2.9: Lab Exercise 11- Muscle Fatigue and Physiology

Lab Summary: The materials for this lab are included in your lab kit, so you can experiment with factors that affect muscle fatigue and usage.

Your objectives for this lab are:

• Describe the effects of cold, heat, and fatigue upon muscle contraction, fine motor skills/dexterity, and chemical reactions involved in muscle contraction.
• Explain four causes of muscle fatigue on a cellular/molecular level
• Describe different types of muscle fibers (type I and II; red, pink, white), types of muscle in which they are predominant, and why it is beneficial to have mixed types in a muscle belly
• Hypothesize about why warm-ups are advisable to maximize muscle performance.

Background

Many exercise physiologists believe that one of the most important factors determining athletic performance is the cellular composition of the contracting muscles. The average human body is made up of approximately 600 muscles-2000 muscles (depending how one counts them). Therefore, all of those muscles must function properly for us to move about in our ordinary lives. When we consider the functioning of our muscles, we refer to it as muscle contraction. There are three types of muscle tissue in the human body: Skeletal, Smooth, and Cardiac muscles.

Skeletal muscles move the bones in the skeleton and have voluntary control. These muscles contract, it happens by the sliding filament theory. This allows the joints to move and lets us engage in physical activity of all kinds.

Smooth muscles are found in the walls of organs and structures that have involuntary control. When these muscles contract, they also use the sliding filament theory however, they use different proteins to do so compared to skeletal and cardiac muscle systems. The use of smooth muscles allows us to move digested food, move the iris of the eye, or constrict/relax blood vessels.

Cardiac muscle is similar to smooth muscle as it has involuntary movement but has a structure more akin to skeletal and is only found in the heart. Cardiac muscle requires extracellular calcium ions for contraction, which is unlike skeletal muscle. The beating of our heart is due to cardiac muscle contraction.

All of the above-mentioned muscle contractions are due to the different types of muscle fibers that generate tension during the sliding filament process, also referred to as actin and myosin cross-bridge cycling. Muscle cells, which are called fibers, can be broadly classified into categories based on their structural and metabolic characteristics. For example, the biceps muscle in the upper arm, a skeletal muscle. This muscle tissue is composed of distinct fiber types that play a critical role in determining the muscle’s performance capacity.

Three main fiber types are commonly identified, although further sub-groupings are known. For our purposes, we will focus on the three major types described here.

White - fast-twitch, glycolytic fibers (FG) are generally quite large in diameter and can generate energy rapidly for quick, powerful contractions. White fibers rely on anaerobic metabolism to produce ATP and become fatigued with the accumulation of lactic acid, a noxious by-product that interferes with muscle contraction. Consequently, white, fast-twitch fibers are generally activated in short-term sprint or “power” activities, as they fatigue rapidly.

Red, slow-twitch, oxidative fibers (SO) are smaller in diameter, and generate a greater yield of ATP by aerobic metabolism and without the formation of lactic acid. As the name implies, red, slow-twitch fibers contract less rapidly and powerfully, but they are not easily fatigued and are well suited for prolonged exercise.

Pink, fast, oxidative-glycolytic (FOG), a third intermediate fiber type shares both the oxidative and glycolytic pathways and is intermediate in size when compared to red and white fibers.
These characteristics are summarized in the table below.

Table \(\PageIndex{1}\): Muscle Fiber Characteristics

Fiber color	Red	Pink – red	White
Predominant metabolic pathway	Aerobic	Aerobic	Glycolysis
Contraction speed	Slow	Fast	Fast
Rate of fatigue	Slow	Intermediate	Fast
Mitochondria	Many	Many	Few

It is widely known among sport physiologists that the “fiber-type” of elite, world-class athletes is a reliable predictor of performance in athletic events. Sprinters, weight-lifters, wrestlers and others that rely on short, powerful bursts of muscle activity generally have a predominance of__________ -twitch fibers, whereas marathon runners, cross-country skiers, cyclists, and other endurance athletes have a greater abundance of _______ - twitch fibers.

