miun.sePublications
Change search
Link to record
Permanent link

Direct link
BETA
Ørtenblad, Niels
Alternative names
Publications (10 of 36) Show all publications
Gejl, K. D., Vissing, K., Hansen, M., Thams, L., Rokkedal-Lausch, T., Plomgaard, P., . . . Ørtenblad, N. (2018). Changes in metabolism but not myocellular signaling by training with CHO-restriction in endurance athletes. Physiological Reports, 6(17), Article ID e13847.
Open this publication in new window or tab >>Changes in metabolism but not myocellular signaling by training with CHO-restriction in endurance athletes
Show others...
2018 (English)In: Physiological Reports, E-ISSN 2051-817X, Vol. 6, no 17, article id e13847Article in journal (Refereed) Published
Abstract [en]

Carbohydrate (CHO) restricted training has been shown to increase the acute training response, whereas less is known about the acute effects after repeated CHO restricted training. On two occasions, the acute responses to CHO restriction were examined in endurance athletes. Study 1 examined cellular signaling and metabolic responses after seven training-days including CHO manipulation (n = 16). The protocol consisted of 1 h high-intensity cycling, followed by 7 h recovery, and 2 h of moderate-intensity exercise (120SS). Athletes were randomly assigned to low (LCHO: 80 g) or high (HCHO: 415 g) CHO during recovery and the 120SS. Study 2 examined unaccustomed exposure to the same training protocol (n = 12). In Study 1, muscle biopsies were obtained at rest and 1 h after 120SS, and blood samples drawn during the 120SS. In Study 2, substrate oxidation and plasma glucagon were determined. In Study 1, plasma insulin and proinsulin C-peptide were higher during the 120SS in HCHO compared to LCHO (insulin: 0 min: +37%; 60 min: +135%; 120 min: +357%, P = 0.05; proinsulin C-peptide: 0 min: +32%; 60 min: +52%; 120 min: +79%, P = 0.02), whereas plasma cholesterol was higher in LCHO (+15-17%, P = 0.03). Myocellular signaling did not differ between groups. p-AMPK and p-ACC were increased after 120SS (+35%, P = 0.03; +59%, P = 0.0004, respectively), with no alterations in p-p38, p-53, or p-CREB. In Study 2, glucagon and fat oxidation were higher in LCHO compared to HCHO during the 120SS (+26-40%, P = 0.03; +44-76%, P = 0.01 respectively). In conclusion, the clear respiratory and hematological effects of CHO restricted training were not translated into superior myocellular signaling after accustomization to CHO restriction.

Keywords
Cycling, endurance performance, fat oxidation, glycogen, train-low
National Category
Health Sciences
Identifiers
urn:nbn:se:miun:diva-34538 (URN)10.14814/phy2.13847 (DOI)000444544300018 ()30175557 (PubMedID)2-s2.0-85053290885 (Scopus ID)
Available from: 2018-09-27 Created: 2018-09-27 Last updated: 2018-10-16Bibliographically approved
Hvid, L. G., Aagaard, P., Ørtenblad, N., Kjaer, M. & Suetta, C. (2018). Plasticity in central neural drive with short-term disuse and recovery - effects on muscle strength and influence of aging. Experimental Gerontology, 106, 145-153
Open this publication in new window or tab >>Plasticity in central neural drive with short-term disuse and recovery - effects on muscle strength and influence of aging
Show others...
2018 (English)In: Experimental Gerontology, ISSN 0531-5565, E-ISSN 1873-6815, Vol. 106, p. 145-153Article in journal (Refereed) Published
Abstract [en]

