Intense exercise evokes a spleen contraction
releasing red blood cells into blood circulation. The same mechanism is found following acute apnea, increasing [Hb] by 2 to 5%. The aim of this study was twofold:  to identify the optimal apnea modalities to acutely increase [Hb] and  use these modalities to examine whether pre-race apnea can improve a 3km time trial (TT).
In part one, 11 male subjects performed 12 different apnea protocols based on 3 modalities: mode, frequency and intensity. Venous blood samples for [Hb] were collected before, immediately and 5 minutes after each protocol. In part two, 12 recreationally active subjects performed 3km cycling TT in 3 different conditions: apnea, control and placebo, following a 10 minute warm-up. Power output, heart rate and oxygen uptake (V[Combining Dot Above]O2
) were continuously measured. Venous [Hb] was sampled at baseline, after warm-up and before TT. Additionally, these subjects performed constant cycling at Δ25 (25% between GET and V[Combining Dot Above]O2
max) in two conditions (control and apnea) to determine V[Combining Dot Above]O2
Although including one single apnea in the warming up evoked a positive change in [Hb] pattern (p=0.049) and one single apnea seemed to improve V[Combining Dot Above]O2
kinetics in constant submaximal cycling (τ: p=0.060, mean response time: p=0.064), performance
during the 3km TT did not differ between conditions (p=0.840, apnea: 264.8 ± 14.1s; control: 263.9 ± 12.9s, placebo: 264.0 ± 15.8s). Average normalized power output (p=0.584) and V[Combining Dot Above]O2
, heart rate and lactate did not differ either (p>0.05).
These results suggest that potential effects of apnea, i.e. speeding of V[Combining Dot Above]O2
kinetics through a transient increase in [Hb], are overruled by a warming-up protocol.