Real and simulated altitude training: physiological and performance effects

Abstract

The use of altitude training has long been of interest to enhance sea-level performance in athletes. Living at altitude and training at sea-level is claimed to be the most effective approach compared to other forms of altitude training. However, interest in intermittent hypoxia has increased over recent decades because it is more convenient than conventional altitude training, which involves transportation and accommodation costs. Benefits of both real and simulated altitude training remain controversial. Additionally, not all subjects respond to altitude in the same way, with some showing improvement in performance (responders) while others exhibit either no change or a decrease in performance (non-responders). The mechanism(s) behind these changes have yet to be identified. Furthermore, the effects of simulated altitude training (using hypoxicators) on muscular strength and endurance are yet to be fully examined. This thesis contains three experimental studies which investigated the effects of both real and simulated altitude training on muscular performance and physiological changes in athletes and well trained subjects.

In Study 1, responders and non-responders were investigated using a live high-train low (LHTL) approach. The Snow Farm Lodge, above the Cadrona Valley in Wanaka (1,545 m), was used for athletes to stay and sleep before travelling down to 300 m each day to train over the experimental period. Based on changes in sea level 800 m swim time trials, athletes were separated into responders (subjects who improved their swim performance after altitude training) or non-responders (athletes whose performance decreased). A submaximal cycling test (10-min at 250 watts for males and 200 watts for females) was performed at altitude at the same time of day, on the first and last day of the training camp. Arterial oxygen saturation (SpO₂) and heart rate were taken before (0 min) and at the end (10 min) of the submaximal test. Compared to non-responders, responders had higher SpO₂ (1.2 ± 1.3%, mean ± SD) and lower heart rate, (-6.3 ± 7.8%) after 10 min of submaximal cycling. A recommendation for coaches from this research is that they could consider identifying responders and non-responders to altitude training by measuring SpO₂ and HR changes during submaximal exercise at altitude.

In studies 2 and 3 Simulated altitude training (intermittent hypoxic training: IHT) approach was used and conducted mainly at Lincoln University. In Study 2, I was interested in finding out whether altitude training (hypoxic exposure) could improve anaerobic fitness. In this study muscle strength and muscular endurance were investigated by using low-load resistance exercise (50% 1RM) combined with simulated altitude training in well trained male subjects. The simulated altitude or hypoxic training group clearly showed improvement in muscle endurance (maximal voluntary contraction force which measured as an area under 30 seconds curve; MVC₃₀) by 14.8 ± 10.4% and fatigue (measured as the decrease in force from the maximum to the minimum from over 30 seconds) improved by 12.7 ± 8.0% compared to a placebo group breathing normal room air. These findings suggest that this exercise regimen is very likely to be worthwhile for enhancing muscle endurance and reducing fatigue in well trained males. Such training may be used by coaches as a compliment to current strength training regimes.

In Study 3, I further investigated the mechanisms behind the apparent enhancement in performance after intermittent hypoxic training from study 2. In addition, I also determined the effect of local blood flow occlusion on muscular performance. To do this, low-load resistance exercise (20% 1RM), combined with either simulated altitude or local blood flow occlusions, was examined in female netball players. Relative to the control training group, both exercise regimes resulted in improvement in all muscular performance variables (maximal voluntary contraction force over 3 second; MVC₃, and over 30 seconds; MVC₃₀ and number of repetitions to be performed at 20% 1RM; Reps201RM ) after five weeks training. Muscle cross-sectional area also significantly increased after training with both blood occlusion (6.6 ± 4.5%) and intermittent hypoxia (6.1 ± 5.1%) compared to training control group (2.9 ± 2.7%). This study indicated that the hypoxic conditions of the muscles, caused by either hypoxia or blood occlusion, may be involved in these positive performance outcomes.

In conclusion, breathing air with a low partial pressure of oxygen due to decreased barometric pressure (real altitude exposure) can result in beneficial aerobic performance changes in some athletes. Additionally, breathing a low partial pressure of oxygen intermittently in a normobaric environment (simulated altitude) can improve anaerobic-based performance such as MVC over 30 seconds and number of repetitions at 50% 1RM. However, considerable variation exists in subjects’ response to such training. Likely indicators for detecting positive adaptation for athletes at altitude are positive changes in oxygen saturation in arterial blood (SpO₂) and heart rate during a 10 minute submaximal cycle test. In addition, the muscle strength and endurance enhancement found in study 2 and 3 suggests intermittent hypoxia may have a beneficial effect on anaerobic performance mechanisms perhaps through changes in neuromuscular recruitment or metabolic changes within the muscles. This research has found that performance (aerobic or anaerobic) improvement seen with altitude training may in part be due to changes resulting from tissue hypoxia. It is clear however, that not all athletes respond in the same way.