Abstract
The purpose of this study was to examine the effects of 5 days of Creatine (Cr) loading on the electromyographic fatigue threshold (EMGFT) in college-aged women. Fifteen healthy college-aged women (mean ± SD = 22.3 ± 1.7 yrs) volunteered to participate in this double-blind, placebo-controlled study and were randomly placed into either placebo (PL – 10 g of flavored dextrose powder; n = 8) or creatine (Cr – 5 g di-creatine citrate plus 10 g of flavored dextrose powder; n = 7; Creatine Edge, FSI Nutrition) loading groups. Each group ingested one packet 4 times per day (total of 20 g/day) for 5 days. Prior to and following supplementation, each subject performed a discontinuous incremental cycle ergometer test to determine their EMGFT value, using bipolar surface electrodes placed on the longitudinal axis of the right vastus lateralis. Subjects completed a total of four, 60 second work bouts (ranging from 100–350 W). The EMG amplitude was averaged over 10 second intervals and plotted over the 60 second work bout. The resulting slopes from each successive work bouts were used to calculate EMGFT. A two-way ANOVA (group [Cr vs. PL] × time [pre vs. post]) resulted in a significant (p = 0.031) interaction. Furthermore, a dependent samples t-test showed a 14.5% ± 3.5% increase in EMGFT from pre- to post-supplementation with Cr (p = 0.009), but no change for the PL treatment (-2.2 ± 5.8%; p = 0.732). In addition, a significant increase (1.0 ± 0.34 kg; p = 0.049) in weight (kg) was observed in the Cr group but no change for PL (-0.2 kg ± 0.2 kg). These findings suggest that 5 days of Cr loading in women may be an effective strategy for delaying the onset of neuromuscular fatigue during cycle ergometry.
Highlights
In a series of electromyographic (EMG) fatigue studies, Moritani et al [1,2] demonstrated an increase in EMG activity during incremental cycling exercise
Several investigations have used surface electromyography to characterize the fatigue-induced increase in EMG amplitude, as well as to identify the power output associated with the onset of neuromuscular fatigue during cycle ergometry [2,8,9,10,11]
Several studies have reported 4 to7 days of Cr loading is effective for enhancing anaerobic performance during repeated sprint cycling [24,25,26,27], resistance training [28,29], and anaerobic treadmill running [30]
Summary
In a series of electromyographic (EMG) fatigue studies, Moritani et al [1,2] demonstrated an increase in EMG activity during incremental cycling exercise. An exercise-induced decrease in intramuscular pH, due to increases in hydrogen ions [H+], may interfere with the excitation-contraction coupling process of skeletal muscle, which, in turn, may lead a to decrease in power output and fatigue [4]. If power output is to be maintained, either additional MUs must be recruited or the firing rates of the already active MUs must increase. A rise in EMG amplitude with power output takes place due to increases in muscle activation. Several investigations have used surface electromyography to characterize the fatigue-induced increase in EMG amplitude, as well as to identify the power output associated with the onset of neuromuscular fatigue during cycle ergometry [2,8,9,10,11]. Surface EMG has been shown to be an acceptable method for non-invasive assessment of muscle fatigue of active muscles [12,13]
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