The nervous system is divided into the central nervous system (CNS) that includes the brain and spinal cord, and the peripheral nervous system (PNS) comprising cranial nerves and spinal nerves. The brain comprises of two regions:
Receptor and effector organs
Receptor organs, which include the ears, eyes and muscles, collect information (stimuli). The CNS then interprets this information and sends it back to 'effector' organs which carry out the body's response to the stimuli. Some actions are largely automatic, such as the stretch/reflex involved in the leg muscles when jumping but others appear to be more interpreted by the brain, like fatigue signals.
Research indicates that prolonged sports involvement influences the way the CNS 'controls' muscular recruitment and patterning.
Researchers from Finland (Eloranta 2003) investigated the influence of sports background on leg muscle coordination during concentric and drop vertical jumps. They discovered that the CNS influenced the firing and recruitment patterns of the sports participants' muscles and they attributed these differences to the specifics of the individuals' sport and the effect years of training had on the CNS.
They went on to conclude that, "Prolonged training in a specific sport will cause the central nervous system to program muscle coordination according to the demands of that sport" and also added, "the learned skill-reflex of the CNS seems to interfere in the performance of another task".
CNS training and 'quickness'
Bompa (2005) identifies two CNS processes as it relates to sports performance - 'excitation' and 'inhibition'. The speed at which signals are sent from the receptors to effectors, and back again, results in levels of excitation or inhibition. For example, to move the body as fast as possible when sprinting, the speed of signal transference through the CNS needs to also to be as fast as possible. An athlete's receptors and effectors therefore need to be optimally excited and uninhibited in order to result in the optimum recruitment of fast-twitch muscle fibre.
However, CNS fatigue will slow the speed of excitation, particularly within fast-twitch fibres, which fatigue much more rapidly than slow-twitch fibres. Consequently, Bompa believes exercises should only be performed as long as 'quickness' is possible.
Potentiation involves the creation of a set of stimulatory circumstances within the muscle firing complex that boost neural excitation, motor unit and muscle fibre recruitment and reduce inhibition. Lifting weights before a plyometric workout (complex training) has been shown to enhance the performance of the plyometric activity. However, any potentiating activity must not fatigue the CNS otherwise the reverse effect will be experienced.
Bompa's philosophy (Bompa 2005) with regards weight training to improve explosive power is that repetitions are the key training variable. He recommends a low number of repetitions (1 to 3), with loadings in excess of 90% of 1RM, in order to develop strength that will boost speed and power and optimise the contribution of the CNS, with a recovery 6 minutes between sets.
These loadings create a higher level of excitation and receptor/effector communication, more motor unit recruitment and greater neural stimulation. These loadings and recoveries are also recommended on the basis of their contribution to maximum power and strength expression, and also because they do not produce a large increase in muscle mass, which could be detrimental to an athlete's power to weight ratio.
Bompa (2005) advocates 48 hours of recovery between high intensity CNS workouts. He also recommends that on the same training day more of the same training can be performed; this is in part due to the effect of potentiation and also to create time, so that the next day can be used for CNS recovery. For example, a sprinter could perform a sprint speed workout and equally intense plyometrics on the same day. On the subsequent training day, workout options would be selected so as not to challenge the CNS - e.g. tempo runs (medium-paced runs that do not overly stress the anaerobic system). Consideration needs to be given to the training conducted in the preceding 24 hours.
Where speed and power are important components in an event or sport then coaches and athletes need to plan CNS specific sessions into the their training programmes. The training focus must be on the quality of execution (quickness) of an exercise not the quantity.
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