While short-term disuse negatively affects mechanical muscle function (e.g. isometric muscle strength) little is known of the relative contribution of adaptions in central neural drive and peripheral muscle contractility. The present study investigated the relative contribution of adaptations in central neural drive and peripheral muscle contractility on changes in isometric muscle strength following short-term unilateral disuse (4 days, knee brace) and subsequent active recovery (7 days, one session of resistance training) in young (n = 11, 24 yrs) and old healthy men (n = 11, 67 yrs). Maximal isometric knee extensor strength (MVC) (isokinetic dynamometer), voluntary muscle activation (superimposed twitch technique), and electrically evoked muscle twitch force (single and doublet twitch stimulation) were assessed prior to and after disuse, and after recovery. Following disuse, relative decreases in MVC did not differ statistically between old (16.4 ± 3.7%, p < 0.05) and young (−9.7 ± 2.9%, p < 0.05) (mean ± SE), whereas voluntary muscle activation decreased more (p < 0.05) in old (−8.4 ± 3.5%, p < 0.05) compared to young (−1.1 ± 1.0%, ns) as did peak single (−25.8 ± 6.6%, p < 0.05 vs −7.6 ± 3.3%, p < 0.05) and doublet twitch force (−23.2 ± 5.5%, p < 0.05 vs −2.0 ± 2.6%, ns). All parameters were restored in young following 7 days recovery, whereas MVC and peak twitch force remained suppressed in old. Regression analysis revealed that disuse-induced changes in MVC relied more on changes in single twitch force in young (p < 0.05) and more on changes in voluntary muscle activation in old (p < 0.05), whereas recovery-induced changes in MVC mainly were explained by gains in voluntary muscle activation in both young and old. Altogether, the present data demonstrate that plasticity in voluntary muscle activation (~central neural drive) is a dominant mechanism affecting short-term disuse- and recovery-induced changes in muscle strength in older adults. 

Keywords
Central neural drive, Disuse, Mechanical muscle function, Muscle contractile properties, Voluntary muscle activation
National Category
Health Sciences
Identifiers
urn:nbn:se:miun:diva-33377 (URN)10.1016/j.exger.2018.02.019 (DOI)000430469000020 ()29476804 (PubMedID)2-s2.0-85043470201 (Scopus ID)
Available from: 2018-03-28 Created: 2018-03-28 Last updated: 2018-05-15Bibliographically approved
Andersson, E., Björklund, G., Holmberg, H.-C. & Ørtenblad, N. (2017). Energy system contributions and determinants of performance in sprint cross-country skiing. Scandinavian Journal of Medicine and Science in Sports, 27(4), 385-398
Open this publication in new window or tab >>Energy system contributions and determinants of performance in sprint cross-country skiing
2017 (English)In: Scandinavian Journal of Medicine and Science in Sports, ISSN 0905-7188, E-ISSN 1600-0838, Vol. 27, no 4, p. 385-398Article in journal (Refereed) Published
Abstract [en]

To improve current understanding of energy contributions and determinants of sprint-skiing performance, 11 well-trained male cross-country skiers were tested in the laboratory for VO2max , submaximal gross efficiency (GE), maximal roller skiing velocity, and sprint time-trial (STT) performance. The STT was repeated four times on a 1300-m simulated sprint course including three flat (1°) double poling (DP) sections interspersed with two uphill (7°) diagonal stride (DS) sections. Treadmill velocity and VO2 were monitored continuously during the four STTs and data were averaged. Supramaximal GE during the STT was predicted from the submaximal relationships for GE against velocity and incline, allowing computation of metabolic rate and O2 deficit. The skiers completed the STT in 232 ± 10 s (distributed as 55 ± 3% DP and 45 ± 3% DS) with a mean power output of 324 ± 26 W. The anaerobic energy contribution was 18 ± 5%, with an accumulated O2 deficit of 45 ± 13 mL/kg. Block-wise multiple regression revealed that VO2 , O2 deficit, and GE explained 30%, 15%, and 53% of the variance in STT time, respectively (all P < 0.05). This novel GE-based method of estimating the O2 deficit in simulated sprint-skiing has demonstrated an anaerobic energy contribution of 18%, with GE being the strongest predictor of performance.

Keywords
Energetic cost, incline, oxygen demand, oxygen uptake, oxygen deficit, technique transitions.
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:miun:diva-27227 (URN)10.1111/sms.12666 (DOI)000395709400002 ()26923666 (PubMedID)2-s2.0-84959270767 (Scopus ID)
Funder
Swedish National Centre for Research in Sports
Note

Article first published online: 29 FEB 2016

Available from: 2016-03-14 Created: 2016-03-14 Last updated: 2017-07-07Bibliographically approved
Ørtenblad, N. & Jensen, K. (2017). Gross efficiency predicts a 6-min double-poling ergometer performance in recreational cross-country skiers. Sports Engineering, 20(4), 329-333
Open this publication in new window or tab >>Gross efficiency predicts a 6-min double-poling ergometer performance in recreational cross-country skiers
2017 (English)In: Sports Engineering, ISSN 1369-7072, E-ISSN 1460-2687, Vol. 20, no 4, p. 329-333Article in journal (Refereed) Published
Abstract [en]

