Øyvind Skattebo

• Pietzner, Maik; Uluvar, Bululca; Kolnes, Kristoffer Jensen; Jeppesen, Per Bendix; Frivold, Victoria & Skattebo, Øyvind [Show all 14 contributors for this article] (2024). Systemic proteome adaptions to 7-day complete caloric restriction in humans. Nature Metabolism. doi: 10.1038/s42255-024-01008-9.
• Clauss, Matthieu; Skattebo, Øyvind; Rasen Dæhli, Malin; Valsdottir, Thorhildur Ditta; Bastani, Nasser Ezzatkhah & Johansen, Egil Ivar [Show all 9 contributors for this article] (2023). Carbohydrate Ingestion during Prolonged Cycling Improves Next-Day Time Trial Performance and Alters Amino Acid Concentrations. Medicine & Science in Sports & Exercise. ISSN 0195-9131. 55(12), p. 2228–2240. doi: 10.1249/MSS.0000000000003264.
• Skattebo, Øyvind & Hallén, Jostein (2022). Individual variations in pre-altitude hemoglobin mass influence hemoglobin mass responses to repeated altitude sojourns. Scandinavian Journal of Medicine & Science in Sports. ISSN 0905-7188. 32(10), p. 1493–1501. doi: 10.1111/sms.14218. Full text in Research Archive Show summary

  Introduction: Previous studies have shown variable within-subject hemoglobin mass (Hbmass) responses to altitude training. We investigated whether Hbmass responses depend on individual variations in pre-altitude Hbmass during repeated altitude sojourns. Methods: Nine elite endurance athletes carried out 3–5 altitude sojourns over 17 ± 10 months (mean ± 95% confidence interval), at an altitude of 1976 ± 62 m, for 21 ± 1 days, and a total hypoxic dose of 989 ± 46 km·h, with Hbmass assessed before and after each sojourn (carbon monoxide rebreathing). The individual mean baseline was calculated as the mean of all pre-altitude Hbmass values for an athlete, and it was investigated whether the percent deviation from the individual mean baseline affected the altitude-induced Hbmass response. Results: On average, Hbmass increased by 3.4 ± 1.1% (p < 0.001) from pre- to post-altitude. The intra-individual changes in Hbmass were highly inconsistent (coefficient of variation, CV: 88%), and we found no relationship between Hbmass changes in successive altitude sojourns (r = 0.01; p = 0.735). However, the percent increase in Hbmass was highly correlated with the pre-altitude Hbmass, expressed as the percent deviation from the individual mean baseline (y = −0.7x + 3.4; r = 0.75; p < 0.001). Linear mixed-model analysis confirmed a −0.6 ± 0.2% smaller increase in Hbmass for each 1% higher pre-altitude Hbmass than the individual mean baseline (p < 0.001) after adjusting for the covariates hypoxic dose (p = 0.032) and the relative Hbmass (g·kg−1 body weight; p = 0.031). Conclusion: Individual variations in pre-altitude Hbmass significantly influence the athletes' Hbmass responses to repeated altitude sojourns, with a potentiated response after traveling to altitude with a low pre-altitude Hbmass.

• Skattebo, Øyvind; Peci, Dafina; Clauss, Matthieu; Johansen, Egil Ivar & Jensen, Jørgen (2022). Increased Mass-Specific Maximal Fat Oxidation Rate with Small versus Large Muscle Mass Exercise. Medicine & Science in Sports & Exercise. ISSN 0195-9131. 54(6), p. 974–983. doi: 10.1249/MSS.0000000000002864. Full text in Research Archive Show summary

