Short-term lowering of carbohydrate intake reduces skeletal muscle glycogen and body weight, but has no effect on short-term exercise capacity or maximal power-output in recreational active men

INTRODUCTION: In the days preceding competition most endurance athletes consume a diet rich in carbohydrates (CHO) with the aim of
storing high amounts of skeletal muscle glycogen. However, glycogen-loading could be associated with increased body weight (glycogen
with associated water) and may not be necessary for short-term (1-15 min.) exercise performance. In this study, we investigated the effect
of a short-term manipulation of dietary CHO intake on muscle glycogen content, body weight and short-term exercise performance.
METHODS: In a randomized and counterbalanced cross-over design twenty-two recreationally active males (maximal oxygen consumption:
56.5 ± 5.4 mL O2 · min-1 · kg-1) completed two maximal ergometer cycling exercise tests of either 1- or 15-min. (Group 1 and 15, respectively), after different CHO consumption strategies in the preceding days. Muscle glycogen was manipulated after a glycogen depletion
training consisting of both arm cranking and cycling exercise where the subjects received a diet consisting of either a moderate (M-CHO: 4
g · kg-1 body weight · day-1) or high (H-CHO: 10 g · kg-1 body weight · day-1) amount of CHO for the remaining of the training day and for
the following two days. Muscle biopsies from vastus lateralis were obtained prior to and immediately after each test and glycogen content
was determined biochemically. Peak power-output was determined pre and immediately after the post-exercise biopsies. All data were
analyzed by validated linear mixed models and presented as mean ± 95 % confidence interval.
RESULTS: The CHO manipulation led to different muscle glycogen contents between conditions (M-CHO: 367 mmol · kg-1 dry weight [DW]
(337:396); H-CHO: 525 mmol · kg-1 DW (496:555), P < 0.00001) and caused a higher body weight (M-CHO: 76.6 kg (74.3:78.8); H-CHO: 77.3
(75.1:79.5), P < 0.00001) in H-CHO compared to M-CHO prior to the maximal cycling tests. The average power-output during the 1- and 15-
min. of maximal cycling did not differ between conditions (Group 1: H-CHO: 590 W (541:639); M-CHO: 569 W (515:622), P = 0.33) (Group
15: H-CHO: 294 W (269:319); M-CHO: 293 W (267:320), P = 0.99). Peak power-output was reduced by 6.1 % (3.8:8.5) (P < 0.00001) and 5.9
% (3.4:8.5) (P < 0.00001) after 1- and 15-min. of maximal cycling exercise comp