Week 10 A&P Lab & Inquiry: Feel the Fatigue

Part 1 — The Big Picture

This week you learned that a muscle fiber shortens because thin actin filaments slide past thick myosin filaments, that a contraction runs in a fixed order from acetylcholine at the neuromuscular junction to the power stroke, that ATP pays for the pull, the release, and the calcium pumps, and that fatigue reflects ATP running low, lactic acid lowering the pH inside the fiber, and ion imbalances. In this lab you measure fatigue on your own hand with nothing but a timer, put your counts in a data table, work the average, the total drop, and the percent decline, and sketch your fatigue curve. Then you explain the curve in words through the contraction order, and you finish by checking a chatbot's account of your lab and catching its slips.

Time budget: Plan for about 120 minutes.

Part 2 — The Task

Guiding question: How does my squeeze count change across five 10-second all-out trials with short rests, and what happening inside my muscle fibers explains that change?

Before you begin — hypothesis: Before you squeeze, write one hypothesis in the if… then… because… form: if you squeeze as fast as you can for five 10-second trials with 15-second rests, then your count will rise, stay level, or fall in a pattern you predict, because of a reason about what happens inside the muscle fibers. Then define your variable so it can be measured: name what you count and the unit, and say exactly what counts as one squeeze.

Workshop data: Your own five 10-second squeeze counts, with an illustrative fallback series

Source: Five squeeze counts you measure on your own hand at home, with no equipment; if you cannot or should not squeeze, the printed fallback series, constructed for this lab and not measured from anyone, stands in for yours.

• Rows: 5 trials, shown as 5 rows of the data table; the inquiry table has 4 rows, the summary table has 1 row, and the contraction-order table has 5 rows
• Columns: trial number, squeeze count in 10 seconds, and the drop from the previous trial
• Timing: 10-second all-out squeezing trials with 15-second rests between them

Part 3 — Materials & Procedure

Tools and materials

• A free virtual anatomy atlas or 3D anatomy viewer (Innerbody, GetBodySmart), a virtual microscope for histology (Histology Guide), free physiology simulations (PhET pH Scale, Membrane Channels, Neuron, Gene Expression Essentials), and a spreadsheet (Google Sheets or any free spreadsheet)

Ways of working

• structure-identification-on-a-virtual-atlas
• histology-on-a-virtual-microscope
• at-home-physiology-measurement-and-data-table

Procedure

1. Read this first: stop at any pain or discomfort, and use the printed fallback series instead if squeezing hurts or you would rather not measure. Sit comfortably, rest your forearm on a table, and decide what one squeeze is: a full close of your hand into a fist and a full open. Set a timer on a phone or any clock with a seconds display. Tool: A free virtual anatomy atlas or 3D anatomy viewer (Innerbody, GetBodySmart), a virtual microscope for histology (Histology Guide), free physiology simulations (PhET pH Scale, Membrane Channels, Neuron, Gene Expression Essentials), and a spreadsheet (Google Sheets or any free spreadsheet). Check: You have a written definition of one squeeze and a timer ready to count 10 seconds and 15 seconds.
2. Start the timer and squeeze as fast and as fully as you can for 10 seconds, counting each full close and open out loud or with tally marks. Write the count in the data table as trial 1. Tool: A free virtual anatomy atlas or 3D anatomy viewer (Innerbody, GetBodySmart), a virtual microscope for histology (Histology Guide), free physiology simulations (PhET pH Scale, Membrane Channels, Neuron, Gene Expression Essentials), and a spreadsheet (Google Sheets or any free spreadsheet). Check: Trial 1 has one whole-number count.
3. Rest for 15 seconds with your hand open, then repeat the 10-second trial. Do this until you have five trials, writing each count in the data table as soon as the trial ends. Tool: A free virtual anatomy atlas or 3D anatomy viewer (Innerbody, GetBodySmart), a virtual microscope for histology (Histology Guide), free physiology simulations (PhET pH Scale, Membrane Channels, Neuron, Gene Expression Essentials), and a spreadsheet (Google Sheets or any free spreadsheet). Check: The data table holds five whole-number counts in trial order.
4. Open a blank spreadsheet. Type the trial numbers 1 to 5 in cells A2 to A6 and your five counts in cells B2 to B6. In B7 type =SUM(B2:B6), in B8 type =AVERAGE(B2:B6), in B9 type =B2-B6, and in B10 type =(B2-B6)/B2*100. Work the same four values by hand in the summary table and check that they match. Tool: A free virtual anatomy atlas or 3D anatomy viewer (Innerbody, GetBodySmart), a virtual microscope for histology (Histology Guide), free physiology simulations (PhET pH Scale, Membrane Channels, Neuron, Gene Expression Essentials), and a spreadsheet (Google Sheets or any free spreadsheet). Check: Cells B7 to B10 show your sum, average, total drop, and percent decline, and each matches your hand-worked line.
5. Select cells A2 to B6 and insert a line chart, with the trial number across the bottom and the squeeze count up the side, or sketch the same line on paper with both axes labeled in words. Note whether the line falls steadily, falls unevenly, or stays level. Tool: A free virtual anatomy atlas or 3D anatomy viewer (Innerbody, GetBodySmart), a virtual microscope for histology (Histology Guide), free physiology simulations (PhET pH Scale, Membrane Channels, Neuron, Gene Expression Essentials), and a spreadsheet (Google Sheets or any free spreadsheet). Check: A labeled fatigue curve shows your five counts in trial order.
6. Fill in the contraction-order table: write the five steps of excitation-contraction coupling in order and the place each one happens, from the chapter, without looking at a chatbot. Tool: A free virtual anatomy atlas or 3D anatomy viewer (Innerbody, GetBodySmart), a virtual microscope for histology (Histology Guide), free physiology simulations (PhET pH Scale, Membrane Channels, Neuron, Gene Expression Essentials), and a spreadsheet (Google Sheets or any free spreadsheet). Check: Every row of the contraction-order table has an event and a place.