  Introduction: Skeletal muscle perfusion and oxygen (O2) delivery are restricted during whole-body exercise due to a limited cardiac output (Q[Combining Dot Above]). This study investigated the role of reducing central limitations to exercise on the maximal fat oxidation rate (MFO) by comparing mass-specific MFO (per kg active lean mass) during one-legged (1 L) and two-legged (2 L) cycling. We hypothesized that the mass-specific MFO would be higher during 1 L- than 2 L cycling. Methods: Twelve male subjects (V[Combining Dot Above]O2peak: 59.3 ± 8.4 mL·kg-1·min-1; mean ± SD) performed step-incremental 2 L- (30-80% of V[Combining Dot Above]O2peak) and 1 L (50% of 2 L power output, i.e., equal power output per leg) cycling (counterbalanced) while steady-state pulmonary gas exchanges, Q[Combining Dot Above] (pulse-contour analysis), and skeletal muscle (vastus lateralis) oxygenation (near-infrared spectroscopy) were determined. MFO and the associated power output (FatMax) were calculated from pulmonary gas exchanges and stoichiometric equations. A counterweight (10.9 kg) was added to the contralateral pedal arm during 1 L cycling. Leg lean mass was determined by DEXA. Results: The absolute MFO was 24% lower (0.31 ± 0.12 vs 0.44 ± 0.20 g·min-1; P = 0.018) while mass-specific MFO was 52% higher (28 ± 11 vs 20 ± 10 mg·min-1·kg-1; P = 0.009) during 1 L- than 2 L cycling. FatMax was similar expressed as power output per leg (60 ± 28 vs 58 ± 22 W; P = 0.649). Q· increased more from rest to exercise during 1 L- than 2 L cycling when expressed per active leg (ANOVA main effect: P = 0.003). The tissue oxygenation index and Δ[deoxy(Hb + Mb)] were not different between exercise modes (ANOVA main effects: P ≥ 0.587), indicating similar skeletal muscle fractional O2 extraction. Conclusions: Mass-specific MFO is increased by exercising a small muscle mass, potentially explained by increased perfusion and more favorable conditions for O2 delivery than during whole-body exercise.

• Skattebo, Øyvind; Johansen, Espen Spro; Capelli, Carlo & Hallén, Jostein (2021). Effects of 150- And 450-mL Acute Blood Losses on Maximal Oxygen Uptake and Exercise Capacity. Medicine & Science in Sports & Exercise. ISSN 0195-9131. 53(8), p. 1729–1738. doi: 10.1249/MSS.0000000000002618. Full text in Research Archive Show summary

  Purpose: This study investigated whether maximal oxygen uptake (V˙O2max) and exercise capacity are affected by small acute blood loss (150 mL) and elucidated compensatory mechanisms. Methods: Thirteen male subjects (V˙O2max, 63 ± 9 mL·kg−1·min−1; mean ± SD) performed incremental exercise to exhaustion on a cycle ergometer in three experimental conditions: in euvolemia (control; blood volume [BV], 6.0 ± 0.7 L) and immediately after acute BV reductions of 150 mL (BVR150mL) and 450 mL (BVR450mL). Changes in plasma volume (PV) and BV during exercise were calculated from hematocrit, hemoglobin concentration, and hemoglobin mass (carbon monoxide rebreathing). Results: The reduction in V˙O2max per milliliter of BVR was 2.5-fold larger after BVR450mL compared with BVR150mL (−0.7 ± 0.3 vs −0.3 ± 0.6 mL·min−1·mL−1, P = 0.029). V˙O2max was not significantly changed after BVR150mL (−1% ± 2%, P = 0.124) but reduced by 7% ± 3% after BVR450mL (P < 0.001) compared with control. Peak power output only decreased after BVR450mL (P < 0.001). At maximal exercise, BV was restored after BVR150mL compared with control (−50 ± 185 mL, P = 0.375) attributed to PV restoration, which was, however, insufficient in restoring BV after BVR450mL (−281 ± 184 mL, P < 0.001). The peak heart rate tended to increase (3 ± 5 bpm, P = 0.062), whereas the O2 pulse (−2 ± 1 mL per beat, P < 0.001) and vastus lateralis tissue oxygenation index (−4% ± 8% points, P = 0.080) were reduced after BVR450mL, suggesting decreased stroke volume and increased leg O2 extraction. Conclusion: The deteriorations of V˙O2max and of maximal exercise capacity accelerate with the magnitude of acute blood loss, likely because of a rapid PV restoration sufficient to establish euvolemia after a small but not after a moderate blood loss.

