Classical Roller Research Articles

The role of external power demand on the choice of technique in classic cross-country skiing.

In cross-country skiing, athletes use different techniques akin to locomotor gaits such as walking and running. Transitions between these techniques generally depend on speed and incline, in a similar way as walk-run transitions. Previous studies have examined the roles of incline, speed, and mechanical power demand in triggering transitions. However, it is still not known if mechanical power demand, as an isolated factor, has any role on the choice of technique. The aim of this study was to examine the isolated role of mechanical power on the choice of technique during classic cross-country roller skiing by changing mechanical power demand at fixed speeds and inclines. Six male and eight female athletes performed classical roller skiing on a treadmill at the four combinations of two speeds (10 and 12 km h-1) and two inclines (5 and 8%) while additional resistive forces were applied via a weight-pulley system. Athletes were free to choose between three techniques: double poling, double poling with kick, and diagonal stride. Power and resistive forces at transition were compared using repeated measure (2x2) ANOVA. At a given incline, technique transitions occurred at similar additional resistive force magnitudes at the two speeds. On the steeper incline, the transitions occurred at smaller additional resistive forces. Importantly, transitions were not triggered at similar mechanical power demands across the different incline/speed/resistive force conditions. This suggests that mechanical power itself is not a key technique transition trigger. Both total and additional resistive force (i.e., the manipulated mechanism to regulate power) may be transition triggers when incline is fixed and speed is changed. In combination with previous findings, the current results suggest that no single factor triggers technique transitions in classic cross-country skiing.

КІЛЬЧАСТО-ШПОРОВІ І ЗУБЧАТО-ШПОРОВІ КОТКИ. ФУНКЦІЙНІ ТА ДИНАМІЧНІ ВИПРОБУВАННЯ

Experimental field research of crosskill and star-wheeled rollers similar by design provides their developers and users with information on understanding their design and functional features. The purpose of the research is to compare the functional features of crosskill and star-wheeled rollers according to the criteria of clods breaking effect, compacting action, resistance to sticking in the range of pre-sowing and surface tillage depth. Methods and materials. Dynamic tests involved the study of three types of rollers. The research hypothesis assumed that the selected criteria for evaluating the work of rollers (intensity of breaking of clods, compacting action of rollers, intensity of bottom compaction and performance of rollers at high soil moisture) depend on roller pressure and different speed regimes, as they are derived from the shape of work surfaces. Sub-criteria studies were supposed to be carried out on the same type of soil: clods breaking characteristics on dry W = (10… 12) %, compacting effect on physically mature soil W = (15… 20) %, efficiency at high humidity - W = (25… 27) %. Evaluation of soil characteristics was performed by thermostatic-weight method according to the generally accepted method of "cutting ring" [Kaczynski NA, 1947], according to the volume of the cylinder 100 cm3. To determine the intensity of bottom compaction used the methodology and technical means of L. Pogorilyy UkrNDIPVT development. Statistical analysis of experimental data was performed by the method of analysis of variance according to [Dospekhov, 1985] and interpreted by standard computer programs Excel in the form of graphs. Results. The intensity of clods breaking with a classic roller is the lowest and depends on the speed of movement. The intensity of breaking by the modernized roller is approximately 1.1 times higher and with increasing speed is almost stable. The intensity of clods breaking by a specialized roller is the highest and almost (10...20) %, respectively, exceeds the previous two rollers and does not significantly depend on the increase in speed. The greatest compaction of the soil (the height of the layer to which the pre-prepared soil asked after the passage of the roller) is characteristic of a specialized roller, which is almost (1.5…1.7) times higher than the classic and modernized, respectively. Depending on the depth of pre-tillage (5…10) cm, compaction by rollers varies approximately twice. The greatest intensity of compaction of a bottom is provided by the specialized roller, and modernized and classical condense accordingly in (1,2…1,4) times below. The specialized roller sticks the fastest, which is facilitated by the 4-tier arrangement of working surfaces and their maximum in comparison with others contact with the ground. Sticking of the modernized roller surface is as that of the specialized. The classic roller surface remains clean for the longest time. Conclusions. The classic roller compacts both the upper and lower horizons of the soil well enough, brings little moisture to the surface, has a medium clods breaking effect, can be recommended for a wide range of works, but its primary purpose is cultivating after sowing; as a compromise it can be used for pre-sowing tillage with good quality indicators. The upgraded roller compacts the top layer of the soil well, carries away little moisture, mulches the surface, distributes the effort well at different depths of cultivation and can be recommended primarily for pre-sowing tillage; as a compromise solution can be used after sowing with good quality indicators. Specialized roller – star-wheeled, has good penetrating ability, works most actively, providing the best clods breaking effect, slightly carries away wet horizons on the surface; can be recommended for leveling and use on the soil after its main cultivation. Each of the studied rollers can be used to some extent in all these technological operations, but the best result will be achieved taking into account their characteristics, type and period of execution.

The Effects of Sub-Technique and Pole Length on Classic Roller Skiing Performance and Physiological Responses at Steep Uphill Inclination.

