| 1. |
- Björklund, Glenn, et al.
(author)
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A comparison between elite and well trained cross-country skiers in physiological response to variations in intensity during prolonged exercise
- 2008
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In: 13th Annual Congress of the European College of Sports Science. - Cologne : Sportools. - 9789727351565 ; , s. 522-
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Conference paper (peer-reviewed)abstract
- Introduction: Cross-country ski racing includes continual variations in intensity due to terrain and tactics {Mygind et al 1994; Norman et al 1989). Consequently, the recovery between periods with higher intensity might affect the outcome of the race. Both blood metabolites and respiratory variables are used for standard performance evaluations for endurance athletes, although there is a lack information if respiratory variables respond similar to blood lactate and acid/base values during prolonged variable exercise. Therefore, the aims with the present study were to 1) evaluate whether respiratory variables are associated with blood lactate and acid/base variables, 2) how/if these variables might predict physical performance and 3) whether a calculated heart rate-oxygen uptake (HR-VO2) relationship is valid during variable intensity exercise. Methods: 12 cross-country skiers classified as elite (E, n=6) and formerly well-trained (FWT, n=6) performed two roller ski tests. 1) An incremental test to establish maximal oxygen uptake (VO2max), maximum heart rate (HRmax) and lactate threshold (LT). Submaximal and maximal VO2 and HR during the incremental test were used for calculating the individual HR-VO2 linear relationship and 2) a 48-min long variable intensity protocol (VIP) at alternating exercise intensities, 90% (HI90) and 70% (MI70) of VO2max. Cardio-respiratory variables and venous blood samples were continuously collected throughout the VIP. Comparisons between E and FWT were performed using a two-tailed unpaired Student’s t-test and a ANCOVA analysis was used to determine which physiological variable best could prognosticate time to exhaustion (TTE). A simple linear regression was used to establish the relationship between HR and VO2. Results: Blood lactate concentrations [La] were higher and base excess [BE] lower for FWT from the first MI70 (P<0.05). FWT had augmented RER during all HI90 and an elevated VE/VO2 during the second and third HI90 in comparison to E (P<0.05). The expected HR were higher during the MI70 exercise intensities regardless of group affiliation (P<0.05). The blood [La] response predicted time to exhaustion earlier than respiratory variables (P<0.05). Discussion: Blood lactate and acid/base fluctuations were not reflected by RER and the ventilatory equivalents. Furthermore, blood lactate is to prefer, in comparison to ventilatory variables, to study performance related recovery processes during endurance exercise with variations in intensity. The expected HR-VO2 relationship was not valid during VIP.
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| 2. |
- Holmberg, Hans-Christer, 1958-, et al.
(author)
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Biomechanical analyses and predictors of diagonal stride performance in elite cross-country skiers
- 2008
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In: Proceedings of the 13th Annual Congress of the European College of Sports Science. - Cologne : Sportools. - 9789727351565 ; , s. 568-
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Conference paper (peer-reviewed)abstract
- Introduction: In cross-country (XC) skiing classical style was the only racing style until the mid 1980s and the main focus of early biomechanical studies was on the diagonal technique (DIAG). With the introduction of the new free style, research became more oriented toward this although both styles have gone through substantial development during the last decade (Smith, 2002). Recently, modern double poling technique has been thoroughly analyzed as regards its biomechanical characteristics and factors related to performance (Holmberg et al., 2005; 2006). However, there is still a lack of biomechanical data describing modern DIAG. Therefore, the aims of the present study were 1) to perform a basic biomechanical description of modern DIAG, and 2) to detect decisive factors related to DIAG performance. Methods: Twelve Swedish elite XC skiers (VO2max-DIAG: 72.3 ± 3.8 ml kg-1 min-1) performed DIAG roller skiing at a treadmill inclination of 9° at 11 km h-1 for biomechanical analyses. DIAG performance was defined by time to exhaustion (TTEDIAG) during a DIAG incremental pre-test (4°-11° [1°/min]; with a constant velocity of 11 km/h). Leg and arm joint angles (goniometers), pole forces (strain gauge transducers; 2000 Hz) and plantar forces (Pedar Mobile; 100 Hz) were recorded continuously. Correlations between DIAG performance (TTEDIAG) and biomechanical variables was examined using Pearson product-moment correlation