title: High-intensity exercise and muscle glycogen availability in humans.
abstract: This study investigated the effects of muscle glycogen availability on performance and selected physiological and metabolic responses during high-intensity intermittent exercise. Seven male subjects completed a regimen of exercise and dietary intake (48 h) to either lower and keep low (LOW-CHO) or lower and then increase (HIGH-CHO) muscle glycogen stores, on two separate occasions at least a week apart. On each occasion the subjects completed a short-term (<10 min) and prolonged (>30 min) intermittent exercise (IEX) protocol, 24 h apart, which consisted of 6-s bouts of high-intensity exercise performed at 30-s intervals on a cycle ergometer. Glycogen concentration (mean +/- SEM) in m. vastus lateralis before both IEx(short) and IEx(long) was significantly lower following LOW-CHO [180 (14), 181 (17) mmol kg (dw)(-1)] compared with HIGH-CHO [397 (35), 540 (25) mmol kg (dw)(-1)]. In both IEx(short) and IEx(long), significantly less work was performed following LOW-CHO compared with HIGH-CHO. In IEx(long), the number of exercise bouts that could be completed at a pre-determined target exercise intensity increased by 265% from 111 (14) following LOW-CHO to 294 (29) following HIGH-CHO (P < 0.05). At the point of fatigue in IEx(long), glycogen concentration was significantly lower with the LOW-CHO compared with HIGH-CHO [58 (25) vs. 181 (46) mmol kg (dw)(-1), respectively]. The plasma concentrations of adrenaline and nor-adrenaline (in IEx(short) and IEx(long)), and FFAand glycerol (in IEx(long)), increased several-fold above resting values with both experimental conditions. Oxygen uptake during the exercise periods in IEx(long), approached 70% of Vo2max. These results suggest that muscle glycogen availability can affect performance during both short-term and more prolonged high-intensity intermittent exercise and that with repeated exercise periods as short as 6 s, there can be a relatively high aerobic contribution.
authors.affiliation: Department of Physiology and Pharmacology, Karolinska Institute and University College of Physical Education and Sports, Stockholm, Sweden.
authors.forename: P D
authors.initials: PD
authors.lastname: Balsom
authors.forename: G C
authors.initials: GC
authors.lastname: Gaitanos
authors.forename: K
authors.initials: K
authors.lastname: Söderlund
authors.forename: B
authors.initials: B
authors.lastname: Ekblom
mesh_terms: D000328:Adult; D001642:Bicycling; D004040:Dietary Carbohydrates / Q000008:administration & dosage; D004837:Epinephrine / Q000097:blood; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test; D005230:Fatty Acids, Nonesterified / Q000097:blood; D005990:Glycerol / Q000097:blood; D006003:Glycogen / Q000378:metabolism*; D006801:Humans; D019271:Hypoxanthine / Q000097:blood; D019344:Lactic Acid / Q000097:blood; D008297:Male; D018482:Muscle, Skeletal / Q000378:metabolism*; D009638:Norepinephrine / Q000097:blood; D010101:Oxygen Consumption / Q000502:physiology
chemical_list: D004040:Dietary Carbohydrates; D005230:Fatty Acids, Nonesterified; D019271:Hypoxanthine; D019344:Lactic Acid; D006003:Glycogen; D005990:Glycerol; D009638:Norepinephrine; D004837:Epinephrine