The aims of this study were to compare performance with physiological and perceptual responses on steep uphill inclines between double poling and diagonal stride and to investigate the effects of pole length when double poling. Eight male, competitive cross-country skiers (22 ± 1.1 yrs, peak oxygen uptake (VO2peak) in the diagonal stride: 69.4 ± 5.5 ml·kg-1·min-1) performed four identical tests, one in the diagonal stride, and three in double poling with different pole lengths (self-selected, self-selected -5 cm and self-selected +10 cm). Each test was conducted at a fixed speed (10 km/h), with inclination rising by 1%, starting with 7%, each until voluntary exhaustion. VO2peak, the heart rate, blood lactate concentration, and the rating of perceived exertion were determined for each pole length in each test. The peak heart rate (p < 0.001) and VO2peak (p = 0.004) were significantly higher in the diagonal stride test compared with double poling with all pole lengths. Time to exhaustion (TTE) differed significantly between all four conditions (all p < 0.001), with the following order from the shortest to the longest TTE: short poles, normal poles and long poles in double poling, and the diagonal stride. Consequently, a significantly higher slope inclination was reached (p < 0.001) using the diagonal stride (17%) than for double poling with long poles (14%), normal (13%) and short (13%) poles. The current study showed better performance and higher VO2peak in the diagonal stride compared to double poling in steep uphill terrain, demonstrating the superiority of the diagonal stride for uphill skiing. However, in double poling, skiers achieved improved performance due to greater skiing efficiency when using long poles, compared to normal and short poles.

The role of incline, speed and work rate on the choice of technique in classical roller skiing.

Cross-country skiers use different sub-techniques like ‘gears’ (diagonals stride, double poling with kick, and double poling) depending on terrain (incline) and demand (speed and external work rate). Previous studies have identified the major effect of speed and incline, but not any potential interaction between these parameters: the incline-speed combination determines the work rate, which in itself may be a controlling factor. The aim of this study was to investigate the role of these task conditions (external work rate, speed, incline) and their interactions on the choice of sub-technique in classical roller skiing. Twelve male and nine female cross-country skiers executed three subsets of protocols in which two of three condition parameters were altered every 15 seconds while roller skiing on a treadmill. This design created a quasi-random set of combinations of speed, incline and work rate that were analysed on sub-technique choice. A repeated measures model with sex as between subject factor was conducted for each subset of protocols. The incline appeared to be the factor affecting sub-technique choice most, but not exclusively; at constant incline, athletes applied different sub-techniques, depending mostly on speed rather than work rate. Most athletes did not use one particular sub-technique for a given speed-incline-work rate combination, but it depended on the protocol and direction of condition change in the constant speed protocol (hysteresis). Only minor differences between men and women existed regarding the impact of condition factor on sub-technique choice. The findings disagree with the notion of a simple mechanism that explains the choice of sub-technique, but rather opt for a complex structure that entangles various mechanisms which play a role in the choice of sub-technique under moderate effort conditions.

The effect of exhaustive exercise on the choice of technique and physiological response in classical roller skiing.

The aim of this study was to investigate the effect of exhaustive exercise on technique preference and the accompanying physiological response during classic skiing at constant workload, but with varying incline-speed combinations. Seven male competitive cross-country skiers performed four tests, each lasting 23min, at constant 200W workload roller skiing on a treadmill using classic style, three in unfatigued state, and one after exhaustion. The incline and speed combination (that determined the 200W) were altered each minute during the tests. The athletes were allowed to change sub-technique at free will. Physiological variables and cycle rate were recorded continuously as well as the incline-speed combinations at which the sub-technique was changed. Exhaustive exercise did not (or hardly) affect cycle rate and choice of technique. The physiological response was most prominent in slight incline-high speed conditions, independent of exercise duration. Exhaustive exercise affected the physiological response in a differentiated manner. HR and RER remained, respectively, higher and lower after fatigue, while [Formula: see text] (and thereby GE) were affected only during approximately the first 8min of post-exhaustion exercise. Exhaustive exercise has a minimal effect on choice of technique in classic cross-country skiing with free choice of sub-technique, even though physiological stress is increased.

On the control of non holonomic systems by active constraints

The paper is concerned with mechanical systems which are controlled by implementing a number of time-dependent, frictionless holonomic constraints. The main novelty is due to the presence of additional non-holonomic constraints. We develop a general framework to analyze these problems, deriving the equations of motion and studying the continuity properties of the "control-to-trajectory" maps. Various geometric characterizations are provided, in order that the equations be affine w.r.t. the time derivative of the control. In this case the system is <em> fit for jumps</em>, and the evolution is well defined also in connection with discontinuous control functions. The classical Roller Racer provides an example where the non-affine dependence of the equations on the derivative of the control is due only to the non-holonomic constraint. This is a case where the presence of quadratic terms in the equations can be used for controllability purposes.

