Oxygen uptake at different intensities and sub-techniques predicts sprint performance in elite male cross-country skiers

Purpose

To investigate the relationship between sprint-prologue performance (using the classical technique) and the oxygen uptake at the lactate threshold (\( {\dot{\text V}{\rm O}} \) ₂obla), maximal oxygen uptake (\( {\dot{\text V}{\rm O}} \) ₂max), and mean oxygen uptake during double poling (\( {\dot{\text V}{\rm O}} \) ₂dp).

Methods

Eight elite male cross-country skiers [age 24.8 ± 4.8 years, (mean ± SD)] completed two treadmill roller-skiing tests using the diagonal-stride technique and a 60 s double-poling test on a ski-ergometer to determine their \( {\dot{\text V}{\rm O}} \) ₂obla, \( {\dot{\text V}{\rm O}} \) ₂max, and \( {\dot{\text V}{\rm O}} \) ₂dp. Performance data were generated from a 1.25 km sprint prologue. Power-function modelling was used to predict the skiers’ race speeds based on the oxygen-uptake variables and body mass.

Results

There were correlations between the race speed and the absolute expression of the \( {\dot{\text V}{\rm O}} \) ₂obla (r = 0.79, P = 0.021), \( {\dot{\text V}{\rm O}} \) ₂max (r = 0.86, P = 0.0069), and \( {\dot{\text V}{\rm O}} \) ₂dp (r = 0.94, P = 0.00062). The following power-function models were established for race-speed prediction: 1.09 · \( {\dot{\text V}{\rm O}} \) ₂obla^0.21, 1.05 · \( {\dot{\text V}{\rm O}} \) ₂max^0.21, and 1.19 · \( {\dot{\text V}{\rm O}} \) ₂dp^0.20; these models explained 60 % (P = 0.024), 73 % (P = 0.0073), and 87 % (P = 0.00073), respectively, of the variance in the race speed. However, body mass did not contribute to any of the models (P = 0.97, 0.88, and 0.21, respectively).

Conclusions

Oxygen uptake at different intensities and sub-techniques is an indicator of elite male sprint-prologue performance. The absolute expression of the investigated oxygen-uptake variables should be used when evaluating elite male sprint-prologue performances; if skiers oxygen uptake differs by 1 %, their performances will likely differ by 0.2 % in favour of the skier with higher oxygen uptake.

     

The influence of incline and speed on work rate, gross efficiency and kinematics of roller ski skating

During competitions, elite cross-country skiers produce higher external work rates on uphill than on flat terrain. However, it is not presently known whether this reflects solely higher energy expenditure. Furthermore, the kinematic factors associated with these higher rates of uphill work have not yet been examined. Therefore, in the present investigation the work rate and associated kinematic parameters at similar metabolic rates during roller ski skating on flat and uphill terrains have been compared. Seven elite male skiers performed six 5-min sub-maximal exercise bouts at the same low, moderate and high metabolic rates on 2 and 8% inclines, while roller skiing on a treadmill employing the G3 skating technique. The work rate was calculated as work against gravity and friction, whereas the energetic equivalent of VO(2) was taken as the metabolic rate. Gross efficiency was defined as work rate divided by metabolic rate. Kinematic parameters were analyzed in three dimensions. At the same metabolic rate, the work rate, cycle rate, work per cycle and relative duration of propulsive phases during a cycle of movement were all higher on the 8% than on the 2% incline at all speeds (all P?相似文献   

Mechanical work and efficiency in level walking and running

1. The mechanical power spent to accelerate the limbs relative to the trunk in level walking and running, _int, has been measured at various `constant' speeds (3-33 km/hr) with the cinematographic procedure used by Fenn (1930a) at high speeds of running.

2. _int increases approximately as the square of the speed of walking and running. For a given speed _int is greater in walking than in running.

3. In walking above 3 km/hr, _int is greater than the power spent to accelerate and lift the centre of mass of the body at each step, _ext (measured by Cavagna, Thys & Zamboni, 1976b). In running _int < _ext up to about 20 km/hr, whereas at higher speeds _int > _ext.

4. The total work done by the muscles was calculated as W_tot = |W_int| + |W_ext|. Except that at the highest speeds of walking, the total work done per unit distance W_tot/km is greater in running than in walking.

