Development of aerobic power in relation to age and training in cross-country skiers.

In most of the training studies on different populations the effects of training have been investigated up to a frequency of five to six times per week and a duration of 45 min per session. These correspond to the training regimens of 15-yr-old cross-country skiers and, consequently, the results cannot be applied to older athletes. The maximal oxygen uptake (VO2max) of cross-country skiers increases with age and training from about 55-60 to 75-80 ml.kg-1.min-1 between 15 and 25 yr of age. After 20 yr of age VO2max starts to level off, but elite skiers are able to increase VO2max further concomitantly with an increase in the volume of training and the volume of intensive training. The activity of oxidative enzymes in muscles of skiers is increased with training, but distance runners have had a higher oxidative capacity in their leg muscles. Although widely used by cross-country skiers, the training effects of roller skiing, skiwalking-skistriding, and long-distance training on skis are to a large extent unknown. However, intensive training at the intensity of "anaerobic threshold" or higher seems to be most effective in inducing improvements in maximal oxygen uptake; distance training at relatively low intensity seems to be most effective in producing improvements in the determinants of submaximal endurance.     

Anterior compartment pressures in cross-country skiers. A comparison of classic and skating skis.

This paper compares the pressure changes in the anterior compartment of the leg when cross-country skiing using the skating method on either skating skis or classic skis. Intracompartmental pressures of the right leg were recorded from the tibialis anterior muscle of 10 subjects at rest and 15 seconds after 10 to 12 minutes of cross-country skiing on a designated course. All subjects completed two trials on different days. In one trial, subjects used skating skis and for the other trial, classic skis were used for the skating technique. Although the average pressure increase was higher for the classic ski trials than for the skating ski trials, the difference was not significant. This finding indicates that cross-country skiers who skate on a classic ski as opposed to a shorter skating ski do not experience a significantly greater increase in their anterior compartment pressure. Thus, it appears that the type of ski used is not the most significant factor contributing to chronic compartment syndrome.     

Upper body aerobic fitness comparison between two groups of competitive surfboard riders

The aim of the present study was to evaluate and compare the upper-body aerobic fitness characteristics in 2 groups of competitive surfers with different performance levels. Thirteen male competitive surfers performed an incremental dry-land board paddling test to determine specific peak oxygen uptake (VO2peak), peak power output (Wpeak) and the exercise intensity (%VO2peak) that elicits a blood lactate concentration of 4 mmol x L(-1) (LT4). As a measure of surfing performance, surfers were ranked according to their competitive season performance (RANK) and divided into 2 groups based on their performance level; European top-level competitive surfers (ELS) (n = 7) and regional level competitive surfers (RLS) (n = 6). ELS reached significantly higher values than RLS for Wpeak (154.71 +/- 36.82 W vs. 117.70 +/- 27.14 W: P = 0.04) and LT4 (95.18 +/- 3.42 %VO2peak vs. 88.89 +/- 5.01 %VO2peak; P = 0.02) but not VO2peak (3.34 +/- 0.31 L x min(-1) vs. 3.40 +/- 0.37 L x min(-1); P = 0.77). Spearman-rank order correlation analysis revealed that RANK was inversely correlated with Wpeak (r = -0.65, P = 0.01) and LT4 (r = -0.58, P = 0.03). These findings identify that better surfers have higher upper body aerobic fitness scores.     

Responses to training in cross-country skiers.

PURPOSE: This study evaluated whether cross-country skiers who did not respond positively to a training program consisting of high volume and low intensity would improve if high-intensity training volume was doubled during a subsequent training year. METHODS: During the first year of the study, cross-country skiers (N = 14) were evaluated for VO2max, VO2threshold, lactate response, max arm power, and competitive results after a standard training program. During the second year, the athletes were divided into a control group (athletes who had responded well to the training) and a treatment group (athletes who had responded poorly to the training). The control group (N = 7) repeated the previous year's training program. The treatment group (N = 7) was given a modified training program which increased high-intensity training time as a percentage of total training from < 17% to > 35% and decreased low-intensity training volume 22%. RESULTS: The treatment group, using the high-intensity training program, demonstrated significantly improved VO2max, VO2threshold, max arm power, and competitive results (P < 0.05). CONCLUSIONS: Increased volume of high-intensity training may improve competitive results in cross-country skiers who fail to respond to increased volume of low-intensity training.     

