 tests from baseline to end of training (all t&#60;1.66, all p&#62;0.12). Finally, combined CCT plus CFST did not differ from CSFT alone on any of the percent-change score measures (all t&#60;1.64, all p&#62;0.11).
Both NC and MCI groups evidenced substantial improvements in performance. CCT supplementation led to similar functional gains with half as many training sessions. The NC participants proceeded through the training fairly rapidly even without CCT supplementation; MCI participants required more training but learned equivalently. These findings suggest that even in cases with memory impairments, functional skills can be efficiently learned with training.

This training protocol uses computerized training to teach technology-related everyday functional skills. These skills include financial skills, travel and transit, as well as medication management.

Today, many functional skills are technology-based, so development of a technology-based training program has broad importance. Here we present a ...

A Real-World High-Intensity Interval Training Protocol for Cardiorespiratory Fitness Improvement

High-Intensity Interval Training (HIIT) has emerged as an interesting time-efficient approach to increase exercise adherence and improve health. However, few studies have tested the efficiency of HIIT protocols in a &#34;real world&#34; setting, e.g., HIIT protocols designed for outdoor spaces without specialized equipment. This study presents a &#34;real world&#34; training protocol, named &#34;beep training&#34;, and compares the efficiency of a HIIT regiment versus a traditional long-duration Moderate-Intensity Continuous Training (MICT) regiment using this beep training protocol on VO2 max of overweight untrained men. Twenty-two subjects performed outdoor running with MICT (n = 11) or HIIT (n = 11). Cardiorespiratory fitness was assessed before and after training protocols using a metabolic analyzer. Both training protocols were performed 3 days a week for 8 weeks using the Beep Test results. The MICT group performed the exercise program at 60%-75% of the maximum speed of the 20 m shuttle test (Vmax) and with a progression of the distance of 3,500-5,000 m. The HIIT group performed the interval exercise with 7-10 bouts of 200 m at 85%-100% of the maximum speed of the 20 m shuttle test (Vmax), interspersed with 1 min of passive recovery. Although the HIIT group presented a significantly lower training volume than the MICT group (p &#60; 0.05) after 8 weeks of beep training, HIIT was superior to MICT in improving VO2 max (MICT: ~4.1%; HIIT: ~7.3%; p &#60; 0.05). The &#34;real world&#34; HIIT regiment based on beep training protocol is a time-efficient, low-cost, and easy-to-implement protocol for overweight untrained men.

This study presents a low-cost and easy-to-implement "real world" high-intensity interval training (HIIT) protocol for scientific research and discusses its efficiency for cardiorespiratory fitness.

High-Intensity Interval Training (HIIT) has emerged as an interesting time-efficient approach to increase exercise adherence and improve health. However, ...