NEUROMUSCULAR RESPONSE TO TRAINING YEAR 12 PE STUDIES UNIT 2A / 2B

In addition to the cardiorespiratory system, another system that responds to training and contributes to improvements in performance is the NEUROMUSCULAR SYSTEM. The neuromuscular system comprises the the nervous system which sends signals to initiate movement and the muscular system, which responds to these signals and produced movement.

1. NERVOUS SYSTEM RESPONSES TO TRAINING  neural adaptations to training occur through a number of processes; disinhibition, motor unit recruitment, motor unit synchronisation and the effect of learning  The MOTOR UNIT is the functional unit that produces muscle action & movement. It comprises the anterior motor neuron & the specific muscle fibre it stimulates  Muscle action results from the individual & combined stimuli of motor units. Although a muscled fibre generally receives signals from only 1 motor neuron, a single motor neuron may stimulate many muscle fibres due to its many branches.

Disinhibition The N.S consantly bombards the muscles with signals to either excite or inhibit muscle action Excitatory signals > inhibitory signals = motor unit ‘fires’.Excitatory signals > inhibitory signals = motor unit ‘fires’. (if the opposite happens the motor unit doesn’t fire) When increased force is produced the body has built-in feedback mechanisms that operate to protect muscles from injury. ie mechanisms in the muscles have the capacity to send out inhibitory signals to motor unitswhich prevent the body from recruiting extra motor units and/or firing existing ones at their maximal rate. This limits the force applied by the muscle. There is a reserve of potential force in the muscles which may not be used in maximal activities.When increased force is produced the body has built-in feedback mechanisms that operate to protect muscles from injury. ie mechanisms in the muscles have the capacity to send out inhibitory signals to motor unitswhich prevent the body from recruiting extra motor units and/or firing existing ones at their maximal rate. This limits the force applied by the muscle. There is a reserve of potential force in the muscles which may not be used in maximal activities.

 By continually exposing the body to high level of tension eg strength training, the sensitivity of these inhibiting mechanisms may reduced through a process called DISINHIBITION.  A greater number of motor units can be recruited and each motor unit is able to fire more rapidly. Motor Unit Synchronisation  a single muscle gp contains 100 to 1000 motor units. When this muscle is activated, these motor units are fired in a random manner (they are independent of each other)  A characteristic of strength-trained athletes is synchronisation of motor unit recruitment ie motor units in the same muscle coordinate their action to fire at the same time = stronger contraction.

Effect of Learning  Training results in a learning effect which produces a greater efficiency in neural recruitment patterns.  When first performing a move’t the coordination b/w various muscles may not be optimal. As the NM system becomes more proficient, through repeated performance, the coordination of the muscles improves = enhanced strength.  Adaptations of the NS are most dominant in the early stages of training, and represent the major cause of strength increase over the first 6 – 8 wks.

2. MUSCULAR SYSTEM RESPONSES TO TRAINING The major contributing factor to increases in muscle strength is an increase in the size of muscle. This is the result of two mechanisms:  Muscle Hypertrophy  Muscle Hyperplasia Muscle hypertrophy Refers to an increase in the size of individual muscle fibres (particularly fast-twitch fibres). This is the major cause of increases in muscle strength due to the following:

 An increase in the number & size of myofibrils per muscle fibre  An increase in the amount of protein filaments  An increase in the size & length of tendons, ligaments & connective tissue Muscle Hyperplasia  Refers to the splitting of individual muscle fibres to increase the number of fibres in the muscle  In order for this splitting to occur, the athlete must undertake many months of heavy resistance training