The purpose of the study was to investigate which physiological parameters would most accurately predict a 6-min, all-out, double-poling (DP) performance in recreational cross-country skiers. Twelve male recreational cross-country skiers performed tests consisting of three series lasting 10 s, one lasting 60 s, plus a 6-min, all-out, DP performance test to estimate mean and peak power output. On a separate day, gross mechanical efficiency (GE) was estimated from a 10-min, submaximal, DP test and maximal oxygen consumption (VO2 max) was estimated from an incremental treadmill running test. Power was measured after each stroke from the acceleration and deceleration of the flywheel that induced the friction on the ergometer. The power was shown to the skier on a small computer placed on the ergometer. A multivariable correlation analysis showed that GE most strongly predicted 6-min DP performance (r = 0.79) and interestingly, neither DP VO2 max, nor treadmill-running VO2 max, correlated with 6-min DP performance. In conclusion, GE correlated most strongly with 6-min DP performance and GE at the ski ergometer was estimated to be 6.4 ± 1.1%. It is suggested that recreational cross-country skiers focus on skiing technique to improve gross mechanical efficiency during intense DP.

Keywords
Cross-country skiing, Double-poling (DP), Gross mechanical efficiency, Performance, Ski-ergometer, Upper body exercise
National Category
Sport and Fitness Sciences
Identifiers
urn:nbn:se:miun:diva-32231 (URN)10.1007/s12283-017-0249-7 (DOI)000415345800010 ()2-s2.0-85029512528 (Scopus ID)
Available from: 2017-12-04 Created: 2017-12-04 Last updated: 2017-12-21Bibliographically approved
Nielsen, J., Gejl, K. D. & Ørtenblad, N. (2017). Is there plasticity in mitochondrial cristae density with endurance training?: Reply [Letter to the editor]. Journal of Physiology, 595(9), 2987-2988
Open this publication in new window or tab >>Is there plasticity in mitochondrial cristae density with endurance training?: Reply
2017 (English)In: Journal of Physiology, ISSN 0022-3751, E-ISSN 1469-7793, Vol. 595, no 9, p. 2987-2988Article in journal, Letter (Refereed) Published
Keywords
Mitochondria, Human muscle, Transmission electron microscopy
National Category
Sport and Fitness Sciences
Identifiers
urn:nbn:se:miun:diva-30837 (URN)10.1113/JP273880 (DOI)000400357800025 ()28452134 (PubMedID)2-s2.0-85018245717 (Scopus ID)
Note

This is a reply to a Letter to the Editor by Larsen et al. To read the Letter to the Editor, visit https://doi.org/10.1113/JP273793

Available from: 2017-06-09 Created: 2017-06-09 Last updated: 2017-06-28Bibliographically approved
Gejl, K. D., Ørtenblad, N., Andersson, E., Plomgaard, P., Holmberg, H.-C. & Nielsen, J. (2017). Local depletion of glycogen with supra-maximal exercise in human skeletal muscle fibres. Journal of Physiology, 595(9), 2809-2821
Open this publication in new window or tab >>Local depletion of glycogen with supra-maximal exercise in human skeletal muscle fibres
Show others...
2017 (English)In: Journal of Physiology, ISSN 0022-3751, E-ISSN 1469-7793, Vol. 595, no 9, p. 2809-2821Article in journal (Refereed) Published
Abstract [en]

