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.
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.
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).
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.
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: firstname.lastname@example.org.
Submitted for publication May 2013.
Accepted for publication October 2013.