Effects of body position on slide boarding performance by cross-country skiers

PURPOSE: In this study, we examined the effects of body position (from deep to high position) in slide boarding by well-trained cross-country skiers. The main hypothesis was that a deeper, more "crouched" position would lead to reduced air resistance and enhanced power production during explosive extension of the lower limbs, and thereby to an increased performance, even though the upper extremity may not be used for poling in this deep position. METHODS: Measurements (air resistance in a wind tunnel, power output, kinematics, gas exchange, and blood lactate levels) were performed during a 30-s maximal test and a 3-min maximal test performing (imitation) ski-skating movements on a sliding board at three different body positions (high, moderate, and deep). RESULTS: Our findings indicate that a deep position enhances power production by 24% and reduces air resistance by 30% for the 30-s maximal test. Power production did not increase in the 3-min test, but lactate levels after exercise were increased in the deep position. Calculated efficiency was not affected by body position. CONCLUSION: The current results indicate that for a short duration, the deeper sit provides sufficient advantages that it may prove useful to apply such a position in sprint ski-skating, even though the use of the upper extremities in poling will be strongly hampered.     

Profiles of cross-country and alpine skiers

Skiers were profiled in regard to cardiovascular fitness, muscle strength, motor control, coordination, and muscle fiber composition. Skiing injuries were also profiled. The profile is useful in determining the potential for injury and in developing training programs to prevent injuries.     

Upper and lower body anaerobic power: comparison between biathletes and control subjects

This study compared power outputs (PO) from both the upper body (UB) and lower body (LB) Wingate tests of anaerobic power between biathletes and control subjects. Ten biathletes (B) selected by the British Ski Federation for potential assignment to the British team and 13 control (C) subjects cranked or pedaled the same Bodyguard ergometer at maximal RPMs for 30 s against resistances of 2.94 and 4.41 J/rev/kg body weight (BW), respectively. POs were calculated in watts (W) and expressed as peak power (PP, highest 5-s interval), mean power (MP, the mean for 30 s), and power decrease (PD, difference between PP and lowest 5-s PO divided by time). Absolute PP and MP for both UB and LB did not differ between groups. A comparison of POs made relative to BW showed B to have higher values than C: 11.25 vs 10.25 W/kg for LB PP (P less than .05) and 9.21 vs 7.96 W/kg for LB MP (P less than .001). The data expressed relative to kg fat free mass (FFM) showed only MP to be significantly greater in B compared with C (P less than .001). Similar PO relationships were found for the UB where PP (P less than .01) and MP (P less than .001) expressed per kg BW and MP (P less than .001) expressed per kg FFM were higher for B than C. Concomitantly, PD was lower in B than C for both the UB (P less than .05) and LB (P less than .01).(ABSTRACT TRUNCATED AT 250 WORDS)     

Physiological characteristics of elite prepubertal cross-country runners.

Eight elite cross-country runners and eight normally active boys 8--11 years of age were studied. The runners were selected on the basis of success in regional and/or national championships. Two of them had the first to third fastest mile run times for their age groups in the U.S. for three years. Tests included submaximal and maximal treadmill runs, an anaerobic capacity bicycle test, a mile run, and various anthropometric measures. A best career mile run (BCM) was used for comparisons within the running group. At submaximal work levels of 5.6 and 7 mph (124, 161, and 187 meters/min) the values for heart rate (HR) and respiratory exchange ratio (R) were significantly lower for the runners than for the non-runners. The VO2max of the runners (56.6 ml kg min) was significantly higher than that of the non-runners (46.0 ml kg min). For all subjects combined, mile run time was highly correlated with percent VO2max and percent max HR at all submaximal running speeds (r greater than 0.8). The correlation coefficient between mile run time and VO2max was -0.88. Within the running group, however, BCM was unrelated to VO2max but was closely related to percent VO2max at 8 mph (213 meters/min) with 4 = 0.86, and to anaerobic capacity (r = -0.88). There were no significant differences between the groups in age, height, weight, max HR, and percent body fat. Thus the runners had higher aerobic and anaerobic capacities, and greater utilization of fat as an enrgy sustrate during submaximal work. Within the running group, anaerobic capacity and running economy were closely related to BCM time, whereas VO2max was not.     

