Compared to findings that describe the influence of moderate volumes of exercise on the production of oxidative stress, relatively little is known of
the relationship between ultra-endurance exercise and oxidative stress. The limited work that has been conducted in this area has focussed almost exclusively on oxidative stress resulting from acute bouts of exercise rather than chronic exercise. In light of epidemiological data that show a relationship between high volume energy expenditure and an increased risk of cardiovascular disease, the present research was conducted to more closely examine the long-term health implications associated with production of oxidative stress in a group of individuals who undertake a very high volume of daily physical activity. Four studies addressing the relationship between ultra-endurance exercise and oxidative stress comprise this thesis.
The purpose of Study One was to examine resting markers of oxidative stress (malondialdehyde (MDA) concentration), arterial stiffness and antioxidant status (glutathione peroxidase (GPX), catalase (CAT) and superoxide (SOD) activities) of ultra-endurance athletes. A secondary aim was to observe changes in the production of oxidative stress and antioxidant status of these athletes in response to a half Ironman distance triathlon race (1.9km swim, 90.1km ride, 21.1km run). Additional data such as training experience, age, gender, antioxidant supplementation and nutritional information were collected and compared to measures of oxidative stress and antioxidant status. Sixteen (13 males & 3 females) triathletes (30 ± 7 years) who completed the triathlon and sixteen gender-, age- and height-matched
healthy subjects participated in the study. Pre-race blood samples were drawn to assess oxidative stress, lipids, lipoprotein (a) (Lp(a)) and antioxidant enzyme activities 7-10 days prior to the competition. Arterial stiffness was also measured at this time. Resting blood samples revealed significantly higher GPX activity in athletes compared to controls (p < 0.001). The athletes also had higher resting peripheral systolic blood pressure (p = 0.037). Resting MDA levels were negatively related to both peripheral systolic blood pressure (p = 0.03) and fat intake (p = 0.006) and positively related to the proportion of polyunsaturated and saturated fats consumed in the athletes diet (both p < 0.001). Post-race blood samples were drawn within 15 minutes of the athletes completing the triathlon. There
was a significant increase in the production of MDA (p = 0.005), a decrease in GPX (p = 0.039), CAT (p = 0.002) and SOD (p = 0.007) activities and an increase in triglycerides (p = 0.007) pre-to-post race. The exercise-induced change in CAT activity was negatively related to the change in low density lipoprotein (LDL) (p = 0.043). This study showed that compared to untrained controls, ultra-endurance athletes had a higher resting activity of GPX. Also found was that ultra-endurance exercise results in an increase in the production of MDA but that this increase was not related to diet or antioxidant supplementation (p = 0.27). Given that ultra-endurance exercise was not related to resting levels of Lp(a) or markers associated with arterial stiffness, it was concluded that
ultra-endurance athletes appear to be at no greater risk cardiovascular risk than age-matched controls.
The purpose of Study Two was to extend the work from Study One and examine markers of oxidative stress and arterial stiffness in a group of athletes training for, and competing in, a full Ironman triathlon (3.8km swim, 180km ride, 42.2km run). A second aim of the study was to examine the impact of high-volume, low-intensity activity on resting markers of cardiovascular risk and compare those markers to healthy untrained age-matched controls. The intention was to better understand the influence of volume and intensity of exercise on
exercise-induced oxidative stress and antioxidants. Data pertaining to training experience, age, gender, menstrual status, and antioxidant supplementation were also collected for comparison with measures of oxidative stress and antioxidant status. Twenty nine (23 males and 6 females) ultra-endurance triathletes (36.6 ± 7.5 years) and 29 control subjects (35.3 ± 8.0 years) who were active for less than 180 minutes per week volunteered to participate in the present study. Pre-race mixed venous blood was sampled at rest, between three and seven days prior to the race to assess oxidative stress, lipids, Lp(a) and antioxidant enzyme activities; arterial stiffness was also determined at this time. Resting blood samples revealed the athletes had significantly lower MDA concentration (p < 0.05) and higher activities of GPX and CAT (p <
0.01 & 0.001 respectively) compared to controls. Athletes also had a significantly lower resting heart rate (p < 0.05). There were no differences between athletes and controls in measures of arterial stiffness or any other blood markers associated with antioxidant status. However, the amount of time spent exercise training was negatively related to race finishing time (r = -0.43; p = 0.019) and positively related to resting MDA concentration (r = 0.37; p = 0.05), resting SOD activity (r = 0.57; p = 0.001) and resting LDL concentration (r = 0.38; p = 0.04). Blood was again sampled from the athletes within 15 minutes of finishing the race. Analysis found a significant increase in MDA concentration (p = 0.03), decreases in the activities of GPX (p <
0.001), CAT (p < 0.001) and SOD (p = 0.001) and increases in triglycerides (p < 0.001) and high density lipoprotein (HDL) (p = 0.02) as a result of the Ironman triathlon. These data showed that compared to control subjects, the high-volume, low-intensity training completed by the triathletes was associated with significantly lower resting MDA concentration, a higher resting activity of GPX, and a lower resting heart rate. Also, as a result of an Ironman triathlon, MDA concentration increased and there was a decrease in antioxidant enzyme activity. These changes were not related to antioxidant supplementation (p > 0.05). Given that there was no difference between controls and athletes in resting levels of Lp(a) or markers associated with arterial stiffness, it was
concluded that ultra-endurance athletes participating in high volume, low intensity activity appear to be at no greater cardiovascular risk than age-matched controls.
