1EXS 387 - BiomechanicsDr. MoranThursday May 3, 2007Spring 2007Muscle MechanicsEffects of TrainingEXS 387 2Muscle FunctionCharacteristics• Strength• Power: • Endurance: ability to exert muscle tension over time2EXS 387 3Mechanisms of Gains in Muscle Strength• Neural Adaptations– Synchronization and recruitment of additional motor units–– Rate coding—the firing frequency of motor units• Muscle Hypertrophy– Fiber hypertrophy–EXS 387 4Muscle Fiber Hypertrophy3EXS 387 5Neural Effects of Muscle Performance• Bilateral deficit: maximum force produced by simultaneous contraction of both limbs less than total force produced with each limb acting singly– EMG activity when activating both limbs concurrently as compared to singlyEXS 387 6• Why?– May be limit of neural drive from higher centers in CNS (central drive)–• Pre-contraction of antagonist can ↓ recruitment of antagonistsNeural Effects of Muscle Performance(continued)4EXS 387 7Effects of Resistance Training• Early ↑ in strength not accompanied by muscle hypertrophy• Caused by neural adaptations ( ↑ EMG activity)• See ↑ in strength in untrained contralateral limb (↑EMG activity) [cross training effect]•EXS 387 8Effects of Resistance Training• Maximal force development requires complete MUA– For many max effort does not induce complete MUA– Training ↑ ability to reach full MUA with max voluntary effort–– Training ↑ duration at which high and low threshold MUs can sustain optimal firing rates– Training ↓ decrement between tension seen with MVC and tension induced with supramaximal stimulation of nerve– Training ↑ motor neuron excitability during voluntary effort•– Training ↑ synchronization in activation/firing rate of MUs•5EXS 387 9Resistance Training Fact• Once your goals for strength development have been achieved, you can reduce training frequency, intensity, or duration and still prevent losses in strength gained for at least 12 weeks. However, you must continue training with a resistance maintenance program that still provides sufficient stress to the muscles.EXS 387 10Effects of Endurance Training• Training causes ↑ in MU activation occurs in early stages, ↑ skill acquistion/coordination•• Training causes rotation of activity among synergists and among MU of prime mover•• Training ↑ consistency of firing rates of motor neurons•• Delays fatigue6EXS 387 11Are muscle fiber type conversions possible?• Early studies showed no change in fiber type but changes in characteristics of muscle fibers•• Possible change from FTb to FTa, and from FTa to ST with endurance training, and FTb to FTa with resistance training• A combination of high intensity resistance training and short-interval speed work can lead to a conversion of ST to FTa
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