The effect of ischemic preconditioning (IPC) on swimming performance was examined. Using a randomized, crossover design, National-and International-level swimmers (n=20; 14 males, 6 females) participated in three trials (Con, IPC-2h, IPC-24h). Lower-body IPC (4 x 5 min bi-lateral blood-flow restriction at 160-228 mmHg, and 5 min reperfusion) was used 2- (IPC-2h) or 24-h (IPC-24h) before a self-selected (100 m, n=15; 200 m, n=5) swimming time-trial (TT). The Con trial used a sham intervention (15 mmHg) 2h prior to exercise. All trials required a 40-min standardized pre-competition swimming warm-up (followed by 20-min rest; replicating pre-competition call room procedures) 1h before TT. Capillary blood (pH, blood gases and lactate concentrations) was taken immediately pre-and post-IPC, pre-TT and post-TT. No effects on TT for 100 m (P=0.995; IPC-2h: 64.94±8.33 s; IPC-24h: 64.67±8.50 s; Con: 64.94± 8.24 s), 200 m (P=0.405; IPC-2h: 127.70±10.66 s; IPC-24h: 129.26±12.99 s; Con: 130.19±10.27 s) or combined total time (IPC-2h: 84.27±31.52 s; IPC-24h: 79.87±29.72 s; Con: 80.55±31.35 s) were observed following IPC. Base excess (IPC-2h: -13.37±8.90 mmol⋅L; Con: -13.35±7.07 mmol⋅L; IPC-24h: -16.53±4.65 mmol⋅L), pH (0.22±0.08; all conditions), bicarbonate (IPC-2h: -11.66±3.52 mmol⋅L; Con: -11.62±5.59 mmol⋅L; IPC-24h: -8.47±9.02 mmol⋅L), total carbon dioxide (IPC-2h: -12.90±3.92 mmol⋅L; Con: -11.55±7.61 mmol⋅L; IPC-24h: 9.90±8.40 mmol⋅L), percentage oxygen saturation (IPC-2h: -0.16±1.86%; Con: +0.20±1.93%; IPC-24h: +0.47±2.10%) and blood lactate (IPC-2h: +12.87±3.62 mmol⋅L; Con: +12.41±4.02 mmol⋅L; IPC-24h: +13.27±3.81 mmol⋅L) were influenced by swimming TT (P<0.001), but not condition (all P>0.05). No effect of IPC was seen when applied 2- or 24-h before swimming TT on any indices of performance or physiological measures recorded.