Less widely appreciated is the extent to which these principles of human exercise physiology apply to other animals and their capacity for exercise. Organisms with predominantly white, fast twitch fibers (FG) also use anaerobic metabolism during exercise. They are capable of producing very high levels of muscle power output (e.g., fast sprints and strong bites), but these animals exhaust quickly. Other animals with a greater abundance of red, slow-twitch fibers (SO), which rely on aerobic metabolism, are capable of producing a moderate level of power for long periods of time. The principal disadvantage for “aerobic animals” is that aerobic metabolism is an expensive system to maintain; it requires a large, active heart, an elaborate vascular system to deliver oxygen, and numerous mitochondria in the muscle cells to produce large quantities of ATP. The high costs of maintaining these features are reflected in the higher rates of metabolism when the animal is at rest. “Anaerobic animals” avoid these energetic costs and have relatively low resting metabolic rates, leaving more energy available for growth and reproduction.

Each muscle tissue has specific roles in the body but they all must work together for overall functioning of the human organism.  This is best seen in terms of exercise, specifically maximal exercise. The two main types of exercise are anaerobic (static exercise) and aerobic (dynamic exercise).  During exercise the oxygen demands of skeletal muscle increase significantly.  The heart is responsible for supplying oxygen-rich blood to the skeletal muscles and smooth muscles. Skeletal muscle needs the oxygen to sustain its aerobic cellular respiration.  Skeletal muscle can switch over and use anaerobic mechanisms for ATP production but cannot continue for long once lactic acid accumulates.

Procedure for Activity 11.1:  The Effects of Temperature on Fine Motor Skills: For this exercise, you will need a pencil, a bowl with warm water, a bowl with ice cold water, and a timer or stopwatch.  The small pencil and ice making bags are provided in your lab kit.  You can use a timer/stopwatch on your phone or use this one:  https://www.online-stopwatch.com/countdown-timer/

Directions:

1. Using the tiny pencil provided to you, write your signature 3 times under the column labeled “Baseline” in Data Table \(\PageIndex{2}\).
2. Submerge your writing hand in ice cold water for 3 minutes, then remove your hand from the water and write your signature 3 times under the column labeled “Cold”.
3. Submerge your writing hand in nice, warm water (not hot!) for 3 minutes, then remove your hand from the water and write your signature 3 times under the column labeled “Warm”.

Table \(\PageIndex{2}\): Signatures Obtained at Cold and Warm Temperatures

BASELINE	COLD	WARM

Observations:  In the space below, write your observations about your hand and handwriting as observed under the three conditions above.

Data Analysis for Activity 1:  Enter Your Answers to the following questions in the Muscle Physiology Labs Assignment on Canvas.  In answering the following questions, you should include observations and data from Activity 1 (handwriting variations with temperature). 

1. Describe three (3) chemical reactions that occur during muscle contraction.  There are hundreds, so pick 3.
2. List 2 factors that increase the rate of a chemical reaction (hint: review chapter 2)
3. What conclusions can you make about the effect of temperature on fine motor skills for your subject?  Be sure to explain your answer using your understanding of the physiology of muscle contraction. 

Procedure for Activity 11.2—The Effects of Muscle Fatigue on Fine Motor Skills—Handwriting: For this experiment, you will need a pen or pencil and a few pieces of paper. 

Directions:

1. Establish Baseline Handwriting Skills:  The subject should write the following sentence in cursive as neatly as possible one time:  “The quick brown fox jumped over the lazy dog.”
2. Now, ask the subject to describe how much they use their hands daily and what activities they do with their hands.  Make note of this information.
3. Observe the Effects of Fatigue:
   • Directions for Observers:  It is important the subject is prompted to write quickly and with consistent speed as much as possible.  In this part, observers should take notes about the subject’s writing mechanics and note the time at which these changes occur.  For example, changes in posture, changes in hand position, is the arm/shoulder/torso being used to move the hand, is there movement in the legs or feet?
   • Directions for Subject: Rewrite the sentence “The quick brown fox jumped over the lazy dog.” as many times as possible and as quickly as possible in ten (10) minutes.  If your hand is not fatigued at the end of ten (10) minutes, continue writing for a few more minutes.

