By Jonathan Howard Show Objectives:
Muscular Physiology Muscles are highly specialized to contract forcefully. Muscles are powered by muscle cells, which contract individually within a muscle to generate force. This force is needed to create movement. There are over 600 muscles in the human body; they are responsible for every movement we make, from pumping blood through the heart and moving food through the digestive system, to blinking and chewing. Without muscle cells, we would be unable to stand, walk, talk, or perform everyday tasks. Muscles are used for movement in the body. The largest portion of energy expenditure in the body happens in muscles while helping us perform daily activities with ease and improving our wellness. Muscular strength is the amount of force that a muscle can produce one time at a maximal effort, and muscular endurance is the ability to repeat a movement over an extended period of time. Resistance training is the method of developing muscular strength and muscular endurance, which in turns improves wellness. This chapter explores many ways to resistance train. However, achieving the best muscular performance requires the assistance of a trained professional. For more information on muscular fitness and endurance, please click on the link below: Muscular Strength and Endurance Types of MuscleThere are three types of muscle:
Responsible for body movement.
Responsible for the contraction of the heart.
Responsible for many tasks, including movement of food along intestines, enlargement and contraction of blood vessels, size of pupils, and many other contractions. Skeletal Muscle Structure and Function Skeletal muscles are attached to the skeleton and are responsible for the movement of our limbs, torso, and head. They are under conscious control, which means that we can consciously choose to contract a muscle and can regulate how strong the contraction actually is. Skeletal muscles are made up of a number of muscle fibers. Each muscle fiber is an individual muscle cell and may be anywhere from 1 mm to 4 cm in length. When we choose to contract a muscle fiber—for instance we contract our bicep to bend our arm upwards—a signal is sent from our brain via the spinal cord to the muscle. This signals the muscle fibers to contract. Each nerve will control a certain number of muscle fibers. The nerve and the fibers it controls are called a motor unit. Only a small number of muscle fibers will contract to bend one of our limbs, but if we wish to lift a heavy weight then many more muscles fibers will be recruited to perform the action. This is called muscle fiber recruitment. Each muscle fiber is surrounded by connective tissue called an external lamina. A group of muscle fibers are encased within more connective tissue called the endomysium. The group of muscle fibers and the endomysium are surrounded by more connective tissue called the perimysium. A group of muscle fibers surrounded by the perimysium is called a muscle fasciculus. A muscle is made up of many muscle fasciculi, which are surrounded by a thick collagenous layer of connective tissue called the epimysium. The epimysium covers the whole surface of the muscle. Muscle fibers also contain many mitochondria, which are energy powerhouses that are responsible for the aerobic production of energy molecules, or ATP molecules. Muscle fibers also contain glycogen granules as a stored energy source, and myofibrils, which are threadlike structures running the length of the muscle fiber. Myofibrils are made up of two types of protein: Actin myofilaments, and myosin myofilaments. The actin and myosin filaments form the contractile part of the muscle, which is called the sarcomere. Myosin filaments are thick and dark when compared with actin filaments, which are much thinner and lighter in appearance. The actin and myosin filaments lie on top of one another; it is this arrangement of the filaments that gives muscle its striated or striped appearance. When groups of actin and myosin filaments are bound together by connective tissue they make the myofibrils. When groups of myofibrils are bound together by connective tissue, they make up muscle fibers. The ends of the muscle connect to bone through a tendon. The muscle is connected to two bones in order to allow movement to occur through a joint. When a muscle contracts, only one of these bones will move. The point where the muscle is attached to a bone that moves is called the insertion. The point where the muscle is attached to a bone that remains in a fixed position is called the origin. How Muscles ContractMuscles are believed to contract through a process called the Sliding Filament Theory. In this theory, the muscles contract when actin filaments slide over myosin filaments resulting in a shortening of the length of the sarcomeres, and hence, a shortening of the muscle fibers. During this process the actin and myosin filaments do not change length when muscles contract, but instead they slide past each other. During this process the muscle fiber becomes shorter and fatter in appearance. As a number of muscle fibers shorten at the same time, the whole muscle contracts and causes the tendon to pull on the bone it attaches too. This creates movement that occurs at the point of insertion. For the muscle to return to normal (i.e., to lengthen), a force must be applied to the muscle to cause the muscle fibers to lengthen. This force can be due to gravity or due to the contraction of an opposing muscle group. Skeletal muscles contract in response