Training for Climbing, 2nd: The Definitive Guide to Improving Your Performance (How To Climb Series)

exist in only very small numbers.
    • Slow twitch (ST): These Type I fibers make up approximately 50 percent of the total skeletal muscle, though genetic variation can range from about 20 percent to 80 percent (Bloomfield, et al., 1992). They are recruited primarily during low-intensity, aerobic endurance activities.
    • Fast twitch (FT): These fibers are recruited during high-intensity movements or activities. Type IIa (FTa) fibers are energized through both aerobic and anaerobic processes and are, therefore, fatigue-resistant. These fibers excel at longer-duration high-intensity activity, and they would be most active when climbing long, hard routes. Type IIb (FTb) fibers have the fastest contraction time and generate energy almost entirely through the anaerobic system. These fibers are recruited during brief, maximum movements such as a difficult boulder problem or a powerful crux move.
     
    Your relative percentage of FT and ST muscle fibers is genetically determined and varies little in response to training. Naturally strong climbers are likely gifted with a higher-than-normal percentage of FT fibers (among other things), whereas gifted mountaineers, who can keep on going like the Energizer Bunny, likely have a higher percentage of ST fibers. Fortunately, ST fibers can be taught to act like FT fibers through use of certain training protocols (Chu 1996), which I will introduce later.
RECRUITMENT
     
    Muscle fibers of the same type are organized into motor units. ST motor units innervate between 10 and 180 fibers, while FT motor units innervate up to 800 fibers (Bloomfield, et al., 1994). When a muscular contraction is triggered, motor units are recruited on an as-needed basis beginning with the smaller ST motor units. As muscular tension increases, a greater number of ST motor units will join in, and if the tension grows further, the larger FT motor units will begin to fire. Maximum muscular force is eventually achieved if all motor units (ST and FT) are recruited into action (see figure 5.1).
    Knowing this physiological process should help you understand why it’s important to train with high intensity and with maximum weight (resistance) if you want to recruit, and make stronger, the FT fibers. Compare this with “just climbing a lot of routes” for training: That way you would recruit primarily ST fibers on the many moderate moves and only occasionally recruit the FTa fibers when you encountered hard moves. The high-threshold FTb fibers would seldom be called into action—only when a move or sequence required explosive power or application of maximum strength.

     
    Figure 5.1 Muscular Force Production
     

Muscular Adaptations to Strength Training
     
    Two primary adaptations occur in response to strength training—adaptation of the neural system and adaptation of the muscular system.
ADAPTATION OF THE NEURAL SYSTEM
     
    The nervous system adapts to strength training in three ways: motor learning, motor unit synchronization, and disinhibition.
    • Motor learning: The first neural adaptation, motor learning, should sound familiar after reading chapter 4. During the initial work at a new exercise (say, uneven-grip pull-ups or even campus training), your primary limitation will be a lack of coordination and feel for the exercise. The first few weeks should yield rapid improvement as a result of motor learning and improved coordination among the prime mover, stabilizer, and antagonist muscles. Beyond this point, further strength gains will depend on other adaptations taking place.
    • Motor unit synchronization: Motor unit synchronization is the second neural adaptation that increases strength. Suppose you have acquired the coordination and motor skills needed for performing a given exercise—or perhaps you’re adding a new exercise that requires no learning (such as hanging on a fingerboard). Initial training triggers motor units to fire in a rather random, asynchronous manner. Continued training, however, enhances motor unit synchronization; eventually most of the motor units will fire in unison, resulting in more strength and power.
    • Disinhibition: The final neural adaptation, disinhibition, is most important (and exciting) for intermediate to advanced climbers in search of gains in maximum strength and power. The neuromuscular system has a built-in feedback mechanism that acts as a safeguard during times of increasing force production. The Golgi tendon organ, located in the musculotendinous