5. The efficiency of positive work was measured from the ratio W_tot/Net energy expenditure: this is greater than 0·25 indicating that both in walking and in running the muscles utilize, during shortening, some energy stored during a previous phase of negative work (stretching).

6. In walking the efficiency reaches a maximum (0·35-0·40) at intermediate speeds, as may be expected from the properties of the contractile component of muscle. In running the efficiency increases steadily with speed (from 0·45 to 0·70-0·80) suggesting that positive work derives mainly from the passive recoil of muscle elastic elements and to a lesser extent from the active shortening of the contractile machinery. These findings are consistent with the different mechanics of the two exercises.

     

Gender differences in the physiological responses and kinematic behaviour of elite sprint cross-country skiers

Gender differences in performance by elite endurance athletes, including runners, track cyclists and speed skaters, have been shown to be approximately 12%. The present study was designed to examine gender differences in physiological responses and kinematics associated with sprint cross-country skiing. Eight male and eight female elite sprint cross-country skiers, matched for performance, carried out a submaximal test, a test of maximal aerobic capacity (VO_2max) and a shorter test of maximal treadmill speed (V _max) during treadmill roller skiing utilizing the G3 skating technique. The men attained 17% higher speeds during both the VO_2max and the V _max tests (P < 0.05 in both cases), differences that were reduced to 9% upon normalization for fat-free body mass. Furthermore, the men exhibited 14 and 7% higher VO_2max relative to total and fat-free body mass, respectively (P < 0.05 in both cases). The gross efficiency was similar for both gender groups. At the same absolute speed, men employed 11% longer cycles at lower rates, and at peak speed, 21% longer cycle lengths (P < 0.05 in all cases). The current study documents approximately 5% larger gender differences in performance and VO_2max than those reported for comparable endurance sports. These differences reflect primarily the higher VO_2max and lower percentage of body fat in men, since no gender differences in the ability to convert metabolic rate into work rate and speed were observed. With regards to kinematics, the gender difference in performance was explained by cycle length, not by cycle rate.     

Metabolic cost, mechanical work, and efficiency during walking in young and older men

Aim: To investigate mechanical work, efficiency, and antagonist muscle co‐activation with a view to better understand the cause of the elevated metabolic cost of walking (C_W) in older adults. Methods: Metabolic, mechanical and electromyographic measurements were made as healthy young (YOU; n = 12, age = 27 ± 3 years) and older (OLD; n = 20, age = 74 ± 3 years) men of equivalent body mass and leg length walked on a treadmill at four speeds (ranging from 0.83 to 1.67 m s^?1). Results: Net (above resting) C_W, determined by indirect calorimetry was 31% higher (average across speeds) in OLD (P < 0.05). The integrity of the passive pendulum like interchange of mechanical energies of the centre of mass (COM_B), an energy‐saving mechanism, was maintained in OLD. Furthermore, total mechanical work, determined from fluctuations in mechanical energy of COM_B and of body segments relative to COM_B, was not significantly elevated in OLD. This resulted in a lower efficiency in OLD (?17%, P < 0.05). Co‐activation, temporally quantified from electromyography recordings, was 31% higher in OLD for antagonist muscles of the thigh (P < 0.05). Thigh co‐activation was moderately correlated with C_W at three speeds (r = 0.38–0.52, P < 0.05). Conclusion: Healthy septuagenarians with no gait impairment have an elevated C_W which is not explained by an elevation in whole body mechanical work. Increased antagonist muscle co‐activation (possibly an adaptation to ensure adequate joint stability) may offer partial explanation of the elevated C_W.     

Tonic heart rate level, social class and antisocial behaviour in adolescents

On the basis of previous empirical research it was hypothesised that (a) antisocial behaviour in adolescence would be characterised by lower tonic heart rate levels and (b) any such relationship would be particularly borne out in the higher social classes where the 'social push' towards antisociality may be relatively weaker. These predictions were tested by relating tonic heart rate levels in a sample of 15 year old male schoolchildren to self-report and teacher ratings of antisocial behaviour/undersocialization. An 'antisocial' group was found to have significantly lower heart rate levels than a 'prosocial' group. Several analyses on high and low class groups resulted in a significant low heart rate/antisociality relationship in the high classes only. It was speculated that the heart rate/antisociality relationship may be mediated by somatotype, or alternatively that low levels in high class antisocials may reflect a vagal passive adaptation to mildly aversive events.     

