Provided are methods for enhancing exercise (e.g., intense, eccentric, elevated temperature, repetitive, aerobic, and high altitude) performance, comprising administering electrokinetically-altered aqueous fluids comprising an ionic aqueous solution of stably configured charge-stabilized oxygen-containing nanostructures predominantly having an average diameter of less than 100 nanometers. In certain aspects, enhancing exercise performance comprises at least one of: reducing plasma inflammatory cytokines (e.g., IFN-alpha, ENA-78 and BDNF); ameliorating muscle/tendon damage or enhancing muscle/tendon recovery; reducing biomarkers of exercise-induced muscle injury (e.g., CK, plasma myoglobin); ameliorating exercise induced tendinosis, tendonitis, tenosynovitis, avulsion, and tendon strain associated with chronic repetitive movement or enhancing recovering therefrom; increasing VO2 max; decreasing RPE; reducing blood lactate; preserving muscle contractile function (e.g., maximal force, joint ROM); reducing muscle soreness; ameliorating onset of fatigue in an excercising subject. Improved methods for producing electrokinetically altered aqueous fluids (including sports beverages) are also provided.