| 1. |
- Andersson, Erik, et al.
(författare)
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Energy contributions and pacing strategies of elite XC skiers during sprint skiing
- 2016
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Konferensbidrag (refereegranskat)abstract
- INTRODUCTION: At present, knowledge regarding energy contributions and pacing strategies during successive sprint time-trials (STTs) in cross-country (XC) skiing is limited and, therefore, the current study was designed to examine these parameters. The results shown have recently been published elsewhere (Andersson et al., 2016).METHODS: Ten well-trained male XC skiers performed four self-paced 1300-m STTs on a treadmill, separated by 45 min of recovery. The simulated STT course was divided into three flat (1°) sections (S1, S3 and S5) involving the double poling (DP) sub-technique interspersed with two uphill (7°) sections (S2 and S4) involving the diagonal stride (DS) sub-technique. Treadmill velocity and VO2 were monitored continuously and technique-specific gross efficiency (based on submaximal pre-tests) was used to estimate anaerobic energy production.RESULTS & DISCUSSION: The average STT performance time was 229 ± 9 s and the aerobic energy contribution was 82 ± 5%. A positive pacing strategy was used during all STTs, with 3-9% more time spent on the second half of the course (P < 0.05). In addition, the pacing strategy was regulated to the terrain, with substantially higher (~30%) metabolic rates, due to primarily higher anaerobic energy production, for uphill compared with flat skiing (P < 0.05). The individually fastest STT was more aggressively paced compared to the slowest STT (P < 0.05), which resulted in a higher O2 deficit rate (13 ± 4 versus 11 ± 4 mL/kg/min, P < 0.05), while the VO2 was similar (both 52 ± 3 mL/kg/min). These findings emphasise the importance of a fast start. The within-athlete coefficient of variation (CV) in performance time, VO2 and O2 deficit were 1.3 ± 0.4%, 1.4 ± 0.9% and 11.2 ± 4.9%, respectively, with the CV in O2 deficit explaining 69% of the CV in performance. The pacing strategies were highly consistent, with an average CV in speed of 3.4%.CONCLUSION: The fastest STT was characterized by more aggressive pacing and a greater anaerobic energy production. Although the individual performance time during the four STTs was highly consistent, the small within-athlete variability in performance was related to variations in anaerobic energy production.
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| 2. |
- Andersson, Erik, 1984-, et al.
(författare)
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Energy system contributions and determinants of performance in sprint cross-country skiing
- 2017
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Ingår i: Scandinavian Journal of Medicine and Science in Sports. - : Wiley. - 0905-7188 .- 1600-0838. ; 27:4, s. 385-398
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 3. |
- Andersson, Erik, 1984-, et al.
(författare)
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Metabolic responses and pacing strategies during successive sprint skiing time trials
- 2016
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Ingår i: Medicine & Science in Sports & Exercise. - 0195-9131 .- 1530-0315. ; 48:12, s. 2544-2554
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Tidskriftsartikel (refereegranskat)abstract
- PURPOSE: To examine the metabolic responses and pacing strategies during the performance of successive sprint time trials (STTs) in cross-country skiing. METHODS: Ten well-trained male cross-country skiers performed four self-paced 1300-m STTs on a treadmill, each separated by 45 min of recovery. The simulated STT course was divided into three flat (1°) sections (S1, S3 and S5) involving the double poling sub-technique interspersed with two uphill (7°) sections (S2 and S4) involving the diagonal stride sub-technique. Treadmill velocity and V˙O2 were monitored continuously and gross efficiency was used to estimate the anaerobic energy supply. RESULTS: The individual trial-to-trial variability in STT performance time was 1.3%, where variations in O2 deficit and V˙O2 explained 69% (P < 0.05) and 11% (P > 0.05) of the variation in performance. The first and last STTs were equally fast (228 ± 10 s), and ~ 1.3% faster than the second and the third STTs (P < 0.05). These two fastest STTs were associated with a 14% greater O2 deficit (P < 0.05), while the average V˙O2 was similar during all four STTs (86 ± 3% of V˙O2max). Positive pacing was used throughout all STTs, with significantly less time spent on the first than second course half. In addition, metabolic rates were substantially higher (~_30%) for uphill than for flat skiing, indicating that pacing was regulated to the terrain. CONCLUSIONS: The fastest STTs were characterized primarily by a greater anaerobic energy production, which also explained 69% of the individual variation in performance. Moreover, the skiers employed positive pacing and a variable exercise intensity according to the course profile, yielding an irregular distribution of anaerobic energy production.
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| 4. |
- Cardinale, Daniele A, et al.
(författare)
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Reliability of maximal mitochondrial oxidative phosphorylation in permeabilized fibers from the vastus lateralis employing high-resolution respirometry.
