Becoming Batman Page 6

  Growth hormone is a protein hormone—here comes that clever naming procedure again—that is involved in regulating cell production and growth. Despite this being a book about becoming Batman and not Superman, growth hormone is part of a “super family” of related hormones. Growth hormone comes from the anterior, or front part, of the pituitary gland, and the levels are much higher during the busiest time for growth and development—adolescence. Too little growth hormone during adolescence can lead to extremely short stature. In adults, low growth hormone levels can lead to decreased energy levels and bone mass and to increased risk of cardiovascular disease. By contrast, too much growth hormone can lead to gigantism (acromegaly). During and after exercise, particularly the kind that is done during strength training (and which we will discuss more fully in Chapter 4), growth hormone levels rise. The increases are largest in the most strenuous exercise, the kind that Batman would engage in, and show a strong relation to the building up of muscle.

  Testosterone is likely one of the hormones that you are most familiar with. It is a steroid hormone, like cortisol, and is made from cholesterol. Testosterone is associated with the testes, but it is also found in the ovaries, the adrenal cortex, and in the placenta. This hormone is closely related to stresses on the body as a result of exercise, and levels of circulating testosterone are elevated during and after exercise. As with growth hormone, the effects are largest with more strenuous exercise. It may be surprising that perhaps the most important role for testosterone may be how it interacts with and augments the effects of growth hormone and insulin-like growth factors rather than how it acts by itself. It may also be surprising that something called luteinising hormone, secreted in the pituitary, is the actual signaling molecule for testosterone release from the testes. The body synthesizes testosterone from cholesterol. The process of synthesizing and releasing this hormone has many steps. During the process intermediate compounds are created. These compounds are involved in the major problems for steroid abuse, because these intermediate compounds, such as androstenedione (made famous—infamous?—in major league baseball), can be taken in and used to boost this pathway.

  Another important grouping of hormones is the insulin-like growth factors (IGFs). The chemical structures of IGFs are similar to insulin (hence the clever name) and generally work as anabolic triggers. So, they lead to increased muscle mass. All across our life spans, IGFs are necessary to help stimulate and maintain our muscle cells.

  The Stress of Life

  We have just outlined how important the hormonal systems are for adjusting the body to stresses and stressors. In the physiological response to stimuli that results in adaptations to exercise, there needs to be some way to convert the energy from all the bodies’ stresses and strains into signals to which the biological organism can respond. Back in 1964 Geoffrey Goldspink showed that the cells in skeletal muscle tissue developed by laying down new cells in series with other cells. This adaptation minimized the stress of the muscle stretch.

  Many types of cells respond to mechanical stresses. There are specialized receptors in skin and muscle, for example, that respond to mechanical stress including a wide variety of cells that provide support (such as bone cells or osteocytes) or covering (such as skin or epidermal cells), as well as produce movement (muscle cells). The term “mechanocyte”—from kytos, the Greek word for cell—is used to refer to these cells of bone, muscle, and skin. In many ways perhaps it is not surprising that these cells respond to mechanical stress and strain, as they are continuously subjected to such forces. The stress and strain experienced by the mechanocytes result in adaptation of the tissue. The main functional outcome of the adaptations is to reduce the negative impact of the stresses on the tissue, be it bone, muscle, or skin. This forms a common physiological system of negative feedback (see Figure 3.1), where the stimulus leads to a response that minimizes the initial effect of the stimulus. This fits within a general principle of physiology related to homeostasis described by Walter Cannon in 1932. Remember him from the beginning of the chapter? Recall too that homeostasis describes the way in which a biological organism maintains itself such that the “internal environment” remains within limits for proper function. This includes the concept of exercise and responses to exercise or training stresses with respect to the regulation of the endocrine system.

  Too much training can actually lead to a cascade of events that leads to muscle wasting, fatigue, and malfunction. Think back to the third stage of Seyle’s GAS, the stage of exhaustion and cell death. This is illustrated in Figure 3.3 where the normal regulation of body function is shown. A body can handle challenges to homeostasis if it is healthy. In a diseased state or in extreme stress, the body is too weak and failure of function occurs.

  Batman hasn’t found himself in that position too often. However, that was precisely where he was in the “The Broken Bat” (Batman #497, 1993). This was the part of the extensive Knightfall story arc in which Bane, Batman’s steroid-laced nemesis, sets Batman up by releasing all the criminals from Gotham’s Arkham Asylum. Batman has to sequentially battle them all, round them up, and send them back to prison. He does this night after night until he finally is exhausted—and would certainly be near stage three of the GAS. That is where he meets up with Bane and comes up against a very atypical Batman fate—he is defeated (we will come back to this story arc in Chapter 13 when we discuss injuries). For now, the main point is that too much training can yield too much stress such that proper adaptation does not in fact occur. This is similar to extreme states of overtraining or “overreaching” in athletes and would be a real problem for Batman.

  Figure 3.3. Different results of challenges to homeostasis.

  In future chapters, when we talk about how Batman’s muscles, bones, skin, and metabolic machinery respond and adapt to exercise stresses, we will do so from the perspectives of stress responses and challenges to homeostasis that do not place him in a similar state of exhaustion.

