教他们一个他们永远不会忘记的教训！握力实验...

Ask students to imagine they are contracting their muscles at their maximum. Have your students rank the following three factors based on which they think will have the biggest effect on increasing muscle fatigue.

他们的答案是假设that will be tested with the grip force experiment.

Ask for a volunteer to perform the electromyography procedure, and attach electrodes to the volunteer.

Electromyography is a technique that measures the electrical activity of muscles. The data recorded is an electromyogram; also known as an "EMG" or "myogram".

使用的设备

使用的数据采集硬件：PowerLab 26T- 包括一个
内置的生物信号放大器

使用的数据分析软件：LT：生命科学教学软件/ldsports体育资讯

使用的其他硬件：握力传感器,电极和配件

设置

Before electrode attachment

Electrode attachment

1. Lightly abrade the skin over the crosses with abrasive gel, then clean with an alcohol swab.
2. Snap the CH1 and CH2 shielded lead wires onto the disposable ECG electrodes.
3. Place the CH1 electrodes over the crosses on the volunteer's biceps, and the CH2 electrodes over the crosses on the volunteer's triceps. Press firmly so they adhere well. It doesn't matter which is positive and which is negative.
4. Check that all 4 electrodes and the dry earth strap are properly connected to the volunteer and the Bio Amp cable before proceeding.

The question for students here is:“ EMG痕迹是什么样的，随着肌肉活动的增加如何改变？”

程序

Part 1

Part 2

1. Ask the volunteer to sit in a relaxed position as before, (ensure their arm is not resting on anything).
2. 开始录制您的数据分析软件.
3. Enter "no books" as a comment or label.
4. After 3–5 s, add the comment: "1 book". Place a book (or a similar weight) on the volunteer's hand and ask them to remain as still as possible.
   记录2-3 s。
5. 停止录音
6. 要记录重量增加的效果，请重复步骤2-5，并每次将书籍数量增加1，直到您达到4本书。为每本书添加添加评论/标签。

在这里，学生将分析自愿肌肉收缩如何随需求增加而变化。

Before beginning:

让您的学生滚动浏览记录的数据，并记录原始痕迹（二头肌和三头肌）与已处理的痕迹（RMS二头肌，RMS三头肌）之间的关系。

RMS跟踪的高度反映了RAW EMG信号的整体活性，并更简单地了解了肌肉的电活动。

Analysis

1. Expand a small section of the biceps activity. (Note how the raw EMG signal is composed of many spikes; this is the electrical activity of many motor units).
2. Use the region selector to highlight the section where one book was added. The maximum RMS values for both the biceps and triceps will be displayed in the value panels.
3. Note these values.
4. 每本书重复步骤2–3。

Some questions to test your students’ understanding:

问题：与来自ECG的离散波形不同，EMG波形是不规则的。为什么是这样？

回答：ECG从心脏记录电活动。与心脏不同，骨骼肌不会以完全同步的方式收缩。取而代之的是，EMG记录了许多肌肉纤维的非同步电活动。

问题：How did the EMG trace change when you added weight to the volunteer's arm? Based on the data you collected, what can you infer is happening to the muscles as weight is added?

回答：当添加更多书籍时，记录的活动（主要在二头肌中）增加了。从记录的数据中，可以推断出需要更大的电动机活动才能产生更多的力，以便在添加更多书籍时将手臂保持在相同的位置。

The question here is:“当我们试图维持最大力量时会发生什么？”

连接握力传感器

Calibrate the equipment for grip force

现在，学生将找到志愿者的最大抓地力，并使用它来校准其握力从0-100％校准。

程序

最大收缩

1. 开始录制分析软件。
2. Leave the grip force transducer undisturbed on the table for 5 s. This will be the baseline data for zero force.
3. Next, ask the volunteer to squeeze the grip force transducer as hard as possible, for as long as possible. This will be the area of maximal grip force.
4. 5秒钟后，告诉志愿者放松并停止记录。

校准

1. 在您的分析软件上，突出显示或选择零力的基线数据区域。键入“ 0”作为相应百分比值。
2. Next, select an area of maximal grip force. Select the small arrow next to Value 2 in the Units Calibration panel to enter this value. Type "100" into the corresponding percentage value.
3. On your software, select “Calibrate” or similar. The Grip Force units should now change to %.

The calibration is now complete.

Run Muscle Fatigue Test

The question here is:“我们如何解释持续收缩期间最大力的下降？”

This phenomenon is called "muscle fatigue".

Before you begin

Ensure the volunteer能够see the computer screen where their signal will appear.

程序

1. Begin recording. Ask the volunteer to apply and maintain 25% of their maximal grip strength while watching the recorded trace. Enter "25%" in as a comment or label on the recording.
2. 25秒钟后，告诉志愿者放松并停止记录。
3. 等待30秒以恢复肌肉功能。
4. Repeat steps 1–3 for contractions of 50%, 75%, and 100% of maximal grip strength. Add a comment for each trial.

Analysis

In this analysis students will determine how fatigue affects grip force at different intensities.

1. Create a table like this:
2. Ask students to scroll to their 25% grip force data.
3. 在增加之前，将标记放在基线上。将点选择器放在1 sinto the contraction. Note the change in grip force from the baseline.
4. 注意这个值在适当的单元格选项卡le (above).
5. 在收缩中重复步骤2–3，5 s，10 s和20 s。
6. Repeat steps 2–4 for 50%, 75%, and 100% grip force.

