Effects of creatine loading on electromyographic fatigue threshold during cycle ergometry in college-aged women

Journal of the International Society of Sports Nutrition, Nov 2007

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.

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Effects of creatine loading on electromyographic fatigue threshold during cycle ergometry in college-aged women

Abbie E Smith 1 Ashley A Walter 1 Trent J Herda 0 Eric D Ryan 0 Jordan R Moon 1 Joel T Cramer 0 Jeffrey R Stout 1 0 Biophysics Laboratory, Department of Health and Exercise Science, University of Oklahoma , Norman, OK 73019 , USA 1 Metabolic and Body Composition Laboratory, Department of Health and Exercise Science, University of Oklahoma , Norman, OK 73019 , USA 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, placebocontrolled 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. - Background In a series of electromyographic (EMG) fatigue studies, Moritani et al. [1,2] demonstrated an increase in EMG activity during incremental cycling exercise. It has been suggested that the rise in electrical activity is a result of progressive recruitment of additional motor units (MU) and/or an increase in the firing frequency of MUs that have already been recruited [3]. 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]. Thus, if power output is to be maintained, either additional MUs must be recruited or the firing rates of the already active MUs must increase. In either case, a rise in EMG amplitude with power output takes place due to increases in muscle activation. The physiological mechanism responsible for the increase in EMG amplitude over time during a fatiguing task is unknown. Three potential mechanisms, however, include the accumulation of metabolic by-products (lactate, hydrogen ions (H+), inorganic phosphate (Pi), and ammonia), the depletion of stored energy substrates (ATP, phosphocreatine (PCr), and glycogen) and/or impaired muscle cation (potassium (K+), sodium (Na+) and calcium (Ca2+) regulation [5-7]. 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 [2,8-11]. Furthermore, surface EMG has been shown to be an acceptable method for non-invasive assessment of muscle fatigue of active muscles [12,13]. Matsumoto et al. [9] and Moritani et al. [2] have proposed an incremental cycle ergometer test utilizing fatigue curves to identify the maximal power output at which an individual can maintain without evidence of fatigue, called the electromyographic fatigue threshold (EMGFT). The EMGFT test is an adaptation to deVries original monopoloar physical working capacity at the fatigue threshold (PWCFT) test [14], using a bipolar supramaximal protocol, which involves determining the rate of rise in electrical activity from the vastus lateralis during four, 60 second work bouts on a cycle ergometer, with varying power outputs. The four power outputs are then plotted as a function of four EMG slope coefficients, with the y-intercept defined as the electromyographic fatigue threshold (EMGFT). Matsumoto et al[9] described the EMGFT as the highest intensity sustainable on a cycle ergometer without signs of neuromuscular fatigue. In addition, Moritani et al. [2] suggested a strong physiological link between myoelectrical changes at fatigue and anaerobic threshold. Furthermore, the EMGFT method has been reported as a valid and reliable technique for examining the transition fro (...truncated)


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Abbie E Smith, Ashley A Walter, Trent J Herda, Eric D Ryan, Jordan R Moon, Joel T Cramer, Jeffrey R Stout. Effects of creatine loading on electromyographic fatigue threshold during cycle ergometry in college-aged women, Journal of the International Society of Sports Nutrition, 2007, pp. 20, 4, DOI: 10.1186/1550-2783-4-20