Handbook of Vitamin C Research

Impact of Vitamin C on Exercise-Induced Oxidative Stress 19exercise (for review, see [99]), as well as the direct assessment of free radical production viaelectron spin resonance following acute exercise in animals [105]and humans [106-111].Aerobic ExerciseThe majority of research within the field has utilized aerobic exercise as the stimulus toinduce oxidative stress. Typical protocols have included submaximal or maximal effortaerobic exercise either on a treadmill or cycle ergometer, with the majority of investigationsutilizing a graded exercise test (GXT) to induce an oxidant stress. Most laboratory basedprotocols have involved short to moderate duration exercise bouts (≤ 2 hours), while a fewlaboratory protocols, and the more common ―field‖ tests, have included much longer times ofexercise (> 2 hours). In addition, some treadmill studies have focused on downhill running,involving eccentric bias in order to induce muscle injury. In general, oxidative stress hasbeen evidenced by an increase in lipid, protein, DNA, and glutathione oxidation, as well asalterations in the antioxidant defense system which are consistent with accelerated RONSproduction (for review, see [99]).In those protocols involving long duration and/or eccentric exercise as a stimulus,elevations in muscle damage have been observed, evident by reported increases in variousmarkers of muscle injury (CK and LDH) [112-115] and muscle soreness in the days (1-14)following exercise. It is believed that the initial mechanical trauma to the musculatureinduced by the exercise bout itself results in a pro-inflammatory response and the secondaryrecruitment of phagocytic cells, ultimately resulting in increased respiratory burst activity andoxidative stress during the recovery period.Although a general trend in favor of a transient oxidative insult induced by aerobicexercise is certainly evident, an increase in oxidative stress has not always been observed, asnull findings for various biomarkers of oxidative stress have also been reported by severalinvestigators in both animals and humans [99]. Recall from above that in order for oxidativestress to occur RONS production must exceed the ameliorating capabilities of the antioxidantdefense system in place. Several factors appear to impact the magnitude of RONS produced,as well as the degree of antioxidant protection. These include the intensity [116,117] andduration [118] of exercise, as well as the age [119], training status [83,84], and dietary intake[3] of the subject population utilized. During low-intensity and duration protocols,antioxidant defenses appear sufficient to combat the elevated production of RONS, but asintensity and/or duration of exercise increases, these defenses are no longer adequate,potentially resulting in oxidative damage to surrounding tissues [120]. With respect to aging,biomarkers of oxidative stress have been shown to be exacerbated as a function of age bothduring resting and exercising conditions [119]. Regular exercise training has been shown toresult in an up-regulation of endogenous antioxidant defenses [58], thereby lowering bothresting and exercise-induced oxidative stress [83,84]. Lastly, because exogenous compoundscontribute to the antioxidant capacity of the system, the composition of antioxidant presentwithin the diet (primarily determined by the intake of fruits and vegetables) may also impactoxidative stress. These examples are a few of the extraneous variables that appear to impactthe actual induction of oxidative stress; however, null findings may also be related to