The between and within day variation in gross efficiency

Before the influence of divergent factors on gross efficiency (GE) [the ratio of mechanical power output (PO) to metabolic power input (PI)] can be assessed, the variation in GE between days, i.e. the test–retest reliability, and the within day variation needs to be known. Physically active males (n = 18) performed a maximal incremental exercise test to obtain VO_2max and PO at VO_2max (PVO_2max), and three experimental testing days, consisting of seven submaximal exercise bouts evenly distributed over the 24 h of the day. Each submaximal exercise bout consisted of six min cycling at 45, 55 and 65% PVO_2max, during which VO₂ and RER were measured. GE was determined from the final 3 min of each exercise intensity with: GE = (PO/PI) × 100%. PI was calculated by multiplying VO₂ with the oxygen equivalent. GE measured during the individually highest exercise intensity with RER <1.0 did not differ significantly between days (F = 2.70, p = 0.08), which resulted in lower and upper boundaries of the 95% limits of agreement of 19.6 and 20.8%, respectively, around a mean GE of 20.2%. Although there were minor within day variations in GE, differences in GE over the day were not significant (F = 0.16, p = 0.99). The measurement of GE during cycling at intensities approximating VT is apparently very robust, a change in GE of ~0.6% can be reliably detected. Lastly, GE does not display a circadian rhythm so long as the criteria of a steady-state VO₂ and RER <1.0 are applied.     

Mechanical work and efficiency in ergometer bicycling at aerobic and anaerobic thresholds

Internal and external mechanical work, energy consumption and mechanical efficiency were studied in constant-load ergometer bicycling at five different power outputs below, equal to, and above the aerobic (AerT) and anaerobic (AnT) thresholds. The gross, net and true efficiencies of the whole body in five male subjects were calculated. The work against the external load was defined as the external mechanical work. The internal mechanical work was calculated as the sum of the increments of kinetic and potential energy in all body segments by using methods of film analysis. Total energy consumption was measured by combining aerobic and anaerobic energy production. When the power output of the bicycle ergometer was increased from 146 +/- 15 to 283 +/- 17 W, oxygen consumption increased from 2.20 +/- 0.98 to 4.22 +/- 0.20 l min-1 (P less than 0.001), while the oxygen consumption at rest was 0.30 +/- 0.03 l min-1. The concentration of blood lactate increased from 2.2 +/- 0.4 at the lowest work load to 8.6 +/- 1.2 mmol l-1 at the highest work load (P less than 0.001). The amount of external work done per revolution increased from 139 +/- 20 to 277 +/- 29 J (P less than 0.001), while the amount of internal work per revolution remained almost constant (56 +/- 12 J). The gross efficiency in the present study was 17-20%, net efficiency 18-22% and true efficiency 21-30%, respectively. The highest gross and net efficiencies were reached at the AerT. The lowest efficiencies were obtained at highest work load.(ABSTRACT TRUNCATED AT 250 WORDS)     

Mechanical work and efficiency in treadmill running at aerobic and anaerobic thresholds

Mechanical work, mechanical power, energy consumption and mechanical efficiency were studied in constant-speed treadmill running of 5 min at seven different exercises around aerobic (AerT) and anaerobic (AnT) thresholds. The true efficiency of concentric (positive) mechanical work and gross efficiency of the whole body in seven male subjects were calculated. The total mechanical work was calculated from film through the translational, potential and rotational energy states as the sum of the changes of all the mechanical energy states in all body segments allowing energy transfer between segments and from energy state to state. The total energy consumption was measured by combining aerobic and anaerobic energy production in resting and working conditions. When the speed of the treadmill was increased from the velocity of 10 km h-1 (2.8 m s-1) to 22 km h-1 (6.1 m s-1), the concentric mechanical work per one step increased from 129 +/- 45 J to 228 +/- 82 J (P less than 0.01). Oxygen consumption increased from 2.22 +/- 0.27 1 min-1 to 4.47 +/- 0.24 1 min-1. The amount of blood lactate increased from 0.94 +/- 0.53 mmol l-1 at the lowest speed to 9.90 +/- 2.89 mmol l-1 at the highest speed (P less than 0.001). The true efficiency of concentric work decreased from 74 +/- 14% to 56 +/- 8% (P less than 0.05). At the speed of the AerT, the economy of running, the vertical rise of different body segments and mechanical efficiency of positive work were high. The highest gross efficiency was found at the running speed between the AerT and AnT.     

