Achten J, Halson S, Moseley L, Rayson M, CaseyA and Jeukendrup AE (2004). The effect of dietary carbohydrate on running performance during a period of intensified training, J Appl Physiol; 96(4):1331-1340.
The aim of this study was to determine if a high-carbohydrate (HCHO) compared to a control (CON) diet during a period of intensified training would prevent the development of overreaching
In a randomized cross-over design, the training of 7 trained male runners (VO2max 64.7 ± 2.6 ml/kg/min) was intensified for 7 days, after 4 days of normal training. On three days, subjects ran 60min steady state on a treadmill followed by a self-paced 8km all out run and on four days they ran 16km all out. During the two trials they consumed either a HCHO (8.5 ± 0.2 g CHO/kg/d) or a CON-diet (5.4 ± 0.1 g CHO/kg/d). Substrate utilization was measured using indirect calorimetry on day 1 and 11 and glucose kinetics were studied using a primed continuous [U-13C]-glucose infusion during 30 min of running at 58% VO2max and 30 min at 77% VO2max on day 11.
Time to complete 8km was significantly increased by 61 ± 23s in the HCHO-trial and by 155 ± 38s in the CON-trial. The 16km times were only significantly increased during the CON diet (8.2 ± 2.1%). Increases in global mood scores as assessed with the POMS were more marked in the CON-trial than the HCHO-trial. Training resulted in 7 ± 2 and 13 ± 2 fold increases in fatigue scores during the HCHO and CON-trials resp. During exercise at 58% VO2max, CHO oxidation decreased significantly from 1.7 ± 0.2 to 1.2 ± 0.2 g/min over the course of the CON-trial, while no changes were seen in the HCHO trial. On day 11, muscle glycogen oxidation was significantly higher during the HCHO trial compared to the CON trial at 58% VO2max (1.7 ± 0.2 vs 1.0 ± 0.1 g/min) and at 77% VO2max (2.2 ± 0.2 vs 1.2 ± 0.2 g/min).
The decrease in CHO oxidation during 7 days of CON was completely accounted for by a decrease in muscle glycogen oxidation. The findings indicate that during a period of intensified running training consuming a HCHO diet compared to a CON diet reduces the symptoms of overreaching, but it cannot prevent it. Supported by a grant of the Chemical Biological Defence and Human Sciences Domain of the UK MOD’s CRP.