• Koivisto-Mørk, Anu; Svendsen, Ida Siobhan; Skattebo, Øyvind; Hallén, Jostein & Paulsen, Gøran (2021). Impact of baseline serum ferritin and supplemental iron on altitude-induced hemoglobin mass response in elite athletes. Scandinavian Journal of Medicine & Science in Sports. ISSN 0905-7188. 31(9), p. 1764–1773. doi: 10.1111/sms.13982. Full text in Research Archive Show summary

  The present study explored the impact of pre-altitude serum (s)-ferritin and iron supplementation on changes in hemoglobin mass (ΔHbmass) following altitude training. Measures of Hbmass and s-ferritin from 107 altitude sojourns (9–28 days at 1800–2500 m) with world-class endurance athletes (males n = 41, females n = 25) were analyzed together with iron supplementation and self-reported illness. Altitude sojourns with a hypoxic dose [median (range)] of 1169 (912) km·h increased Hbmass (mean ± SD) 36 ± 38 g (3.7 ± 3.7%, p < 0.001) and decreased s-ferritin −11 (190) µg·L−1 (p = 0.001). Iron supplements [27 (191) mg·day−1] were used at 45 sojourns (42%), while only 11 sojourns (10%) were commenced with s-ferritin <35 µg/L. Hbmass increased by 4.6 ± 3.7%, 3.4 ± 3.3%, 4.2 ± 4.3%, and 2.9 ± 3.4% with pre-altitude s-ferritin ≤35 µg·L−1, 36–50 µg·L−1, 51–100 µg·L−1, and >100 µg·L−1, respectively, with no group difference (p = 0.400). Hbmass increased by 4.1 ± 3.9%, 3.0 ± 3.0% and 3.7 ± 4.7% without, ≤50 mg·day−1 or >50 mg·day−1 supplemental iron, respectively (p = 0.399). Linear mixed model analysis revealed no interaction between pre-altitude s-ferritin and iron supplementation on ΔHbmass (p = 0.906). However, each 100 km·h increase in hypoxic dose augmented ΔHbmass by an additional 0.4% (95% CI: 0.1–0.7%; p = 0.012), while each 1 g·kg−1 higher pre-altitude Hbmass reduced ΔHbmass by −1% (−1.6 to −0.5; p < 0.001), and illness lowered ΔHbmass by −5.7% (−8.3 to −3.1%; p < 0.001). In conclusion, pre-altitude s-ferritin or iron supplementation were not related to the altitude-induced increase in Hbmass (3.7%) in world-class endurance athletes with clinically normal iron stores.

• Skattebo, Øyvind; Calbet, Jose Antonio Lopez; Rud, Bjarne; Capelli, Carlo & Hallén, Jostein (2020). Contribution of oxygen extraction fraction to maximal oxygen uptake in healthy young men. Acta Physiologica. ISSN 1748-1708. 230(2). doi: 10.1111/apha.13486. Full text in Research Archive Show summary

