The Limitations Of Functional Anatomical Analysis

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Anatomy classifies muscles into functional groups (flexors/extensors, abductors/adductors, etc.) based on hypothesized actions. These muscle groups are useful general classifications and are commonly used in fitness education, weight training, and rehabilitation. These hypothesized muscle actions in movements and exercises are used to judge the relevance of various exercise training or rehabilitation programs. This section will show that such qualitative estimations of muscle actions are often incorrect. Similarly, many of the muscle actions hypothesized by coaches and thera

Mechanical Method of Muscle Action Analysis

Functional anatomy, while not an oxymoron, is certainly a phrase that stretches the truth. Functional anatomy classifies muscles actions based on the mechanical method of muscle action analysis. This method essentially examines one muscle's line of action relative to one joint axis of rotation, and infers a joint action based on orientation and pulls of the muscle in the anatomical position (Figure 3.12). In the sagittal plane, the biceps brachii is classified as an elbow flexor because it is assumed that (1) the origins are at the shoulder joint, (2) the insertion is on the radial tuberosity, and (3) the anterior orientation

Anatomy Orientation Terminology Radial

Figure 3.12. The mechanical method of muscle action analysis applied to biceps and elbow flexion in the sagittal plane. It is assumed that in the anatomical position the biceps pulls upward toward its anatomical origin from its anatomical insertion (radial tuberosity). The motion can be visualized using a bicycle wheel with the axle aligned on the joint axis. If the the muscle were pulling on the wheel from its illustrated direction and orientations relative to that joint axis (visualize where the line of action crosses the medial-lateral and superior-inferior axes of the sagittal plane), the wheel would rotate to the left, corresponding to elbow flexion. Unfortunately, the actions of other muscles, external forces, or other body positions are not accounted for in these analyses. More thorough and mathematical biomechanical analyses of the whole body are required to determine the true actions of muscles.

and superior pull, as well as the superior orientation and posterior pull, would create elbow flexion. When a muscle is activated, however, it pulls both attachments approximately equally so that which end moves (if one does at all) depends on many biome-chanical factors. Recall that there are three kinds of muscle actions, so that what the biceps brachii muscle does at the elbow in a particular situation depends on many bio-mechanical factors this book will explore.

Notice that the tension at both ends of a muscle often might not be the same because of the force transmitted to nearby muscles and extramuscular connective tissue (Hui-jing, 1999; Maas et al, 2004).

While the biceps is clearly an elbow flexor, this analysis assumes quite a bit and does not take into consideration other muscles, other external forces, and the biarticu-lar nature of the biceps. The long head of the biceps brachii crosses the shoulder joint. What if the movement of interest was the eccentric phase of the pull-over exercise (Figure 3.13), where the shoulder was the origin because the elbow angle essentially did not change while shoulder flexion and extension were occurring? It is not entirely clear if the long head of the biceps is in isometric or concentric action in this pull-over exercise example. Biomechanical data and analysis are necessary to determine the actual actions of muscles in movement. There are even cases where muscles accelerate a

Pullover Exercise

Figure 3.13. In the eccentric phase of the pullover exercise, the motion primarily occurs at the shoulder joint, with the elbow angle remaining unchanged. The isolated mechanical method of muscle action does not help in this situation to determine if the long head biceps (crossing both the elbow and shoulder joints) is isometrically active, concentrically active, or inactive. Do you think a biarticular muscle like the biceps can be doing two kinds of muscle actions at once? We will see later that extensive kinetic biomechanical models and EMG research must be combined to determine the actual action of muscles in many movements. Image courtesy of VHI Kits, Tacoma, WA.

Figure 3.13. In the eccentric phase of the pullover exercise, the motion primarily occurs at the shoulder joint, with the elbow angle remaining unchanged. The isolated mechanical method of muscle action does not help in this situation to determine if the long head biceps (crossing both the elbow and shoulder joints) is isometrically active, concentrically active, or inactive. Do you think a biarticular muscle like the biceps can be doing two kinds of muscle actions at once? We will see later that extensive kinetic biomechanical models and EMG research must be combined to determine the actual action of muscles in many movements. Image courtesy of VHI Kits, Tacoma, WA.

joint in the opposite direction to that inferred by functional anatomy (Zajac, 1991; Zajac & Gordon, 1989).