to an electric signal called an action potential. Action potentials are conducted along nerve cells before reaching the muscle fibers. The nerve cells regulate the function of skeletal muscles by controlling the number of action potentials that are produced. The action potentials trigger a series of chemical reactions that result in the contraction of a muscle. When a nerve impulse stimulates a motor unit within a muscle, all of the muscle fibers controlled by that motor unit will contract. When stimulated, these muscle fibers contract on an all-or-nothing basis. The all- or-nothing principle means that muscle fibers either contract maximally along their length or not at all. Therefore, when stimulated, muscle fibers contract to their maximum level and when not stimulated there is no contraction. In this way, the force generated by a muscle is not regulated by the level of contraction by individual fibers, but rather it is due to the number of muscle fibers that are recruited to contract. This is called muscle fiber recruitment. When lifting a light object, such as a book, only a small number of muscle fibers will be recruited. However, those that are recruited will contract to their maximum level. When lifting a heavier weight, many more muscle fibers will be recruited to contract maximally. When one muscle contracts, another opposing muscle will relax. In this way, muscles are arranged in pairs. An example is when you bend your arm at the elbow: you contract your bicep muscle and relax your tricep muscle. This is the same for every movement in the body. There will always be one contracting muscle and one relaxing muscle. If you take a moment to think about these simple movements, it will soon become obvious that unless the opposing muscle is relaxed, it will have a negative effect on the force generated by the contracting muscle. A muscle that contracts, and is the main muscle group responsible for the movement, is called the agonist or prime mover. The muscle that relaxes is called the antagonist. One of the effects that regular strength training has is an improvement in the level of relaxation that occurs in the opposing muscle group. Although the agonist/antagonist relationship changes, depending on which muscle is responsible for the movement, every muscle group has an opposing muscle group. Below are examples of agonist and antagonist muscle group pairings:
Smaller muscles may also assist the agonist during a particular movement. The smaller muscle is called the synergist. An example of a synergist would be the deltoid (shoulder) muscle during a press-up. The front of the deltoid provides additional force during the press-up; however, most of the force is applied by the pectoralis major (chest). Other muscle groups may also assist the movement by helping to maintain a fixed posture and prevent unwanted movement. These muscle groups are called fixators. An example of a fixator is the shoulder muscle during a bicep curl or tricep extension. Types of Muscular Contraction
This is a static contraction where the length of the muscle, or the joint angle, does not change. An example is pushing against a stationary object such as a wall. This type of contraction is known to lead to rapid rises in blood pressure.
This is a moving contraction, also known as dynamic contraction. During this contraction the muscle fattens, and there is movement at the joint. Types of Isotonic Contraction
This is when the muscle contracts and shortens against a resistance. This may be referred to as the lifting or positive phase. An example would be the lifting phase of the bicep curl.
This occurs when the muscle is still contracting and lengthening at the same time. This may be referred to as the lowering or negative phase. Muscle Fiber TypesNot all muscle fibers are the same. In fact, there are two main types of muscle fiber:
Often called slow-twitch or highly- oxidative muscle fibers
Often called fast-twitch or low- oxidative muscle fibers Additionally, Type II muscle fibers can be further split into Type II A and Type II B. Type II b fibers are the truly fast twitch fibers, whereas Type II a are in between slow and fast twitch. Surprisingly, the characteristics of Type II a fibers can be strongly influenced by the type of training undertaken. Following a period of endurance training, they will start to strongly resemble Type I fibers, but following a period of strength training they will start to strongly resemble Type II b fibers. In fact, following several years of endurance training they may end up being almost identical to slow-twitch muscle fibers. Type I (Slow-Twitch Muscle Fibers)Slow-twitch muscle fibers contain more mitochondria, the organelles that produce aerobic energy. They are also smaller, have better blood supply, contract more slowly, and are more fatigue resistant than their fast-twitch brothers. Slow-twitch muscle fibers produce energy, primarily, through aerobic metabolism of fats and carbohydrates. The accelerated rate of aerobic metabolism is enhanced by the large numbers of mitochondria and the enhanced blood supply. They also contain large amounts of myoglobin, a pigment similar to hemoglobin that also stores oxygen. The myoglobin provides an additional store of oxygen for when oxygen supply is limited. This extra oxygen, along with the slow-twitch muscle fibers’ slow rate of contraction, increases their endurance capacity and enhances their fatigue resistance. Slow-twitch muscle fibers are recruited during continuous exercise at low to moderate levels.
