TY - JOUR
T1 - The effect of metabolic alkalosis on central and peripheral mechanisms associated with exercise-induced muscle fatigue in humans
AU - Siegler, Jason C.
AU - Marshall, Paul
N1 - Publisher Copyright:
© 2015 The Authors. Experimental Physiology © 2015 The Physiological Society.
PY - 2015/4/20
Y1 - 2015/4/20
N2 - New Findings: What is the central question of this study? Does metabolic alkalosis affect central and peripheral mechanisms associated with exercise-induced muscle fatigue in humans? What is the main finding and its importance? Inducing metabolic alkalosis before exercise preserved voluntary activation, but not muscle excitation, after a 2 min maximal voluntary contraction (MVC) followed by ischaemia. An effect of pH was also observed in maximal rates of torque development, where alkalosis mitigated the reduction in maximal rates of torque development after the initial 2 min MVC. For the first time, these results demonstrate a differential effect of pH on voluntary activation as well as maximal rates of torque development after sustained, maximal voluntary knee extension in humans. The increased concentration of protons during fatiguing exercise may contribute to increased activation of group III and IV afferents and subsequently reduced central drive, but this has yet to be confirmed in exercising humans. Here, we determined whether inducing metabolic alkalosis differentially affects descending central drive after fatiguing exercise and whether this effect may, in part, be explained by attenuating group III and IV afferent firing. Eleven men performed a maximal 2 min voluntary knee extension (MVC) followed by a 2 min rest and subsequent 1 min MVC with an occlusive cuff either in placebo [PLA; 0.3 g (kg body weight)-1 calcium carbonate] or alkalosis conditions [ALK; 0.3 g (kg body weight)-1 sodium bicarbonate]. Femoral nerve stimulation was applied before exercise, after the 2 min MVC and at 40-60 s intervals throughout the remainder of the protocol to explore central and peripheral mechanisms associated with reductions in maximal force and rate of torque development. Although voluntary activation declined to a similar extent after the 2 min MVC, during the ischaemic period voluntary activation was higher during ALK (PLA, 57 ± 8%; ALK, 76 ± 5%). Maximal voluntary torque declined at similar rates during the task (203 ± 19 N m), but maximal rate of torque development was significantly higher in the ALK conditions after the 2 min MVC (mean difference of 177 ± 60 N m s-1). These results demonstrate the effect of pH on voluntary activation as well as maximal rates of torque development after sustained, maximal voluntary knee extension in humans.
AB - New Findings: What is the central question of this study? Does metabolic alkalosis affect central and peripheral mechanisms associated with exercise-induced muscle fatigue in humans? What is the main finding and its importance? Inducing metabolic alkalosis before exercise preserved voluntary activation, but not muscle excitation, after a 2 min maximal voluntary contraction (MVC) followed by ischaemia. An effect of pH was also observed in maximal rates of torque development, where alkalosis mitigated the reduction in maximal rates of torque development after the initial 2 min MVC. For the first time, these results demonstrate a differential effect of pH on voluntary activation as well as maximal rates of torque development after sustained, maximal voluntary knee extension in humans. The increased concentration of protons during fatiguing exercise may contribute to increased activation of group III and IV afferents and subsequently reduced central drive, but this has yet to be confirmed in exercising humans. Here, we determined whether inducing metabolic alkalosis differentially affects descending central drive after fatiguing exercise and whether this effect may, in part, be explained by attenuating group III and IV afferent firing. Eleven men performed a maximal 2 min voluntary knee extension (MVC) followed by a 2 min rest and subsequent 1 min MVC with an occlusive cuff either in placebo [PLA; 0.3 g (kg body weight)-1 calcium carbonate] or alkalosis conditions [ALK; 0.3 g (kg body weight)-1 sodium bicarbonate]. Femoral nerve stimulation was applied before exercise, after the 2 min MVC and at 40-60 s intervals throughout the remainder of the protocol to explore central and peripheral mechanisms associated with reductions in maximal force and rate of torque development. Although voluntary activation declined to a similar extent after the 2 min MVC, during the ischaemic period voluntary activation was higher during ALK (PLA, 57 ± 8%; ALK, 76 ± 5%). Maximal voluntary torque declined at similar rates during the task (203 ± 19 N m), but maximal rate of torque development was significantly higher in the ALK conditions after the 2 min MVC (mean difference of 177 ± 60 N m s-1). These results demonstrate the effect of pH on voluntary activation as well as maximal rates of torque development after sustained, maximal voluntary knee extension in humans.
UR - http://www.scopus.com/inward/record.url?scp=84929658827&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=84929658827&partnerID=8YFLogxK
U2 - 10.1113/EP085054
DO - 10.1113/EP085054
M3 - Article
C2 - 25727892
AN - SCOPUS:84929658827
SN - 0958-0670
VL - 100
SP - 519
EP - 530
JO - Experimental Physiology
JF - Experimental Physiology
IS - 5
ER -