Rather invasive biomechanical measurements are usually required to determine exactly what muscle actions are occurring in normal movement. Many studies conducted on animals have shown that muscles often have surprising and complex actions (see Biewener, 1998; Herzog, 1996a,b). One such study of the turkey (Roberts et al., 1997) gastrocnemius (plantar flexor) found the muscle acted in essentially an isometric fashion in the stance phase of level running (Figure 3.14A), while concentric actions were used running uphill (Figure 3.14B). The invasive nature of these kinds of measurements and the interesting variations in the musculoskeletal structure of animals (fish, kangaroo rats, wallabies; Biewener, 1998; Griffiths, 1989; Shadwick, Steffensen, Katz, & Knower, 1998) makes animal studies a major area of interest for the biome-chanics of muscle function.

Similar complex behavior of muscle actions has been observed in humans using

Emg Turkey Gastrocnemius

Figure 3.14. Simultaneous muscle force, length, and activation (EMG) measurements of the gastrocnemius of running turkeys. (A) Note that in level running the muscle creates considerable force but the fibers do not shorten, so the muscle is in isometric action and length changes are in the stretching and recoiling of the tendon. (B) in the stance phase of uphill running, the muscle fibers shorten (concentric action), doing mechanical work to lift the turkey's body. Reprinted with permission from Roberts et al. (1997). Copyright © 1997 American Association for the Advancement of Science.

Figure 3.14. Simultaneous muscle force, length, and activation (EMG) measurements of the gastrocnemius of running turkeys. (A) Note that in level running the muscle creates considerable force but the fibers do not shorten, so the muscle is in isometric action and length changes are in the stretching and recoiling of the tendon. (B) in the stance phase of uphill running, the muscle fibers shorten (concentric action), doing mechanical work to lift the turkey's body. Reprinted with permission from Roberts et al. (1997). Copyright © 1997 American Association for the Advancement of Science.

recent improvements in ultrasound imaging (Finni, Komi, & Lepola, 2000; Finni et al., 2001: Fukunaga, Ichinose, Ito, Kawaka-mi, & Fukashiro, 1997; Fukunaga, Kawaka-mi, Kubo, & Keneshisa, 2002; Kubo, Kawakami, & Fukunaga, 1999) and im-plantable fiberoptic force sensors (Komi, Belli, Huttunen, Bonnefoy, Geyssant, & La-cour, 1996). Recent studies of the human tibialis anterior have also documented nonlinear and nonisometric behavior of the muscle (lengthening of tendon and aponeurosis while fibers shorten) in isometric actions (Maganaris & Paul, 2000; Ito et al., 1998). This is an area of intense research in biomechanics because the lengthening and shortening of muscle fibers, aponeurosis, and tendon from several different muscles can all be documented in vivo during human movements (Finni, 2006; Fukashiro et al., 2006; Kawakami & Fuku-naga, 2006). It is clear now that muscle actions in animal movements are more complicated than can be predicted by the concentric, single-joint analysis of functional anatomy.

Given these many examples of the complexity of muscle actions at the macro and microscopic levels, the hypothesized muscle actions from functional anatomy in many human movements should be interpreted with caution. Seemingly simple questions of what muscles contribute most to walking, jumping, or any movement represent surprisingly complex biomechanical issues. For example, should the word "eccentric" be used as an adjective to describe phases in weight training exercise (eccentric phase), when all the active muscles are clearly not in eccentric actions in the movement? If the active muscle group, body position, and resistance are well defined, this terminology is likely accurate. When the lifter "cheats" with other muscles in the exercise, modifies exercise technique, or performs a similar sporting movement, the eccentric adjective may not be accurate. The

