Anticipatory, Feedforward and Central Regulation of Pacing Strategies in Time Trial Cycling
Mauger, Alexis R
Date: 24 November 2009
Thesis or dissertation
University of Exeter
PhD in Sport and Health Sciences
The aim of this thesis was to directly test the key underpinnings of recent propositions for systems of central control of exercise regulation. Fatigue and exercise tolerance have traditionally been explained through peripheral mechanisms, such as excitation-contraction coupling failure and the inability to supply sufficient metabolic ...
The aim of this thesis was to directly test the key underpinnings of recent propositions for systems of central control of exercise regulation. Fatigue and exercise tolerance have traditionally been explained through peripheral mechanisms, such as excitation-contraction coupling failure and the inability to supply sufficient metabolic substrate to contracting muscle in order to meet increasing energy demand. More recently, models of central control, which are proposed to regulate exercise intensity in an anticipatory/feedforward manner, with the ultimate aim of avoiding physiological ‘catastrophe’, have received a great deal of attention. This thesis investigated several of the key requirements and mechanisms stated in these models. The central governor model (CGM) and teleoanticipation are stated to use a combination of prior experience and distance knowledge of an exercise bout to work in a feedforward manner, so that a pacing strategy is set before exercise commences which ensures the bout is completed in an optimum time but in the absence of premature fatigue. Study one examined the influence of distance knowledge, prior experience and distance feedback on the setting and regulation of a pacing strategy in 4 km time trial (TT) cycling in trained cyclists (n = 18). When performing 4 × 4 km TT intervals, it was found that prior experience of the exercise (in the absence of distance feedback and distance knowledge) allowed the creation of a pacing strategy that produced a performance which was as competitive as cyclists who were provided with prior experience, distance knowledge and distance feedback. The difference in TT completion time between groups (CON = feedback group, EXP = no feedback group) was reduced with subsequent TT (CON TT1 367 ± 21 s; EXP TT1 409 ± 45 s; CON TT2 373 ± 19 s; EXP TT2 389 ± 30 s; CON TT3 375 ± 18 s; EXP TT3 383 ± 26 s; CON TT4 373 ± 20 s; EXP TT4 373 ± 14 s), so that by the final TT, completion time between groups was almost exactly the same. It was concluded that when sufficient prior experience is attained in the absence of distance knowledge and feedback, a successful pacing strategy can be set. In order for pacing to be set prior to an exercise bout and adjusted in a feedforward/anticipatory manner during exercise, an internal mechanism must exist which monitors the passage of time. Study two examined the accuracy and robustness of this ‘internal clock’ by assessing cyclist’s (n = 16) ability to gauge the distance they had cycled during repeated 4 km and 6 km TT. The internal clock was shown to be inaccurate to absolute measures of distance, but showed a calibration capacity following experience of a TT of unknown distance (24.6 ± 18.2 % error in distance judged completed vs. 8.2 ± 5.5 % error in distance judged completed). This process was fragile and occurred in the absence of any significant performance improvement. It was concluded that relative quantities appear more important in creating a pacing strategy, and that times are of greater importance than distances. Study three examined the influence of comparative performance feedback in a field setting in 4 km track TT cycling in trained cyclists (n = 5). Correct feedback produced a significantly faster TT time (t4 = -3.10, p < 0.05) than non-contingent feedback (341 ± 8 s vs. 350 ± 12 s), with differences in mean lap speed apparent between the conditions at the start of the TT (t4 = 4.71, p < 0.05) and at the end of the TT (t4= 3.45, p < 0.05; t4 = 3.30, p < 0.05). The study provided empirical support for the assumption that performance feedback is advantageous during exercise and provided insights into past and present exercise comparison and its role on the setting of a pacing strategy. A central component of the CGM and theories of central exercise regulation is the role of afferent feedback during exercise and the premature termination of exercise before a true maximum intensity has been reached. Study four used acetaminophen to blunt cyclists’ (n = 13) pain response during ten mile (16.1 km) TT in order to disrupt the afferent feedback processes. When using acetaminophen, cyclists produced significantly faster (t12 = 2.55, p < 0.05) TT completion times (1575 ± 96 s) than under a placebo condition (1605 ± 122 s). When using acetaminophen, cyclists had a higher power output during the middle section of the TT (F1, 12 = 4.79, p < 0.05), yet showed no significant difference in RPE (F1,12 = 0.72, p > 0.05) or pain scores (F1,12 = 0.30, p > 0.05). It was concluded that acetaminophen reduced levels of pain during the TT, thereby disrupting the comparative afferent feedback mechanism and allowing cyclists access to a ‘metabolic reserve’. The research presented has advanced our knowledge and supported propositions of models of central control and regulation during exercise. The research has provided further insight in the role of prior experience, distance knowledge, distance feedback, the internal clock, performance feedback and afferent feedback on the setting and maintenance of a pacing strategy in 4, 6 and 16.1 km TT cycling.
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