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Number of Sit-Ups | ||||||
Men | Very Poor | Poor | Fair | Good | Excellent | Superior |
Age:Under 20 | Below 36 | 36 – 40 | 41 -46 | 47 – 50 | 51 – 61 | Above 61 |
20 – 29 | Below 33 | 33 -37 | 38 – 41 | 42 – 46 | 47 – 54 | Above 54 |
30 – 39 | Below 30 | 30 – 34 | 35 – 38 | 39 – 42 | 43 – 50 | Above 50 |
40 – 49 | Below 24 | 24 – 28 | 29 – 33 | 34 – 38 | 39 – 46 | Above 46 |
50 – 59 | Below 19 | 19 – 23 | 24 – 27 | 28 – 34 | 35 – 42 | Above 42 |
60 and over | Below 15 | 15 – 18 | 19 – 21 | 22 – 29 | 30 – 38 | Above 38 |
Number of Sit-Ups | ||||||
Women | Very Poor | Poor | Fair | Good | Excellent | Superior |
Age:Under 20 | Below 28 | 28 – 31 | 32 – 35 | 36 – 45 | 46 – 54 | Above 54 |
20 – 29 | Below 24 | 24 – 31 | 32 – 37 | 38 – 43 | 44 – 50 | Above 50 |
30 – 39 | Below 20 | 20 – 24 | 25 – 28 | 29 – 34 | 35 – 41 | Above 41 |
40 – 49 | Below 14 | 14 – 19 | 20 – 23 | 24 – 28 | 29 – 37 | Above 37 |
50 – 59 | Below 10 | 10 – 13 | 14 – 19 | 20 – 23 | 24 – 29 | Above 29 |
60 and over | Below 3 | 3 – 5 | 6 – 10 | 11 – 16 | 17 – 27 | Above 27 |
The Push-Up Test
- Equipment:
Mat or towel (optional)
In this test, you will perform either standard push-ups, or modified push-ups, in which you support yourself with your knees. The Cooper Institute developed the ratings for this test with men performing push-ups and women performing modified push-ups.
Biologically, males tend to be stronger than females; the modified technique reduces the need for upper-body strength in a test of muscular endurance. Therefore, for an accurate assessment of upper-body endurance, men should perform standard push-ups and women should perform modified push-ups. (However, in using push-ups as part of a strength-training program, individuals should choose the technique most appropriate for increasing their level of strength and endurance, regardless of gender.)
Instructions
- For push-ups: Start in the push-up position with your body supported by your hands and feet. For the modified push-ups: Start in the modified push-up position with your body supported by your hand and knees. For both positions, your arms and your back should be straight and your fingers pointed forward.
- Lower your chest to the floor with your back straight, and then return to the starting position.
- Perform as many push-ups as you can without stopping.
Number of push-ups: Number of modified push-ups:
Rating Your Push-Up Test Result
Your score is the number of completed push-ups or modified push-ups. Refer to the appropriate portion of the table on page 19 for a rating of your upper-body endurance.
Record your rating below and in the chart at the end of this lab.