Interdisciplinary Issue: Anthropometry

Anthropometry is the science concerned with measurement of the physical properties (length, mass, density, moment of inertia, etc.) of a human body. Kinanthropometry is an area within kinesiology that studies how differences in anthropometry affect sport performance (see chapters 5 and 7 in Bloomfield,Ack-land, & Elliott, l994).The main organization in this area is the International Society for the Advancement of Kinanthropometry (ISAK). Since humans move in a wide variety of activities, many professionals use anthropometric data. Engineers use these measurements to design tools and workstations that fit most people and decrease risk of overuse injuries. Prosthetic and orthotic manufacturers often make anthropometric measurements on individuals to customize the device to the individual. Motor development scholars track the changes in anthropometric characteristics with growth and development. While people seem to have a wide variety of shapes and sizes, the relative (scaled to size) size of many anthropometric variables is more consistent. Biomechanists use many of these average physical measurements to make quite accurate kinetic or center-of-gravity calculations.

actions of other muscles, external forces like gravity, and the complexity of the muscu-loskeletal system can make the isolated analyses of functional anatomy in the anatomical position inaccurate for dynamic movement. Some biomechanical issues that illustrate this point are summarized here and developed throughout the book.

The Need for Biomechanics to Understand Muscle Actions

The traditional "kinesiological" analysis of movements of the early twentieth century essentially hypothesized how muscles contributed to motion in each phase of the skill by noting anatomical joint rotations and as suming muscles that create that joint rotation are active. Muscle actions in human movements, however, are not as simple as functional anatomy assumes (Bartlett, 1999). Several kinds of biomechanical research bear this out, and show that the combination of several kinds of quantitative biomechanical analysis are necessary to understand the functions of muscles in movements.

First, electromyographic (EMG) studies have documented general trends in activation of muscles in a particular muscle group, but with considerable potential variation in that trend or in activation between subjects (Basmajian & De Luca, 1985). The primary source of this variation may be the considerable redundancy (muscles with the same joint actions) of the muscular system. Nearly identical movements can be created by widely varying muscular forces or joint torques (Hatze, 2000; Patla, 1987; Winter, 1984).

EMG studies show that the activation patterns of individual muscles are not representative of all muscles in the same functional group (Arndt, Komi, Bruggemann, & Lukkariniemi, 1998; Bouisset, 1973), and there are differences in how muscles within a muscle group respond to training (Rabita et al., 2000). Even individual muscles are quite sophisticated, with different motor unit activation depending on the task or muscle action (Babault, Pousson, Ballay, & Van Hoecke, 2001; Enoka, 1996; Gandevia, 1999; Gielen, 1999). Muscles within a muscle group can alternate periods of activity in low-level activities to minimize fatigue (Kouzaki, Shinohara, Masani, Kanehisa, & Fukunaga, 2002). Muscle activation can vary because of differences in joint angle, muscle action (Kasprisin & Grabiner, 2000; Nakazawa, Kawakami, Fukunaga, Yano, & Miyashita, 1993) or the degree of stabilization required in the task (Kornecki, Kebel, & Siemienski, 2001). For example, a manual muscle test for the biceps used by physical therapists uses isometric elbow flexion with the forearm in supination to minimize bra-chioradialis activity and maximize biceps activity (Basmajian and De Luca, 1985). Recent EMG studies, however, have also demonstrated that some of these procedures used to isolate specific muscles in physical therapy do not always isolate the muscle hypothesized as being tested (see Kelly, Kadrmas, & Speer, 1996; Rowlands, Wertsch, Primack, Spreitzer, Roberts, Spre-itzer, & Roberts, 1995).

The activation of many muscles to create a specific force or action is called a muscle synergy. A muscle synergy is a combination of muscle actions that serves to optimally achieve a motor task. There is considerable recognition of the importance of muscle synergies and force sharing of muscles in biomechanical research (Arndt et al., 1998; Herzog, 1996b, 2000) and in current rehabilitation and conditioning trends (see Interdisciplinary Issue on training muscles versus movements). How individual muscles share the load is complicated, depending on fiber type, contractile properties, cross-sectional area, moment arm, and antagonism (Ait-Haddou, Binding, & Herzog, 2000). Motor control uses the term synergy to refer to underlying rules of the neuro-muscular system for using muscles to coordinate or create movements (Aruin, 2001; Bernstein, 1967).

