Gabe Beltrami, F., De Groot, R., Rauch, L., Tucker, R., Rae, D. E., & Noakes, T. D. (2009). Effects of prior exhaustive leg or arm exercise on subsequent performance, power, and EMG activity. A paper presented at the 14th Annual Congress of the European College of Sport Science, Oslo, Norway, June 24-27.

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"A prior bout of exhaustive exercise is known to result in early exhaustion being reached during a subsequent bout of maximal exercise. Much of the research to date has examined peripheral factors for this phenomenon." This study investigated the contribution of central regulation on the performance of maximal exercise preceded by a bout of exhaustive exercise using a different muscle group.

Well-trained males (five cyclists and five canoeists) completed two exercise trials. In trial 1, Ss performed an incremental leg ergometry test to exhaustion, followed 15 minutes later by an incremental arm ergometry test to exhaustion. In trial 2, the order was reversed (arms followed by legs). The two trials were separated by at least three days and the order in which the Ss performed the trials was randomized. Time to exhaustion, power output, heart rate, rating of perceived exertion, oxygen consumption, ventilation rate, plasma lactate, and electromyography (EMG) of two lower (rectus femoris and vastus lateralis) and two upper limb (triceps and biceps) muscles were measured during all trials.

During the first exercises, Ss reached exhaustion faster and at a higher power output during legs compared to arms. While heart rate and rating of perceived exhaustion were similar in the leg and arm tests at exhaustion, VO2 and ventilation rate were lower in the arm test. Arm performance was unaffected by prior leg exercise. Prior arm activity significantly reduced time to exhaustion and peak power output during subsequent leg exercise. There were no changes in VO2max, heart rate, rating of perceived exhaustion, ventilation rate, and plasma lactate between the first and second trial part for each muscle group. Plasma lactate was higher at the beginning of both muscle groups when they were the second exercise compared to their respective first exercise. Prior exercise affected subsequent arm heart rate for the first 40% of the trial. During leg exercise as the second component of the experience, heart rate differed only at the start and 20% of the test. EMG increased linearly during all the trials and maximal EMG activity measured during the tests was only 55% of previous values. Rating of perceived exertion rose linearly during all tests, regardless of different levels of plasma lactate and heart rate. None of the measured physiological/neuromuscular variables measured showed a plateau at exhaustion.

Implication. Prior maximal arm exercise reduces peak power output during a subsequent bout of exhaustive leg exercise without altering physiological or EMG variables. In contrast, prior leg exercise does not alter peak power output during subsequent arm exercise. Rating of perceived exertion is set in anticipation, being independent of the amount of muscle mass activated, heart rate, or plasma lactate. These findings are difficult to interpret according to traditional peripheral models of exercise fatigue and deserve further investigation.

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