Effect of reinfusion of autologous blood on exercise performance in cross-country skiers

The effect of reinfusion of autologous blood (1350 ml) on exercise time over a specified distance (approx. 15 km) 4 weeks after phlebotomy ("blood doping") were investigated in six well-trained cross-country skiers. An additional control group of six well-trained skiers was included in the study. Test races were performed before phlebotomy, 3 h after, and 14 days after reinfusion of blood. In each test race, the mean time of the control group was set to 100% and the time of the blood-doped subjects expressed in percentage of the control group mean time. In the first control race, the mean time of the subjects who were later "blood doped" was 99.4% of the control group. However, both 3 h and 14 days after the reinfusion of autologous blood, the mean time of the blood-doped subjects was significantly lower (94.1%; P less than 0.05; 96.3%, P less than 0.05, respectively) than the control group. In conclusion, reinfusion of autologous blood stored in a refrigerator for 4 weeks after phlebotomy significantly increased performance expressed as race time in cross-country skiers. The significantly increased performance was observed both 3 h and 14 days after reinfusion.     

Serum erythropoietin in cross-country skiers

Serum erythropoietin (Epo) activity, hemoglobin (Hb), and hematocrit (Ht) were determined in 21 cross-country skiers during the training season. The Epo levels were not significantly reduced in the skiers relative to the normal population (P less than 0.01 and P less than 0.001, respectively). In 11 athletes Epo, Ht, urinary gamma-glutamyltransferase, N-acetyl-beta-glucosaminidase, and microalbuminuria were determined before and after a 50-km ski race at 1600 m above sea level. A significant increase of these variables (except for Ht) was found after the competition (P less than 0.001). It is concluded that while the reductions in Hb and Ht, which are typical of several endurance exercises, are not accompanied by a renal hypoxia sufficient to stimulate Epo overproduction, the renal hypoxia reached during the strenuous exercise of the race at altitude may be effective in determining blood increases in Epo.     

Serum erythropoietin in cross-country skiers

Serum erythropoietin concentration and hemoglobin concentration were determined during the winter season in 41 male and 31 female well-trained, cross-country skiers. The athletes both lived and trained at low altitude (below 300 m above sea level). No significant differences in serum erythropoietin concentration were seen between male skiers (13.6 +/- 5.0 mU.ml-1), female skiers, (14.9 +/- 5.6 mU.ml-1), and normal controls (12.6 +/- 3.9 mU.ml-1) (mean +/- SD). In 18 of the skiers (12 males and 6 females), a second sample was taken after 2.3 +/- 0.18 months. No significant difference in either serum erythropoietin concentration or hemoglobin concentration was detected between the two samples in this combined group of skiers. The present study indicates that normal serum erythropoietin concentration is to be expected during the winter season at sea level in cross-country skiers living and training at low altitude.     

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.     

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.     

Low back pain in elite cross-country skiers

Low back pain is a common complaint among competitive cross-country skiers. Fifty-three top male and 34 female skiers in the age group 16–25 were interviewed with a questionnaire regarding anthropometric parameters, training variables, back pain and other injuries. The frequency of back pain was 64% in the whole group, men affected slightly more often than women. Back pain was defined as previous or present recurrent skiing correlated backache that more or less affected skiing ability. Diagonal skiing style was the most commonly back pain-inducing style, whereas no skier experienced back pain when "skating" only. The low back was the predominant location of pain. Anthropometric and training variables seemed to be of little value in predicting back pain.     

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.     

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 obstructive airway symptoms are common in young cross-country skiers

The reported high use of anti-asthmatic drugs in cross-country skiers prompted a study to assess the prevalence of self-reported asthma, asthma-associated symptoms and the use of anti-asthmatic medication among cross-country skiers. A self-administered questionnaire based on the Medical Research Council questionnaire was answered by cross-country skiers in the Swedish national ski team, in upper secondary school ski-classes and in the Swedish army ( n =305). Controls ( n =141) were pupils from regular classes in the same upper secondary schools. Skiers more often gave posi- tive answers to all questions on asthma and asthma-associated symptoms. The cumulative prevalence of asthma was 15% in skiers and 6% in controls. We conclude that the common use of anti-asthmatic drugs among cross-country skiers reflects a high prevalence of self-reported asthma and asthma-associated symptoms. The causes of these differences are un-known.     

