Time limit and V̇O(2) kinetics at maximal aerobic velocity: Continuous vs. intermittent swimming trials

The time sustained during exercise with oxygen uptake (V̇O(2)) reaching maximal rates (V̇O(2peak)) or near peak responses (i.e., above second ventilatory threshold [t@VT(2)) or 90% V̇O(2peak) (t@90%V̇O(2peak))] is recognized as the training pace required to enhance aerobic power and exercise tolerance in the severe domain (time-limit, t(Lim)). This study compared physiological and performance indexes during continuous and intermittent trials at maximal aerobic velocity (MAV) to analyze each exercise schedule, supporting their roles in conditioning planning. Twenty-two well-trained swimmers completed a discontinuous incremental step-test for V̇O(2peak), VT(2), and MAV assessments. Two other tests were performed in randomized order, to compare continuous (CT) vs. intermittent trials (IT(100)) at MAV until exhaustion, to determine peak oxygen uptake (Peak-V̇O(2)) and V̇O(2) kinetics (V̇O(2)K). Distance and time variables were registered to determine the t(Lim), t@VT(2), and t@90%V̇O(2peak) tests. Blood lactate concentration ([La(−)]) was analyzed, and rate of perceived exertion (RPE) was recorded. The tests were conducted using a breath-by-breath apparatus connected to a snorkel for pulmonary gas sampling, with pacing controlled by an underwater visual pacer. V̇O(2peak) (55.2 ± 5.6 ml·kg·min(−1)) was only reached in CT (100.7 ± 3.1 %V̇O(2peak)). In addition, high V̇O(2) values were reached at IT(100) (96.4 ± 4.2 %V̇O(2peak)). V̇O(2peak) was highly correlated with Peak-V̇O(2) during CT (r = 0.95, p < 0.01) and IT(100) (r = 0.91, p < 0.01). Compared with CT, the IT(100) presented significantly higher values for t(Lim) (1,013.6 ± 496.6 vs. 256.2 ± 60.3 s), distance (1,277.3 ± 638.1 vs. 315.9 ± 63.3 m), t@VT(2) (448.1 ± 211.1 vs. 144.1 ± 78.8 s), and t@90%V̇O(2peak) (321.9 ± 208.7 vs. 127.5 ± 77.1 s). V̇O(2)K time constants (IT(100): 25.9 ± 9.4 vs. CT: 26.5 ± 7.5 s) were correlated between tests (r = 0.76, p < 0.01). Between CT and IT(100), t(Lim) were not related, and RPE (8.9 ± 0.9 vs. 9.4 ± 0.8) and [La(−)] (7.8 ± 2.7 vs. 7.8 ± 2.8 mmol·l(−1)) did not differ between tests. MAV is suitable for planning swimming intensities requiring V̇O(2peak) rates, whatever the exercise schedule (continuous or intermittent). Therefore, the results suggest IT(100) as a preferable training schedule rather than the CT for aerobic capacity training since IT(100) presented a significantly higher t(Lim), t@VT(2), and t@90%V̇O(2peak) (∼757, ∼304, and ∼194 s more, respectively), without differing regards to [La(−)] and RPE. The V̇O(2)K seemed not to influence t(Lim) and times spent near V̇O(2peak) in both workout modes.