Competition performance and basal nocturnal catecholamine excretion in cross-country skiers.

Objective techniques to determine whether an athlete is optimally prepared for a competition are virtually nonexistent. Preparedness for sports competition is commonly judged through the experience of the athletes and their coaches. Evidence from overtraining studies suggests that catecholamine (Cat) excretion rates may correlate with performance in athletes. PURPOSE: We therefore attempted to determine whether a relationship existed between performances of world-class cross-country skiers and basal nocturnal Cat excretion (BNCE). METHOD: During the Cross-Country Skiing World Championships, we determined BNCE in nine cross-country skiers of the Swiss national team by measuring free Cat concentration (dopamine = D, norepinephrine = NE, epinephrine = E) in morning urine samples, using high performance liquid chromatography. Expert judgments of competition performance (ECP) were assessed by two experienced professional coaches of the national team by using an 11-step scale. RESULTS: The BNCE correlated significantly with ECP in cross-country skiers (r2 = 0.84 and P < for NE; r2 = 0.86 and P < 0.001 for D). Athletes who had their best absolute competition results (ACR) showed the highest NE and D concentrations. CONCLUSION: These data suggest that competitive cross-country skiers with higher D and NE excretion may reach better competition levels compared with those with lower levels. Measures of BNCE provide objective information about competition performance, which may benefit athletes in their precompetition preparation.     

Detection of autologous blood transfusions in cross-country skiers

Transfusion of autologous blood (blood doping) has been used by athletes to improve performance in sports events. This practice has been banned by the International Ski Federation (FIS) and the International Olympic Committee (IOC). So far, no reliable method for detection of blood doping has been available. In the present study, a group of six elite cross-country skiers, who were phlebotomized and retransfused with 1350 ml of blood 4 weeks later, was compared with a control group (n = 7) in whom no blood doping was performed. The blood was stored at +4 degrees C for 4 weeks. Hemoglobin increased by 7.9% from the prephlebotomy level and by 14% from the preinfusion level. The reinfusion of blood caused a 60% reduction (P less than 0.001) in serum erythropoietin in 24 h and a sharp increase (P less than 0.05) in serum iron and bilirubin after a test race performed on the day of reinfusion. It is therefore concluded that a combination of measurements of hemoglobin and bilirubin, iron, and erythropoietin in serum could detect 50% of the blood-doped athletes by a single test sample during the 1st week after reinfusion. If two test samples were used, an increase in Hb of more than 5%, and a decrease in serum erythropoietin by more than 50%, would be discussed in 50% of the blood-doped athletes throughout the first 2 weeks after reinfusion and without implicating any of the controls.     

Iron supplementation and running performance in female cross-country runners.

The purpose of this study was to determine the effects of two weeks of high dosage iron supplementation on various blood iron indices and metabolic parameters in non-anemic, iron-depleted competitive female cross-country runners. The subjects were highly trained members of the Colorado State University cross-country team and were completing 40 to 50 miles of training weekly. A pretest, post-test single-blind crossover design was employed. Upon collection of baseline exercise blood and metabolic data, five subjects were randomly assigned to iron supplementation (650 mg ferrous sulfate; 130 mg elemental iron) and five subjects to placebo treatment. At two weeks the treatments were reversed. Exercise blood and metabolic data were collected at two-week intervals. Dietary iron intake was assessed using a three-day dietary survey. Dietary analysis revealed deficiencies in vitamin B-6, iron, magnesium, and zinc according to USRDA standards. Baseline blood samples revealed no deficiencies in iron storage or transport proteins. Two weeks of iron supplementation resulted in no significant increases in blood iron indices. Metabolic parameters related to running performance were also unchanged after iron supplementation. High dosage, short-term iron supplementation appears to have no effect on blood or metabolic parameters in iron-depleted but non-anemic female cross-country runners.     