检查学生的理解

问题：Did this experiment help you decide which of the factors proposed to explain fatigue are important?

回答：您可能已经注意到，与剧烈的收缩（25％，50％）相比，在更剧烈的收缩（75％，100％）期间，志愿者的抓地力下降了。这是存在的“视觉反馈”，志愿者可以看到下降，并可以试图纠正它。在更剧烈的收缩期间，显然发生了更多的疲劳。“中央驱动器”的下降也将影响一些结果。

鼓励测试运行力

The question for students here is:“我们可以通过口头鼓励改变肌肉疲劳的程度，还是短暂休息？”

Before you begin

Ensure the volunteer能够notsee the computer screen where their signal will appear.

程序

鼓励

1. Start recording, and ask the volunteer to produce a sustained maximal contraction (100% grip force).
2. After 8–10 s or when the force has obviously declined, enter the comment/label “Encouragement” and immediately instruct the volunteer to try harder.
3. 在另外8-10 s之后，将评论重新输入“鼓励”，然后重复鼓励。
4. Repeat step 3, so the volunteer has been encouraged a total of 3 times.
5. 几秒钟后，请志愿者放松并停止录音。

休息

1. Start recording.
2. 要求志愿者产生持续的最大收缩（100％）。
3. 8–10 s输入评论 /标签“休息”，并指示志愿者非常短暂放松（〜0.5 s），然后返回最大收缩。
4. Repeat step 3 another 2 times, so the volunteer has rested for a total of 3 times.
5. After 30–40 s, stop recording.

Analysis

In this analysis students will determine the effects of encouragement and brief rest on sustained maximal grip force.

1. Create a table like this:
2. 在录音中，让学生滚动以“鼓励”评论。
3. 注意第一个收缩开始时的值。在第一个“鼓励”之前，请注意最低点的值。计算握力的变化。
4. Enter the value into the appropriate cell in the table.
5. 对于每个试验，重复步骤2–3（在鼓励期间之后使用值，以及在下一个鼓励时期之前计算握力变化之前的值）。
6. 在休息期间重复步骤2–4。

检查学生的理解

问题：From your data, do you think that verbal encouragement or brief rests limited the extent of muscle fatigue?

回答：在持续的最大抓地力期间，鼓励和短暂的休息被证明可以在一定程度上限制疲劳。

问题：在持续的骨骼肌收缩期间，您能想到可能发生真正疲劳的三个地方吗？

回答：真正疲劳的主要位置可能是骨骼肌细胞，其中：

A reduction in Ca²⁺离子释放（由于Ca的耗竭²⁺ions from intracellular stores) could potentially inhibit excitation-contraction coupling, or

肌肉细胞的代谢变化（例如乳酸积聚，可以使骨骼肌酸性产生，从而抑制任何进一步的厌氧性糖酵解），这在极端运动中更有可能发生。

实际的肌肉疲劳可能不仅在骨骼肌细胞中出现。它也可能发生在神经肌肉连接（NMJ）上，可能是由于乙酰胆碱储存的耗竭或ACH受体的敏感性（脱敏），从而导致神经肌肉传播的有效性降低。这也可能是由于血液流量减少而发生的（因此有限O₂）由于血管压缩而肌肉。

进行视觉反馈测试

The question for students here is:"What effect does visual feedback have on the ability to maintain a grip contraction with constant force?"

Before you begin

Ensure the volunteer能够请参阅计算机屏幕。如果握住传感器已经变得痛苦，请允许志愿者使用另一只手。

程序

1. Start recording. Ask the volunteer to produce a 50% contraction while watching the trace.
2. After 20 s add the comment / label “eyes closed”. Ask the volunteer to close his or her eyes and attempt to maintain exactly the same contraction force for the next 20 s.
3. 在要求志愿者睁开眼睛并将收缩力调整回50％时，写评论 /标签“睁开眼”，并添加它。
4. 调整为50％时，请停止记录。

Analysis

在此分析中，学生将确定视觉反馈如何影响持续的最大抓地力。

对于分析，创建这样的表：

视觉反馈

1. Have students scroll to the visual feedback data.
2. Note the value near the beginning of the contraction when it has reached 50%.
   在“闭合”评论之前，请注意该值直接。
   Calculate the change in grip force and note this value.
3. Enter the value into the appropriate cell in the table.

没有视觉反馈

1. Note the value just after the "eyes closed" comment.
   Note the value just before the "eyes open" comment.
   Calculate the change in grip force and note this value.
2. Enter the value into the appropriate cell in the table.

检查学生的理解

问题：Examine the data recorded when the volunteer attempted to maintain a 50% contraction with their eyes shut.

Almost all volunteers will show a declining force (pseudo-fatigue) while their eyes are shut that is very similar to actual fatigue. This is not true fatigue because the full 50% force can be exerted easily, as can be seen when the volunteer's eyes are opened again. What explanations can you think of for pseudo-fatigue?

回答：在没有有关实际产生的力的信息的情况下，疲劳的内部感觉会占主导地位并导致产生的力下降。

在本实验室的开头，您要求学生通过对三个因素进行排名，以根据他们认为对增加肌肉疲劳的影响最大的因素。

Discuss with students how their experience of testing each of the factors in the lab would require them to reform your hypothesis? If so how?