Observations:  You will need your observations and the subject’s handwriting pages to answer analysis questions at the end of Activity 3.

Procedure for Activity 11.3—The Effects of Muscle Fatigue on Fine Motor Skills Using Beans:

Materials: beans, a beaker (or a cup or mug, which should have an opening that is smaller than your fist, smaller is better and more fun to observe!).

Directions: The same subject must complete all parts and all three trials of this experiment.

Part A—Fine motor skills before muscle fatigue: In this part of the experiment, you will observe normal fine motor skills by having the subject move beans from a tabletop into a cup using the thumb and ring finger (digits 1 and 4 of the subject’s dominant hand). Beans must be moved one at a time.

1. The time keeper and observer should record observations and record # of beans moved in the data table below.

2. When the time keeper says go, the subject will use his/her 1st and 4th digits (thumb and ring finger) to move as many beans as possible one at a time from the tabletop to a cup for 60 seconds. Record the number of beans moved for Trial 1 in Data Table \(\PageIndex{3}\) below.

Part B—Fine motor skills after muscle fatigue: In this part of the experiment, you will observe fine motor skills after muscle fatigue. Please read all directions for this part before you begin.

1. To produce fatigue, have the subject perform one of the following until the hand feels tired. This will usually take 3-5 minutes.
   • Make a tight fist and keep squeezing the fist tightly until the hand feels fatigued. Don’t let the subject shake out the hand before moving the beans as in Step A.1 above, or
   • If you have a handgrip exerciser, have the subject continually squeeze the handgrip as fast, tightly, and as long as possible without swinging the arm, until the hand feels fatigued.
2. Now, have the subject repeat the exercise of using his/her 1st and 4th digits to move as many beans as possible from the tabletop to the cup for 60 seconds. Record the results for this trial in the “after fatigue” column for Trial 1 in Data Table 2 below.

Repeat for Trials 2 and 3: Repeat the steps of parts A and B two times and record the results for Trials 2 and 3 in the table below.

Observations:

Table \(\PageIndex{3}\): Fine Motor Skills-Chopstick Use

Trial Number	# of Beans Moved BEFORE Muscle Fatigue	# of Beans Moved AFTER Muscle Fatigue
1
2
3

Data Analysis for Activities 11.2 and 11.3: Enter your answers to the following questions in the Muscle Physiology Labs Assignment on Canvas. In answering the following questions, you should also include observations and data from Activity 11.2 (The Effects of Muscle Fatigue on Fine Motor Skills—Handwriting) and Activity 11.3 (The Effects of Muscle Fatigue on Fine Motor Skills Using Beans).

4. On a cellular/molecular level, explain 3 causes of muscle fatigue.

5. What conclusions can you make about the effect of muscle fatigue on fine motor skills for your subject? If possible, compare your results to others who use their hands differently than your subject.

6. In either Activity 2 or 3, did the subject’s performance get better after fatigue? If so, why do you think this could have happened?

7. What type of muscle fibers (red, white, or pink) do you expect to find the most of in the muscles of the hand? Why?

Procedure for Activity 11.4:  Review of Muscle Physiology on the Molecular Level

If available, you will also perform an online lab simulation to review the biochemistry of muscle physiology.  Online simulations may include any of the following:

• https://www.biointeractive.org/classroom-resources/neurophysiology-virtual-lab
• Labster 
• PHET Simulations

Additional Learning Resources:

• Watch this video to learn more about different types of muscle fibers:           https://www.khanacademy.org/science/health-and-medicine/human-anatomy-and-physiology/introduction-to-muscles/v/type-1-and-2-muscle-fibers