Carbohydrate Dependence During Hard-Intensity Exercise in Trained Cyclists in the Competitive Season: Importance of Training Status

Abstract

To test the hypothesis that intensive endurance training increases CHO utilisation during hard-intensity exercise, seven competitive road cyclists (Cy) performed three 50-min steady-state exercise tests on a cycle ergometer above their ventilatory threshold (+ 15 %) over the course of a cycling season (January [ET1], May [ET2] and September [ET3]). We compared the data with the baseline values of seven sedentary controls (Sed). CHO oxidation in Cy was higher in ET2 and ET3 than in ET1 (p < 0.05), was lower in ET3 than in ET2 (p < 0.05) and was higher in Cy than in Sed only in ET2 (p < 0.05). Lactate kinematics were lower in Cy than in Sed in all conditions (p < 0.05), but in Cy they were lower in ET2 than in ET1 and higher in ET3 than in ET2 (p < 0.05). Race performance was impaired and the overtraining score was increased at ET3 in comparison with ET2 (p < 0.05). We conclude that competitive cyclists increase CHO oxidation during hard-intensity exercise over the course of a season, but show a decline by the end of the season in association with the appearance of an overtraining state. Thus, well-trained cyclists develop a CHO dependence, which is modified with training status.

Training-induced improvement in lipid oxidation in type 2 diabetes mellitus is related to alterations in muscle mitochondrial activity. Effect of endurance training in type 2 diabetes

“…Since the LIPOXmax occurs at very low intensity in T2D (38% of VO 2max th [6], 37 % of VO 2max th in this study), it is likely that most training protocols targeted above 50 % of VO 2max have quite different effects. Exercise sessions set at such levels, where carbohydrate are the almost only substrate used for oxidation, may mostly enhance the ability to oxidize carbohydrate rather than lipids, as already demonstrated by our group during a longitudinal study of training in cyclists [24].…”

Measurement and Physiological Relevance of the Maximal Lipid Oxidation Rate During Exercise (LIPOXmax)

“…While low intensity training, as shown above, increases lipid oxidation, high intensity training has been reported to improve the ability to oxidize carbohydrates (Manetta et al, 2002a(Manetta et al, , 2002b. Varlet-Marie et al (Varlet-Marie et al, 2006) described the profile of lipid oxidation in 90 trained athletes: 28 cyclists, 32 male soccer players, 19 male rugby players, 11 rugbywomen (national level in soccer and male rugby and regional level in cyclism and female rugby) and 41 healthy sedentary volunteers.…”

“…Based on our previous studies on calorimetry during long duration steady-state workloads (Manetta et al, 2002a(Manetta et al, , 2002bManetta et al, 2005) we developped a test ) consisting of five 6-min submaximal steps, in which we assumed that a steady-state for gas exchanges was obtained during the 2 last minutes. We proposed ) a diagnostic test including four or five 6-minutes workloads, that may be followed by a series of fast increases in power intensity until the tolerable maximum under these conditions is reached.…”

“…Although in our study we can only present data on soccer, this pattern is likely to occur in several sports. Since exercise training at high intensity (Manetta et al, 2002a(Manetta et al, , 2002b and intermittent exercise both increase the ratio between CHO and fat used for oxidation during muscular activity, this pattern may reflect an adaptation of muscle metabolism to short repeated bouts of high intensity. Interestingly, such a "glucodependence" is also found in obesity ) and type 2 diabetes (Blanc et al, 2000).…”

Substrate oxidation during exercise: impact of time interval from the last meal in obese women

“…8,9 By contrast, exercise training targeted at intensity levels where the muscle mostly oxidizes CHO improves principally the ability to oxidize CHO. 26 Moreover, this study focuses only on the balance of substrates during an exercise bout, and gives no information on the delayed increase in lipid oxidation that occurs for several hours during recovery, and that may play an important role in the energetic metabolism of subjects submitted to regular exercise training. For all these reasons, we think that our finding of a better lipid oxidation at 3-h is an useful finding for investigators aiming at improving exercise training protocols in obesity.…”