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Hypoxia is known to reduce isometric contractile properties of isolated rat diaphragm bundles. Its effect on isotonic contractile properties (i.e. force-velocity relationship and power output) has not been studied. We hypothesized that hypoxia reduces velocity of shortening and consequently power output of the unfatigued muscle, and shortens endurance time during isotonic contractions. Force-velocity relationship, power output, and fatigue resistance of rat diaphragm muscle bundles were measured during hypoxia (PO2: 6.6 +/- 0.2 kPa) and compared with hyperoxia (PO2: 91.8 +/- 0.7 kPa). Force was clamped from 1 to 100% of maximal tetanic force (Po). Fatigue during isotonic contractions was induced by repeated stimulation every 2 s at a clamp level of 33% of Po. Hypoxia did not affect isometric force generation compared with hyperoxia, nor contraction or relaxation time. In contrast, maximum shortening velocity decreased significantly (hypoxia: 4.2 +/- 0.3, hyperoxia: 6.0 +/- 0.2 Lo/s, P < 0.05). The force-velocity curve shifted downwards (P < 0.05). Hypoxia lowered power output at each load compared with hyperoxia (P < 0.05). The isotonic endurance time was shorter during hypoxia compared with hyperoxia (80 +/- 2 vs. 130 +/- 3 s, P < 0.05). These data show that hypoxia depresses isotonic contractile properties and power output, and reduces endurance time during repeated isotonic contractions.

Doping is an area of ongoing public, legal, and medical debate and in recent years it has been reported to be connected with many sports including athletics, cycling, body building, soccer, and swimming. Ethical issues related to doping include the honesty of the sports competition and the safety of drugs and other methods applied to improve the physical performance. These issues are of increasing interest and importance since drugs on the prohibited list are easily accessible by medically uncontrolled means such as the Internet. According to the International Olympic Committee (IOC)1doping consists of (1) the administration of substances belonging to prohibited classes of pharmacological agents and/or (2) the use of various prohibited methods. There are five prohibited classes of substances: stimulants, narcotics, anabolic agents, diuretics, and peptide and glycoprotein hormones and their analogues (table 1). Prohibited methods include blood doping and pharmacological, chemical and physical manipulation. View this table: Table 1 Prohibited classes of substances and prohibited methods (shortened and adapted from IOC1) Several respiratory drugs are included in the list of prohibited substances unless they are administered by inhalation. This paper reviews the current literature concerning the effects of respiratory and some other drugs on the respiratory system in the broadest sense—that is, from the respiratory controllers to the respiratory muscles and the lungs themselves. We will focus on the effects in athletes and healthy trained and untrained subjects but, where appropriate, we will also refer to studies in patients, to animal studies, and to studies in peripheral skeletal muscles. In general, the respiratory system does not limit maximal oxygen consumption (V˙o 2max) in healthy subjects.2 3 Only in highly trained endurance athletes may blood oxygen saturation fall during heavy exercise.4 5 The maximal sustainable ventilation decreases with time, and the level that can be sustained …