Influence of Caffeine on Heart Rate Variability and Exercise Performance in in Tetraplegic and Paraplegic Subjects Compared to Able-bodied Subjects

This study will be conducted in a placebo-controlled, double-blind and randomised study protocol. Every subject has to undergo three test session at the sports medicine in Nottwil. At the first visit, the investigators will check the subjects fitness using a health questionnaire with specific question about diseases and family health history. Additionally, subjects has to perform a maximal exercise test (ramp protocol at the arm crank ergometer) to measure maximal oxygen uptake, maximal heart rate and maximal power output. After a little break, subjects have to perform a familiarization trial at the arm crank ergometer. They have to perform exactly the same test as they have to perform later in the two test sessions.

Minimum two days later the subjects visits the sports medicine Nottwil for the first test session. At first, they have to answer some specific question about sleep, recent training, recent nutritional intake and the actual health condition. Afterwards, they have to lie down for a 10min rest where after 9min blood pressure will be measured. With a heart rate monitor HRV will be measured during 5 min in supine position and afterwards during 6 min in sitting position. Metronomic breathing (15x/min) is mandatory and will be simulated through a metronome. During the HRV measurement also tidal volume will be measured. As the first HRV measurement session is finished, a blood withdrawal will be taken to measure catecholamine concentrations. Then, when all these measurements are completed, a supplement (either caffeine or the placebo) will be ingested in gelatine capsules. After the ingestion of these capsules, the subject has a 40 min break where they can read something or just relax. During these 40 min physical activity or the ingestion of any nutrition is prohibited.

After these 40min, the second HRV measurement starts. The process of this measurement is exactly the same as for the first HRV measurement. They lay down for a 10min rest with blood pressure measurement after 9 min. Afterwards again a 5min HRV measurement in supine position and a 6min measurement in sitting position. Tidal volume is measured during this HRV measurement.

When this second HRV measurement session is finished, a second blood withdrawal has to be taken. That means, one hour after the ingestion of either placebo or caffeine, catecholamine are analysed for a second time. If the blood is taken, the warm up can start. After the standardised warm up lactate concentration of the blood is analysed taking 10 ul of blood from the earlobe. The subject will be asked to evaluate the warm up with the rate of perceived exertion (following the Borg scale). If everything is in order, the 3min exercise test can start. During this test, respiratory parameters will be measured using an Oxycon Pro device (device to measure oxygen consumption). Just after having finished these 3 min of exercising, for a second time lactate concentration will be measured and again they have to rate the exertion using the Borg scale.

After a short 5min break the third HRV measurement starts. Again HRV will be measured during a 5min time in supine position and a 6min time in sitting position. Tidal volume will be measured during the whole HRV measurement. With this HRV measurement the first test session is finished and a second test session will be conducted at least more than two days later in a randomised manner.