CHAPTER IX â€“ THE MEASUREMENT OF MUSCULAR STRENGTH
Measuring Muscular Strength Objectives After reading this chapter the student should be able to answer the following questions: 1. What is muscular strength? 2. What is the difference between isotonic, isometric and isokinetic exercises? 3. How do you measure muscular strength? 4. What is relative and absolute muscular strength 5. What are some of the administrative problems involved in measuring strength? 6. What are the directions for administering tests of strength?
KeyTerms Isometrics: An isometric exercise is an exercise in which a force is applied against an immovable object. Isotonic: Isotonics are exercises in which force is applied against a moveable resistance. Isokinetics: Technically speaking, isokinetic exercise is the same as isotonic exercises. The difference is that the resistance used in isokinetic exercises is such that the speed of movement is constant throughout the entire exercise. Strength: Strength may be defined as the ability to exert maximum force against either a movable or immovable resistance. Most weightlifters define it as your 1-RM. Absolute Strength: Absolute strength can be defined as the most weight you can lift (1-RM) regardless of your body weight. Relative Strength: Relative strength can be defined as the most weight you can lift relative to your body weight. Concentric contraction: Concentric contraction is the shortening of a muscle fiber. Eccentric contraction: Eccentric contraction is the lengthening of a muscle fiber.
Strength Strength is frequently recognized by physical educators as the most important factor in the performance of physical skills. While strength may be defined generally as the muscular force exerted against movable and immovable objects, it is best measured by tests that require one maximum effort for a given movement or position. The two types of muscular contraction most frequently measured in physical education classes are static (isometric) and dynamic (isotonic and isokinetics). An isometric exercise is an exercise in which a force is applied against an immovable object. The muscles attempt to contract but are unable to overcome the resistance being used. An example would be if you stood in a doorway and pushed against the sides of the door with your handsâ€Śprovided of course, you donâ€™t move the walls! During such an exercise, the muscles involved are statically contracted (isosame; metric-measure). It might be noted that in isometric contraction, muscular force is exerted over a brief period (usually 6 to 10 sec) without movement of the object of resistance or the body joints involved. Isotonics are exercises in which force is applied against a moveable resistance. During this type of exercise, the muscle is either concentrically contracted (shortened) such as when you curl a weight with your arm, or eccentrically contracted (lengthened) as when you slowly lower the weight. The use of the term isotonic (iso = same; tonos = tension) is somewhat misleading because as a weight is moved, the tension is not really constant but varies with the joint angle or position of the weight. With isotonics muscular force moves an object of resistance through a range of movement. Probably the greatest advantage is that isotonic exercises develop the muscle through a full range of motion, thus eliminating the problem of specificity associated with isometric exercises. We will talk about the importance of strength specificity in a moment. Another exercise that is of significance when talking about strength development and measurement is isokinetics. Technically speaking, isokinetic exercises (iso=same; kinetic=movement) are simply a variation of isotonic exercises. The difference is that the resistance used in isokinetic exercises is such that the speed of movement is constant throughout the entire exercise. This enables the individual to place maximum resistance on the muscle at every point throughout the range of motion. In isokinetic exercises, no matter how much (or how little) force is generated, the resistance continues to move at a constant speed. Thus, a muscle that is loaded isokinetically can be exercised throughout the full range of motion with maximum resistance, provided that the individual exerts maximum force. Practically the same advantages that were mentioned for isotonics are inherent to isokinetics. However, as previously stated, unlike isotonics, isokinetics have the advantage of putting the muscle under maximum tension at every point in the range of motion. Since isokinetic exercises are always performed with the use of machines, isokinetics can be somewhat safer than isotonics. Unfortunately, most of these machines are expensive and therefore are cost prohibitive for most average school settings. Conversely, isometrics and isotonics can be measured easily and inexpensively in most average school situations. While a certain degree of strength is necessary in performing daily activities, strength in most sports activities is regard as essential for success. It is also considered one of the major aspects of physical fitness. Consequently, it is extremely important to physical education instructors and sports coaches
What Is Strength?
