During transition from rest to exercise, metabolic reaction rates increase substantially to sustain intracellular ATP use. These metabolic demands activate several kinases that initiate signal transduction pathways which modulate transcriptional regulation of mitochondrial biogenesis. The purpose of this study was to determine whether metabolic fluctuations per se affect the signaling cascades known to regulate peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α). On two separate occasions, nine men performed a continuous (30-min) and an intermittent exercise (30 × 1-min intervals separated by 1-min of recovery) at 70% of . Skeletal muscle biopsies from the vastus lateralis were taken at rest and at +0 h and +3 h after each exercise. Metabolic fluctuations that correspond to exercise-induced variation in metabolic rates were determined by analysis of VO2 responses. During intermittent exercise metabolic fluctuations were 2.8-fold higher despite identical total work done to continuous exercise (317 ± 41 vs. 312 ± 56 kJ after intermittent and continuous exercise, respectively). Increased phosphorylation of AMP-activated protein kinase (AMPK) (˜2.9-fold, P < 0.01), calcium/calmodulin-dependent protein kinase II (CaMKII) (˜2.7-fold, P < 0.01) and p38-mitogen-activated protein kinase (MAPK) (˜4.2-fold, P < 0.01) occurred immediately in both exercises and to a greater extent after the intermittent exercise (condition x time interaction, P < 0.05). A single bout of intermittent exercise induces a greater activation of these signaling pathways regulating PGC-1α when compared to a single bout of continuous exercise of matched work and intensity. Chronic adaptations to exercise on mitochondria biogenesis are yet to be investigated.
BackgroundWhile continuous exercise (CE) induces greater ventilation (E) when compared to intermittent exercise (IE), little is known of the consequences on airway damage. Our aim was to investigate markers of epithelial cell damage – i.e. serum levels of CC16 and of the CC16/SP-D ratio - during and following a bout of CE and IE of matched work.MethodsSixteen healthy young adults performed a 30-min continuous (CE) and a 60-min intermittent exercise (IE; 1-min work: 1-min rest) on separate occasions in a random order. Intensity was set at 70% of their maximum work rate (WRmax). Heart rate (HR) and E were measured throughout both tests. Blood samples were taken at rest, after the 10th min of the warm-up, at the end of both exercises, half way through IE (matched time but 50% work done for IE) as well as 30- and 60-min post-exercise. Lactate and CC16 and SP-D were determined.ResultsMean E was higher for CE compared to IE (85 ± 17 l.min− 1 vs 50 ± 8 l.min− 1, respectively; P < 0.001). Serum-based markers of epithelial cell damage remained unchanged during IE. Interaction of test × time was observed for SP-D (P = 0.02), CC16 (μg.l− 1) (P = 0.006) and CC16/SP-D ratio (P = 0.03). Maximum delta CC16/SP-D was significantly correlated with mean E sustained (r = 0.83, P < 0.001) during CE but not during IE.ConclusionThe 30-min CE performed at 70% WRmax induced mild airway damage, while a time- or work-matched IE did not. The extent of the damage during CE was associated with the higher ventilation rate.
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The succession of on-transient phases that induce a repetition of metabolic changes is a possible mechanism responsible for the greater response to intermittent training (IT). The objective of this study was to quantify [Formula: see text] fluctuations during intermittent exercise characterised by the same work:rest ratio, but different durations and identify which duration leads to the greatest fluctuations. Ten participants (24 ± 5 years; [Formula: see text]: 42 ± 7 mL·min·kg) performed (1) an incremental test to exhaustion to determine peak work rate (WR) and oxygen uptake ([Formula: see text]), (2), and three 1 h intermittent exercises alternating work period at 70% WR with passive recovery period of different 1:1 work:recovery duty cycles (30 s:30 s, 60 s:60 s, 120 s:120 s). [Formula: see text] response analysis revealed differences in the fluctuations across the intermittent conditions despite an identical total energy expenditure. The sum of the cycle's nadir-to-peak [Formula: see text] differences (ΣΔ[Formula: see text]) and the oxygen fluctuation index (OFI) were both greater in the 60 s:60 s condition (ΣΔ[Formula: see text]: +38% ± 13% and +19% ± 18% vs. 120 s:120 s and 30 s:30 s, P < 0.05; OFI: +41% ± 29% and +67% ± 62% vs. 120 s:120 s and 30:30 s, P < 0.05). [Formula: see text] fluctuation analysis was successful in identifying the intermittent condition associated with the greatest disturbances: the 60 s:60 s duty cycle induces more [Formula: see text] fluctuations. The present findings also demonstrate that the selection of the duty cycle duration for submaximal intermittent exercise (70% of WR) prescription is of interest to produce high [Formula: see text] fluctuations.
VO2 fluctuations are argued to be an important mechanism underpinning chronic adaptations following interval training. We compared the effect of exercise modality, continuous vs. intermittent realized at a same intensity, on electrical muscular activity, muscular oxygenation and on whole body oxygen uptake. Twelve participants (24 ± 5 years; VO2peak: 43 ± 6 mL· min·kg) performed (i) an incremental test to exhaustion to determine peak work rate (WR); two randomized isocaloric exercises at 70%WRpeak; (ii) 1 bout of 30 min; (iii) 30 bouts of 1 min work intercepted with 1 min passive recovery. For electromyography, only the CON exercise showed change for the vastus lateralis root-mean-square (+6.4 ± 5.1%, P < .01, 95%CI 3.2, 8.3) and mean power frequency (-5.2 ± 4.8, P < .01, 95%CI -8.2, -3.5). Metabolic fluctuations (i.e. Oxygen Fluctuation Index and HHb Fluctuation Index) were higher in the intermittent modality, while post-exercise blood lactate concentrations (4.80 ± 1.50 vs. 2.32 ± 1.21 mM, respectively, for the CON and INT, P < .01, 95%CI 1.72, 3.12) and the time spent over 90% of VO2 target (1644 ± 152 vs. 356 ± 301 sec, respectively, for the CON and INT, P < .01, 95%CI 1130, 1446) were higher in the continuous modality. In conclusion, despite a similar energy expenditure and intensity, intermittent and continuous exercises showed two very different physiological responses. The intermittent modality would lead to a larger recruitment of fast twitch fibres that are less mitochondria-equipped and therefore may be more likely respondent to mitochondrial adaptations. In addition, this modality induces greater metabolic variations, a stimulus who could lead to mitochondrial development.
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