coefficient tests (P<0.05). Results: Correlations were found for cycle time and cycle length (r=0.688; P<0.01), cycle rate (r=-0.731; P<0.01), relative foot ground contact time (r=-0.658; P<0.05), absolute and relative leg swing time (r=0.756, P<0.01; r=0.658; P<0.05), amplitude and angular velocity of hip angle during leg swing (r=0.634; r=0.652; P<0.05), hip angle at ski plant (r=-0.616; P<0.05), absolute and relative hip extension time (gliding phase) (r=0.689, P<0.01; r=0.592, P<0.05), absolute peak foot force (r=0.606, P<0.05), duration and amplitude of the knee angle extension from ski in, e.g. when the skis came in contact with the ground, to the knee angle maximum (r=0.743; r=0.710, P<0.01), rear foot force at minimal hip angle before push-off (r=-0.634; P<0.05), relative (%BW) peak pole force (r=-0.706; P<0.01), pole force at start of forward swing of the opposite leg (r=-0.681; P<0.01), amplitude of elbow extension during poling (r=0.741; P<0.01) and duration of elbow extension after pole out (r=-0.615; P<0.01). Discussion: It can be concluded that better DIAG skiers have 1) a longer and more distinct forward swing in their legs, 2) shorter ground contact, characterised by a lower body position when the skis come into contact with the ground, 3) a more distinct hip and knee angle extension (preparation) just before push-off, 4) a higher absolute production of leg force during push-off and 5) arm work characterised by lower and later peak pole forces (late accentuation).
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| 3. |
- Holmberg, Hans-Christer, 1958-, et al.
(author)
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Depletion and resynthesis of glycogen in arm and leg muscles after a classical 15-K cross-country ski race
- 2008
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In: Proceedings of the 13th Annual Congress of the European College of Sports Science. - Cologne : Sportools. - 9789727351565 ; , s. 660-
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Conference paper (peer-reviewed)abstract
- Introduction: Bicycle exercise or running has been most frequently used in studies of glycogen usage during exercise and the replenishment in the recovery afterwards. In cross-country skiing muscle glycogen is probably a dominant factor for maintaining speed and can be crucial in the finish. In this sport the arms may be more critical than the legs both for speed and finish, especially in the classical technique. Thus, in the present study we examined muscle glycogen content in arm and leg muscle in connection with a race and the first 24 hrs after the race with two specific aims. 1) Evaluate whether arm muscles use more glycogen than the leg muscles and whether there is a muscle fibre type specific glycogen depletion pattern for the type 2 fibres, 2) Evaluate whether water intake instead for carbohydrates during the first 4 hrs after the race affect the resynthesis of glycogen acutely and next morning. Methods: Ten elite male competitive cross-country skiers (Age:22; Body height:182 cm; Body mass:80.8 kg; VO2max:72 ml kg-1 min-1) performed a 15K classical race in varying terrain. The subjects were placed into two groups; a H2O-group and a CHO-group. Directly after the race the H20-group was only allowed to drink water whereas the CHO-group used a normal post-race strategy to refill CHO with sport drink and gel and thereafter a meal. After 4 hrs both groups had the same carbohydrate enriched food intake. Muscle biopsies were obtained from an arm (triceps brachii) and a leg (v. lateralis) muscle before, directly after, as well as 4 and 20 hrs after the race. Muscles samples were analyzed for fibre types and glycogen as well as glycogen depletion pattern. Results: Muscle glycogen measured directly after the race was reduced by 32 % (484.7 to 331.3 mmol kg-1dw) in the legs and 69 % (from 540.2 to 167.1 mmol kg-1dw) in the arms. Type 1 muscle fibre type depletion was the dominant finding for both arms and legs, with some type 2A fibres being partly depleted in the arms. After 4 hrs with water no elevation in neither arm nor leg muscle glycogen content was observed but with CHO the legs did increase with 80 and the arms with 110 mmol kg-1dw and significantly more in the legs compared to the arms(P<0.05). Next morning regardless of being in H20- or the CHO group all subjects had returned to close to their pre-race muscle glycogen content in both arms and legs. Conclusion: The main findings were 1) in classical/diagonal skiing is the recruitment pattern of muscle fibre types the typical for prolonged exercise with primarily type 1 fibres being glycogen depleted but equally clear is that the arms are more used than the leg muscle as muscle glycogen stores were more markedly utilized in the arm as compared to the leg muscles.2) Restoration of the muscle glycogen stores are dependant of a carbohydrate intake but of note is that in only 20 hrs of recovery was the pre exercise glycogen level reached regardless of no carbohydrate intake for 4 hrs immediately after the race.
