Muscle Physiology, Fatigue and Stretch-Shortening Cycle

Exercise 1: EMG Readings 

Describe what occurs to the triceps muscle when the biceps muscle is contracted. Even though these muscles are antagonists, why might this be beneficial? 

The triceps relax and rest when the biceps are contracted. These antagonist actions aid in the lifting of things in the day to day activities. 

Which figure (13 or 14) represents a muscle twitch, and which figure represents muscle summation? What is the difference in the force of the muscle contraction of the thumb from the two sets of data? 

Figure 13 represents a muscle twitch while figure 14 represents a muscle summation. In figure 13, the stimulation takes place every 0.5 seconds which allows the muscle to relax. On the other hand, the stimulation in figure 14 happens every 0.05 seconds meaning that the muscle does not relax fully. The force in muscle contraction during the summation is greater than the force produced by a muscle twitch because of the increased stimulation frequencies. 

Exercise 2: Muscle Fatigue 

Data Table 1. Data from Forearm Exercise 

Amount of Time per Trial	30 seconds
Amount of Rest between Trials	30 seconds
	Trial 1	Trial 2	Trial 3
Repetitions Completed during Trial	36	39	38
Rating of Perceived Exertion	12	13	17

Data Table 2. Scatter Plot of Results: Number of Repetitions 

Scatter Plot

Data Table 3. Scatter Plot of Results: Rating of Perceived Exertion 

Scatter Plot

What effect did repeating the exercise over time have on the muscles used? 

Repeating the exercise over time causes fatigue on the muscle 

Reflect on how muscles work. What physiological factors are responsible for fatigue? 

Fatigue is the loss of a muscles ability to contract and generate force after a period of sustained contractions. There are several causes of muscle fatigue. They include 

Hyperpolarization of the cells due to the accumulation of extracellular potassium. 

Reduced ATP availability. 

PH alterations in the muscle as a result of the accumulation of lactic acid. 

How well do you think the exercised muscles would work after 30 minutes of rest instead of 30 seconds of rest between trials? How do you think the muscle function would change if microscopic tears were created during exertion? 

The muscles would work better after 30 minutes of rest as compared to a 30 seconds rest because of the adequate period of relaxation. The muscle would have a decreased functionality if microscopic tears are created during exertion. 

What can be learned from the slope of the line in the graph? How does the slope change as fatigue increases? What does a steeper or flatter slope indicate? 

The slope indicates how the muscle responds to stimulation over a period of sustained activity. The slope becomes flatter and starts to decline as fatigue increases. A steeper slope indicates the inconsistency in the ability of the muscle to generate force with each exercise while a flatter slope indicates consistency. 

Were you using aerobic or anaerobic pathways throughout this exercise? Explain your answer. 

Anaerobic pathway. Due to the limited time between the trials, there are minimal amounts of oxygen and thus the energy has to come from anaerobic respiration. 

Exercise 3: Utilizing the Stretch-Shortening Cycle by Measuring Maximal Vertical Jump Height 

Data Table 4. Data for Maximum Vertical Jump Height Trials 

Standing Height (cm):
	Maximum vertical jump height without  stretch-shortening cycle (cm)	Maximum vertical jump height  with  stretch-shortening cycle (cm)
Trial 1	223.1	232.4
Trial 2	231.8	237.2
Trial 3	226.4	238.6
Average	227.1	236.07
Average - Standing Height	167.6	176.3

Questions: 

What is the stretch-shortening cycle and how did it affect your jump height? 

A stretch-shortening cycle is an active stretch of the muscle followed by an immediate concentric shortening. The stretch-shortening cycle enabled me to jump higher compared to when I jumped without the stretch-shortening cycle. 

Why is a muscle spindle is considered a proprioceptor? 

The muscle spindle is a proprioceptor because it recognizes when the muscle has been stretched quickly and then sends a signal for the muscle to contract to prevent further stretching. 

Exercise 4: Modeling the Fiber Arrangement of Skeletal Muscle 

Data Table 5. Muscle Models 

Muscle Model	Skeleton Photograph
Pectoralis Major Muscle
Biceps Brachii

Questions: 

Describe the movements of transverse adduction and flexion for the pectoralis major and biceps brachii muscles. 

Transverse adduction and flexion of the pectoralis major are smooth medial motions at the shoulder joint. There is a shorter extension in the biceps brachii as seen in the pectoralis major. 

How did adding more rubber bands affect the strength of each joint that each “muscle” moved? 

The addition of more rubber bands made the joints harder to move. 

How does the addition of the rubber bands affect the range of motion of the joint? 

The addition of rubber bands limits the range of the motion for a joint. 

The biceps brachii and the pectoralis major muscles both cross the shoulder. How does each muscle affect the movement of the shoulder? 

The biceps brachii affects the shoulder by helping in its flexion. The pectoralis major helps in the adduction, flexion, and rotation of the humerus.