Inspiratory muscle training (IMT) may have an additional effect on cardiovascular autonomic modulation, which could improve the metabolism and vascular function of the muscles. Aim: To determine the effects of IMT on vascular and metabolic muscle changes and their relationship to changes in physical performance. Methods: Physically active men were randomly placed into an experimental (IMTG; n = 8) or IMT placebo group (IMTPG; n = 6). For IMT, resistance load was set at 50% and 15% of the maximum dynamic inspiratory strength (S-Index), respectively. Only the IMTG’s weekly load was increased by 5%. In addition, both groups carried out the same concurrent training. Besides the S-Index, a 1.5-mile running test, spirometry, and deoxyhemoglobin (HHbAUC during occlusion) and reperfusion tissue saturation index (TSIMB and TSIMP: time from minimum to baseline and to peak, respectively) in a vascular occlusion test were measured before and after the 4-week training program. In addition, resting heart rate and blood pressure were registered. Results: IMTG improved compared to IMTPG in the S-Index (Δ = 28.23 ± 26.6 cmH2O), maximal inspiratory flow (MIF: Δ = 0.91 ± 0.6 L/s), maximum oxygen uptake (Δ = 4.48 ± 1.1 mL/kg/min), 1.5-mile run time (Δ = −0.81 ± 0.2 s), TSIMB (Δ = −3.38 ± 3.1 s) and TSIMP (Δ = −5.88 ± 3.7 s) with p < 0.05. ΔVO2max correlated with S-Index (r = 0.619) and MIF (r = 0.583) with p < 0.05. Both ΔTSIMB and TSIMP correlated with ΔHHbAUC (r = 0.516 and 0.596, respectively) and with Δ1.5-mile run time (r = 0.669 and 0.686, respectively) with p < 0.05. Conclusion: IMT improves vascular function, which is related to additional improvements in physical performance.