Fallback route

When to use it: Use this route if squeezing causes pain or discomfort, if you cannot do the hand test, or if you would rather not measure your own hand.

Use the illustrative fallback series below, constructed for this lab and not measured from anyone, as your five counts. Complete every table, the fatigue curve, every analysis question, and the critique step with it, and submit the same items for equal credit. Fill the drop column yourself.

This route earns the same credit as the primary route.

An illustrative fallback series, constructed for this lab, that stands in for your own five counts.

Fallback model data

Trial	Squeeze count in 10 seconds	Drop from the previous trial
1	25	none (first trial)
2	23
3	20
4	18
5	14

Part 4 — The Scaffold

Name the parts of your inquiry before you squeeze, so your count can be measured the same way every trial.

Student scaffold table 1

Part of the inquiry	Your answer
Hypothesis (if… then… because…)
The variable you count, and its unit
What counts as one squeeze
One thing you keep the same for every trial

Record each trial as soon as it ends, so the counts stay in their true order.

Student scaffold table 2

Trial	Squeeze count in 10 seconds	Drop from the previous trial
1		none (first trial)
2
3
4
5

Work each summary value by hand, showing the arithmetic, so a reader can rebuild it from your counts.

Student scaffold table 3

Sum of the five counts	Average per trial	Total drop (trial 1 minus trial 5)	Percent decline

Put a single squeeze in order, so your explanation of the curve rests on the right sequence.

Student scaffold table 4

Step	What happens	Where it happens
1
2
3
4
5

Part 5 — Analysis Questions

1. Show the sum, the average, the total drop, and the percent decline for your own five counts, writing each step in words and numbers, and say in one sentence what the percent decline means for your hand.
2. Describe the shape of your fatigue curve. Did the count fall steadily, fall unevenly, or stay level, and in which gap between trials was the largest drop?
3. Explain your curve through the inside of a muscle fiber: say what happens to the cross-bridges as the count falls, name the three causes of fatigue this course uses, and say what does not happen to the filaments.
4. Your hand relaxed during each 15-second rest. Using the relaxation steps and ATP's three jobs, explain why the rests still cost the fibers energy, and connect that cost to the fall in your count.
5. Answer one option. (a) Name one way your own measurement could be off, such as counting a half squeeze or a slightly late timer start, and say how it would change your percent decline. (b) Name one thing this hand test cannot show you about what is happening inside the fibers, and say which part of this week's chapter fills that gap.

Part 6 — AI-Critique Moment

Choose one equal-credit critique route. Route A: ask an approved AI tool to critique your completed work, then check its response against your own evidence. Route B is the no-AI equivalent printed below.

Approved tools: Claude, Gemini, ChatGPT, Grok, Microsoft Copilot.

Prompt to paste:

I've pasted my completed Feel the Fatigue tables above: five 10-second all-out squeeze counts from my own hand, with 15-second rests between trials, and the arithmetic I did on them. Please do six things. First, check my sum, my average, my total drop, and my percent decline, showing each step. Second, list in order the steps that happen inside a skeletal muscle fiber from the moment the nerve signal arrives to the moment the myosin heads pull, and say where each step happens. Third, name which filament is thick and which is thin, and say what each one is made of. Fourth, say what happens to the length of the filaments as my count falls. Fifth, name the kind of muscle tissue doing the squeezing and say whether I control it. Sixth, tell me the typical percent decline for adults doing this test, with a source.

Test the response for these likely failures:

• Chatbots sometimes put calcium first, saying the sarcoplasmic reticulum releases Ca²⁺ and then the nerve signal arrives, or skip the muscle action potential entirely.
• Chatbots often say the neuromuscular junction releases calcium onto the muscle fiber, giving the junction the sarcoplasmic reticulum's job.
• Chatbots sometimes say ATP is needed only to make the muscle contract, so resting between trials costs nothing.
• Chatbots sometimes call actin the thick filament and give it the heads, or say both filaments shorten as the count falls.
• Chatbots often divide the drop by the last trial, or by the average, instead of by the first trial when they work a percent decline.
• Chatbots sometimes call the gripping muscles smooth muscle or cardiac muscle, or call the squeeze involuntary.
• Chatbots readily supply a typical percent decline for adults or a norm for squeeze counts, with a confident citation this lab never gave.