Skeletal muscle glycogen is heterogeneous distributed in three separated compartments (intramyofibrillar, intermyofibrillar and subsarcolemmal). Although only constituting 4-15% of the total glycogen volume, the availability of intramyofibrillar glycogen has been shown to be of particular importance to muscle function. The present study was designed to investigate the depletion of these three sub-cellular glycogen compartments during repeated supra-maximal exercise in elite athletes. Ten elite cross-country skiers (age: 25 +/- 4 yrs., VO2 max : 65 +/- 4 ml kg-1 min-1 , mean +/- SD) performed four approximately 4-minute supra-maximal sprint time trials (STT 1-4) with 45 min recovery. The sub-cellular glycogen volumes in m. triceps brachii were quantified from electron microscopy images before and after both STT 1 and STT 4. During STT 1, the depletion of intramyofibrillar glycogen was higher in type I fibres (-52% [-89:-15%]) than type 2 fibres (-15% [-52:22%]) (P = 0.02), while the depletion of intermyofibrillar glycogen (main effect: -19% [-33:0], P = 0.006) and subsarcolemmal glycogen (main effect: -35% [-66:0%], P = 0.03) was similar between fibre types. In contrast, only intermyofibrillar glycogen volume was significantly reduced during STT 4, in both fibre types (main effect: -31% [-50:-11%], P = 0.002). Furthermore, for each of the sub-cellular compartments, the depletion of glycogen during STT 1 was associated with the volumes of glycogen before STT 1. In conclusion, the depletion of spatially distinct glycogen compartments differs during supra-maximal exercise. Furthermore, the depletion changes with repeated exercise and is fibre type-dependent. 

National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:miun:diva-29782 (URN)10.1113/JP273109 (DOI)000400357800010 ()27689320 (PubMedID)2-s2.0-85002244062 (Scopus ID)
Funder
Swedish National Centre for Research in Sports, #FO2013-0033
Available from: 2016-12-23 Created: 2016-12-23 Last updated: 2017-07-04Bibliographically approved
Hvid, L. G., Brocca, L., Ørtenblad, N., Suetta, C., Aagaard, P., Kjaer, M., . . . Pellegrino, M. A. (2017). Myosin content of single muscle fibers following short-term disuse and active recovery in young and old healthy men. Experimental Gerontology, 87(Part A), 100-107
Open this publication in new window or tab >>Myosin content of single muscle fibers following short-term disuse and active recovery in young and old healthy men
Show others...
2017 (English)In: Experimental Gerontology, ISSN 0531-5565, E-ISSN 1873-6815, Vol. 87, no Part A, p. 100-107Article in journal (Refereed) Published
Abstract [en]

Short-term disuse and subsequent recovery affect whole muscle and single myofiber contractile function in young and old. While the loss and recovery of single myofiber specific force (SF) following disuse and rehabilitation has been shown to correlate with alterations in myosin concentrations in young, it is unknown whether similar relationships exist in old. Therefore, the purpose of the present study was to examine the effect of 14 days lower limb disuse followed by 28 days of active recovery on single muscle fiber myosin content in old (68 yrs) and young (24 yrs) recreationally physically active healthy men. Following disuse, myosin content decreased (p < 0.05) in MHC 1 (young − 28%, old − 19%) and 2a fibers (young − 23%, old − 32%). In old, myosin content decreased more (p < 0.05) in MHC 2a vs 1 fibers. Following recovery, myosin content increased (p < 0.05) and returned to pre-disuse levels for both young and old in both fiber types, with MHC 2a fibers demonstrating an overshooting in young (+ 31%, p < 0.05) but not old. Strong correlations were observed between myosin content and single fiber SF in both young and old, with greater slope steepness in MHC 2a vs 1 fibers indicating an enhanced intrinsic contractile capacity of MHC 2a fibers. In conclusion, adaptive changes in myofiber myosin content appear to occur rapidly following brief periods of disuse (2 wks) and after subsequent active recovery (4 wks) in young and old, which contribute to alterations in contractile function at the single muscle fiber level. Changes in myosin content appear to occur independently of age, while influenced by fiber type (MHC isoform) in young but not old.

Keywords
Aging, Disuse, Myofiber, Myosin content, Retraining
National Category
Health Sciences
Identifiers
urn:nbn:se:miun:diva-29817 (URN)10.1016/j.exger.2016.10.009 (DOI)000393528000013 ()27794458 (PubMedID)2-s2.0-85002892361 (Scopus ID)
Available from: 2017-01-03 Created: 2017-01-03 Last updated: 2017-11-29Bibliographically approved
Gejl, K. D., Thams, L. B., Hansen, M., Rokkedal-Lausch, T., Plomgaard, P., Nybo, L., . . . Ørtenblad, N. (2017). No Superior Adaptations to Carbohydrate Periodization in Elite Endurance Athletes. Medicine & Science in Sports & Exercise, 49(12), 2486-2497
Open this publication in new window or tab >>No Superior Adaptations to Carbohydrate Periodization in Elite Endurance Athletes
Show others...
2017 (English)In: Medicine & Science in Sports & Exercise, ISSN 0195-9131, E-ISSN 1530-0315, Vol. 49, no 12, p. 2486-2497Article in journal (Refereed) Published
Abstract [en]

