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1、第四节、影响肌肉力量的因素,（一）概述 人体在肌肉活动中所表现出来的力量、速度、耐力、灵敏及柔韧等机能能力统称为身体素质。 身体素质是人体各器官系统功能协同作用在骨骼肌工作中的综合表现。,力量素质是其他身体素质的基础。 肌肉力量表现为：绝对肌力、相对肌力、肌肉爆发力、肌肉耐力等。,绝对肌力和肌肉的横断面大小有关,横断面越大，绝对肌力越大 肌肉横断面的大小取决于肌纤维数量和每条肌纤维的粗细 绝对肌力只能反应整体力量，不能反映肌肉每条肌纤维的性能,绝对肌力,相对肌力 肌肉单位横断面积（ /cm2 ）所具有的肌力。但日常应用一般以绝对肌力/体重代替 与肌纤维类型及神经对肌肉的调节能力有关 相对力量可
2、更好地评价运动员的力量素质,相对与绝对爆发力的训练,力量型项目如：举重、柔道等应增加肌肉的体积增长肌肉块，追求绝对力量的增加 短跑、跳跃、体操等以速度和灵敏为特点的项目，应该保持轻体重的同时增加肌肉的相对力量主要靠神经募集更多的肌纤维参与动作。,运动单位的动员,（二）决定肌肉力量的因素,1. 肌肉的横断面积 力量训练引起肌肉体积增加及肌肉力量的增长，主要是由于肌纤维横截面积增加造成的。 一般认为，训练使横断面积的增加是由于训练促使肌原纤维合成增加所致，而对于肌纤维数目无明显影响。,2. 肌纤维类型能量代谢为其关键因素 快肌纤维的收缩力 慢肌纤维，供能速率快，单位时间内可完成更多的机械功。,CK
3、,Fast and Slow Muscle Fibers. Fast muscle fibers are adapted for rapid, powerful contractions. Thick for strength but results in poor O2 diffusion Fatigue relatively quickly. Slow muscle fibers are adapted for sustained contraction. Thin to aid diffusion of O2 but weaker Relative to fast fibers, slo
4、w fibers have. Less SR Ca2+ remains in the cytosol longer. More mitochondria, a better blood supply, and myoglobin.,3. 肌纤维收缩时的初长度,肌纤维处于一定的长度时，横桥与细肌丝的肌动蛋白结合的数目最多，从而使肌纤维收缩力增加。,4. 运动单位的动员（Recruitment of motor units ）,运动单位（Motor Unit, MU） 一个运动神经元和受其支配的肌纤维所组成的基本的肌肉收缩的单位称为，运动单位。,运动单位的动员,生活经验： 熟睡时的肌力？ 早晨刚刚
5、苏醒时的肌力？ 晨练后精神倍加振奋时的肌力？ 激烈运动后倍感疲劳时的肌力？,运动单位动员定义： 参与兴奋的运动单位数目与兴奋频率的结合，称为运动单位动员（Motor Unit Involvement）或运动单位募集（Motor Unit Recruitment）,A whole muscle is a group of muscle fibers,A tendon attaches a muscle to a bone. A single action potential in a muscle fiber produces a twitch. Gradations of whole musc
6、le tension depend on the number of muscle fibers contracting （1）一块肌肉由多条肌纤维组成，并受多个神经元控制，单纯一个神经元的兴奋只表现出肌肉的震颤，参与收缩的神经元越多，力量越大，参与神经元数目多少取决于神经系统的兴奋性。,Whole muscle tension depends on the size of the muscle, the extend of motor unit recruitment, & the size of each motor unit.,The number of muscle fibers va
7、ries among different motor units. Muscles performing refined, delicate movements have few muscle fibers per motor unit. Muscles performing coarse, controlled movements have a large number of fibers per motor unit. （2）不同神经元，其所支配的肌纤维数目存在差异，因此兴奋时表现出的收缩力量不同。,（3）一个运动单位中肌纤维数目越少越灵活；数目越多产生的力量越大。,因此，运动单位的募集包
8、括两方面：运动单位的数目和运动单位的种类,A motor unit is one motor neuron and the muscle fibers it innervates.,Each motor neuron controls several to thousands of muscle fibers When a motor neuron fires, every muscle fiber controlled by it contracts The asynchronous recruitment of motor units delays or prevents muscle f
9、atigue. （4）当某一个神经元兴奋时，其所支配的所有肌纤维都收缩。但肌肉收缩时，并不是所有神经元支配的所有肌纤维都同时参与。,A A B B 持续最大力量收缩 持续50%最大力量收缩,100%,MUI,MUI,力量,力量,100%,50%,100%,100%,5. 神经系统的机能状态(nerve system activity ) 神经系统兴奋性越高，募集的运动单位越多；发放的刺激频率越高，强直收缩力量越大 即使运动神经中枢处于最大兴奋状态，也不能同时调动所有肌纤维参与收缩。有训练者可动员90%，无训练者可动员60%,Muscle tension also depends on the
10、frequency of stimulation,A muscle twitch (contraction) lasts longer than the action potential that initiates it. Thus a second action potential can occur before the muscle fiber relaxes Repetitive stimulation of a muscle increases its tension by twitch summation. If a muscle fiber is stimulated very
11、 rapidly, it cannot relax between stimuli. The twitches merge into a smooth, sustained, maximal contraction called tetanus.,Figure 8.17Page 271,Contractile activity,Action potentials,Single twitch,Twitch summation,Tetanus,Stimulation ceases or fatigue begins,Action potentials separated by time: Musc
12、le fibers relax: Weak contraction,Action potentials in close sequence: Muscle fibers relax less: Stronger contraction,Action potentials in close sequence: Muscles dont relax: Creates maximal sustained contraction,Single twitch,6. 年龄与性别因素 进入青春期后男性肌力开始明显高于女性；20-30岁肌力最大，以后增龄性下降。 7. 体重因素,These are two t
13、ypes of fatigue.,Muscle fatigue occurs when an exercising muscle can no longer respond to the same degree of stimulation with the same degree of contractile activity.（外周疲劳） Factors for this include an increase in inorganic phosphate, accumulation of lactic acid, and the depletion of energy reserves.
14、 （电解质紊乱、代谢产物堆积、能量储备受限） Increased oxygen consumption is needed to recover from exercise (paying off an oxygen debt).（缺氧） Central fatigue occurs when the CNS can no longer activate motor neurons supplying working muscles. （中枢疲劳） It is often psychological and is related to biochemical changes at the sy
15、napses in the brain.,Muscle atrophy if not used!,Skeletal muscles atrophy when not used. disuse atrophy denervation atrophy Skeletal muscles have a capacity for limited repair. Can replace limited numbers of damaged muscle fibers Large scale damage results in the replacement of damaged muscle fibers with non contractile connective tissue,
