The project represents a well powered study of the human response to altitude exposure combined with rHuEPO treatment. A total of 20 male and 20 female non-competing athletes will participate. The participants will be exposed to a period of hypobaric hypoxia at 2.320 m for four weeks and a sea-level intervention period of four weeks. The participants will be blinded and randomly allocated to intra venous injection with 20 IU per kg body weight of recombinant human erythropoietin or placebo every second day for the initial three weeks of each intervention. Included subjects will be runners due to the good possibility of recruitment and conduction of training at altitude. Samples are collected weekly for four weeks prior to each intervention period, during the four week intervention and four weeks after. This approach yields a highly valuable biobank for identification of markers sensitive to initiation of rHuEPO injections as well as termination of injections.

The main hypothesis for this study is that metabolomics and proteomics methods can identify biomarkers that are sensitive to altitude exposure and recombinant human erythropoietin treatment, respectively. Secondarily, the hypothesis is that the identified biomarkers can distinguish between altitude exposure and abuse of rHuEPO.

We will include 20 Danish men and 20 Danish women aged 18-35 years. The inclusion criteria are a maximum oxygen uptake rate (VO2max) > 48 ml / kg / min for men and > 43 ml / kg / min for women. All trial participants must have > 2 years of history in regular exercise including running (> 2 times a week; > 30 min per session) and capable of performing a 5 km run in 22 min for men and 25 min for women at sea level on a level surface in dry conditions and a temperature between 10 and 20 degrees C. Furthermore, the participants must not have experienced running related injuries within the past two years.

The experimental protocol consists of two experimental periods, both of which must be performed by all participants. Both periods contain a baseline period of four weeks followed by four weeks training camp and four weeks follow up. The training camp in one period of experiments is performed at sea level while the training camp in the other period is performed at 2320 m above sea level. Each period is separated by a minimum of two months to ensure that the participants have returned to baseline values. During the two intervention periods, the participants will be transported by air and car to the destination of the respective training camp. It is expected that the participants train for 1-2 hours a day on average and that the time spent for the measurements described is ~ 5-7 hours a week.

To investigate whether the described methods can identify sensitive biomarkers for the physiological response due to rHuEPO treatment, the participants will be treated with rHuEPO.

The distribution of participants allows the following:

• 28 participants receive rHuEPO at sea level, thereby identifying biomarkers sensitive for use of rHuEPO
• 28 participants receive placebo under altitude exposure, whereby biomarkers sensitive to altitude exposure can be identified
• 12 participants receive placebo at sea level, whereby random fluctuations of the identified biomarkers can be determined.
• 12 participants receive rHuEPO under altitude exposure, whereby the identified rhuEPO biomarkers and altitude exposure can be tested for whether they can be used to separate individuals receiving rHuEPO under altitude exposure from individuals receiving placebo under altitude exposure.
• 8 participants receive placebo at sea level and altitude exposure, whereby natural and random individual fluctuations can be determined over a longer period (> 6 months). Since random individual fluctuations can be determined at n = 1, n = 8 will be sufficient to determine this.

Inclusion Criteria:

• Male: VO2max > 48 ml/min/kg bodyweight and 5km run < 22 min, Female: VO2max > 43ml/min/kg bodyweight and 5km run < 25 min A minimum of 2 years injury running training

Exclusion Criteria:

• Age, insufficient fitness or injury

Fully anonymous data will be shared with other researchers.