Participants and procedure
After ethical approval from the institutional review board according to the guidelines of Helsinki, study participants were recruited by public advertisements. Subjects signed an informed consent form prior to the study. Thirty two healthy persons, 19 women and 13 men (38.8 ± 11.8 years, min: 20 years, max: 59 years; BMI 22.7 ± 2.5 kg/m2) volunteered for the study. At least 2 previous high-altitude exposures ≥3000 m within the last 2 years and known AMS susceptibility were inclusion criteria. 88 % of the volunteers live at a height between 500 and 700 m and 12 % between 700 and 1040 m.
The high-altitude exposure took place at the Mönchsjochhut (Jungfrau-Aletsch, Switzerland) at 3650 m for the duration of 45 h. 50 % of the subjects had a placebo and 50 % an intermittent acclimatization process in the test chamber of the university. None of the subjects knew if they were intervention or control group. For the high-altitude exposure, the subjects were driven to the bottom of the Jungfraujoch (Switzerland) at an altitude of 570 m where they spent their first night. The next morning they took the railway which carried them within 50 min to a height of 3454. The last 200 m were climbed on foot within 1 h. The volunteers slept in shared rooms and filled in the questionnaires described below during the afternoon of the second day.
Measures
Affective valence was assessed by the Feeling Scale (FS) (Hardy and Rejeski 1989). This single-item rating scale ranges from +5 to −5, with anchors at zero (‘‘neutral’’) and at all odd integers, ranging from ‘‘very good’’ (+5) to ‘‘very bad’’ (−5). Subjects were asked to estimate their actual well-being by marking one number on the Scale. Convergent validity information for the FS has been provided (Hardy and Rejeski 1989; van Landuyt et al. 2000).
Perceived activation was assessed by the Felt Arousal Scale (FAS) (Sevebak and Murgatroyd 1984). This single-item rating scale ranges from 1 (‘‘low arousal’’) to 6 (‘‘high arousal’’). Volunteers were asked to note one number on the scale according to their actual arousal state. Arousal was explained through examples of high arousal states (anger, excitement, fear) or low arousal states (relaxation, boredom, calmness). The FAS has been used in previous physical activity studies, demonstrating convergent validity with other measures of perceived activation (van Landuyt et al. 2000).
The Activation Deactivation Adjective Check List (ADACL) (Thayer 1978) is a 20-item measure of two bipolar dimensions, namely Energetic Arousal (EA) and Tense Arousal (TA). EA extends from Energy (e.g., energetic, lively) to Tiredness (e.g., tired, drowsy), and TA extends from Tension (e.g., tense, jittery) to Calmness (e.g., calm, at rest). The ADACL was administered with its standard instructions and its 4-point response scale, which ranges from ‘‘definitely feel’’ to ‘‘definitely do not feel’’. Evidence for the reliability and structural validity of the ADACL has been provided (Thayer 1978). In previous research in the context of physical activity, the scales of the ADACL have shown satisfactory internal consistency, with values of Cronbach’s alpha coefficients ranging from .70 to .96 (Ekkekakis et al. 2005).
The VAS used in this study was developed for the purpose of subjective ratings of drug effects and called the Line Analogue Rating Scales for Sedation (LARS) (Hindmarch and Gudgeon 1980). In previous studies (Gudgeon and Hindmarch 1983; Subhan and Hindmarch 1985), 100 mm line analogue rating scales were used to assess perceived drug effects, whereas the mean score of the assessments was used as an index of subjective mood and sedation. In this study, the VAS included along the LARS items fatigue, drowsiness, dizziness, alertness and energetic, also the items relaxation and acute mountain sickness, which were rated on a 100 mm analogue line. Thereby the left side covered the non-occurrence of symptoms known in AMS (e.g. “not tired” or “not dizzy”), or the occurrence of symptoms oppositional to those known in AMS (e.g. “extremely awake”, “energetic”). The right side covered their most severe expansion (e.g. “extremely tired”, “extremely dizzy” or “not awake”, “extremely unenergetic”). The total VAS score is the mean of all accumulated items used by the VAS questionnaire.
The LLS (Roach et al. 1993) is filled in on a 4-point Likert scale (0–3) and consists of the five items headache, gastrointestinal symptoms, fatigue and weakness, dizziness and lightheadedness, and difficulty sleeping. For the diagnosis of AMS, headache is an obligatory criterion with at least one other symptom of the LLS and a total score of ≥3 (Roach et al. 1993). In line with other research a more valid cut-off score in presence of headache is 5 (Kayser et al. 2010; Dellasanta et al. 2007; Wagner et al. 2012).
Data analyses
Mann–Whitney U test was used to calculate group differences. A correlation test by Spearman was applied to calculate correlations between ADACL, VAS and LLS. The statistical program used was SPSS (version 21.0; SPSS Inc., Chicago, USA, 2013). The significance level was set at p < .05.