Purpose The present study investigated the effects of periodic carbohydrate (CHO) restriction on endurance performance and metabolic markers in elite endurance athletes. Methods Twenty-six male elite endurance athletes (maximal oxygen consumption (VO2max), 65.0 mL O(2)kg(-1)min(-1)) completed 4 wk of regular endurance training while being matched and randomized into two groups training with (low) or without (high) CHO manipulation 3 dwk(-1). The CHO manipulation days consisted of a 1-h high-intensity bike session in the morning, recovery for 7 h while consuming isocaloric diets containing either high CHO (414 2.4 g) or low CHO (79.5 1.0 g), and a 2-h moderate bike session in the afternoon with or without CHO. VO2max, maximal fat oxidation, and power output during a 30-min time trial (TT) were determined before and after the training period. The TT was undertaken after 90 min of intermittent exercise with CHO provision before the training period and both CHO and placebo after the training period. Muscle biopsies were analyzed for glycogen, citrate synthase (CS) and -hydroxyacyl-coenzyme A dehydrogenase (HAD) activity, carnitine palmitoyltransferase (CPT1b), and phosphorylated acetyl-CoA carboxylase (pACC). Results The training effects were similar in both groups for all parameters. On average, VO2max and power output during the 30-min TT increased by 5% +/- 1% (P < 0.05) and TT performance was similar after CHO and placebo during the preload phase. Training promoted overall increases in glycogen content (18% +/- 5%), CS activity (11% +/- 5%), and pACC (38% +/- 19%; P < 0.05) with no differences between groups. HAD activity and CPT1b protein content remained unchanged. Conclusions Superimposing periodic CHO restriction to 4 wk of regular endurance training had no superior effects on performance and muscle adaptations in elite endurance athletes.

Keywords
DIET MANIPULATION, GLYCOGEN, ENZYME ACTIVITY, TRIATHLETES, ENDURANCE PERFORMANCE
National Category
Sport and Fitness Sciences
Identifiers
urn:nbn:se:miun:diva-32564 (URN)10.1249/MSS.0000000000001377 (DOI)000416209900014 ()28723843 (PubMedID)2-s2.0-85025146684 (Scopus ID)
Available from: 2017-12-21 Created: 2017-12-21 Last updated: 2018-02-22Bibliographically approved
Nielsen, J., Gejl, K. D., Hey-Mogensen, M., Holmberg, H.-C., Suetta, C., Krustrup, P., . . . Ørtenblad, N. (2017). Plasticity in mitochondrial cristae density allows metabolic capacity modulation in human skeletal muscle. Journal of Physiology, 595(9), 2839-2847
Open this publication in new window or tab >>Plasticity in mitochondrial cristae density allows metabolic capacity modulation in human skeletal muscle
Show others...
2017 (English)In: Journal of Physiology, ISSN 0022-3751, E-ISSN 1469-7793, Vol. 595, no 9, p. 2839-2847Article in journal (Refereed) Published
Abstract [en]

Mitochondrial energy production involves the movement of protons down a large electrochemical gradient via ATP synthase located on the folded inner membrane, known as cristae. In mammalian skeletal muscle, the density of cristae in mitochondria is assumed to be constant. However, recent experimental studies have shown that respiration per mitochondria varies. Modelling studies have hypothesized that this variation in respiration per mitochondria depends on plasticity in cristae density, although current evidence for such a mechanism is lacking. In the present study, we confirm this hypothesis by showing that, in human skeletal muscle, and in contrast to the current view, the mitochondrial cristae density is not constant but, instead, exhibits plasticity with long-term endurance training. Furthermore, we show that frequently recruited mitochondria-enriched fibres have significantly increased cristae density and that, at the whole-body level, muscle mitochondrial cristae density is a better predictor of maximal oxygen uptake rate than muscle mitochondrial volume. Our findings establish an elevating mitochondrial cristae density as a regulatory mechanism for increasing metabolic power in human skeletal muscle. We propose that this mechanism allows evasion of the trade-off between cell occupancy by mitochondria and other cellular constituents, as well as improved metabolic capacity and fuel catabolism during prolonged elevated energy requirements.