Activity: Muscle Synergy

Make a tight fist in your dominant hand as forcefully and quickly as you can. Observe the actions of the superficial muscles of your arm. Why do you think biceps and triceps are isometrically activated in a power grip muscle synergy?

Recent EMG research has in addition begun to focus on different activation of intramuscular sections within a muscle beyond the traditional gross segmentation in classical anatomy (Brown, et al., 2007; Mir-ka, Kelaher, Baker, Harrison, & Davis, 1997; Paton & Brown, 1994; Wickham & Brown, 1998; Wickham et al, 2004). Wickham and Brown (1998) have confirmed different activation of seven distinct segments of the deltoid muscle, rather than the typical three sections (anterior, intermediate, posterior) of muscle fibers usually identified in anatomy. This line of research supports the EMG studies mentioned earlier which indicate that activation of muscles is much more complex than had been previously thought. Further microanatomy and EMG research on muscles, particularly those with large attachments, will most likely increase our understanding of how parts of the muscles are activated differently to create movement.

Second, the descriptions of muscu-loskeletal anatomy often do not account for variations in muscle attachment sites across individuals. The numbers and sites of attachments for the rhomboid and scalene muscles vary (Kamibayashi & Richmond, 1998). A person born with missing middle and lower fibers of trapezius on one side of their body must primarily rely on rhomboids for scapular retraction. Variations in skeletal structure are also hypothesized to contribute to risk of injury. For example, the shape of the acromion process of the scapula is believed to be related to a risk of impingement syndrome (Whiting & Zernicke, 1998). The role of anatomical variation in gross anatomy or in muscle architecture (Richmond, 1998) and their biomechanical effects of muscles actions and injury risk remain an important area of study.

Third, the linked nature of the human body makes the isolated functional anatomical analysis incomplete. This linking of body segments means that muscle actions have dramatic effects on adjacent and other joints quite distant from the ones the mus cles cross (Zajac, 1991; Zajac & Gordon, 1989). This redistribution of mechanical energy at distant joints may be more important to some movements than the traditional joint action hypothesized by functional anatomy (Zajac, Neptune, & Kautz, 2002). Zajac and Gordon (1989), for example, showed how soleus activity in a sit-to-stand movement tends to extend the knee joint more than it plantar flexes the ankle joint. Physical therapists know that the pectoralis major muscle can be used to extend the elbow in closed kinetic chain (see chapter 6) situations for patients with triceps paralysis (Smith, Weiss, & Lehmkuhl, 1996). Functional anatomy does not analyze how forces and torques created by a muscle are distributed throughout all the joints of the skeletal system or how these loads interact between segments. Zajac and Gordon (1989) have provided a convincing argument that the classification of muscles as agonists or antagonists should be based on biomechani-cal models and joint accelerations, rather than torques the muscles create.

Dramatic examples of this wide variety of effects of muscles can be seen in multiar-ticular muscles (van Ingen Schenau et al., 1989; Zajac, 1991). There is considerable interest in the topic of biarticular or multiar-ticular muscles, and it is known that they have different roles compared to similar monoarticular muscles (Hof, 2001; Prilut-sky & Zatsiorsky, 1994; van Ingen Schenau et al., 1995). Another example of the complexity of movement is how small differences in foot placement (angle of ankle plantar/dorsiflexion) dramatically affects which joint torques are used to cushion the shock in landing (DeVita & Skelly, 1992; Ko-vacs, Tihanyi, DeVita, Racz, Barrier, & Hor-tobagyi, 1999). A flat-footed landing minimizes a plantar flexor's ability to absorb shock, increasing the torque output of the hip and knee extensors. Small differences in foot angle in walking also affect the flexor or extensor dominance of the knee torque

Interdisciplinary Issue: Training Muscles vs. Movements

In the strength and conditioning field an area of philosophical debate is related to a greater emphasis on training functional movements rather than training specific muscle groups (Gambetta, 1995, l997).This debate is quite similar to the debate about the relative benefits of training with free weights or with machines.Training with free weights can more easily simulate the balance and stabilizing muscle actions in normal and sport movements.The advantage of machines is that they provide more muscle group-specific training with resistance that is not as dependent on position relative to gravity as free weights are. How might rehabilitation and conditioning professionals use biomechanics and EMG research to help match training to the demands of normal movement?

