Purpose: This double-blind study investigated the effects of vitamin and mineral complex supplementation on the neuromuscular function of the knee-extensor muscles after a prolonged trail running race.
Methods: Twenty-two well-trained endurance runners took either placebo (Pl group) or vitamins and minerals (Vm group) for 21 d before the race and for 2 d after the race. Maximal voluntary contractions (MVC) and surface EMG activity of the vastus lateralis (VL) muscle were recorded before (pre) and 1 h (post), 24 h (post 24) and 48 h (post 48) after the race. Central activation ratio (CAR), neural (M-wave), and contractile (muscular twitch) properties of the quadriceps muscles were analyzed using electrical stimulation techniques.
Results: The knee-extensor MVC was significantly (P < 0.01) reduced after exercise for both groups (Vm: 36.5 ± 3.0 %; Pl: 36.9 ± 2.1%), but MVC recovery was greater for Vm than Pl after 48 h (11%, P < 0.05). The reduced MVC after exercise was associated with a significant reduction in maximal EMG normalized to the M-wave in VL muscle and in CAR for both groups. Characteristics of the muscular twitch were not significantly altered for either groups, whereas M-wave duration increased significantly (P < 0.05) after exercise.
Conclusions: The reduction of MVC immediately after the race appeared to result from peripheral mechanisms such as a failure in muscle membrane excitation and, to a lesser extent, from reduced central activation. The cause of the depressed MVC 24 h after the race seemed to be located within the muscle itself. A dietary supplementation of a vitamin and mineral complex does not attenuate the loss of contractile function immediately after the running exercise, and it may accelerate the recovery of maximal force capacity.
1Laboratory of Biomechanics and Physiology, National Institute of the Sport and Physical Education, Paris, FRANCE; 2Faculty of Sport Sciences, University of Burgundy, Dijon, FRANCE; 3Laboratory of University of Toulon-Var, Unit Sporting Ergonomics and Performance, La Garde, FRANCE; and 4School of Human Movement and Exercise Science, University of Western Australia, Crawley, AUSTRALIA
Address for correspondence: Christophe Hausswirth, Ph.D., Laboratory of Biomechanics and Physiology, National Institute of the Sport and Physical Education, 11 Avenue du Tremblay, 75012 Paris, France; E-mail: firstname.lastname@example.org.
Submitted for publication June 2005.
Accepted for publication May 2006.