Splenic contraction induced by repeated apneas has been shown to increase oxygen availability. Our aim was to determine whether repeated maximal voluntary apnea enhances the performance of cyclists in a subsequent 4-km time trial. Seven male cyclists [age: 27.1 +/- A 2.1 years; height: 182 +/- A 8 cm; body mass: 74.8 +/- A 9.2 kg; peak oxygen uptake: 56.9 +/- A 6.6 mL min(-1) kg(-1) (mean +/- A SD)] performed a 4-km time trial on an ergometer with and without four prior maximal bouts of apnea interspersed with 2 min of recovery. The average power output during the time trial was similar with (293 +/- A 48 W) and without (305 +/- A 42 W) prior apnea (P = 0.11, d = 0.27). The spleen was reduced in size after the fourth bout of apnea (-12.4 +/- A 9.0 %), as well as one (-36.6 +/- A 10.3 %) and 10 min (-19.5 +/- A 17.9 %) after the time trial, while with normal breathing the spleen was smaller one (-35.0 +/- A 11.3 %) and 10 min (-23.4 +/- A 19.7 %) after the time trial. Heart rate; oxygen uptake and carbon dioxide production; tissue oxygen saturation; and the lactate concentration, pH, oxygen saturation, level of hemoglobin and hematocrit of the blood were similar under both conditions. Our present findings reveal that four apneas by cyclists prior to a 4-km time trial led to splenic contraction, but no change in mean power output, the level of hemoglobin, hematocrit, oxygen saturation of the m. vastus lateralis or oxygen uptake.