The Effect of Creatine Loading on Neuromuscular Fatigue in Women

SMITH-RYAN, ABBIE E.1; RYAN, ERIC D.1; FUKUDA, DAVID H.2; COSTA, PABLO B.3; CRAMER, JOEL T.4; STOUT, JEFFREY R.2

Medicine & Science in Sports & Exercise:
doi: 10.1249/MSS.0000000000000194
Applied Sciences
Abstract

Purpose: This study aimed to examine the effects of intermittent isometric fatigue on maximal voluntary contraction (MVC) strength, percent voluntary activation (%VA), peak twitch force (PTF), peak rate of force development (PRFD), half relaxation time (HRT), and maximal compound action potential (M-wave) amplitude of the soleus and medial gastrocnemius muscles before and after creatine (Cr) loading.

Methods: Using a double-blinded, placebo-controlled, randomized design, 12 women were assigned to a Cr (n = 6; mean age ± SD = 23.3 ± 3.0 yr) or placebo (PL; n = 6; mean age ± SD = 21.3 ± 1.6 yr) group. Participants supplemented four times daily for 5 d with 5 g of Cr + 10 g of fructose or 10 g of fructose. At baseline and after testing, an isometric MVC and the twitch interpolation procedure were used before and after a 4-min isometric fatigue protocol of the plantarflexor muscles, which consisted of six intermittent duty cycles per minute (7-s contraction, 3-s relaxation) at 70% MVC.

Results: There were no interactions between the Cr and PL groups (P > 0.05) for any dependent variable. The fatigue protocol reduced voluntary strength (−17.8%, P < 0.001) and %VA (−3.7%, P = 0.005). Baseline PTF (P < 0.005) and PRFD (P < 0.001) values were less than those of all respective time points, but PTF value decreased from 3 min to 4 min and after testing (P < 0.005). HRT increased from baseline to minutes 1 and 2 and then returned to baseline at minutes 3 and 4 and after testing. The M-wave did not change (P > 0.05).

Conclusions: Five days of Cr loading did not influence isometric force, %VA, evoked twitch properties, or the central and peripheral aspects of fatigue measured in this study.

Author Information

1Department of Exercise and Sport Science, University of North Carolina Chapel Hill, Chapel Hill, NC; 2Sport and Exercise Science, University of Central Florida, Orlando, FL; 3Department of Kinesiology, California State University–San Bernardino, San Bernardino, CA; and 4Department of Nutrition and Health Sciences, University of Nebraska-Lincoln, Lincoln, NE

Address for correspondence: Abbie E. Smith-Ryan, Ph.D., 312 Woollen Gym, CB#8700, University of North Carolina Chapel Hill, Chapel Hill, NC 27599; E-mail: abbiesmith@unc.edu.

Submitted for publication May 2013.

Accepted for publication October 2013.

© 2014 American College of Sports Medicine