Before you evaluate something, you undoubtedly have to know what you are evaluating…that, as they say, is a blinding flash of the obvious…right? With that being said, strength may be defined as the ability to exert maximum force against either a movable or immovable resistance. I know I already said that but something need to said more than once. Most weightlifters define it as your 1-RM (one-repetition maximum). Now here is something you may have noticed if you watch Popeye a lot. Big isn’t always better. Just because an individual has larger muscles than another person does not mean that he is stronger. How many times did Popeye kick Brutus’ butt? Trust me on this one, it wasn’t the spinach. Is it possible that Popeye was stronger even though he was a lot smaller? The answer is yes. Two muscles that have the same circumference may differ in strength because of the amount of fat tissue they contain. Although fat adds to the circumference of the muscle, it lacks contractile power, and in fact limits the contractibility of the muscle. Most likely, Brutus was carrying a lot of body fat. Also, the arrangement of muscle fibers determines the force with which a muscle can contract. Research has revealed that when muscle fibers run at oblique angles, they can exert greater force than when they run parallel to the long axis of the muscle. Thus, two muscles could be the same size, but have different contractile power because of the arrangement of the muscle fibers. Perhaps, Popeye’s muscles, although smaller, were more contractually efficient than Brutus’ muscles. However, all factors being equal, the larger the muscle the greater the strength. In fact, the absolute strength of a muscle is directly proportional to its circumference. In other words, there is a relationship between strength and muscle size and/or mass. In general, the stronger you get, the bigger your muscles will get.
Problems Associated with Strength Testing Several of the problems and limitations associated with the measurement of strength are listed and discussed here. 1. The muscular strength tests most frequently used during the past few decades have included test items of …well…dubious validity. For example, the use of sit-ups in the isotonic strength test designed by Johnson or the inclusion of the lung capacity measure in the Rogers strength test, and the use of push-ups in the AAHPER fitness test have raised many eyebrows among fitness experts over the years. Also, inclusion of muscular endurance items, such as pull-ups and dips for maximum repetition, has added to the confusion concerning strength test results and their interpretation. For one good reason too… the aforementioned items do NOT measure strength. And the designers of these tests obviously don’t know what the heck they are talking about and that list includes the brilliant people in physical education who came to together and designed the AAHPER fitness. It is garbage, but I will save that little tidbit for later on in the book. 2. A number of tests provide accurate strength measurement but require expensive equipment; consequently, many schools are unable to include such tests in their physical education program. Isokinetic equipment falls under this category. 3. At the present time, measurement of abdominal strength has been quite limited. Many of the better known strength tests have avoided this area entirely, although abdominal strength is important in various activities. The sit-up test with maximum (or near maximum) resistance behind the neck presented in many strength test batteries is rather dangerous. Just as significant is the fact that they are NOT a
valid measure of strength. However, with the advent of crunch machines this problem is being addressed. Unfortunately, this equipment is rather expensive. 4. Different grip widths can produce different strength performance results. Thus, it is important to specify which grip width should be used when testing strength. 5. In measuring static strength, establishment of precisely the same position or angle is difficult for certain exercises for all subjects. Differences in the amount of musculature and fatty tissue and different lengths of body segments pose special problems for accurate testing. It is imperative that such tests start at the same angle and from the same reference point for each student. For example, specific phrases such as "starting with the elbows at a 90-degree angle" or "starting with the bar between the eyebrows and the hairline" are necessary if comparisons are to be made within a group or with established norms. Furthermore, in using any type of gauge such as the tensiometer that does not have a memory pointer (a pointer that remains in place after pressure is released), the tester must keep his or her eyes at the same level as the scale to secure an accurate reading. 6. Most importantly though, it should be understood that strength is body specific. This is something else you need to consider when evaluating strength. There is no single exercise that correlates very highly with total strength except the squat and deadlift. This is probably due to the fact that strength is body specific. For example, just because your arms are strong does not necessarily mean that your legs will be strong, or vice versa. Therefore, in order to measure total body strength each muscle group would have to be tested independently. To do this, you first find an exercise in which the muscle you want to test is the prime mover, and then simply determine your 1-RM in that exercise. The most common exercises used for evaluating strength are the bench press, squat, deadlift and pulldowns. The scores on these four lifts are generally considered a predictor of total body strength based on face validity. 7. Another important factor in evaluating strength isotonically is skill level and the standardization of the test. As I just mentioned, the squat is one of the few exercises that actually correlates fairly high with total body strength when it is used to evaluate elite athletes. The key words here are “elite athletes.” Unfortunately, from a biomechanical standpoint, squats are one of the most difficult exercises to master. Although the squat is a relatively simple skill, it requires the individual to focus on significantly more environmental cues than most other exercises. Consequently, a disadvantage of using free weight exercises to evaluate strength is the subject’s skill level or the lack of his skill level. That is where the words elite athletes come in. With elite athletes the factor of skill is neutralized to a great extent. With novice athletes or just plain folk, like you and me, skill level can cause variations in scoring that are not attributed to strength at all, thereby rendering the test invalid. Using the squat as our example let me explain what can happen if the biomechanics for testing are not standardized. Please bare with me here for a second while I run you through the fine points of squatting. With the weight still in the rack you have four options to consider concerning bar placement on your back for the squat. First, you can carry the bar high on your back. With the bar in this position, it's easier to keep your back upright when you squat. With your back in a more vertical and/or upright position, you are also afforded a number of advantages: It's safer, you will be able to reach your depth quicker, and it looks pretty. On the down side, by carrying the bar high, you're raising your center of gravity thereby making the lift a little harder…actually a lot harder.
