Neurophysiological Reserve With Caffeine Manipulation

• Neurophysiological reserve evidenced by caffeine [ Time Frame: Immediately after the administration (around 10 minutes) ] [ Designated as safety issue: No ]
  The time to cover a 4-km trial (closed-loop) or the time to exhaustion in an incremental intensity test (opened-loop) can show if the caffeine manipulation affects the performance. In addition, measures of CNS excitability such as EMG during the closed-loop exercise or at the exhaustion point in the opened-loop exercise, and measures such as the amplitude of H reflex, the rate of increase in H reflex/M wave relationship, can indicate if some central or peripheral alteration occurred during the exercises.
  
  
• Neurophysiological reserve evidenced by caffeine [ Time Frame: Immediately after the administration (around 10 minutes) ] [ Designated as safety issue: No ]
  The time to cover a 4-km trial (closed-loop) or the time to exhaustion in an incremental intensity test (opened-loop) can show if the placebo manipulation affects the performance. In addition, measures of CNS excitability such as EMG during the closed-loop exercise or at the exhaustion point in the opened-loop exercise, and measures such as the amplitude of H reflex, the rate of increase in H reflex/M wave relationship, can indicate if some central or peripheral alteration ocurred during the exercises.
  
  

• Neurophysiological reserve evidenced by placebo [ Time Frame: Immediately after the administration (around 10 minutes) ] [ Designated as safety issue: No ]
  The placebo should also promote decrease in time of trial or increase in mean power output during a closed-loop exercise, elevation in time to exhaustion and maximal power output during an opened-loop exercise, and increase in maximal voluntary isometric contraction (MVIC) and time to contraction in a target force. Also, there should be a higher CNS excitability such as: 1) higher EMG during closed-loop exercise and higher EMG at the exhaustion point in an opened-loop exercise; 2) increased amplitude of H reflex; 3) elevation on the rate of increase in H reflex/M wave relationship.
  
  

A neurophysiological reserve related to central mechanisms is supposed to be present, which should be observed when an increased central drive occurs. In theory, according to the central regulation model of effort, an increased performance could be due to the elevation on Central Nervous System excitability and activity, since exercise is not peripherally limited. Conversely, the absence of muscle performance improvement to the increased central drive promoted by caffeine would be an evidence for a peripherally localized neurophysiological limit and would indicate the absence of reserve. Therefore, if present, this reserve could be verified by using peripheral and central measures derived from electric-stimulation, evoked twitch and interpolated twitch techniques, associated to measures of EMG and peripheral metabolism, when caffeine is manipulated during closed- and opened-loop exercise.

In addition, there should also be possible to access the reserve without stimulant substance manipulation (placebo effect). By teleological argument derived from the central regulation model of effort, a neurophysiological reserve would be a natural mechanism to protect the cellular integrity. Therefore, it would be reasonable to hypothesize that, if present, a reserve would be observed by an increase in performance promoted by an elevation in central drive when placebo is perceived as caffeine. Unfortunately, however, no study utilized this experimental approach, including measures of central and peripheral activity during closed- and opened-loop exercise, to consistently respond the reserve question.