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Effects of prior exercise and a low-carbohydrate diet on muscle sarcoplasmic reticulum function during cycling in women

Department of Kinesiology, University of Waterloo, Waterloo, Ontario, Canada

Submitted 18 January 2006 ; accepted in final form 15 May 2006

The effects of exercise and diet on sarcoplasmic reticulum Ca²⁺-cycling properties in female vastus lateralis muscle were investigated in two groups of women following four different conditions. The conditions were 4 days of a low-carbohydrate (Lo CHO) and glycogen-depleting exercise plus a Lo CHO diet (Ex + Lo CHO) (experiment 2) and 4 days of normal CHO (Norm CHO) and glycogen-depleting exercise plus Norm CHO (Ex + Norm CHO) (experiment 1). Peak aerobic power (O_2peak) was 38.1 ± 1.4 (SE); n = 9 and 35.6 ± 1.4 ml·kg^–1·min^–1; n = 9, respectively. Sarcoplasmic reticulum properties measured in vitro in homogenates (µmol·g protein^–1·min^–1) indicated exercise-induced reductions (P < 0.05) in maximal Ca²⁺-ATPase activity (0 > 30, 60 min > fatigue), Ca²⁺ uptake (0 > 30 > 60 min, fatigue), and Ca²⁺ release, both phase 1 (0, 30 > 60 min, fatigue) and phase 2 (0 > 30, 60 min, fatigue; 30 min > fatigue) in Norm CHO. Exercise was without effect in altering the Hill slope (n_H), defined as the slope of relationship between Ca²⁺-ATPase activity and Ca²⁺ concentration. No differences were observed between Norm CHO and Ex+Norm CHO. Compared with Norm CHO, Lo CHO resulted in a lower (P < 0.05) Ca²⁺ uptake, phase 1 Ca²⁺ release (30 min), and n_H. Ex + Lo CHO resulted in a greater (P < 0.05) Ca²⁺ uptake and n_H compared with Lo CHO. The results demonstrate that Lo CHO alone can disrupt SR Ca²⁺ cycling and that, with the exception of Ca²⁺ release, a glycogen-depleting session of exercise before Lo CHO can reverse the effects.

Ca²⁺ release; Ca²⁺ uptake; Ca²⁺-ATPase activity; vastus lateralis; submaximal; female

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