Low carbohydrate diet affects the oxygen uptake on-kinetics and rating of perceived exertion in high intensity exercise ADRIANO E. LIMA-SILVA, a,b FLA ´ VIO O. PIRES, a RO ˆ MULO C. M. BERTUZZI, a FA ´ BIO S. LIRA, c DULCE CASARINI, d and MARIA AUGUSTA P. D. M. KISS a a School of Physical Education and Sport, University of Sa˜ o Paulo, Sa˜ o Paulo, Brazil b Sports Science Research Group, Federal University of Alagoas, Maceio´ , Brazil c Department of Physiology, Division of Nutrition Physiology, Federal University of Sa˜ o Paulo, Sa˜ o Paulo, Brazil d Nephrology Division, Hospital of the Kidney and Hypertension, Federal University of Sa˜ o Paulo, Sa˜ o Paulo, Brazil Abstract The aim of this study was to determine if the carbohydrate (CHO) availability alters the rate of increase in the rating of perceived exertion (RPE) during high intensity exercise and whether this would be associated with physiological changes. Six males performed high intensity exercise after 48 h of controlled, high CHO (80%) and low CHO (10%) diets. Time to exhaustion was lower in the low compared to high CHO diet. The rate of increase in RPE was greater and the VO 2 slow component was lower in the low CHO diet than in the control. There was no significant condition effect for cortisol, insulin, pH, plasma glucose, potassium, or lactate concentrations. Multiple linear regression indicated that the total amplitude of VO 2 and perceived muscle strain accounted for the greatest variance in the rate of increase in RPE. These results suggest that cardiorespiratory variables and muscle strain are important afferent signals from the periphery for the RPE calculations. Descriptors: Perceived exertion, Fatigue, Afferent signals, Cardiorespiratory and metabolic systems In performing a high intensity exercise at a fixed power output, fatigue can be operationally defined as the inability to maintain a pre-determined pedal cadence (Eston, Faulkner, St. Clair Gibson, Noakes, & Parfitt, 2007; Pitsiladis & Maughan, 1999). The tra- ditional theory used to explain the mechanisms involved in fatigue development during high exercise intensity holds that the exercise termination is due to impaired muscle contractile function caused by a failure in homeostasis (Hill & Lupton, 1923; Noakes & St. Clair Gibson, 2004). However, evidence that the homeostasis failure is the specific cause of exercise termination in high exercise intensity still needs to be provided (Kayser, 2003; Noakes & St. Clair Gibson, 2004; Noakes, St. Clair Gibson, & Lambert, 2004). On the other hand, a centrally regulated system model has been recently proposed as an alternative model of fatigue. In this model, the work and metabolic rate during exercise are regulated by the central nervous system (CNS) in a non-linear manner, which pre- vents the homeostasis failure in bodily systems (Noakes et al., 2004). Specifically, it has been suggested that a centrally localized governor controls the muscle recruitment pattern in order to pre- vent any potential metabolic disturbance (Lambert, St. Clair Gibson, & Noakes, 2005; Noakes et al., 2004; Tucker, 2009). This model holds that fatigue is not a simple physical event that must occur whenever a critical metabolic limit is overreached. Rather, fatigue could be considered as a conscious sensation of effort that results from interpretations of multiple physiological and psycho- logical signals integrated in the CNS. As a consequence of this integrated mechanism, the rating of perceived exertion (RPE) may represent the conscious/verbal manifestation when these multiple afferent signals are integrated (Noakes, 2004, 2008; Tucker, 2009). Additionally, the RPE seems to be set at the beginning of the exercise bout as part of a feedforward/feedback mechanism (Crewe, Tucker, & Noakes, 2008). In fact, the scalar behavior of RPE as exercise progresses supports the idea that it is part of a feedforward/feedback mechanism, suggesting that RPE is set as a function of remaining exercise time. Using Baldwin’s data (Bald- win, Snow, Gibala, Garnham, Howarth, & Febbraio, 2003), Noakes (2004) showed that the rate of increase in RPE was higher during exercise with initial low muscle glycogen content than with high muscle glycogen content. However, when plotted against the percentage of the time to exhaustion, the RPE increased at the same rate in both conditions. Similar results have been obtained when comparing fatiguing to non-fatiguing conditions (Eston et al., 2007) and hot to cool environments (Crewe et al., 2008). Fla´ vio Pires is grateful to Coordenac¸a˜ o de Aperfeic¸oamento de Pessoal de Nı´vel Superior (CAPES) for his PhD scholarship. This study had financial support provided by the Fundac¸ a˜ o de Amparo a Pesquisa do Estado de Sa˜ o Paulo (FAPESP) (2006-60641-6). Address correspondence to: Adriano E. Lima-Silva, Sports Science Research Group, Faculty of Nutrition, Federal University of Alagoas, Lorival Melo Mota S/N Avenue, Campus A. C. Simo˜ es, Tabuleiro do Martins, Maceio´ , Alagoas, Brazil, 7072970. E-mail: adrianosilva@usp.br Psychophysiology, 48 (2011), 277–284. Wiley Periodicals, Inc. Printed in the USA. Copyright r 2010 Society for Psychophysiological Research DOI: 10.1111/j.1469-8986.2010.01059.x 277