Evidence for complex system integration and dynamic neural regulation of skeletal muscle recruitment during exercise in humans

Research Unit for Exercise Science and Sports Medicine, University of Cape Town, Newlands, South Africa. <>
British Journal of Sports Medicine (Impact Factor: 5.03). 01/2005; 38(6):797-806. DOI: 10.1136/bjsm.2003.009852
Source: PubMed

ABSTRACT A model is proposed in which the development of physical exhaustion is a relative rather than an absolute event and the sensation of fatigue is the sensory representation of the underlying neural integrative processes. Furthermore, activity is controlled as part of a pacing strategy involving active neural calculations in a "governor" region of the brain, which integrates internal sensory signals and information from the environment to produce a homoeostatically acceptable exercise intensity. The end point of the exercise bout is the controlling variable. This is an example of a complex, non-linear, dynamic system in which physiological systems interact to regulate activity before, during, and after the exercise bout.

Download full-text


Available from: Timothy Noakes, Sep 03, 2014
1 Follower
  • Source
    • "Based on the fact that the PFC is associated with cognitive tasks, motivation and decision-making, decreasing oxygenation at high exercise intensity prior to exhaustion in the PFC has been assumed to trigger centrally mediated fatigue and the decision to stop exercise in numerous former studies [3] [6] [9] [12] [13] [14] [15]. Hypoxia is proposed to accelerate cerebral deoxygenation, thus central fatigue [2] [8] [10] [11] [15] [16]. "
    [Show abstract] [Hide abstract]
    ABSTRACT: The correlation of NIRS (near-infrared spectroscopy) and EEG (electro-cortical activity) in exercise studies has never been shown. Eight sport students performed an incremental bicycle exercise test under normoxic and hypoxic (12.7% O2) conditions respectively. EEG and NIRS recordings of the prefrontal cortex (PFC, Brodmann area 10. 46) were performed synchronously to shed light on their correlation. ANOVA revealed a higher absolute workload (231.3 ± 37.2 W), and relative PFC oxygenation under normoxic conditions, whereas hypoxic conditions resulted in earlier exhaustion (200 ± 26.7 W) and reduced PFC oxygenation. NIRS parameters increased remarkably with exercise intensity (P < 0.001) and differed between conditions (O2Hb: P < 0.001; HHb: P = 0.023; tHb: P = 0.016) and hemispheres (O2Hb: P = 0.023). For EEG, higher prefrontal cortical current density during compared to pre and post exercise was revealed for both conditions (P < 0.001). No difference between conditions and hemispheres were found. In conclusion, brain cortical activity is not impaired by hypoxia. No correlation between NIRS and EEG, but a moderate correlation between EEG and cardio-vascular parameters and a moderate to high correlation between NIRS and cardio-vascular parameters were found. The results emphasize that the transfer of EEG and NIRS results need to be done with caution.
  • Source
    • "The rate at which RPE increases during opened-loop, constant-load exercises (in which exercise intensity cannot be reduced) seems to be set at the beginning of the exercise and regulated as a function of the remaining time to exhaustion [1]. Thus, the time to exhaustion during a given exercise bout can be predicted by the rate of increase of RPE [4] [5] [6] [7] [8]. It is interesting to note that some psychological manipulation techniques alter the RPE response during opened-loop exercise [9] [10]. "
    [Show abstract] [Hide abstract]
    ABSTRACT: We examined the effects of listening to music on time to exhaustion and psychophysiological responses during moderate-intensity exercise performed in fatigued and non-fatigued conditions. Fourteen healthy men performed moderate-intensity exercise (60% Wmax) until exhaustion under four different conditions: with and without pre-fatigue (induced by 100 drop jumps) and listening and not listening to music. Time to exhaustion was lower in the fatigued than the non-fatigued condition regardless listening to music. Similarly, RPE was higher in the fatigued than the non-fatigued condition, but music had no effect. On the other hand, listening to music decreased the associative thoughts regardless of fatigue status. Heart rate was not influenced by any treatment. These results suggest that listening to music changes attentional focus but is not able to reverse fatigue-derived alteration of performance.
    Physiology & Behavior 02/2015; 139:274-280. DOI:10.1016/j.physbeh.2014.11.048 · 3.03 Impact Factor
  • Source
    • "It has been suggested that such strategies are regulated, and established before the initiation of exercise in order to enhance performance and to avoid depletion of energy resources. By doing so, premature fatigue and injuries can be avoided (Gibson and Noakes, 2005; Noakes, 2012). Furthermore, the chosen pacing strategy is continuously regulated throughout the activity based on external and internal environmental changes such as knowledge of end point (Billaut et al., 2011; Halperin et al., 2014), motivation (Blanchfield et al., 2013; Stone et al., 2012), and core temperature (Tucker et al., 2004; 2006). "
    [Show abstract] [Hide abstract]
    ABSTRACT: Most studies have examined pacing strategies with cycli-cal activities (running and cycling). It has been demon-strated that males employ different pacing strategies dur-ing repeated maximal voluntary contractions (MVCs) dependent upon a known endpoint. Since different fatigu-ing mechanisms have been identified between the gen-ders, it is not known if females use comparable pacing strategies. The purpose of this study was to examine if informing female subjects regarding the number of MVCs to perform would affect force and electromyography (EMG). Twenty well-trained females completed 3 fatigu-ing protocols in a randomized order. In the control condi-tion participants were informed they would perform twelve MVCs and then actually completed twelve. In the unknown condition they were not told how many MVCs to perform but were stopped after twelve. In the deception condition they were initially informed to perform 6 MVCs, but after the 6 th MVC they were asked to perform a few more MVCs and were stopped after twelve. During the first 6 MVCs, forces in the deception condition were greater compared to the unknown (p = 0.021, ES = 0.65, 5%) and control (p = 0.022, ES = 0.42, 3%) conditions. No differences were found between conditions in the last 6 MVCs. A main effect for repetitions showed force defi-cits during the first 6 MVCs (p = 0.000, ES = 1.81, 13%) and last 6 MVCs (p = 0.05, ES = 0.34, 3%). No differ-ences were found between conditions in biceps and tri-ceps EMG. However, EMG decreased during the first 6 MVCs for biceps (p = 0.001, ES = 1.0, 14%) and triceps (p = 0.001, ES = 0.76, 14%) across conditions. No differ-ences were found in the last 6 MVCs. The anticipation of performing fewer MVCs led to increased force, whereas no endpoint led to decreased force production.
    Journal of sports science & medicine 08/2014; 13:736-741. · 0.90 Impact Factor
Show more