In order to better understand the time course of adaptations that afford protection against oxidative stress from ultra-endurance training, two further studies were undertaken. The purpose of Study Three was to extend on the work from Studies One and Two and examine changes in oxidative stress and arterial stiffness in an ultra endurance athlete throughout a progressive increase in training volume leading up to a full Ironman triathlon over a six month period (and the
subsequent influence of reduced training over a two month period) compared to an untrained age-, gender-, height-, weight and VO2max-matched control subject. Height, weight, arterial stiffness, and maximal oxygen uptake were measured at the commencement of the study. Blood was also sampled for the analysis of oxidative stress, lipids, Lp(a) and antioxidant activities. Arterial stiffness and blood pressure were measured each fortnight and the athlete also completed a 100km time trial every two weeks; VO2max and dietary analysis were completed every two months during the training program. Following the triathlon race, the athlete returned to moderate levels of training. Two months following the race, a full set of laboratory assessments were again completed. Analysis revealed that there was no significant difference in any of the
blood measures for the athlete or the control subject over the training or reduced training period. The study showed that in regards to adaptations to oxidative stress, either they occur over a longer period than six months or that the present subject's previous history in ultra-endurance exercise negated changes in the variables under investigation.
The purpose of Study Four was to examine changes in markers of oxidative stress, antioxidant status and arterial stiffness in a group of six moderately trained individuals in response to eight weeks of increased training volume. Data pertaining to training experience, nutritional intake, age, gender,
menstrual status and antioxidant supplementation were first assessed. Venous blood (10ml) was also sampled and arterial stiffness was measured prior to the commencement of the eight-week training period. Blood was sampled and arterial stiffness was again measured prior to and following fortnightly time-trials; the blood was analysed for markers of a marker of oxidative stress (MDA) and antioxidant defences (GPX, CAT & SOD activities). Resting MDA concentration significantly increased in response to the eight week training program (p < 0.05), however there was no change in resting antioxidant activity (GPX, SOD & CAT) and resting Lp(a) concentration (p > 0.05). Significant increases in post time-trial production of MDA (p < 0 .014) and arterial stiffness (p < 0.001) were found over the training
period. Although there was no change in resting antioxidant activity, a significant increase in the post-time trial activity of catalase was found (p < 0.001). The increase in training hours was positively related to the increase in both resting levels (r = 044;p = 0.015) and post time-trial production of MDA (r = 0.6; p < 0.001). These data showed that an increase in the volume of endurance training with moderately trained individuals elicited an increase in the production of MDA without an associated change in antioxidant status. The study showed that an increase in training volume can increase arterial stiffness, which contrasts to previous studies and may be related to maladaptation.
In summary, the present series of studies established that i) training associated with half Ironman triathlon distance results in higher resting GPX concentration compared to controls, ii) ultra-endurance exercise results in an increase in the production of MDA but that this increase is not related to diet or antioxidant supplementation, iii) ultra-endurance exercise does not cause an increase in resting levels of Lp(a) or markers associated with arterial stiffness and based upon these measures, ultra-endurance athletes are not at an increased risk of developing CVD, iv) compared to control subjects, full Ironman triathlon ultra-endurance training (low-intensity training) was associated with a significantly lower MDA concentration, and higher resting GPX
activity, v) high volume, low intensity ultra-endurance training promotes positive adaptations that improve protection against oxidative stress, vi) a large increase in ultra-endurance training without adequate rest in moderately trained individuals can elicit an increase in the production of MDA and can increase arterial stiffness without an associated increase in antioxidant status.