Gymnastik- och idrottshögskolan, GIH

PURPOSE: The present study investigated the effects of periodic CHO restriction on endurance performance and metabolic markers in elite endurance athletes.

METHODS: Twenty-six male elite endurance athletes (VO2max: 65.0 ml O2[BULLET OPERATOR]kg[BULLET OPERATOR]min) completed 4 weeks of regular endurance training, while matched and randomized into two groups training with (Low) or without (High) carbohydrate (CHO) manipulation three days a week. The CHO manipulation days consisted of a 1-hr high intensity bike session in the morning, recovery for 7 hrs while consuming isocaloric diets containing either high CHO (414±2.4 g) or low CHO (79.5±1.0 g), and a 2-hr moderate bike session in the afternoon with or without CHO. VO2max, maximal fat oxidation and power output during a 30-min time trial (TT) were determined before and after the training period. The TT was undertaken after 90 mins of intermittent exercise with CHO provision before the training period and both CHO and placebo after the training period. Muscle biopsies were analyzed for glycogen, citrate synthase (CS) and β-hydroxyacyl-coenzyme A dehydrogenase (HAD) activity, carnitine palmitoyltransferase (CPT1b) and phosphorylated acetyl-CoA carboxylase (pACC).

RESULTS: The training effects were similar in both groups for all parameters. On average, VO2max and power output during the 30-min TT increased by 5 ± 1% (P<0.05) and TT performance was similar after CHO and placebo during the preload phase. Training promoted overall increases in glycogen content (18 ± 5%), CS activity (11 ± 5%) and pACC (38 ± 19%) (P<0.05) with no differences between groups. HAD activity and CPT1b protein content remained unchanged.

CONCLUSION: Superimposing periodic CHO restriction to 4 weeks of regular endurance training had no superior effects on performance and muscle adaptations in elite endurance athletes.