- 2018
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Ingår i: Physiological Reports. - : Wiley. - 2051-817X. ; 6:4
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Tidskriftsartikel (refereegranskat)abstract
- The purpose was to assess the impact of various factors on methodological errors associated with measurement of maximal oxidative phosphorylation (OXPHOS) in human skeletal muscle determined by high-resolution respirometry in saponin-permeabilized fibers. Biopsies were collected from 25 men to assess differences in OXPHOS between two muscle bundles and to assess the correlation between OXPHOS and the wet weight of the muscle bundle. Biopsies from left and right thighs of another five subjects were collected on two occasions to compare limbs and time-points. A single muscle specimen was used to assess effects of the anesthetic carbocaine and the influence of technician. The difference in OXPHOS between two fiber-bundles from the same biopsy exhibited a standard error of measurement (SEM) of 10.5 pmol · s-1 · mg-1 and a coefficient of variation (CV) of 15.2%. The differences between left and right thighs and between two different time-points had SEMs of 9.4 and 15.2 pmol · s-1 · mg-1 and CVs of 23.9% and 33.1%, respectively. The average (±SD) values obtained by two technicians monitoring different bundles of fibers from the same biopsy were 31.3 ± 7.1 and 26.3 ± 8.1 pmol · s-1 · mg-1 . The time that elapsed after collection of the biopsy (up to a least 5 h in preservation medium), wet weight of the bundle (from 0.5 to 4.5 mg) and presence of an anesthetic did not influence OXPHOS. The major source of variation in OXPHOS measurements is the sample preparation. The thigh involved, time-point of collection, size of fiber bundles, and time that elapsed after biopsy had minor or no effect.
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| 5. |
- Cheng, Arthur J., et al.
(författare)
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Post-exercise recovery of contractile function and endurance in humans and mice is accelerated by heating and slowed by cooling skeletal muscle
- 2017
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Ingår i: Journal of Physiology. - : John Wiley & Sons. - 0022-3751 .- 1469-7793. ; 595:24, s. 7413-7426
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 6. |
- Gejl, Kasper D., et al.
(författare)
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Changes in metabolism but not myocellular signaling by training with CHO-restriction in endurance athletes
- 2018
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Ingår i: Physiological Reports. - : Wiley. - 2051-817X. ; 6:17
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 7. |
- Gejl, Kasper D., et al.
(författare)
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Local depletion of glycogen with supra-maximal exercise in human skeletal muscle fibres
- 2017
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Ingår i: Journal of Physiology. - 0022-3751 .- 1469-7793. ; 595:9, s. 2809-2821
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 8. |
- Gejl, Kasper Degn, et al.
(författare)
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No Superior Adaptations to Carbohydrate Periodization in Elite Endurance Athletes
- 2017
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Ingår i: Medicine & Science in Sports & Exercise. - 0195-9131 .- 1530-0315. ; 49:12, s. 2486-2497
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 9. |
- Hostrup, Morten, et al.
(författare)
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Mechanisms underlying enhancements in muscle force and power output during maximal cycle ergometer exercise induced by chronic beta(2)-adrenergic stimulation in men
- 2015
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Ingår i: Journal of applied physiology. - : American Physiological Society. - 8750-7587 .- 1522-1601. ; 119:5, s. 475-486
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Tidskriftsartikel (refereegranskat)abstract
- The study was a randomized placebo-controlled trial investigating mechanisms by which chronic beta(2)-adrenergic stimulation enhances muscle force and power output during maximal cycle ergometer exercise in young men. Eighteen trained men were assigned to an experimental group [oral terbutaline 5 mg/30 kg body weight (bw) twice daily (TER); n = 9] or a control group [placebo (PLA); n = 9] for a 4-wk intervention. No changes were observed with the intervention in PLA. Isometric muscle force of the quadriceps increased (P <= 0.01) by 97 +/- 29 N (means +/- SE) with the intervention in TER compared with PLA. Peak and mean power output during 30 s of maximal cycling increased (P <= 0.01) by 32 +/- 8 and 25 +/- 9 W, respectively, with the intervention in TER compared with PLA. Maximal oxygen consumption ((V) over dotO(2)max) and time to fatigue during incremental cycling did not change with the intervention. Lean body mass increased by 1.95 +/- 0.8 kg (P <= 0.05) with the intervention in TER compared with PLA. Change in single fiber cross-sectional area of myosin heavy chain (MHC) I (1,205 +/- 558 mu m(2); P <= 0.01) and MHC II fibers (1,277 +/- 595 mu m(2); P <= 0.05) of the vastus lateralis muscle was higher for TER than PLA with the intervention, whereas no changes were observed in MHC isoform distribution. Expression of muscle proteins involved in growth, ion handling, lactate production, and clearance increased (P <= 0.05) with the intervention in TER compared with PLA, with no change in oxidative enzymes. Our observations suggest that muscle hypertrophy is the primary mechanism underlying enhancements in muscle force and peak power during maximal cycling induced by chronic beta(2-)adrenergic stimulation in humans.
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| 10. |
- Hvid, Lars G., et al.
(författare)
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Myosin content of single muscle fibers following short-term disuse and active recovery in young and old healthy men
- 2017
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Ingår i: Experimental Gerontology. - : Elsevier BV. - 0531-5565 .- 1873-6815. ; 87:Part A, s. 100-107
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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