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CHAPTER MUSCLES AT WORK 6 ASSESSMENT CATEGORIES Application Communication Knowledge and Understanding Thinking Activities in this chapter: 1 2 Types of Muscle Action 68 Review Your Key Terms Get into Action Factors Influencing Muscle Action 69 Review Your Key Terms Graph the Relationships Factors Affecting Muscle Contraction 3 Check Your Understanding 71 4 Chapter Culminating Assignment 73 CHAPTER Muscles at Work 6.1 TYPES OF MUSCLE ACTION (Textbook pages 118-121) 1 6.1.1 Review Your Key Terms concentric action dynamic action eccentric action isokinetic action isometric action plyometric action static action 6.1.2 Get into Action A. Complete the flow chart below and provide an example for each numbered muscle action. ER S Muscle Action Dynamic W 1. Static 2. Concentric Order of dynamic muscle actions may vary. 1. Static: any isometric activity such as arm wrestling, pushing against a door frame, maintaining a hold in gymnastics 3. Eccentric 4. Isokinetic 3. Eccentric: Movement that involves muscle lengthening such as lowering weights during an arm curl, leg curl, bench press AN S 6 5. Plyometric 5. Plyometric: Box/depth jumping; bounding exercises 2. Concentric: Movement that involves 4. Isokinetic: Weight training with muscle shortening to overcome resistance dynamometers such as CYBEX, Nautilus such as arm/leg curl, bench press B. Identify the types of muscle action represented by each of the following activities. Activity 68 Type of Muscle Action Activity Type of Muscle Action Isometric Concentric/Eccentric Concentric/Eccentric Isometric Plyometric Concentric/Eccentric Isokinetic Concentric/Eccentric (Isometric if position is held) Kinesiology Student Workbook CHAPTER Muscles at Work 6.2 FACTORS INFLUENCING MUSCLE ACTION (Textbook pages 121-130) 2 6.2.1 Review Your Key Terms absolute strength apoptosis maximal strength muscular endurance one repetition maximum (1RM) power relative strength repetition maximum (RM) sarcopenia speed–strength strength endurance 6.2.2 Graph the Relationships S If you consider Olympic lifting events as an example, definite relationships can be graphed comparing (A) body mass and maximum load lifted and (B) body mass and relative strength. Graph the linear relationships on the graphs below, and explain what factors account for these effects. A ER 450 400 350 300 250 0 52 67.5 SW Total Load Lifted (kg) 500 There is a close connection between body mass and strength. The greater one’s stature the greater one’s strength – provided body mass is composed mainly of muscle and not fat. This fact is emphasized by the performances of weightlifters across various weight categories. The world record in the bantamweight division (56 kg) is greater than that in the flyweight (52 kg) division; and in the featherweight (60 kg) division it is higher than in the bantamweight division. The heaviest weights of all are lifted by athletes of the super-heavyweight category. 82.5 100 110 B AN Body Mass (kg) A linear relationship exists between body mass and relative strength – as one increases the other decreases. The performance of athletes classified by weight (such as weightlifters), and athletes who must overcome their own body mass (such as jumpers, runners, gymnasts, etc.), depends less on maximal strength than on the proportion of maximal strength to body mass. Relative strength can be increased by increasing strength and stabilizing body mass or by stabilizing maximal strength and reducing body mass. 5.8 Relative Strength 5.4 5.0 4.6 4.2 3.8 3.4 52 67.5 82.5 100 110 Body Mass (kg) Studying Human Movement and Health 69 6 CHAPTER Muscles at Work 6.2.3 Factors Affecting Muscle Action A. List the main factors that influence muscle contraction and force output in humans. 1 Joint angle 4 Muscle fibre type 2 Muscle cross-sectional area 3 Speed of movement 5 Age 6 Sex B. Expand your knowledge by conducting research on one of the factors you listed above. Discuss how and why the selected factors influence muscle contraction. Answers will vary. _______________________________________________________________________________________________________ S _______________________________________________________________________________________________________ _______________________________________________________________________________________________________ ER _______________________________________________________________________________________________________ _______________________________________________________________________________________________________ _______________________________________________________________________________________________________ _______________________________________________________________________________________________________ W _______________________________________________________________________________________________________ _______________________________________________________________________________________________________ _______________________________________________________________________________________________________ _______________________________________________________________________________________________________ AN S 6 C.Minor-league hockey teams can see a 45-kg difference between players, especially players 11 to 14 years old. Discuss the advantages and disadvantages of organizing minor hockey teams by weight categories instead of simply by age. This question can be debated as a class or completed on your own. Answers will vary. Reduction of injuries.... _______________________________________________________________________________________________________ _______________________________________________________________________________________________________ _______________________________________________________________________________________________________ _______________________________________________________________________________________________________ _______________________________________________________________________________________________________ _______________________________________________________________________________________________________ _______________________________________________________________________________________________________ _______________________________________________________________________________________________________ _______________________________________________________________________________________________________ _______________________________________________________________________________________________________ _______________________________________________________________________________________________________ 70 Kinesiology Student Workbook CHAPTER Muscles at Work Name: ______________________________________ CHECK YOUR UNDERSTANDING 3 1. Which of the following statements regarding static muscle actions is false: A) Maximal static action can occur in sports such as gymnastics and wrestling. B) Most sport activities require low to submaximal static action. C) Maximal static action is very common in most sports. D)Flexing the arm against the resistance of a fixed bar is an example of static contraction. E) None of the above. Answer: C 3. Which of the following is not a factor that affects a muscle’s force and power output: A) muscle length B) joint angle C) age D)sex E) none of the above AN Answer: A Fill in the blanks for the following statements using words from the word bank below. Place the corresponding letter from the word bank in the blank spaces provided. 1. Dynamic contraction occurs whenever the internal force generated by the muscle contraction results in movement. 2. In isokinetic contraction, the neuromuscular system can work at a constant speed during each phase of movement against a preset high resistance. 3. The main components of strength are maximal strength, power, and muscular endurance. 4. The ability of an athlete to resist fatigue in strength performances of longer duration is known as muscular endurance. SW Answer: D Fill in the Blanks ER 2. Which of the following statements regarding dynamic muscle action is false: A) It can include both concentric and eccentric actions. B) It occurs when the external force is smaller than the internal force generated by the athlete. C) It is very common in all types of sports events. D)It may occur without any visible change in muscle length. E) None of the above. D)All of the above. E) None of the above. Answer: E S Multiple Choice Date: _______________________________________ 4. Which of the following statements regarding power is true: A) It is often referred to as speed–strength. B) It is desirable in sporting events such as the high jump. C) It determines the speed of movement execution. D)All of the above. E) A and B only. 5. During maximal responses, the greater the FT fibre content of a muscle, the greater the force output, the greater the overall speed of contraction, and the lower the resistance to fatigue. Word Bank a. concentric e. isometric i. power b. dynamic f. lower j. relative strength c. greater g. maximal strength k. stamina d. isokinetic h. muscular endurance l. static Answer: D True or False 5. Which of the following statements regarding the relationship between maximal strength and power is false: A) The higher the external resistance to be overcome, the more important maximal strength is for power performance. B) The greater the proportion of maximal strength mobilized to perform the movement, the slower the movement occurs. C) The greater the maximal strength, the higher the movement acceleration. Indicate whether each statement is true (T) or false (F). If the statement is false, provide the correct answer. 1.Isometric contraction occurs against a load that is beyond the capability of the muscle(s) to move. Answer: true 2.During a concentric contraction, extension usually occurs. Answer: false (Correct: flexion) Studying Human Movement and Health 71 6 CHAPTER Muscles at Work 3.The importance of maximal strength for an athletic performance decreases as the resistance that must be overcome in competition is reduced and as the period of competition decreases. 5.The process of preprogrammed death of muscle cells is called sarcopenia. Answer: false (Correct: apoptosis) Answer: true; false (Correct: increases) 4.Strength training and increases in maximal strength lead to slowed muscle performance. Answer: false (Correct: do not lead to) Think and Link 1.Using a leg curl to provide examples, explain the differences between concentric and eccentric contractions. W ER S A concentric contraction is one in which the muscle shortens as it goes through the range of motion; this is usually termed flexion. An eccentric contraction is one in which the muscle lengthens during the movement, usually termed extension. During a leg curl, bringing the heels towards the buttocks (i.e., flexion of the hamstrings) is a concentric contraction. The movement of the heels away from the buttocks area (i.e., extension of hamstrings) is an eccentric contraction. AN S 2.Explain the figure below, and describe the relationship between FT muscle fibre hypertrophy and strength training. Development of Strength Capacity 6 The figure illustrates the development of maximal strength through muscle hypertrophy and increased intra-muscular