Upper body training and the triceps brachii muscle of elite cross country skiers

This study aimed at evaluating whether addition of extensive upper body training in well-trained cross country skiers induces an adaptation of the triceps brachii (TB) muscle and whether this affects performance. Muscle biopsies were obtained from TB muscle in six male elite cross country skiers before and after 20 weeks of increased upper body training. The cross-sectional area of type I and IIA fibers increased by 11.3% and 24.0%, respectively, and so did the number of capillaries per fiber (2.3-3.2) (all P<0.05). SDS-polyacrylamide electrophoresis revealed in single fibers that the number of fibers expressing myosin heavy chain (MHC) type I isoform decreased from 68.7% to 60.9% (P<0.05), MHC I/IIA isoform was unaltered, while MHC IIA fibers increased from 21.6% to 35.7% and the 4.8% MHC IIA/IIX disappeared with the training (both P<0.05). Citrate synthase and 3-hydroxyacyl coenzyme A dehydrogenase activities increased by 23.3% and 15.4%, respectively, and double poling 10 km time-trial by 10.4% (all P<0.05). The values for TB are similar to what has been demonstrated for leg muscles after exercise training. The subjects who demonstrated the largest improvement in performance exhibited the largest muscle adaptation, which, in turn, was related to the pre-maximal oxygen uptake.     

Trait and state anxiety in male and female cross-country runners.

The purpose of this study was to explore the relationships between state/trait anxiety and competitive cross-country performance for males and females. A-trait and A-state pre- and post-competition were monitored in 38 females and 26 males at major meetings. The females' A-trait was correlated with pre-race A-state (p less than .05) which was itself correlated significantly with race performance (p less than .05). A significant post-race A-state reduction occurred only with the better runners. The correlation between A-trait and pre-race A-state was also found in the male athletes (p less than .05) while A-trait significantly correlated with race performance (p less than .05). A-state was significantly reduced post-race, the greatest decrease being observed in the top performers. It is concluded that trait as well as transient dispositions are relevant when psychological determinants of performance are considered.     

Biomechanical analysis of double poling in elite cross-country skiers

PURPOSE: To further the understanding of double poling (DP) through biomechanical analysis of upper and lower body movements during DP in cross-country (XC) skiing at racing speed. METHODS: Eleven elite XC skiers performed DP at 85% of their maximal DP velocity (V85%) during roller skiing at 1 degrees inclination on a treadmill. Pole and plantar ground reaction forces, joint angles (elbow, hip, knee, and ankle), cycle characteristics, and electromyography (EMG) of upper and lower body muscles were analyzed. RESULTS: 1) Pole force pattern with initial impact force peak and the following active force peak (PPF) correlated to V85%, (r = 0.66, P < 0.05); 2) active flexion-extension pattern in elbow, hip, knee, and ankle joints with angle minima occurring around PPF, correlated to hip angle at pole plant (r = -0.89, P < 0.01), minimum elbow angle (r = -0.71), and relative poling time (r = -0.72, P < 0.05); 3) two different DP strategies (A and B), where strategy A (best skiers) was characterized by higher angular elbow- and hip-flexion velocities, smaller minimum elbow (P < 0.01) and hip angles (P < 0.05), and higher PPF (P < 0.05); 4) EMG activity in trunk and hip flexors, shoulder, and elbow extensors, and several lower body muscles followed a specific sequential pattern with changing activation levels; and 5) EMG activity in lower body muscles showed DP requires more than upper body work. CONCLUSIONS: DP was found to be a complex movement involving both the upper and lower body showing different strategies concerning several biomechanical aspects. Future research should further investigate the relationship between biomechanical and physiological variables and elaborate training models to improve DP performance.     

Maximal strength training improves work economy in trained female cross-country skiers.

