Endurance exercise begun with reduced muscle glycogen stores seems to potentiate skeletal muscle protein abundance and gene expression. However, it is unknown whether this greater signaling responses is due to performing two exercise sessions in close proximity—as a first exercise session is necessary to reduce the muscle glycogen stores. In the present study, we manipulated the recovery duration between a first muscle glycogen‐depleting exercise and a second exercise session, such that the second exercise session started with reduced muscle glycogen in both approaches but was performed either 2 or 15 hours after the first exercise session (so‐called “twice‐a‐day” and “once‐daily” approaches, respectively). We found that exercise twice‐a‐day increased the nuclear abundance of transcription factor EB (TFEB) and nuclear factor of activated T cells (NFAT) and potentiated the transcription of peroxisome proliferator‐activated receptor‐ɣ coactivator 1‐alpha (PGC‐1α), peroxisome proliferator‐activated receptor‐alpha (PPARα), and peroxisome proliferator‐activated receptor beta/delta (PPARβ/δ) genes, in comparison with the once‐daily exercise. These results suggest that part of the elevated molecular signaling reported with previous “train‐low” approaches might be attributed to performing two exercise sessions in close proximity. The twice‐a‐day approach might be an effective strategy to induce adaptations related to mitochondrial biogenesis and fat oxidation.

Caffeine increased total work done above CP, but this was not associated with greater anaerobic work. Rather, this was associated with a higher tolerance to maintain exercise at maximal oxidative metabolic rate.

Exercise training performed with lowered muscle glycogen stores can amplify adaptations related to oxidative metabolism, but it is not known if this is affected by the “train-low” strategy used (i.e., once-daily versus twice-a-day training). Fifteen healthy men performed 3 wk of an endurance exercise (100-min) followed by a high-intensity interval exercise 2 (twice-a-day group, n = 8) or 14 h (once-daily group, n = 7) later; therefore, the second training session always started with low muscle glycogen in both groups. Mitochondrial efficiency (state 4 respiration) was improved only for the twice-a-day group (group × training interaction, P < 0.05). However, muscle citrate synthase activity, mitochondria, and lipid area in intermyofibrillar and subsarcolemmal regions, and PGC1α, PPARα, and electron transport chain relative protein abundance were not altered with training in either group ( P > 0.05). Markers of aerobic fitness (e.g., peak oxygen uptake) were increased, and plasma lactate, O2 cost, and rating of perceived exertion during a 100-min exercise task were reduced in both groups, although the reduction in rating of perceived exertion was larger in the twice-a-day group (group × time × training interaction, P < 0.05). These findings suggest similar training adaptations with both training low approaches; however, improvements in mitochondrial efficiency and perceived effort seem to be more pronounced with twice-a-day training. NEW & NOTEWORTHY We assessed, for the first time, the differences between two “train-low” strategies (once-daily and twice-a-day) in terms of training-induced molecular, functional, and morphological adaptations. We found that both strategies had similar molecular and morphological adaptations; however, only the twice-a-day strategy increased mitochondrial efficiency and had a superior reduction in the rating of perceived exertion during a constant-load exercise compared with once-daily training. Our findings provide novel insights into skeletal muscle adaptations using the “train-low” strategy.

Endurance exercise begun with reduced muscle glycogen stores seems to potentiate skeletal muscle protein abundance and gene expression. However, it is unknown whether this greater signaling responses is due to performing two exercise sessions in close proximity—as a first exercise session is necessary to reduce the muscle glycogen stores. In the present study, we manipulated the recovery duration between a first muscle glycogen‐depleting exercise and a second exercise session, such that the second exercise session started with reduced muscle glycogen in both approaches but was performed either 2 or 15 hours after the first exercise session (so‐called “twice‐a‐day” and “once‐daily” approaches, respectively). We found that exercise twice‐a‐day increased the nuclear abundance of transcription factor EB (TFEB) and nuclear factor of activated T cells (NFAT) and potentiated the transcription of peroxisome proliferator‐activated receptor‐ɣ coactivator 1‐alpha (PGC‐1α), peroxisome proliferator‐activated receptor‐alpha (PPARα), and peroxisome proliferator‐activated receptor beta/delta (PPARβ/δ) genes, in comparison with the once‐daily exercise. These results suggest that part of the elevated molecular signaling reported with previous “train‐low” approaches might be attributed to performing two exercise sessions in close proximity. The twice‐a‐day approach might be an effective strategy to induce adaptations related to mitochondrial biogenesis and fat oxidation.

We investigated whether caffeine ingestion before submaximal exercise bouts would affect supramaximal oxygen demand and maximal accumulated oxygen deficit (MAOD), and if caffeine-induced improvement on the anaerobic capacity (AC) could be detected by different methods. Nine men took part in several submaximal and supramaximal exercise bouts one hour after ingesting caffeine (5 mg·kg-1) or placebo. The AC was estimated by MAOD, alternative MAOD, critical power, and gross efficiency methods. Caffeine had no effect on exercise endurance during the supramaximal bout (caffeine: 131.3 ± 21.9 and placebo: 130.8 ± 20.8 s, P = 0.80). Caffeine ingestion before submaximal trials did not affect supramaximal oxygen demand and MAOD compared to placebo (7.88 ± 1.56 L and 65.80 ± 16.06 kJ vs. 7.89 ± 1.30 L and 62.85 ± 13.67 kJ, P = 0.99). Additionally, MAOD was similar between caffeine and placebo when supramaximal oxygen demand was estimated without caffeine effects during submaximal bouts (67.02 ± 16.36 and 62.85 ± 13.67 kJ, P = 0.41) or when estimated by alternative MAOD (56.61 ± 8.49 and 56.87 ± 9.76 kJ, P = 0.91). The AC estimated by gross efficiency was also similar between caffeine and placebo (21.80 ± 3.09 and 20.94 ± 2.67 kJ, P = 0.15), but was lower in caffeine when estimated by critical power method (16.2 ± 2.6 vs. 19.3 ± 3.5 kJ, P = 0.03). In conclusion, caffeine ingestion before submaximal bouts did not affect supramaximal oxygen demand and consequently MAOD. Otherwise, caffeine seems to have no clear positive effect on AC.

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