In 3–4 sentences, name what the chatbot got right, quote at least two of its errors, and correct each one with evidence from your tables or the chapter.

Equivalent route (no AI required)

No AI account is required for this lab. Instead of the chatbot, critique this flawed analysis, printed here in full: "My five counts were 25, 23, 20, 18, and 14 squeezes. The total drop is 25 − 14 = 11, and the percent decline is 11 ÷ 14 × 100, about 79%. When I squeeze, the sarcoplasmic reticulum releases calcium first, and then the nerve signal reaches the junction. The neuromuscular junction releases the calcium onto the fiber. Actin is the thick filament with the heads, and as I tire, both filaments get shorter. The squeezing is done by smooth muscle, which works on its own. During the rests my muscles need no ATP, because ATP is only for contracting. A large study shows that adults lose exactly 42 percent of their squeezes on this test." Mark it up: quote each flawed sentence, name what is wrong (a mislabeled structure, a wrong structure-to-function pairing, a miscomputed value, an order scrambled, a confused tissue type, or an invented figure), cite the evidence from your tables or this week's chapter, and write a corrected sentence beneath it. This route assesses the same objectives (Objective 5 and Objective 2) as the chatbot critique, takes comparable effort (about 30 minutes and 200–300 words), is scored by the same scoring criteria for the same credit, and its own submission artifact is the marked-up flawed analysis, posted in place of the chatbot share link and report.

Part 7 — What to Submit

• All four completed scaffold tables, with the data table filled from your own counts or the illustrative fallback series
• Your fatigue curve, as a spreadsheet chart or a labeled sketch
• Written answers to all five analysis questions, including the option you chose for question 5
• The chatbot critique report with its share link, or the equivalent route's marked-up flawed analysis

Deliverable:

A short A&P Lab & Inquiry report on fatigue: four completed tables (the parts of your inquiry, your five counts, the summary values, and the contraction order), a fatigue curve, written answers to five analysis questions, and a critique of a chatbot's account of your lab, or, on the equivalent route, a marked-up correction of the printed flawed analysis. Submit in any accessible file type or as a link; a recorded response may be submitted as audio or video with a transcript, or as text. Choose a written, recorded, or visual form for your answers; every form is graded by the same scoring criteria.

Rubric

The rubric below shows how each submitted part is evaluated; bands are full, partial, or none.

Workshop evaluation criteria

Criterion	Full	Partial	None
Testable hypothesis and a measurable variable	A falsifiable if… then… because… hypothesis appears before the first trial, the counted variable and its unit are named, one squeeze is defined, and one condition held the same is named.	A hypothesis appears but is not falsifiable, or the variable, its unit, or the definition of one squeeze is missing.	No hypothesis, and the parts of the inquiry are not named.
Data table, summary values, and fatigue curve	Five counts from the student's own trials or the fallback series, every drop filled in, the sum, average, total drop, and percent decline worked with each step shown and the drop divided by the first trial, and a fatigue curve with both axes labeled.	The counts are recorded, but a summary value is missing or miscomputed, the percent decline uses the wrong divisor, or the curve is missing or unlabeled.	The data table is blank, or the counts are not from the student's trials or the fallback series.
Contraction order and the mechanism	The five steps appear in the right order with their places, and the curve is explained as fewer cross-bridges cycling, with the three causes of fatigue named and the filaments said to keep their length.	The steps are mostly in order but one is misplaced or missing its place, or the mechanism names only some causes or leaves the filament length unstated.	No contraction order, or the explanation says the filaments shorten or gives no mechanism.
Analysis questions	Answers all five questions with evidence from the tables and the curve, including the relaxation cost in question 4 and one chosen limitation option.	Answers most questions but leaves one unsupported, or the relaxation cost is stated without the pump step.	Analysis questions are unanswered or unsupported by the tables.
Critique of the chatbot or of the printed flawed analysis	On either route, at least two errors are quoted and corrected with evidence from the student's own tables or the chapter, and one correct point is acknowledged; both routes earn this band equally.	On either route, errors are named but corrected without evidence, or only one error is caught.	No critique appears, or pasted output is submitted without any checking.

Quality Gate

• Every count in the data table comes from your own five trials or the printed fallback series, never from memory, a classmate, or a chatbot.
• The hypothesis was written before the first trial, has the if… then… because… form, and the variable is defined so it can be measured.
• The percent decline divides the total drop by the first trial and multiplies by 100, with every step shown.
• The explanation reads a falling count as fewer cross-bridges cycling and never says the filaments shorten.
• No measurement, percentage, norm, study, or source is invented anywhere in the submission.
• You stopped at any pain or discomfort, and your write-up treats your counts as your own values, not a norm.
• The critique quotes the chatbot or the flawed analysis and corrects at least two errors with evidence from your tables or the chapter.