  We analysed the importance of systemic and peripheral arteriovenous O2 difference ( urn:x-wiley:17481708:media:apha13486:apha13486-math-0001 difference and a‐vfO2 difference, respectively) and O2 extraction fraction for maximal oxygen uptake ( urn:x-wiley:17481708:media:apha13486:apha13486-math-0002). Fick law of diffusion and the Piiper and Scheid model were applied to investigate whether diffusion versus perfusion limitations vary with urn:x-wiley:17481708:media:apha13486:apha13486-math-0003. Articles (n = 17) publishing individual data (n = 154) on urn:x-wiley:17481708:media:apha13486:apha13486-math-0004, maximal cardiac output ( urn:x-wiley:17481708:media:apha13486:apha13486-math-0005; indicator‐dilution or the Fick method), urn:x-wiley:17481708:media:apha13486:apha13486-math-0006 difference (catheters or the Fick equation) and systemic O2 extraction fraction were identified. For the peripheral responses, group‐mean data (articles: n = 27; subjects: n = 234) on leg blood flow (LBF; thermodilution), a‐vfO2 difference and O2 extraction fraction (arterial and femoral venous catheters) were obtained. urn:x-wiley:17481708:media:apha13486:apha13486-math-0007 and two‐LBF increased linearly by 4.9‐6.0 L · min–1 per 1 L · min–1 increase in urn:x-wiley:17481708:media:apha13486:apha13486-math-0008 (R2 = .73 and R2 = .67, respectively; both P < .001). The urn:x-wiley:17481708:media:apha13486:apha13486-math-0009 difference increased from 118‐168 mL · L–1 from a urn:x-wiley:17481708:media:apha13486:apha13486-math-0010 of 2‐4.5 L · min–1 followed by a reduction (second‐order polynomial: R2 = .27). After accounting for a hypoxemia‐induced decrease in arterial O2 content with increasing urn:x-wiley:17481708:media:apha13486:apha13486-math-0011 (R2 = .17; P < .001), systemic O2 extraction fraction increased up to ~90% ( urn:x-wiley:17481708:media:apha13486:apha13486-math-0012: 4.5 L · min–1) with no further change (exponential decay model: R2 = .42). Likewise, leg O2 extraction fraction increased with urn:x-wiley:17481708:media:apha13486:apha13486-math-0013 to approach a maximal value of ~90‐95% (R2 = .83). Muscle O2 diffusing capacity and the equilibration index Y increased linearly with urn:x-wiley:17481708:media:apha13486:apha13486-math-0014 (R2 = .77 and R2 = .31, respectively; both P < .01), reflecting decreasing O2 diffusional limitations and accentuating O2 delivery limitations. In conclusion, although O2 delivery is the main limiting factor to urn:x-wiley:17481708:media:apha13486:apha13486-math-0015, enhanced O2 extraction fraction (≥90%) contributes to the remarkably high urn:x-wiley:17481708:media:apha13486:apha13486-math-0016 in endurance‐trained individuals.

• Skattebo, Øyvind; Bjerring, Anders W.; Auensen, Marius; Sarvari, Sebastian; Cumming, Kristoffer Toldnes & Capelli, Carlo [Show all 7 contributors for this article] (2020). Blood volume expansion does not explain the increase in peak oxygen uptake induced by 10 weeks of endurance training. European Journal of Applied Physiology. ISSN 1439-6319. 120(5), p. 985–999. doi: 10.1007/s00421-020-04336-2. Full text in Research Archive Show summary