Contribution of the legs to double-poling performance in elite cross-country skiers

PURPOSE: In the classical style of cross-country skiing, the double-poling (DP) technique, which is regarded as an upper-body exercise, is used on the flatter parts of a course. Limited biomechanical and physiological data are available about DP compared with other cross-country skiing techniques. The purpose of the present study was to evaluate the possible role of the lower body during DP. METHODS: Eleven elite cross-country skiers performed two incremental tests using DP roller skiing at 1 degree inclination on a treadmill with or without locking the knee and ankle joints (DPLOCKED and DPFREE). Maximal and peak oxygen uptake (VO2max and VO2peak) during classic diagonal skiing and DP, respectively, were measured. In addition, heart rate, blood lactate concentration, and maximal DP velocity (Vmax) were determined. Pole-ground reaction forces and joint angles (elbow, hip, knee, and ankle) were analyzed. RESULTS: The skiers obtained 7.7% higher VO2peak, 9.4% higher Vmax, and 11.7% longer time to exhaustion during DPFREE compared with DPLOCKED (all P < 0.05). There was a higher heart rate and blood lactate concentration in DPLOCKED at submaximal stages (all P < 0.05), with no difference in oxygen consumption. At 85% Vmax, corresponding to approximately 81% VO2peak FREE, the differences in physiological variables were accompanied by a 13.6% higher poling frequency, a 4.9% shorter poling phase, 13.3% shorter recovery phase, and 10.9% lower relative pole force in DPLOCKED (all P < 0.05). CONCLUSIONS: Movements of the knee and ankle joints are an integrative part in the skillful use of the DP technique, and restriction of the motion in these joints markedly affects both biomechanical and physiological variables, impairing DP performance.     

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.     

Blood profiles in elite cross-country skiers: a 6-year follow-up

Following the doping scandals at the World Championships in cross-country skiing in 2001, the International Ski Federation decided to generate individual blood profiles. From 2001 to 2007, 7081 blood samples from 1074 male and female elite cross-country skiers were collected and analyzed for hemoglobin concentration [Hb] and % reticulocytes (%rets). Data were applied to blood algorithms wherefrom blood model scores were calculated. From 1997–1999 to 2001–2002, the mean [Hb] was reduced by 0.9 g/dL to 15.3 g/dL in male skiers and by 0.4 g/dL to 13.8 in female skiers. From 2002–2003 to 2006–2007, the combination of increases in [Hb] and decreases in %rets led to pronounced increases in mean OFF-model scores. [Hb] was 0.2 g/dL higher at Olympic Games/World Championships (WOCs) than at World Cups competitions <4 weeks before and after WOCs. [Hb] and %rets increased with altitude in both genders. Since the introduction of an enlarged blood testing program, the mean [Hb] values were lowered to close to normal levels, but over the last 2–3 years there has been a small elevation and an increase in OFF-model scores, which may indicate a change in the manipulations used to elevate the [Hb].     

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.     

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.     

Changes in hemoglobin values in elite cross-country skiers from 1987-1999

Hemoglobin data have been available from ski teams beginning from 1987, and from 1989 to 1999 we have followed hemoglobin values in elite cross-country skiers in international competitions. The mean values at the 1989 World Nordic Ski Championships were lower than population reference values, as would be expected from plasma volume expansion associated with endurance training. However, an increase, particularly in the maximal values, became obvious in 1994 and rose further in 1996. These extreme values provide both a health risk to the individual athlete and unfair competition. After a rule limiting hemoglobin values was introduced, the drop of the highest values was remarkable: among men 15 g/l (0.23 mmol/l) and among women 42 g/l (0.65 mmol/l). It would appear that the rule had achieved its goal of limiting extreme hemoglobin values. Yet the mean hemoglobin concentrations in men and women have continued to rise, suggesting the continued use of artificial methods to increase total hemoglobin mass.     

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.