  So now let’s look at the first of those body parts—the muscles!

  PART II

  BASIC BATBODY TRAINING

  Laying the foundation for

  Batman’s physical prowess to

  be later exploited by his skill

  CHAPTER 4

  Gaining Strength and Power

  DOES THE BAT THAT FLIES

  THE HIGHEST OR THE FASTEST

  GET THE WORM?

  What is the point of all those push ups if you can’t even lift a bloody log?

  —Alfred to Bruce, while pinned under a burning beam in Wayne Manor; from the film Batman Begins

  Think of the strongest person you know. Or know about. Or can imagine. Think about how much this person could lift physically—a breadbox? A car? Now, how fast do you think this person could move? Would you measure their fastest movement with an egg timer or a precision Swiss stopwatch? Muscles do lots of different things, and all of them involve producing forces. But producing large forces—being strong—and producing force while moving quickly—being powerful—are not exactly the same things. Would Batman need to be really strong or really powerful? I will show that Batman needs a base of batstrength but really he needs to be powerful. We will explore the adaptations that could occur in muscle as a result of specialized training to obtain strength and power.

  To begin let’s describe exactly what we are trying to understand here. How is it that we develop strength and get stronger in the first place? What physiological systems are “stressed”—used in the sense established in the previous chapter—and what are the adaptations? A useful way to proceed is to think of the stresses associated with exercise as being a challenge to homeostasis that requires some compensation to restore balance. As part of this exploration of how muscle adapts to exercise and training stresses, we need also to back up one step and consider how muscle is activated. That is, what are the effects of Batman’s neural commands to activate his muscles? What is the process by which you activate your muscles now as you sit or stand a
nd read this book? I will follow up later in Chapter 7 on the more complex issue of skill training and adaptation at various levels of the nervous system.

  Making Muscles Contract

  Let’s look at how our muscles contract and generate the forces that then move our limbs around when we want to produce movement. It probably comes as no surprise that the trigger or command for voluntary muscle activity comes from the brain. Indeed, over three hundred years ago the Irish natural philoso pher Robert Boyle (1627–1691), famous in chemistry for formulation of Boyle’s law (which outlined the relationship between pressure, temperature, and volume of gases), described the case of a knight with a depressed skull fracture who was returning from battle. The knight had little movement in his arm and leg on one side of his body, and Boyle called this condition a “dead palsy.” This suggested that some areas of the brain had a role to play in motor output—in physiological lingo, movement is typically described as “motor.”

  Boyle’s work was followed by other scientists in the nineteenth and twentieth centuries. English neurologist John Hughlings Jackson (1835–1911) studied epilepsy and, based upon his clinical observations, suggested that some area of the cerebral cortex must be responsible for governing simple motor commands. These speculations were later confirmed in 1870 by G. T. Fritsch and Eduard Hitzig, who used electrical stimulation to map brains of cats and dogs.

  A very important discovery was made by Wilder Penfield and Edwin Boldrey through their extensive survey of the human motor cortex: electrically stimulating cells in particular parts of the brain activated muscles in the body. From their work they generated a map of the surface of the motor areas of the brain that corresponded to the muscles of the body. The shape that this map took gave rise to a “little man map” (called a “homunculus”; see Figure 4.1). Notice how large is the area of the map for the muscles controlling the fingers, thumb, and hand. This can be contrasted with the much smaller map area for the foot and speaks to the fine motor skill we humans have for the careful control of our fingers.

  Figure 4.1. “Map” of the brain’s neurons used for muscle activation. The “homunculus”(or little man) shows the relative numbers of neurons controlling particular body parts. For reference, the smaller cortical area for the toes is contrasted with that for the hand. Modified from Penfield Rasmussen (1950).

  The Brain Says Go!

  To begin let’s think about some basic principles of how the nervous system and activation of muscle actually work. To signal for a contraction to occur, messages from the nervous system (as activity in nerve cells) are sent out to the muscles of our limbs. It’s helpful to think about nerve cells as being a lot like trees. This might seem kind of weird at first, but the analogy actually works well. A typical nerve cell, or neuron, is composed of a cell body, an axon, and a receiving area made up of dendrites. The axon is really an elongated trunk relaying the output commands from the neuron and typically extends from one side, while the dendrites form a huge net of receiving posts on the other side. If you think of the tree analogy, imagine the dendrites (which are often described as a “dendritic tree”) as being like the roots of the tree, the base of the tree is the cell body, the trunk is the axon, and the branches and leaves are the terminal connections where the neuron makes connections with other trees (neurons). Put your single tree in a dense rain forest where there is close contact between lots of leaves from different trees and you get the general idea.

  So, to begin, you decide you want to do something. It could be a motion as simple as picking this book up from the bookstore shelf. Upon that decision, a relayed command arrives at the main movement output center of your brain—your primary motor cortex. Inside the primary motor cortex (from here on we’ll refer to it simply as motor cortex) live the nerve cells, the neurons, which relay the command to activate muscle down into the spinal cord. This is outlined in the diagram shown in Figure 4.2.