  Purpose: The endurance training (ET)-induced increases in peak oxygen uptake (V˙O2peak) and cardiac output (Q˙peak) during upright cycling are reversed to pre-ET levels after removing the training-induced increase in blood volume (BV). We hypothesised that ET-induced improvements in V˙O2peak and Q˙peak are preserved following phlebotomy of the BV gained with ET during supine but not during upright cycling. Arteriovenous O2 difference (a-v¯O2diff; V˙O2/Q˙), cardiac dimensions and muscle morphology were studied to assess their role for the V˙O2peak improvement. Methods: Twelve untrained subjects (V˙O2peak: 44 ± 6 ml kg−1 min−1) completed 10 weeks of supervised ET (3 sessions/week). Echocardiography, muscle biopsies, haemoglobin mass (Hbmass) and BV were assessed pre- and post-ET. V˙O2peak and Q˙peak during upright and supine cycling were measured pre-ET, post-ET and immediately after Hbmass was reversed to the individual pre-ET level by phlebotomy. Results: ET increased the Hbmass (3.3 ± 2.9%; P = 0.005), BV (3.7 ± 5.6%; P = 0.044) and V˙O2peak during upright and supine cycling (11 ± 6% and 10 ± 8%, respectively; P ≤ 0.003). After phlebotomy, improvements in V˙O2peak compared with pre-ET were preserved in both postures (11 ± 4% and 11 ± 9%; P ≤ 0.005), as was Q˙peak (9 ± 14% and 9 ± 10%; P ≤ 0.081). The increased Q˙peak and a-v¯O2diff accounted for 70% and 30% of the V˙O2peak improvements, respectively. Markers of mitochondrial density (CS and COX-IV; P ≤ 0.007) and left ventricular mass (P = 0.027) increased. Conclusion: The ET-induced increase in V˙O2peak was preserved despite removing the increases in Hbmass and BV by phlebotomy, independent of posture. V˙O2peak increased primarily through elevated Q˙peak but also through a widened a-v¯O2diff, potentially mediated by cardiac remodelling and mitochondrial biogenesis.

• Skattebo, Øyvind; Capelli, Carlo; Rud, Bjarne; Auensen, Marius; Calbet, Jose Antonio Lopez & Hallén, Jostein (2020). Increased oxygen extraction and mitochondrial protein expression after small muscle mass endurance training. Scandinavian Journal of Medicine & Science in Sports. ISSN 0905-7188. 30(9), p. 1615–1631. doi: 10.1111/sms.13707. Show summary

  When exercising with a small muscle mass, the mass‐specific O2 delivery exceeds the muscle oxidative capacity resulting in a lower O2 extraction compared with whole‐body exercise. We elevated the muscle oxidative capacity and tested its impact on O2 extraction during small muscle mass exercise. Nine individuals conducted six weeks of one‐legged knee extension (1L‐KE) endurance training. After training, the trained leg (TL) displayed 45% higher citrate synthase and COX‐IV protein content in vastus lateralis and 15%‐22% higher pulmonary oxygen uptake ( urn:x-wiley:09057188:media:sms13707:sms13707-math-0001) and peak power output ( urn:x-wiley:09057188:media:sms13707:sms13707-math-0002) during 1L‐KE than the control leg (CON; all P < .05). Leg O2 extraction (catheters) and blood flow (ultrasound Doppler) were measured while both legs exercised simultaneously during 2L‐KE at the same submaximal power outputs (real‐time feedback‐controlled). TL displayed higher O2 extraction than CON (main effect: 1.7 ± 1.6% points; P = .010; 40%‐83% of urn:x-wiley:09057188:media:sms13707:sms13707-math-0003) with the largest between‐leg difference at 83% of urn:x-wiley:09057188:media:sms13707:sms13707-math-0004 (O2 extraction: 3.2 ± 2.2% points; arteriovenous O2 difference: 7.1 ± 4.8 mL· L−1; P < .001). At 83% of urn:x-wiley:09057188:media:sms13707:sms13707-math-0005, muscle O2 conductance (DMO2; Fick law of diffusion) and the equilibration index Y were higher in TL (P < .01), indicating reduced diffusion limitations. The between‐leg difference in O2 extraction correlated with the between‐leg ratio of citrate synthase and COX‐IV (r = .72‐.73; P = .03), but not with the difference in the capillary‐to‐fiber ratio (P = .965). In conclusion, endurance training improves O2 extraction during small muscle mass exercise by elevating the muscle oxidative capacity and the recruitment of DMO2, especially evident during high‐intensity exercise exploiting a larger fraction of the muscle oxidative capacity.

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• Grendstad, Halvard & Skattebo, Øyvind (2022). Puberty, more important for cardiovascular adaptations than endurance training? Journal of Physiology. ISSN 0022-3751. 600(11), p. 2817–2818. doi: 10.1113/JP283081.

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