Your second option is to carry the bar lower…no lower than 13 cm below the posterior deltoid, unless you're trying to kill yourself…on your back. As you might expect, the advantages and disadvantages of placing the bar at this position are near opposite of carrying the bar high. The lower bar placement will lower your center of gravity, thereby increasing your mechanical efficiency, and consequently making the lift much easier. The problem with a lower bar placement is that it's hard to keep your back erect…it doesn't look pretty either. Fortunately, there are no points subtracted for "ugly" and with practice, you can learn to keep your back fairly close to vertical. Your third option is to place the bar somewhere between options one and two. Does that make sense? If it doesn't, read options one and two again! This is probably the best bar placement for testing and should be required for each individual being tested. Your fourth option is to leave the weight in the rack. Go home, get a cold one, and tune in the Beyonce videos. The advantage of this option is that it's a lot easier, safer, and a heck of a lot more fun. The disadvantage is that you can only watch the dancers (It's kind of like psychological masturbation with a masochistic slant) and your teacher most likely will give you a G for the course which is one below F. Unless, of course, you take him with you Once you have bar placement on your back it's time to squat. God, that sounds gross! Anyway, after you unrack the weight, "Simon says" take one very short step backwards. Ten inches is plenty of distance between you and the rack. There are a couple of excellent reasons for setting up so close to the rack. First of all, you don't get any extra points for walking the weight all over the platform. Not only don't you get extra points, but you burn up a lot of energy doing so, while at the same time scaring the heck out of everyone in the class. When you are in position to set up, you have a few more options to consider. First, you can squat with a wide foot spacing. For what it's worth, most world class athletes use an extremely wide stance. By using a wide stance and keeping your back in an upright position during your descent, you can reach parallel (or any other depth required) much faster than if you use a narrow stance. Of course, by reaching parallel quickly, you are shortening the distance that you must lift the weight and consequently are doing less mechanical work. This is another important reason to standardize your testing procedures. According to biomechanical studies, you have a greater availability and utilization of muscle mass with a wide stance than you do with a narrow stance. The disadvantages of using a wide stance are few. From a strictly empirical standpoint, a wide stance can predispose you to more back injuries than will a narrow stance…but significantly less knee injuries. This is another thing to consider when testing your students and/or subjects. Of course, you can find yourself a foot spacing between the two extremes we just discussed or you could go home and watch the Beyonce videos, but we're not getting into all that again. If you are testing, I would suggest a standardized foot spacing that is a few inches past should width. If you don’t standardize the testing procedure you can already see the advantages that can be gained by using a wide stance and carrying the bar low on your back. Okay, now for your descent. This is the easy part. In fact, I have never seen anyone miss a descent. It's ascending that's the real trick. First things first though. As mentioned, when descending with the weight, try to keep your back in an upright position. It's important to keep your calves straight and your knees directly over your feet. Try to keep the weight back over your heels, aligning your position so that your power is centered vertically. It's also a good idea to point your toes slightly outward. This will allow you to lift the weight further back over your heels. It will also help you to flare your knees outward at the bottom of the lift. Again biomechanics can significantly affect your subject’s performance. This brings up yet another question…how deep should the subjects go. In the isotonic strength test designed by Johnson (1981) it is suggested that the subject descend to a bench and then come back up. The problem with
using a bench is that a tall person might actually have to break parallel before he comes in contact with the bench while a short person maybe two or three inches above parallel when he contacts the bench. Obviously, the smaller person would have a tremendous advantage performing the test. Now for the fun part...getting back up to the starting position.. As soon as you break parallel or the depth that is requiredâ€Śnote that you don't get any points for going deeperâ€Śtilt your back slightly forward, thereby bringing your hips into play to lead your ascent. As you drive the weight upward, gradually drive your thighs inward and upward. This will help you to channel your power vertically. When you reach your sticking point, drive your shoulders backward and your hips inward until you are in an upright position. Why am I telling you all of this? Simple, I am trying to illustrate to you that by simply changing the biomechanics of the lift you can drastically change the performance on that lift. Consequently, if the movement is not standardizing for everyone, you can get a variation in strength scores that can be contributed more to skill than to strength per seâ€™. This is a major problem with isotonic strength testing in which free weight is used. As soon as you start testing large groups of subjects, even the individuals who have experience with free weights, you will find a wide variation in their form and technique. That is why as a tester you should go to great lengths to standardize the procedures for your subjects. Enough said about that.