National Category
Sport and Fitness Sciences
Identifiers
urn:nbn:se:miun:diva-30838 (URN)10.1113/JP273040 (DOI)000400357800012 ()27696420 (PubMedID)2-s2.0-85006380667 (Scopus ID)
Available from: 2017-06-09 Created: 2017-06-09 Last updated: 2017-07-04Bibliographically approved
Cheng, A. J., Willis, S. J., Zinner, C., Chaillou, T., Ivarsson, N., Ørtenblad, N., . . . Westerblad, H. (2017). Post-exercise recovery of contractile function and endurance in humans and mice is accelerated by heating and slowed by cooling skeletal muscle. Journal of Physiology, 595(24), 7413-7426
Open this publication in new window or tab >>Post-exercise recovery of contractile function and endurance in humans and mice is accelerated by heating and slowed by cooling skeletal muscle
Show others...
2017 (English)In: Journal of Physiology, ISSN 0022-3751, E-ISSN 1469-7793, Vol. 595, no 24, p. 7413-7426Article in journal (Refereed) Published
Abstract [en]

Key points: We investigated whether intramuscular temperature affects the acute recovery of exercise performance following fatigue-induced by endurance exercise. Mean power output was better preserved during an all-out arm-cycling exercise following a 2 h recovery period in which the upper arms were warmed to an intramuscular temperature of ˜ 38°C than when they were cooled to as low as 15°C, which suggested that recovery of exercise performance in humans is dependent on muscle temperature. Mechanisms underlying the temperature-dependent effect on recovery were studied in intact single mouse muscle fibres where we found that recovery of submaximal force and restoration of fatigue resistance was worsened by cooling (16-26°C) and improved by heating (36°C). Isolated whole mouse muscle experiments confirmed that cooling impaired muscle glycogen resynthesis. We conclude that skeletal muscle recovery from fatigue-induced by endurance exercise is impaired by cooling and improved by heating, due to changes in glycogen resynthesis rate.

Manipulation of muscle temperature is believed to improve post-exercise recovery, with cooling being especially popular among athletes. However, it is unclear whether such temperature manipulations actually have positive effects. Accordingly, we studied the effect of muscle temperature on the acute recovery of force and fatigue resistance after endurance exercise. One hour of moderate-intensity arm cycling exercise in humans was followed by 2 h recovery in which the upper arms were either heated to 38°C, not treated (33°C), or cooled to ∼15°C. Fatigue resistance after the recovery period was assessed by performing 3 × 5 min sessions of all-out arm cycling at physiological temperature for all conditions (i.e. not heated or cooled). Power output during the all-out exercise was better maintained when muscles were heated during recovery, whereas cooling had the opposite effect. Mechanisms underlying the temperature-dependent effect on recovery were tested in mouse intact single muscle fibres, which were exposed to ∼12 min of glycogen-depleting fatiguing stimulation (350 ms tetani given at 10 s interval until force decreased to 30% of the starting force). Fibres were subsequently exposed to the same fatiguing stimulation protocol after 1-2 h of recovery at 16-36°C. Recovery of submaximal force (30 Hz), the tetanic myoplasmic free [Ca2+] (measured with the fluorescent indicator indo-1), and fatigue resistance were all impaired by cooling (16-26°C) and improved by heating (36°C). In addition, glycogen resynthesis was faster at 36°C than 26°C in whole flexor digitorum brevis muscles. We conclude that recovery from exhaustive endurance exercise is accelerated by raising and slowed by lowering muscle temperature.

Keywords
Cold-water immersion, Fatigue, Glycogen, Recovery, Skeletal muscle, Temperature
National Category
Sport and Fitness Sciences
Identifiers
urn:nbn:se:miun:diva-32275 (URN)10.1113/JP274870 (DOI)000418228800014 ()28980321 (PubMedID)2-s2.0-85031895429 (Scopus ID)
Available from: 2017-12-05 Created: 2017-12-05 Last updated: 2018-02-22Bibliographically approved
Organisations

Search in DiVA

Show all publications