Rating:
Ratings for the Push-Up and Modified Push-Up Test:
Men | Number of Modified Push-Ups | |||||
Very Poor | Poor | Fair | Good | Excellent | Superior | |
Age: 18 – 29 | Below 22 | 22 – 28 | 29 – 36 | 37 – 46 | 47 – 61 | Above 61 |
30 – 39 | Below 17 | 17 – 23 | 24 – 29 | 30 – 38 | 39 – 51 | Above 51 |
40 – 49 | Below 11 | 11 – 17 | 18 – 23 | 24 – 29 | 30 – 39 | Above 39 |
50 – 59 | Below 9 | 9 – 12 | 13 – 18 | 19 – 24 | 25 – 38 | Above 38 |
60 and over | Below 6 | 6 – 9 | 10 – 17 | 18 – 22 | 23 – 27 | Above 27 |
Women | Number of Modified Push-Ups | |||||
Very Poor | Poor | Fair | Good | Excellent | Superior | |
Age:18 – 29 | Below 17 | 17 – 22 | 23 – 29 | 30 – 35 | 36 – 44 | Above 44 |
30 – 39 | Below 11 | 11 – 18 | 19 – 23 | 24 – 30 | 31 – 38 | Above 38 |
40 – 49 | Below 6 | 6 – 12 | 13 – 17 | 18 – 23 | 24 – 32 | Above 32 |
50 – 59 | Below 6 | 6 – 11 | 12 – 16 | 17 – 20 | 21 – 27 | Above 27 |
60 and over | Below 2 | 2 – 4 | 5 – 11 | 12 – 14 | 15 – 19 | Above 19 |
SOURCE: Based on norms from the Cooper Institute for Aerobic Research, Dallas, Texas; from the Physical Fitness Specialist Manual, Revised 2002. Used with permission.
The Squat Endurance TestInstructions
- Stand with your feet placed slightly more than shoulder width apart, toes pointed out slightly, hands on hips or across your chest, head neutral, and back straight. Center your weight over your arches or slightly behind.
- Squat down, keeping your weight centered over your arches, until your thighs are parallel with the floor. Push back up to the starting position, maintaining a straight back and neutral head position.
- Perform as many squats as you can without stopping.
Number of squats:
Rating your Squat Endurance Test Result
Your score is the number of completed squats. Refer to the appropriate portion of the table for a rating of your leg muscular endurance. Record your rating below and in the summary at the end of this lab.
Rating:
Number of Squats Performed
Men | Very Poor | Poor | Below Average | Average | Above Average | Good | Excellent |
Age: 18-25 | <25 | 25-30 | 31-34 | 35-38 | 39-43 | 44-49 | >49 |
26-35 | <22 | 22-28 | 29-30 | 31-34 | 35-39 | 40-45 | >45 |
36-45 | <17 | 178-22 | 23-26 | 27-29 | 30-34 | 35-41 | >41 |
46-55 | <9 | 13-17 | 18-21 | 22-24 | 25-38 | 29-35 | >35 |
56-65 | <9 | 9-12 | 13-16 | 187-20 | 21-24 | 25-31 | >31 |
65 + | <7 | 7-10 | 11-14 | 15-18 | 19-21 | 22-28 | >28 |
Women | Very Poor | Poor | Below Average | Average | Above Average | Good | Excellent |
Age: 18-25 | <18 | 18-24 | 25-28 | 29-32 | 33-36 | 37-43 | >43 |
26-35 | <20 | 13-20 | 21-24 | 25-28 | 29-32 | 33-39 | >39 |
36-45 | <7 | 7-14 | 15-18 | 19-22 | 23-26 | 27-33 | >33 |
46-55 | <5 | 5-9 | 10-13 | 14-17 | 18-21 | 22-27 | >27 |
56-65 | <3 | 3-6 | 7-9 | 10-12 | 13-17 | 18-24 | >24 |
65 + | <2 | 2-4 | 5-10 | 11-13 | 14-16 | 17-23 | >23 |
SOURCE: Top End Sports. www.topendsports.com/testing/tests/home-squat.htm
Summary of Results
Test | Number Performed | Rating |
Sit-up Test | ||
Push-up Test | ||
Squat Endurance Test | ||
Using Your Results
- Are you at all surprised by your ratings for muscular endurance?
- What factors, if any, influenced your scores?
- Are you satisfied with your current level of muscular endurance as evidenced in your daily life, for example, your ability to carry groceries or your books, hike, and do yard work?