coordination using short-term maximal resistance training. FT fibres respond very effectively to high-resistance training, which generates an increase in diameter of the contractile elements (myofibrils) of the fibres. Furthermore, this type of training results in a progressive increase in the number of fast motor units that can be mobilized. This results in improved intra-muscle coordination. Strength Capacity Initial Value 1st Cycle 2nd Cycle Strength Training Time _______________________________________________________________________________________________________ _______________________________________________________________________________________________________ _______________________________________________________________________________________________________ _______________________________________________________________________________________________________ _______________________________________________________________________________________________________ 72 Kinesiology Student Workbook CHAPTER Muscles at Work Name: __________________________________________________________ Date: _______________________________ CHAPTER CULMINATING ASSIGNMENT 4 Case Study: An Absolute and Relative Comparison Pia, Michelle, Marco, and Paul decide to have a weightlifting competition on the bench press using a 70-kg barbell. Use the following information to determine and then compare their absolute (1RM) and relative muscle strength (kg for kg). Use information in Table 6.1 on page 127 to aid in your calculations. No. of Repetitions 1RM or Absolute Strength (kg) Relative Strength (kg) Pia 54 1 70 1.30 Michelle 78 3 74 0.95 Marco 85 12 88 1.03 Paul 100 16 93 0.93 ER Sample answer for Pia: S Athlete’s Weight (kg) Athlete 1RM = Load (kg) / [Achieved resistance level (% from Table 6.1) / 100] SW Absolute strength = 70 / (100 / 100) = 70 kg Relative Strength = Maximal strength (kg) / Body mass (kg) AN Relative strength = 70 / 54 = 1.30 kg Define absolute strength. Who has the greatest absolute strength? Absolute strength is a measure of strength independent of a person’s body mass – the ability to perform maximal voluntary muscular contractions in order to overcome powerful external resistance. It is the greatest force an individual can exert for a given contraction of muscles or the greatest load that individual can lift in one attempt. In this case, Paul possesses the greatest absolute strength. Define relative strength. Who has the greatest relative strength? Relative strength – also known as pound-for-pound or kilogram-for-kilogram strength – is a measure of strength that depends on a person’s body mass, and is calculated by dividing maximal strength by body mass. In this case, Pia has the greatest relative strength. Describe two ways to increase relative strength. Relative strength can be increased by stabilizing maximal strength and reducing body mass, which may be the strategy used by recreational and overweight athletes. It is of little use to competitive athletes, however, because a reduction of body mass is often linked with loss of muscle mass and therefore with a decrease in maximal and relative strength. Another way to increase relative strength is to increase strength and stabilize body mass. As maximal strength is not only dependent upon muscle diameter, but also upon intramuscle coordination, this variation is often quite promising, provided that the correct and relevant training methods are chosen. Studying Human Movement and Health 73 6 CHAPTER Muscles at Work Discuss the relationship between maximal strength and endurance among the athletes. The number of repetitions against high resistance is dependent on the maximal strength of the athlete. See example on textbook page 127. W ER S The maximal feasible number of repetitions of a particular load is referred to as the repetition maximum (RM). If the RM of an exercise is 2-3, it can be deduced that an athlete can resist a force corresponding to approximately 95 percent of maximal strength capacity. If the athlete is able to perform maximally 7-8 repetitions with a particular weight, then this weight approximates 85 percent of maximal strength capacity. Therefore, it is not always necessary that you work against maximal resistance (which may be very dangerous in most cases) in order to calculate your maximal strength capacity for a given exercise. Determining an athlete’s maximal number of repetitions against submaximal resistance will produce an accurate assessment of maximal strength. However, as the number of repetitions increases (or as the level of resistance decreases), the RM becomes a less accurate criterion of maximal strength. It is a commonly held belief that the development of strength hinders and even impairs the development of endurance, and vice versa. The validity of this notion depends upon the type of training and event in question. Vigorous training for running long distances leads to an increase in cardiorespiratory fitness (increased aerobic power). However, the simultaneous decrease in the diameter of the fast twitch muscle fibres causes a corresponding decrease in muscle volume. These processes, then, result in increased endurance and decreased muscle strength. Conversely, repetitive maximal strength training decreases endurance but increases strength. Thus, the training of a weightlifter or shot-putter is geared towards the development of maximal strength and power; endurance is hardly improved. However, unless a specific sports event requires the possession of a maximal level of endurance or strength, training should achieve a balance between strength and endurance. AN S 6 74 Kinesiology Student Workbook