During heavy and severe constant-load exercise, VO₂ displays a slow component (VO_2sc) typically interpreted as a loss of efficiency of locomotion. In the ongoing debate on the underpinnings of the VO_2sc, recent studies suggested that VO_2sc could be attributed to a prolonged shift in energetic sources rather than loss of efficiency. We tested the hypothesis that the total cost of cycling, accounting for aerobic and anaerobic energy sources, is affected by time during metabolic transitions in different intensity domains. Eight active men performed 3 constant load trials of 3, 6, and 9 min in the moderate, heavy, and severe domains (i.e., respectively below, between, and above the two ventilatory thresholds). VO₂, VO₂ of ventilation and lactate accumulation ([La⁻]) were quantified to calculate the adjusted oxygen cost of exercise (AdjO_2Eq, i.e., measured VO₂ − VO₂ of ventilation + VO₂ equivalent of [La⁻]) for the 0–3, 3–6, and 6–9 time segments at each intensity, and compared by a two-way RM-ANOVA (time × intensity). After the transient phase, AdjO_2Eq was unaffected by time in moderate (ml*3 min⁻¹ at 0–3, 0–6, 0–9 min: 2126 ± 939 < 2687 ± 1036, 2731 ± 1035) and heavy (4278 ± 1074 < 5121 ± 1268, 5225 ± 1123) while a significant effect of time was detected in the severe only (5863 ± 1413 < 7061 ± 1516 < 7372 ± 1443). The emergence of the VO_2sc was explained by a prolonged shift between aerobic and anaerobic energy sources in heavy (VO₂ − VO₂ of ventilation: ml*3 min⁻¹ at 0–3, 0–6, 0–9 min: 3769 ± 1128 < 4938 ± 1256, 5091 ± 1123, [La⁻]: 452 ± 254 < 128 ± 169, 79 ± 135), while a prolonged metabolic shift and a true loss of efficiency explained the emergence of the VO_2sc in severe.

在重度和剧烈的恒定负荷运动期间，VO ₂显示出缓慢的成分（VO _2sc ），通常被解释为运动效率的损失。在关于 VO _2sc基础的持续争论中，最近的研究表明 VO _2sc可能归因于能源的长期转变，而不是效率的损失。我们测试了这样的假设：考虑到有氧和无氧能量来源的骑行总成本受到不同强度域代谢转变期间时间的影响。八名活跃的男性在中度、重度和重度领域（即分别低于、介于和高于两个通气阈值）进行了 3 次持续 3 分钟、6 分钟和 9 分钟的恒定负荷试验。量化 VO ₂ 、通气 VO ₂和乳酸积累 ([La ⁻ ])，以计算调整后的运动耗氧量 (AdjO _2Eq ，即测量的 VO ₂ − 通气 VO ₂ + 相当于 [La ⁻ ] 的 VO ₂ )对于每个强度的 0-3、3-6 和 6-9 时间段，并通过双向 RM-ANOVA（时间 × 强度）进行比较。过渡阶段后，AdjO _2Eq不受中度（ml*3 min ^{-1，0-3、0-6、0-9}分钟：2126 ± 939 < 2687 ± 1036、2731 ± 1035）和重度（4278 ± 1074 < 5121 ± 1268、5225 ± 1123），而仅在严重情况下检测到时间的显着影响（5863 ± 1413 < 7061 ± 1516 < 7372 ± 1443）。 VO _2sc的出现可以通过重负荷时有氧和无氧能源之间的长期转变来解释（通气的 VO ₂ − VO ₂ ：ml*3 min ⁻¹在 0–3、0–6、0–9 分钟：3769 ± 1128 < 4938 ± 1256, 5091 ± 1123, [La ⁻ ]: 452 ± 254 < 128 ± 169, 79 ± 135)，而长期的代谢变化和真正的效率损失解释了严重 VO _2sc的出现。