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| 4. |
- Mattsson, C. Mikael, et al.
(author)
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Unexpected cardiovascular response during ultra-endurance exercise.
- 2008
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In: 13th Annual Congress of the European College of Sport Science (ECSS), Estoril, Lissabon, Portugal.. - 9789727351565 ; , s. 142-
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Conference paper (other academic/artistic)abstract
- During prolonged exercise at fixed work rate heart rate (HR) increases slowly with concomitant decrease in stroke volume (SV) in order to maintain cardiac output. Simultaneously, an increased oxygen uptake (VO2) occurs. In this paper we report an unexpected and previously not observed cardiovascular response to ultra-endurance exercise. Nine well-trained male athletes performed 24-h exercise in a controlled laboratory setting, with altering blocks of kayaking, running and cycling. Each block consisted of 110 min of exercise and 10 min of rest. Measurements (HR, VO2 and blood samples) were conducted during cycling at fixed work rate every 6th hour. The average work intensity was approximately 55 % of respective VO2peak. HR was increased at 6 h with 15 beats/min (13 %) compared to pre-exercise (Pre-Ex), but thereafter unexpectedly returned towards initial values. VO2 on the other hand was increased with 0.22 l/min (10 %) at 6 h and 0.37 l/min (17 %) at 12 h compared to Pre-Ex, and thereafter remained stable. This implies an increased oxygen pulse (VO2/HR) with approximately 10 % compared to Pre-Ex at the later half of the exercise. The cardiovascular drift did not progress continuously, but instead changed drastically when duration exceeded 6 hours. The changes in HR and VO2 might have different and complex explanations. HR drift might be explained mainly by central circulatory adaptation (e.g. desensitisation of cardiac adrenergic receptors) whereas drift in VO2 may depend upon peripheral changes (e.g. decreased mitochondrial efficiency). Consequently, using solely HR for determining exercise intensity and energy expenditure becomes invalid during ultra-endurance exercise, if the cardiovascular drift is not measured and taken into account.
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| 5. |
- Tesch, Per, et al.
(author)
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Peak oxygen uptake using a training device for combined resistance and aerobic exercise in space and on earth
- 2008
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In: 13th Annual Congress of the European College of Sports Science. - Cologne : Sportools. - 9789727351565 ; , s. 523-
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Conference paper (peer-reviewed)abstract
- Astronauts traveling in Orbit are mandated to perform both aerobic and resistance exercise to combat cardiovascular and muscular deconditioning. A non-gravity dependent flywheel resistance exercise device (FWD), proven to be effective in blunting muscle atrophy when used by bedridden subjects, has been configured to allow for aerobic exercise as well. The current study aimed at determining aerobic energy yield and related physiological demands during exercise using this novel apparatus. Methods: Eight men and women (23±3 yrs, 65±5 kg, 170±6 cm) performed all-out, indoor, stationary rowing exercise randomly on either a commercially available Concept II ergometer (CII) or the FWD. Using a magnetic brake system, the FWD and similar to the CII, produced mainly concentric resistance exercise with the aid of the inherent inertia of rotating flywheels. Progressive exercise protocols (increased frequency and magnetic force) assessed peak oxygen uptake and heart rate, rate of perceived exertion and post lactate concentration. Results Peak oxygen uptake averaged 3.18±0.50 and 3.11±0.49 l/min, respectively during exercise using CII and FWD. Peak oxygen uptake, plasma lactate concentration, heart rate and rate of perceived exertion were not different (p>0.05) across exercise using these two devices. However, time to exhaustion was somewhat (p<0.05) longer for the FWD. Conclusion: Collectively the current results suggest that the novel method of offering an aerobic exercise stimulus is as effective as the most established technology for indoor rowing used by crew. Given that the space agencies have recognized the need for effective exercise countermeasures hardware that has a feasible mass and envelope and features allowing for multiple purposes (e.g., concentric/eccentric resistance and aerobic exercise) in a single piece of apparatus, the current technology should be considered for use in space.
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