(Simonsen, Dyhre-Poulsen, Voigt, Aagaard, & Fallentin, 1997), and the frontal plane knee torques that may be related to knee injury (Gregersen, Hull, & Hakansson, 2006; Teichtahl et al., 2006). The kinematics and kinetics chapters (5 and 6 & 7, respectively) will expand on the effects of the joints and segment actions in human movement.

The fourth line of biomechanical research documenting the complexity of muscular actions creating movement are modeling and simulation. Modeling involves the development of a mathematical representation of the biomechanical system, while simulation uses biomechanical models to examine how changes in various techniques and parameters affect the movement or body. Biomechanical models of the human body can be used to simulate the effects of changes in any of the parameters of the model. The more simple the model, the easier the interpretation and application of results. For example, models of the motion of body segments in airborne skills in gymnastics and diving are quite effective in determining their effect on flight and rotation (Yeadon, 1998). As biomechanics models get more complicated and include more elements of the musculoskeletal system, the more difficult it is to validate the model. Interpretation is even complicated because of the many interrelated factors and variations in model parameters across subjects (Chow, Darling, & Ehrhardt, 1999; Hub-bard, 1993).

Despite the many controversial issues in biomechanical modeling, these kinds of studies show that the actions of muscles in movements are quite complex and are related to segment and muscle geometry (Bobbert & van Ingen Schenau, 1988; Doo-renbosch, Veeger, van Zandwij, & van Ingen Schenau, 1997), muscle elasticity (Anderson & Pandy, 1993), coordination (Bobbert & van Soest, 1994; Hatze, 1974; Nagano & Gerritsen, 2001), and accuracy or injury (Fujii & Hubbard, 2002; Thelen et al., 2006). One simulation found that non-extensor muscles of the legs could be used to improve jumping performance (Nagano et al., 2005), and it is also possible that coordination in a movement even varies slightly across people because of differences in muscle mechanics (Chowdhary & Challis, 2001). Here we have the paradox of learning again. What muscles do to create movement is quite complex, so kinesiology scholars and professionals must decide what level of biomechanical system to study to best understand movement. The strength and conditioning field commonly groups muscles into functional groups like the knee extensors (quadriceps) or knee flexors (hamstrings). Whatever movements or level of analysis a kinesiology professional chooses, biomechanics needs to be added to anatomical knowledge to make valid inferences about human movement. The next section briefly shows how the sports medicine professions have integrat ed more biomechanical information into their professional practice.

Sports Medicine and Rehabilitation Applications

Musculoskeletal anatomy and its motion terminology are important in kinesiology and sports medicine, but it cannot be the sole basis for determining the function of muscles in human movement. Medical doctors specializing in sports medicine found that their extensive training in anatomy was not enough to understand injuries and musculoskeletal function in the athletes they treated (McGregor & Devereux, 1982).

This recognition by MDs that their strong knowledge of anatomy was incomplete to understand function and that they needed the sciences of kinesiology was a factor in the fusion of medical and kinesiology professionals that formed the American College of Sports Medicine (ACSM).

Today, many kinesiology students prepare for careers in medicine- and sports medicine-related careers (athletic training, physical therapy, orthotics, prosthetics, strength & conditioning). These professions are concerned with analyzing the actions of muscles in movement. Where can sports medicine professionals (athletic trainers, physical therapists, physical medicine, strength and conditioning) get the most accurate information on the biomechanical function of specific areas of the human body? Fortunately, there are several sources that strive to weigh the anatomical/clinical observations with biomechanical research. These sources focus on both normal and pathomechanical function of the human body. The following sources are recommended since they represent this balanced treatment of the subject, not relying solely on experience or research (Basmajian & Wolf, 1990; Kendall, McCreary, & Provance, 1993; Smith, Weiss, & Lehmkuhl, 1996).

It is important to remember that biome-chanics is an indispensable tool for all kine-siology professionals trying to understand how muscles create movement, how to improve movement, and how problems in the musculoskeletal system can be compensated for. The last two sections of this chapter illustrate how biomechanical principles can be used to understand and improve human movement.

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