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- Hvid, L. G., et al.
(författare)
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Transient impairments in single muscle fibre contractile function after prolonged cycling in elite endurance athletes
- 2013
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Ingår i: Acta Physiologica. - : Wiley. - 1748-1708 .- 1748-1716. ; 208:3, s. 265-273
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Tidskriftsartikel (refereegranskat)abstract
- Aim Prolonged muscle activity impairs whole-muscle performance and function. However, little is known about the effects of prolonged muscle activity on the contractile function of human single muscle fibres. The purpose of this study was to investigate the effects of prolonged exercise and subsequent recovery on the contractile function of single muscle fibres obtained from elite athletes. Methods Nine male triathletes (26 +/- 1years, 68 +/- 1mL O2min-1 kg-1, training volume 16 +/- 1hweek-1) performed 4h of cycling exercise (at 73% of HRmax) followed by 24h of recovery. Biopsies from vastus lateralis were obtained before and following 4h exercise and following 24h recovery. Measurements comprised maximal Ca2+-activated specific force and Ca2+ sensitivity of slow type I and fast type II single muscle fibres, as well as cycling peak power output. Results Following cycling exercise, specific force was reduced to a similar extent in slow and fast fibres (-15 and -18%, respectively), while Ca2+ sensitivity decreased in fast fibres only. Single fibre-specific force was fully restored in both fibre types after 24h recovery. Cycling peak power output was reduced by 4-9% following cycling exercise and fully restored following recovery. Conclusion This is the first study to demonstrate that prolonged cycling exercise transiently impairs specific force in type I and II fibres and decreases Ca2+ sensitivity in type II fibres only, specifically in elite endurance athletes. Further, the changes in single fibre-specific force induced by exercise and recovery coincided temporally with changes in cycling peak power output.
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| 2. |
- Gejl, K. D., et al.
(författare)
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Muscle glycogen content modifies SR Ca2+ release rate in elite endurance athletes
- 2014
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Ingår i: Medicine & Science in Sports & Exercise. - 0195-9131 .- 1530-0315. ; 46:3, s. 496-505
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: The aim of the present study was to investigate the influence of muscle glycogen content on sarcoplasmic reticulum (SR) function and peak power output (Wpeak) in elite endurance athletes. Methods: Fourteen highly trained male triathletes (V̇O2max = 66.5 ± 1.3 mL O2·kg·min), performed 4 h of glycogen-depleting cycling exercise (HRmean = 73% ± 1% of maximum). During the first 4 h of recovery, athletes received either water (H2O) or carbohydrate (CHO), separating alterations in muscle glycogen content from acute changes affecting SR function and performance. Thereafter, all subjects received CHO-enriched food for the remaining 20-h recovery period. Results: Immediately after exercise, muscle glycogen content and SR Ca release rate was reduced to 32% ± 4% (225 ± 28 mmol·kg dw) and 86% ± 2% of initial levels, respectively (P < 0.01). Glycogen markedly recovered after 4 h of recovery with CHO (61% ± 2% of preexercise) and SR Ca release rate returned to preexercise level. However, in the absence of CHO during the first 4 h of recovery, glycogen and SR Ca release rate remained depressed, with the normalization of both parameters at the end of the 24 h of recovery after receiving a CHO-enriched diet. Linear regression demonstrated a significant correlation between SR Ca release rate and muscle glycogen content (P < 0.01, r = 0.30). The 4 h of cycling exercise reduced Wpeak by 5.5%-8.9% at different cadences (P < 0.05), and Wpeak was normalized after 4 h of recovery with CHO, whereas Wpeak remained depressed (P < 0.05) after water provision. Wpeak was fully recovered after 24 h in both the H2O and the CHO group. Conclusion: In conclusion, the present results suggest that low muscle glycogen depresses muscle SR Ca release rate, which may contribute to fatigue and delayed recovery of Wpeak 4 h postexercise. © 2014 by the American College of Sports Medicine.
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| 3. |
- Gejl, K. D., et al.
(författare)
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Repeated high-intensity exercise modulates Ca2+ sensitivity of human skeletal muscle fibers
- 2016
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Ingår i: Scandinavian Journal of Medicine and Science in Sports. - : Wiley. - 0905-7188 .- 1600-0838. ; 26:5, s. 488-497
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Tidskriftsartikel (refereegranskat)abstract
- The effects of short-term high-intensity exercise on single fiber contractile function in humans are unknown. Therefore, the purposes of this study were: (a) to access the acute effects of repeated high-intensity exercise on human single muscle fiber contractile function; and (b) to examine whether contractile function was affected by alterations in the redox balance. Eleven elite cross-country skiers performed four maximal bouts of 1300m treadmill skiing with 45min recovery. Contractile function of chemically skinned single fibers from triceps brachii was examined before the first and following the fourth sprint with respect to Ca2+ sensitivity and maximal Ca2+-activated force. To investigate the oxidative effects of exercise on single fiber contractile function, a subset of fibers was incubated with dithiothreitol (DTT) before analysis. Ca2+ sensitivity was enhanced by exercise in both MHC I (17%, P<0.05) and MHC II (15%, P<0.05) fibers. This potentiation was not present after incubation of fibers with DTT. Specific force of both MHC I and MHC II fibers was unaffected by exercise. In conclusion, repeated high-intensity exercise increased Ca2+ sensitivity in both MHC I and MHC II fibers. This effect was not observed in a reducing environment indicative of an exercise-induced oxidation of the human contractile apparatus.
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