Manipulation of dietary carbohydrates after prolonged effort modifies muscle sarcoplasmic reticulum responses in exercising males

Abstract

The hypothesis tested was that disturbances in the sarcoplasmic reticulum (SR) Ca2+-cycling responses to exercise would associate with muscle glycogen reserves. Ten untrained males [peak O2 consumption (VO2 peak) = 3.41 +/- 0.20 (SE) l/min] performed a standardized cycle test (approximately 70% VO2 peak) on two occasions, namely, following 4 days of a high (Hi CHO)- and 4 days of a low (Lo CHO)-carbohydrate diet. Both Hi CHO and Lo CHO were preceded by a session of prolonged exercise designed to deplete muscle glycogen. SR Ca2+ cycling in crude homogenates prepared from vastus lateralis samples indicated higher (P < 0.05) Ca2+ uptake (microM x g protein(-1) x min(-1)) in Hi CHO compared with Lo CHO at 30 min (2.93 +/- 0.10 vs. 2.23 +/- 0.12) and at 67 min (2.77 +/- 0.16 vs. 2.10 +/- 0.12) of exercise, the point of fatigue in Lo CHO. Similar effects (P < 0.05) were noted between conditions for maximal Ca2+-ATPase (microM x g protein(-1) x min(-1)) at 30 min (142 +/- 8.5 vs. 107 +/- 5.0) and at 67 min (130 +/- 4.5 vs. 101 +/- 4.7). Both phase 1 and phase 2 Ca2+ release were 23 and 37% higher (P < 0.05) at 30 min of exercise and 15 and 34% higher (P < 0.05), at 67 min during Hi CHO compared with Lo CHO, respectively. No differences between conditions were observed at rest for any of these SR properties. Total muscle glycogen (mmol glucosyl units/kg dry wt) was higher (P < 0.05) in Hi CHO compared with Lo CHO at rest (+36%), 30 min (+53%), and at 67 min (+44%) of cycling. These results indicate that exercise-induced reductions in SR Ca2+-cycling properties occur earlier in exercise during low glycogen states compared with high glycogen states.

Muscle Glycogen Content Modifies SR Ca2+ Release Rate in Elite Endurance Athletes

“…Another study from the same group of researchers supported these observations by reporting a similar association following 4 days of low or high CHO diet in untrained women (9). Thus, there are convincing data demonstrating a direct association between SR vesicle Ca 2+ release rate and muscle glycogen content and these data gives further support to the existence of a critical threshold of glycogen required to protect SR Ca 2+ release as previously suggested by Duhamel and colleagues and Ørtenblad and colleagues (10,33). As SR Ca 2+ regulation is quantitatively, but not qualitatively, different between fiber types with an approximately 4 times higher SR uptake and -release rates in MHC II fibers (33).…”

“…Recent findings from human studies support the findings in animal models where Ca 2+ kinetics is influenced by glycogen levels (9,10,33). Duhamel and colleagues (10) examined the relation between muscle glycogen content and SR vesicle Ca 2+ release rate in untrained males during a prolonged fatiguing cycling session at ≈70 % of ̇O 2peak . The cycling session was preceded by a glycogen depleting exercise session and four days of either low or high carbohydrate (CHO) diet.…”

“…Hence, both muscle glycogen and SR Ca 2+ release rate remained depressed in the H 2 O group whereas muscle glycogen and SR Ca 2+ release were significantly elevated in the CHO group in comparison to the Post measurement. (10,26) and unaltered (19,33) following exercise. These discrepancies in research may be related to the exercise mode and training status of individuals.…”

“…Based on existing human data, there is a critical level of muscle glycogen at around 250-300 mmol . kg -1 dw below which the SR Ca 2+ release rate is impaired (10,33 and functional muscle performance, as peak power output, is at present unknown. Furthermore, little is known about the glycogen re-synthesis rate in these highly trained endurance athletes.…”

Post-exercise taurine administration enhances glycogen repletion in tibialis anterior muscle

“…Many researchers have demonstrated that higher glycogen content in skeletal muscle before exercise results in improved performance in both prolonged endurance exercise and high-intensity intermittent exercise [2][3][4][5] . Recent in vitro studies also have shown that higher glycogen content before contraction is associated with the attenuation of force reduction during repeated tetanic contractions [6][7][8][9] . Therefore, during the post-exercise phase, glycogen repletion in skeletal muscle should be one of the most important factors for performance in the subsequent exercise.…”