PURPOSE: The present study examines the hypothesis that maximal strength training improves work economy and anaerobic threshold in trained female cross-country skiers while working on a ski ergometer. METHODS: Fifteen female cross-country skiers (17.9 +/- 0.3 yr, 166.7 +/- 1.3 cm, 60.1 +/- 1.9 kg, and 55.3 +/- 1.3 mL x kg(-1) x min(-1)) participated in the study. Eight skiers made up the high-intensity strength-trained group, and seven served as the control group. Endurance performance was tested on a specially instrumented ski ergometer. Strength training and testing simulated double poling in cross-country skiing. RESULTS: A significant (P < 0.001) improvement in double-poling economy on the ski ergometer was observed among the strength-trained group. Anaerobic threshold did not change during the experimental period for either group. After a 9-wk training period, time to exhaustion increased from 5.2 (+/-0.9) to 12.3 (+/-1.6) min (P < 0.001) and from 4.0 (+/-0.9) to 6.3 (+/-0.9) min (P < 0.01) for the strength and control group, respectively. Time to exhaustion was significantly higher (P < 0.001) for the strength group compared with the control group after training. One repetition maximum increased 14.5% (1.8) (P < 0.001) in the strength group but was unchanged in the control group. Expressed in relation to peak force at one repetition maximum, strength training resulted in a significant reduction in the relative available force employed working on the ski ergometer (P < 0.01). Time to peak force at maximal aerobic velocity on the ski ergometer was significantly reduced in the strength-training group (P < 0.01). CONCLUSIONS: It is concluded that maximal strength training in the upper-body improved the double-poling performance by improved work economy. Work economy was improved by a reduction in relative workload and time to peak force while double poling.     

Pre- and post-season heart rate variability in adolescent cross-country skiers

To investigate the effects on cardiac autonomic control after a competitive cross-country skiing season, 9 females and 8 males, 16-19 years old, performed tilt-table heart rate variability (HRV) recordings and incremental treadmill tests before (August), and after (April the following year) the most intensive period of training and competition. Spectral analysis of HRV showed increased total variability at rest and reduced low frequency variability in the tilted position (LFtilt) at the second test (P<0.05). The female subgroup showed consistently higher high frequency (HF) and total heart rate variability than males. Total run time (RunT) increased from 18.5+/-1.9 min to 19.4+/-1.7 min (mean+/-SD) in the entire group (P<0.05), while VO2max only showed a non-significant increase (0.05相似文献   

Self-reported asthma and exercise-induced asthma symptoms in high-level competitive cross-country skiers

The prevalence of asthma and exercise-induced respiratory symptoms in 153 high-level Norwegian cross-country skiers and 306 control subjects were assessed in a postal survey. The response rates were 100% for the skiers and 79% for the controls. A present or past history of asthma was reported by 14% of the skiers and 5% of the controls. The prevalence of asthma increased signhcantly with increasing age among the skiers but not among the control subjects. The majority of the controls who reported asthma dated the onset of the disease to childhood, while the skiers dated the onset of asthma primarily to late adolescence or early adult life. The skiers used anti-asthmatic medication significantly more often than did the controls. Exercise-induced respiratory symptoms such as chest tightness, shortness of breath, cough, wheezing and sputum production were re- ported by 2–3 times as many skiers as controls. Exacerbation of respiratory symptoms was frequently associated with cold weather, humid weather or with recovering from an airway infection. The results of the present study indicate that cross-country skiers may be at an increased risk for acquiring obstructive respiratory disorders.     

Longitudinal variations in bronchial responsiveness in cross-country skiers and control subjects

Longitudinal variations in bronchial responsiveness to methacholine was studied in 19 male crosscountry skiers 19–21 years old during the season of their sport and compared with the response in 22 age-matched control subjects with minimal physical activity. The methacholine concentration required for a 10% fall in the forced expiratory volume in the first second (PC₁₀) remained stable from August to November in the group of skiers, then decreased from November to February and finally increased from February to June. In the control group, PC₁₀ increased from August to November, increased further to February and finally decreased from February to June. Alternative methods for expressing bronchial responsiveness as the linear dosc-response slope or the logarithmic dose-response slope gave no more information than did PC₁₀ alone. High correlations were found between PC₁₀ and either of the dose-response slopes. PC₁₀ and the dose response-slopes were equally reproducible when measured on two successive days. In contrary to the control group, high-performance cross- country skiers demonstrated increased bronchial responsiveness in the winter. The PC₁₀ was an advantageous method for studying longitudinal changes in bronchial responsiveness among healthy subjects.