Lecture NotesExercise EvaluationInstructions: Read through the lecture while watching the PowerPoint slide show that accompanies these notes. When you see the <ENTER> prompt, press enter for the slide show so that you can progress through the show in a manner that corresponds to these notes.SLIDE 1: Let’s take some of the concepts that we have learned this semester and use them to help us evaluate exercises for training and for rehabilitation. An exercise analysis serves to enhance the physical training of an individual by evaluating a particular exercise for specificity toa skill or sport for which an individual is training or rehabilitating. We have already learned how to use a muscular analysis to help us determine which muscles an exercise is training and how those muscles are being used with regard to agonist function, antagonist function, neutralization, and stabilization. Now, we want to apply some other concepts that we have learned this semester to exercise evaluation. <ENTER>SLIDE 2: The primary concept that we want to examine in this lecture is that of strength curve similarity. This concept helps evaluate whether the principle of progressive overload is being applied appropriately throughout the range of motion in an exercise. You have already been introduced to this concept in lab when you analyzed the horizontal and inclined crunch exercise. Let’s examine this concept in more detail. <ENTER>SLIDE 3: A strength curve is a plot of how maximum strength varies as a function of joint angle. We previously used the concept of a strength curve to illustrate the torque output for a single muscle when we examined the biceps brachii and the brachioradialis. From a practical perspective, strength curves are most useful for muscle groups, as opposed to individual muscles. Obviously, the strength curve for a muscle group is the cumulative effect of the strength curves ofthe individual muscles that make up the group. As we have already seen, these curves are influenced by moment arm and length changes of the muscles. Strength curves have been developed for numerous joints in the body. Strength can be defined in a number of ways. We will define strength as the ability of a muscle group to develop torque against an unyielding resistancein a single contraction of unrestricted duration. Before we discuss the concept of strength curve similarity, let’s review how the strength curve for an individual muscle is determined. <ENTER> SLIDE 4: Because a strength curve is a plot of how maximum strength (torque) varies as a function of joint angle, then a strength curve can easily be generated if understand the factors that affect muscle torque throughout the ROM. Earlier in the semester we also identified the two factors that affect torque production of a muscle, as expressed by the equation, t=Fd. The first factor is the muscle force. Anything that affects muscle force output ultimately affects the torque output of that muscle as well. <ENTER>SLIDE 5: There are numerous factors that affect the force output of a muscle, but only one of these factors changes predictably throughout the ROM – the force-length relationship. Therefore, this is the only factor that can be used to predict and explain strength curves for muscles. The force-length relationship of the whole muscle is influenced by the force-length relationship of the its two tissue components – the muscle tissue and the connective tissue. Before we can understand the force-length relation of the whole muscle, let’s examine the individual components. <ENTER>SLIDE 6: The diagram on the slide presents the force-length relationship for the muscle fiber. Muscle fibers produce their greatest force at a length slightly greater than resting length – somewhere between 80-120% of resting length. Most muscles in the body operate within this range of lengths. However, when the muscle fiber is shortened to a length that is less than this, force output decreases due to overlap of the myosin and actin filaments which reduces the number of cross-bridges formed. At lengths greater than this range, force output of the fiber also decreases because the myosin and actin filaments are too far apart to allow all CBs to form. <ENTER>SLIDE 7: Therefore, on this figure, the force-length relationship for the active component of the muscle organ (the muscle tissue is depicted by this curve. <ENTER> <ENTER>SLIDE 8: This curve <ENTER> represents the force-length relationship for the SEC and PEC components of the muscle. These components develop tension when stretched (due to elastic properties), which assists to stop over-lengthening of the muscles. The force produced by CT depends on velocity of stretch. A greater velocity will result in greater force production by the CT.Force of CT varies across muscles due to differences in CT’s resting lengths and the amount of CT in each muscle. The SEC and PEC contribute ~47% of passive torque produced in the midrange of movement. The other half is produced by the joint capsule. Because the SEC and PEC produce passive force, they can protect joint by resisting at the ends of the ROM when muscle activation is delayed, especially with an unexpected perturbation. <ENTER>SLIDE 9: This curve <ENTER> represents the total force output of the muscle organ as a function of length. At short lengths, the force produced in the muscle is due only to the active muscle contraction. This force is then transferred to the SEC, which then transfers the force to thebone. At extreme lengths of the muscle, the force in the muscle is almost exclusively elastic or passive. Total force output is maximized at longer muscle lengths due to the elastic contribution, but activation and initiation of movement is difficult because the active component has very low force producing potential. <ENTER>SLIDE 10: Now let’s consider the practical application for this force-length relationship. The shortest length at which a muscle can produce active force is 60% of resting length. Therefore, a whole muscle can produce force and shorten to ~half its resting length (not including its tendons).The longest length at which a muscle can actively produce force is ~1.5X its resting length, or 160% of resting length. Therefore, the range of lengths that a muscle can actively produce force is~60-160%. Passive force in the SEC and PEC is developed once a muscle is stretched beyond its resting length, developing force at lengths up to 200% of resting