4 Neuron and Motor Unit Neuron is a single nerve cell 1014 neurons in brainSynapses convey information via chemicalsAfferent-from periphery to CNSEfferent-from CNS to peripheryNeuron body, dendrites and axon (myelin sheath)
5 Action Potential Alteration in permeability Sodium influx and potassium outflowNegative to positiveNerve conduction velocity120 m/s or 270mph for myelinated400 f/s5 m/s or 2mph for unmyelinated
15 ThresholdAP results from the quick and dramatic alteration to ionic permeability following chemical or electrical intervention. Muscle resting at -90 millivoltsAfter stimulation of an excitable cell membrane sodium ions move into the cell and the transmembrane potential is reduced - referred to as depolarizationWhen a critical voltage level called the threshold is reached, voltage-sensitive sodium gates are opened followed by slower acting potassium gates (move out)At +35 millivolts the sodium channels and the potassium channels are fully opened, resulting in restoration of the negative transmembrane potential - called repolarizationThe amplitude of voltage changes in response to stimulation is constant from stimulus to stimulus and is described as "all or none"Electrical stimulation of excitable cells is possible up to 1000 pps.
22 Stretch Shortening Cycle Concentric force is increased as a function of eccentric action or stretching.Increased force with speed of the motion.Stored elastic energy responsible.
23 Fatigue Repeated contractions diminish relaxation time. Neural signals continue to propagate.Contracture occurs at the muscle site.
24 Mechanical FactorsAngle of pull is optimum at right angles or 90 degrees to the bone.Length is optimum at midpoint or resting length.
25 Exercise Modes Isokinetic=constant velocity. Isotonic=constant resistance (DCER).Isometric=static and without muscle movement.
26 Neuromuscular Adaptations to Exercise Hypertrophy- enlargement and increase in number of muscle myofibrils (not fibers), increasing the size of actin and myosinHyperplasia-increase in the number of fibers (not in humans, only in birds).Fast twitch muscle fibers hypertrophy to a greater extent than slow twitch muscle fibersEarly increases in muscle strength have a large neural componentLong term increases in strength also have a neural component
29 Electromyography (EMG) Records electrical signals from the brain.EMG reflects muscle activation.Surface electrodes (summated) or fine needle electrodes (individual).Amplitude increases with recruitment (summation).Integration of signal equals true mean of firing (RMS).
30 EMG cont… Positive relationship between EMG and force/velocity. A measure of intensity.Efficiency of electrical activity = stronger individuals require less activation.Learning curve demonstrates greater force with less EMG.
31 EMG and Fatigue EMG increases with fatigue. Recruitment responsible. Local fatigue is a function of individual muscle and joint.
32 Resistance Training and Aerobic Power Resistance training does not improve aerobic powerResistance training does not impair an individual’s ability to develop maximal aerobic powerAerobic training does not enhance muscle strength or sizeAerobic training may compromise the benefits of strength training on muscle force production