Pulmonary diffusing capacity in pregnancy at sea level and at high altitude

The impact of pregnancy on respiratory function and whether this is influenced by living conditions, such as altitude of residence, must be determined if the management of pregnant women, particularly those with pulmonary disease is to be optimized. Pulmonary diffusing capacity, corrected for haemoglobin concentration (DL(COc)), therefore, was measured in 112 healthy Peruvian women with singleton pregnancies living at sea level and 192 living at 4300 m. At each location, 19 non-pregnant women were studied. The mean DL(COc)s of the pregnant and non-pregnant women studied at sea level were similar but lower than those of their high altitude counterparts (P<0.001, P<0.001). At high altitude, the mean DL(COc)s of women studied in the first and second trimester were similar to that of non-pregnant women, but the mean DL(COc) of pregnant women studied in the third trimester was lower than that of the non-pregnant women (P<0.01). Our results demonstrate that the effect of pregnancy on pulmonary diffusing capacity is influenced by altitude of residence.     

Blood flow in thigh muscle during bicycling exercise at varying work rates

16 male subjects exercised at 25, 50, 75, 90, 100 and 120% of on a von Döbeln bicycle ergometer. The muscle mass was measured in a whole body counter. Muscle blood flow (MBF) estimated from the rate of¹³³Xe clearance from m. rectus femoris showed a levelling-off at about 0.5 l of blood per min and liter of muscle tissue (equal to an irrigation coefficient of 0.5 min^–1) at work rates above 50 to 60% of . This concurs with clearance data from the literature. However, when MBF is calculated from , muscle mass, and reliable values for differences, MBF in the present subjects would: 1. Not level off before 90 to 100% , 2. reach a value of 1.0 min^–1. The underestimation of MBF calculated from¹³³Xe clearance and the levelling-off shown by this method may be due to a systematic error inherent in the method, the¹³³Xe clearance being diffusion limited at high flow rates.This study was supported by a grant from the Swedish Medical Council and from Statens lægevidenskabelige forskningsråd, Denmark, project no 512–667 and 512–1156.     

Relationship between heart rate and sinus arrhythmia in air traffic controllers at work

Summary Sinus arrhythmia and mean heart rate were calculated from continuous electrocardiogram recordings of ten air traffic controllers. The telemetric recordings were carried out during 1 day of work and the following day's night shift. The individual variations of sinus arrhythmiz were very large. The different situations (rest, relaxed work, intense work, eating, movements within the control room) had no specific effect on sinus arrhythmia. For each subject and for each group it was the value of the mean heart rate and its temporal variations that had the greatest influence on variations of sinus arrhythmia. This study was carried out thanks to a financial support of the D.G.R.S.T.     

The relationship between cadence,pedalling technique and gross efficiency in cycling

Technique and energy saving are two variables often considered as important for performance in cycling and related to each other. Theoretically, excellent pedalling technique should give high gross efficiency (GE). The purpose of the present study was to examine the relationship between pedalling technique and GE. 10 well-trained cyclists were measured for GE, force effectiveness (FE) and dead centre size (DC) at a work rate corresponding to ~75% of VO₂max during level and inclined cycling, seat adjusted forward and backward, at three different cadences around their own freely chosen cadence (FCC) on an ergometer. Within subjects, FE, DC and GE decreased as cadence increased (p < 0.001). A strong relationship between FE and GE was found, which was to great extent explained by FCC. The relationship between cadence and both FE and GE, within and between subjects, was very similar, irrespective of FCC. There was no difference between level and inclined cycling position. The seat adjustments did not affect FE, DC and GE or the relationship between them. Energy expenditure is strongly coupled to cadence, but force effectiveness, as a measure for pedalling technique, is not likely the cause of this relationship. FE, DC and GE are not affected by body orientation or seat adjustments, indicating that these parameters and the relationship between them are robust to coordinative challenges within a range of cadence, body orientation and seat position that is used in regular cycling.