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Motorcycling is a motor sport modality that includes several disciplines such as speed, enduro, trial and motocross. Several particular features in off-road motocross markedly increase the physical and physiological demands for the riders. These include the irregular terrain, dirt and sharp turns that lead to the so-called "arm pump"-a muscular stress sited in the upper limbs because several enduring isometric and/or eccentric muscular contractions are necessary to absorb shocks caused by roughness and motorbike handling during the constant surface driving and landings. Given that motor sports are representative of psychoemotional stress activities, further catecholamine release is expected during this type of exercise. Notwithstanding the markedly increased number of isometric contractions, the mean oxygen consumption previously reported in motocross 1 is suggestive of the increased metabolic aerobic contribution for performance. In this regard, it is tempting to hypothesise that these characteristics, isolated or in combination, may favour the generation of enhanced reactive oxygen and nitrogen species (RONS). This so-called oxidative stress results from an imbalance between production of RONS such as superoxide (O2- ), hydrogen peroxide (H2 O2 ), hydroxyl radical (OH- ) and peroxinitrite (ONOO- ), and the ability of body antioxidant systems to counteract RONS. The consequent muscle oxidative damage, which has been widely reported after different types of physical exercise, predominantly during eccentric exercise, 2 contributes to temporary loss of the exercising capacity of the muscle for force production, compromising exercising capacity.
To date and to the best of our knowledge, there has been no published study analysing the effect of motocross on oxidative stress and damage biomarkers. Thus, the purpose of this study was to examine the effect of a motocross heat on the plasma content of oxidative stress (total (TGSH), reduced (GSH) and oxidised (GSSG) glutathione and total antioxidant status (TAS)) and damage (malondialdehyde (MDA), sulphydryl and carbonyls). Levels of urine catecholamine, plasma uric acid and blood leucocyte counts were also determined.
METHODS
Participants
Ten top elite non-smoker male off-road motocross riders with international experience participated in this research after being informed about the aims and experimental protocol, and after giving written consent to participate. This protocol was approved by the ethics committee of the Faculty of Sport, University of Porto, Porto, Portugal, which followed...