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Old 05-19-2007, 10:56 AM   #4
Paul Kayley
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Morning Robb. Great to have somewhere new and different to discuss stuff. The website looks great.

IME, apart from the obvious injury prevention benefits, strength training is definately of benefit to some aerobic and endurance activities, especially in cycling for example, where peripheral performance limitation is more likely due to the restricted muscle mass involved in an enclosed range of motion. However, trying to explain the physiological reasons for this has for some time eluded me.

A rather simplistic but nontheless potentially valid reasoning - "The answer could be efficiency, could simply be the fact that if you increase near max strength, any submaximal force output requires less muscle fiber. That is, if you need 100 lbs of force to generate a certain wattage and your max is 100, you're working at 100% of your maximum. If your max is 200 lbs, that same 100 lbs of force is only 50% of maximum." This however does not take into account the significance of the anaerobic systems upon strength, nor the almost insignificant impact of the anaerobic systems upon maximal aerobic capacity or lactate threshold.

I believe that weights is likely to be far more beneficial to athletes whose limiter is not central VO2max but peripheral fatigue, due to a low LT resulting from a restricted range of endurance trained fibres. An individual with a high % of ST fibres, either from being genetically gifted or via long-term training and altered gene-expression, is more able to easily recruit more fibres due to their lower innervation threshold. The workload is therefore better distributed resulting in a lower respiration rate per cell, resulting in better fuel economy and a higher OBLA threshold.

It may be that weight training improves/increases muscle fibre recruitability and coordination of innervation, leading to a wider and more organised fibre 'team-effort'. Also, could it not be possible that neural adaptations lead to improved intermediate muscle fibre innervation thresholds... that is, for less percieved effort these fibres can be recruited resulting in their more frequent use during sport specific training. In effect, intermediate fibres' innervation thresholds are reduced to near ST innervation charateristics. Which in turn, during aerobic actvities, results in them becoming more aerobic and endurance trained, raising the LT, and in turn increasing time to exhaustion and functional power output.

Have you ever come across any research pertaining to the effects of resistance/strength training upon innervation thresholds of different muscle fibre types? I believe that the following is suggesting that they reduce... I have read the study a few times, but I'm still not 100% sure that this is their point? Perhaps they're suggesting that less innervation occurs for the same force output as a result of improved motor unit coordination follwing resistance training?

The sites of neural adaptation induced by resistance training in humans
Timothy J. Carroll, Stephan Riek and Richard G. Carson


Although it has long been supposed that resistance training causes adaptive changes in the CNS, the sites and nature of these adaptations have not previously been identified. In order to determine whether the neural adaptations to resistance training occur to a greater extent at cortical or subcortical sites in the CNS, we compared the effects of resistance training on the electromyographic (EMG) responses to transcranial magnetic (TMS) and electrical (TES) stimulation. Motor evoked potentials (MEPs) were recorded from the first dorsal interosseous muscle of 16 individuals before and after 4 weeks of resistance training for the index finger abductors (n = 8), or training involving finger abduction-adduction without external resistance (n = 8). TMS was delivered at rest at intensities from 5 % below the passive threshold to the maximal output of the stimulator. TMS and TES were also delivered at the active threshold intensity while the participants exerted torques ranging from 5 to 60 % of their maximum voluntary contraction (MVC) torque. The average latency of MEPs elicited by TES was significantly shorter than that of TMS MEPs (TES latency = 21.5 1.4 ms; TMS latency = 23.4 1.4 ms; P < 0.05), which indicates that the site of activation differed between the two forms of stimulation. Training resulted in a significant increase in MVC torque for the resistance-training group, but not the control group. There were no statistically significant changes in the corticospinal properties measured at rest for either group. For the active trials involving both TMS and TES, however, the slope of the relationship between MEP size and the torque exerted was significantly lower after training for the resistance-training group (P < 0.05). Thus, for a specific level of muscle activity, the magnitude of the EMG responses to both forms of transcranial stimulation were smaller following resistance training. These results suggest that resistance training changes the functional properties of spinal cord circuitry in humans, but does not substantially affect the organisation of the motor cortex.

(BTW dont buy that book I recommended as I've sent you my copy.)
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