Durability of the moderate-to-heavy-intensity transition is related to the effects of prolonged exercise on severe-intensity performance.

PURPOSE: Power output at the moderate-to-heavy-intensity transition decreases during prolonged exercise, and resilience to this has been termed 'durability'. The purpose of this study was to assess the relationship between durability and the effect of prolonged exercise on severe-intensity performance, and explore intramuscular correlates of durability. METHODS: On separate days, 13 well-trained cyclists and triathletes (V̇O2peak, 57.3 ± 4.8 mL kg-1 min-1; training volume, 12 ± 2.1 h week-1) undertook an incremental test and 5-min time trial (TT) to determine power output at the first ventilatory threshold (VT1) and severe-intensity performance, with and without 150-min of prior moderate-intensity cycling. A single resting vastus lateralis microbiopsy was obtained. RESULTS: Prolonged exercise reduced power output at VT1 (211 ± 40 vs. 198 ± 39 W, ∆ -13 ± 16 W, ∆ -6 ± 7%, P = 0.013) and 5-min TT performance (333 ± 75 vs. 302 ± 63 W, ∆ -31 ± 41 W, ∆ -9 ± 10%, P = 0.017). The reduction in 5-min TT performance was significantly associated with durability of VT1 (rs = 0.719, P = 0.007). Durability of VT1 was not related to vastus lateralis carnosine content, citrate synthase activity, or complex I activity (P > 0.05). CONCLUSION: These data provide the first direct support that durability of the moderate-to-heavy-intensity transition is an important performance parameter, as more durable athletes exhibited smaller reductions in 5-min TT performance following prolonged exercise. We did not find relationships between durability and vastus lateralis carnosine content, citrate synthase activity, or complex I activity.

Plasma Acidosis and Peak Power after a Supramaximal Trial in Elite Sprint and Endurance Cyclists: Effect of Bicarbonate.

PURPOSE: This study aimed to determine whether (i) a plasma acidosis contributes to a reduction of mechanical performance and (ii) bicarbonate supplementation blunts plasma acidosis and arterial oxygen desaturation to resist fatigue during the end spurt of a supramaximal trial in elite sprint and endurance cyclists. METHODS: Elite/world-class cyclists ( n = 6 sprint, n = 6 endurance) completed two randomized, double-blind, crossover trials at 105%V̇O 2peak simulating 3 min of a 4-km individual pursuit, 90 min after ingestion of 0.3 g·kg -1 BM sodium bicarbonate (BIC) or placebo (PLA). Peak power output (PPO), optimal cadence and optimal peak torque, and fatigue were assessed using a 6-s "all-out sprint" before (PPO1) and after (PPO2) each trial. Plasma pH, bicarbonate, lactate - , K + , Na + , Ca 2+ , and arterial hemoglobin saturation (SpO 2 (%)), were measured. RESULTS: Sprint cyclists exhibited a higher PPO, optimal pedal torque, and anaerobic power reserve (APR) than endurance cyclists. The trial reduced PPO (PLA) more for sprint (to 47% initial) than endurance cyclists (to 61% initial). Optimal cadence fell from ~151 to 92 rpm and cyclists with higher APR exhibited a reduced optimal peak torque. Plasma pH fell from 7.35 to 7.13 and plasma [lactate - ] increased from 1.2 to 19.6 mM (PLA), yet neither correlated with PPO loss. Sprint cyclists displayed a lesser plasma acidosis but greater fatigue than endurance cyclists. BIC increased plasma [HCO 3- ] (+6.8 mM) and plasma pH after PPO1 (+0.09) and PPO2 (+0.07) yet failed to influence mechanical performance. SpO 2 fell from 99% to 96% but was unrelated to the plasma acidosis and unaltered with BIC. CONCLUSIONS: Plasma acidosis was not associated with the decline of PPO in a supramaximal trial with elite cyclists. BIC attenuated acid-base disturbances yet did not improve arterial oxygen desaturation or mechanical performance at the end-spurt stage.

The Importance of 'Durability' in the Physiological Profiling of Endurance Athletes.

Profiling physiological attributes is an important role for applied exercise physiologists working with endurance athletes. These attributes are typically assessed in well-rested athletes. However, as has been demonstrated in the literature and supported by field data presented here, the attributes measured during routine physiological-profiling assessments are not static, but change over time during prolonged exercise. If not accounted for, shifts in these physiological attributes during prolonged exercise have implications for the accuracy of their use in intensity regulation during prolonged training sessions or competitions, quantifying training adaptations, training-load programming and monitoring, and the prediction of exercise performance. In this review, we argue that current models used in the routine physiological profiling of endurance athletes do not account for these shifts. Therefore, applied exercise physiologists working with endurance athletes would benefit from development of physiological-profiling models that account for shifts in physiological-profiling variables during prolonged exercise and quantify the 'durability' of individual athletes, here defined as the time of onset and magnitude of deterioration in physiological-profiling characteristics over time during prolonged exercise. We propose directions for future research and applied practice that may enable better understanding of athlete durability.