An investigation of a novel, non-invasive technique for the assessment of oxidative stress in aerobic and isometric exercise

The oxidative stress response to exercise is a well-established phenomenon; however, the time course of this response has not been well characterised. There is little information in the literature regarding the oxidative stress response during exercise; most authors have measured oxidative stress solely during the recovery period from exercise. There are several different invasive methods available for assessment of oxidative stress, although there is no “gold standard” technique. A novel non-invasive technique utilising laser spectroscopy to quantify expired ethane concentration has become available, but has not yet been tested in relation to exercise. The first study described here aimed to use the laser spectroscopy technique for the first time to assess exercise-induced oxidative stress in three species: humans, horses and dogs; and to determine the utility of carbon monoxide monitoring as a means of assessment of oxidative stress. A further objective was to better characterise the oxidative stress response by the collection of data at frequent intervals during exercise and during recovery. Eight endurance-trained males performed incremental treadmill exercise to volitional exhaustion. Twelve racehorses and twelve racing greyhounds performed maximal exercise on a race track. Expired ethane concentration was measured throughout exercise in humans, and pre- and post-exercise in horses and dogs. Carbon monoxide concentration was assessed pre- and post-exercise in all species. Results indicated that the technique of laser spectroscopy was viable for use in relation to exercise in all three species. Oxidative stress was shown to increase significantly following exercise in all three species, thus supporting previous literature, and extending this finding to a trained human population for the first time. The pattern of response during incremental treadmill exercise was characterised for the first time and indicated a non-significant increase in oxidative stress in humans within 2 minutes of the onset of exercise, with the response progressively increasing alongside increases in work rate until exercise was terminated at exhaustion. The response returned close to the resting value by 20 minutes into the recovery period. Low subject number may have contributed to the lack of significant findings during exercise. Carbon monoxide was not a useful indicator of oxidative stress in any species. Increased functionality of the laser spectroscopy technique was investigated by pilot work in which real-time monitoring of expired ethane was attempted for the first time in relation to exercise. This allowed the observation of the oxidative stress response on a breath by breath basis. Initial tests, in which two healthy males performed incremental cycle ergometer exercise to exhaustion whilst breathing through a valve connected directly to the spectrometer, indicated that a useful output could be recorded during a prolonged period of exercise. However, the measurement of ambient ethane concentration, essential for accuracy, was not undertaken in the initial tests. Thus, further pilot work was successfully carried out in three healthy males to replicate the initial tests with concurrent ambient ethane monitoring. This pilot testing allowed development of data editing techniques. The oxidative stress response profile for incremental exercise in real-time was similar to that reported in the previous chapter. Additional tests were undertaken which illustrated that the rise in ethane output observed during incremental exercise was not simply a manifestation of the ventilatory response to exercise, rather than an indication of exercise-induced oxidative stress. This was accomplished by forcing an increase in ventilation, by imposition of an additional dead space volume during normal breathing in two individuals. This technique shows promise for more detailed characterisation of the time course of the oxidative stress response in future exercise studies via the capability for extremely high density data collection. The main aims of the second study were to investigate the oxidative stress response throughout the entire work rate range from rest to volitional exhaustion, rather than just the higher end of the work rate range as observed in study one; and to examine the magnitude and time course of the oxidative stress response to constant load exercise performed below and above the lactate threshold. Six healthy males performed incremental cycle ergometer exercise to exhaustion during which blood samples were collected regularly for later analysis for the presence of F2-isoprostanes. Results of the analysis were disappointing, with a high proportion of samples displaying a concentration outwith the range of the assay. However, preliminary malondialdehyde analysis suggested that the oxidative stress response may increase progressively alongside work rate throughout the entire work rate range. However, this observation is far from conclusive as it is based on data from a single subject only. The final study was intended to investigate the effect of contraction intensity on the oxidative stress response to isometric handgrip exercise sustained to exhaustion, and to clarify the time course of the oxidative stress response during the recovery period. Due to logistical limitations, it was possible to study one contraction intensity only. Initially, pilot work was undertaken to determine the suitability of the novel non-invasive technique for ethane assessment in relation to isometric exercise, since this assessment method had not been used previously with this exercise mode. Then, six healthy males performed sustained isometric exercise at 60 % of maximal voluntary contraction until fatigue. Oxidative stress was assessed during a 30 minute recovery period via expired ethane and also via F2-isoprostanes concentration in blood collected from both the exercised arm and the non-exercised arm. This was intended to allow comparison of blood sampling site, and of the systemic oxidative stress response measured both invasively and non-invasively; however this was not possible due to poor assay results. The previous finding of a peak oxidative stress response following isometric exercise within the first 5 minutes of the recovery period was supported. Oxidative stress was assessed by ethane output for the first time in relation to isometric exercise and was found to be a viable technique; however, its use remains to be validated against more traditional plasma markers. The potential value of non-invasive assessment was underlined by F2-isoprostanes analysis issues. In conclusion, the use of laser spectroscopy, including the use of real-time monitoring, appears to be a viable technique for the non-invasive assessment of exercise-induced oxidative stress, and may enhance our ability to characterise this response in future studies.