  These command motor output cells are often referred to as upper motoneurons—simply meaning the motor output neurons at the physically highest (uppermost) part of the nervous system. That relayed command arrives at the spinal cord level for the appropriate muscles and makes connection with some more motoneurons. This time we are talking about lower motoneurons—the cells that directly relay the electrical command for movement into activation of muscle. This is so because the lower motoneurons send their axons (trunks) out to connect with the muscle cells that will actually produce movement when activated.

  The pairing of a motoneuron and the muscle cells (or fibers) it innervates is the basic functional unit of movement control. This was called the “motor unit” by Sir Charles Sherrington. Sherrington (1857–1952) was a pioneering British neurophysiologist who shared the 1932 Nobel Prize for Physiology or Medicine with Edgar Douglas Adrian for “discoveries regarding the functions of neurons.” Sherrington is also my own favorite “science superhero.” We will talk more about Sherrington’s discoveries in later chapters.

  Figure 4.2. Links for commands to move, showing path from a neuron in the motor cortex. Courtesy Sale (1992).

  Figure 4.3 gives an example of a motor unit showing only a few muscle fibers. When the electrical signal to contract from the motoneurons arrives at the synapse between the axon from the motoneuron and the muscle fibers—conveniently called the neuromuscular junction—it changes to a chemical signal. At this “synapse” (also a term coined by Sherrington) a chemical neurotransmitter called acetylcholine, or ACH, is released that leads to depolarization of the muscle fibers. The signal is now again electrical and will trigger the release of calcium ions (shown in chemical terms as Ca2+) that are directly involved in regulating the process of muscle contraction. Who knew there was so much biochemistry involved in moving your little finger!

  Figure 4.3. The motor unit concept, showing a motor neuron in the spinal cord, the axon in the peripheral nerve, and the muscle fibers innervated. Courtesy Noth (1992).

  At this point muscle contraction will occur in all the muscle fibers of the active motor unit. It is all or none within the unit. Now let’s pretend we have a microscope and are zooming in on just one muscle fiber within a motor unit. Batman’s (and your) muscle fibers are composed of many different proteins, some that have an indirect role and some (called the contractile proteins) that have a direct role in producing muscle force. The contractile proteins come in two types only: actin and myosin molecules.

  How actin and myosin produce force during muscle contraction can be thought of like pulling on a rope. The rope is the actin and your hands pulling on the rope are the myosin molecules. In the case of your actual muscles, the more ropes and the larger the ropes that you have within a muscle fiber, the greater the force that can be produced. This is often described for the whole muscle—which has lots of muscle fibers in it—as the cross-sectional area. So, if the cross-sectional area is increased with training (and it is), strength will go up.

  The neat thing about these proteins is that they have the ability to bond together and to separate depending on the availability of an energy molecule called ATP (otherwise known as adenosine 5′-triphosphate, which we will revisit in Chapter 6). In this case you can think of the bonding between myosin and actin as being like the tightening and relaxation of your grip when you pull the rope along. An interesting thing is that the energy taken from ATP is needed for muscle relaxation, not contraction. This is why after an animal dies the condition of rigor mortis ensues. This rigidity is due to the lack of energy (in the form of ATP) to release the bonds between actin and myosin.

  When Batman wants to change how much force he needs to produce—say, while fighting the Joker or Penguin—he has two main choices (although he cannot really choose them voluntarily). He can either bring into action more active muscle tissue by using more motor units by a process known as recruitment, or he can make the motor units that are already active become active at a higher rate. Both of these processes will result in increased muscle force.

  To see why that happens,
imagine that our ropes are now in a tug of war. Let’s say you were in a competition that allowed 20 members on your team. To begin, though, you are so confident that your team can beat the first team you’re facing that you let eight of your members sit out the first round. That leaves 12 to pull against the other team. As you get started, though, you notice you aren’t doing well, so you add more team members. You recruit them to the cause, as it were. Well, each muscle that you have has a “pool” of motor units that can be recruited to become active and produce force. If you add more, you get more force.

  As for increasing the rate of the motor units—called rate coding—the idea of tug of war also works here. Having learned your lesson from the first match—which you still won—you go to your next match with all 20 team members ready to pull on the rope. Now to get more force you have each team member pull more rapidly and frequently on the rope. This will mean more force is produced, and the rope will move toward your victory.

  Where our analogy falls flat is that motor units aren’t actually either just recruited or just altered in terms of their rate. Both of these actions occur in your nervous system. What is for sure, though, is that with higher and faster contractions you recruit more motor units and make them fire at higher rates.

  One of the training adaptations that happens in the nervous system is that you are able to alter the way in which you can recruit and fire motor units. After training, Batman’s motor units will be easier to recruit—they won’t scuff and drag their feet when asked to join in—and will briefly fire at very high rates. This leads to the more powerful and stronger contractions that Batman produces. By the way, when someone begins a strength-training program, the initial gains in strength that occur over the first six weeks of training are mostly due to the adaptations the nervous system is making in activating motor units. It is only later, after the six weeks, that your muscle tissue—your muscle cells—actually change and become stronger themselves. What’s really happening early on in training is a kind of change in coordination to give more strength and make use of your muscles more efficiently.