Hydrodynamic and biochemical effects of isolated hypothermic renal perfusion depending on the pump model and perfusion solution

Objectives To evaluate hydrodynamic, biochemical, and histological consequences of hypothermic isolated renal perfusion using a new computerized perfusion system. Materials and methods The device that allowed us to obtain on renal hydrodynamics during perfusion included multiple parts. The organ was perfused at 4°C with a constant flow either using a classic roller pump or a pump designed in our laboratory to employ vacuum or atmospheric pressure sequentially to achieve a truly pulsatile wave (vacuum-powered tubular pump). The study included 16 minipigs with Eurocollins or Belzer perfusion solutions sampled at predefined interval and histological studies of the organs performed. Results There was a significant difference in weight increase between the two types of pumps; those perfused with Eurocollins showed greater values than those with Belzer solution. Onset of nitric oxide (NO) in the perfusion solution increased inversely with the renal vascular resistance. The highest NO levels were observed with the Belzer solution and vacuum pump. Conclusions Changes in renal hydrodynamics, as induced by perfusion wave form and solution type, may be recorded in real time using a computerized system. A vacuum pump with the Belzer solution achieved the best experimental results.

Efectos hidrodinámicos y bioquímicos de la perfusión hipotérmica de riñón aislado según el tipo de bombautilizada

ObjectiveTo study on isolated kidney perfusions by means of a self-designed computer-controlledorgan perfusion system the hydrodynamic and biochemical effects of two types of pumps: a self-designedvacuum powered tubular pump and a classical roller pump. Basic ProceduresExperimental study performed on 12 right mini-pig kidneys. After transperitonealbilateral nephrectomy, organs are perfused with Eurocollins solution in a randomised manner with one typeof pump. The system records continuously perfusion pressure, flow and renal resistance. ResultsMedium renal vascular resistance was significantly lower in vacuum powered tubular pumpperfusions. LDH level in the solution showed correlation with perfusion flow. ConclusionsVacuum powered tubular pump increases renal flow and lowers renal vascular resistancesignificantly in comparison to roller pump. LDH level in the solution is related to good-quality hydrodynamicperfusion parameter values.

Experimental evaluation of the Dideco D903 Avant 1.7 hollow-fibre membrane oxygenator.

Membrane oxygenators have now gained wide acceptance. A new hollow-fibre membrane oxygenator, the Dideco D903 Avant 1.7, with an optimized membrane surface (1.7 m2) and a wavy blood flow pattern, was tested for gas transfer and blood path resistance in a standardized setting with surviving animals. Three calves (mean body weight 63.29 +/- 2.9 kg) were connected to cardiopulmonary bypass by jugular venous and carotid arterial cannulation, classic roller pump and the Dideco D903 oxygenator with a mean flow rate of 53 +/- 0.1 ml/kg/min for 6 h. After this time, the animals were weaned from the CPB and thereafter from the ventilator. After 7 days, the animals were killed electively. Blood gas analysis was performed before bypass, after mixing (10 min) and then hourly for the 6 h of perfusion. Further samples were taken 30 min (spontaneous breathing) and 60 min after bypass (extubated). Physiological blood gas values could be maintained throughout perfusion in all animals. Mean arterial oxygen saturation varied between 99.3% and 99.7% for the arterial side of the oxygenator compared to 64.6% and 71% for the venous side. The highest mean pressure drop through the oxygenator was 54 mmHg. Postbypass blood gas analysis showed physiological values and no evidence of major lung trauma or pulmonary oedema in relation to the 6 h perfusion. The hollow-fibre membrane oxygenator, Dideco D903, offers excellent gas exchange capabilities and a low pressure drop under experimental conditions, despite reduced membrane surface area. The post mortem examination did not show any deleterious lesion.

Experimental evaluation of the Dideco Masterflo paediatric hollow-fibre membrane oxygenator

Nine mongrel dogs (mean bodyweight: 29 ± 6kg) were connected to cardiopulmonary bypass byfemorojugularvenous and femoral arterial cannulation, classic roller pump and the integrated Dideco D702 Masterflo hollow-fibre membrane oxygenatorwith a mean flow rate of 70ml/kg/min for six hours. Then the animals were weaned from cardiopulmonary bypass and thereafter weaned from the ventilator. After seven days all animals were sacrificed electively for necropsy. A standard battery of blood samples was taken before the bypass, after mixing (10 minutes), after two hours, five hours and six hours of perfusion. Further samples were taken 30 minutes after bypass (spontaneous breathing), 60 minutes after bypass (after extubation), 24 hours after bypass, 48 hours after bypass and seven days after bypass. Physiologic blood gas values could be maintained throughout perfusion in all animals. Mean arterial oxygen saturation varied between 99.7% and 99.9% for the arterial side of the oxygenator compared to 77.8% and 86.6% on the venous side. Post bypass blood gas analyses showed physiologic values and no evidence of major lung trauma or pulmonary oedema in relation to the six hours' bypass. Red blood count was 5.84 ± 0.02 before and 4.63 + 0.1 million/mm3 after mixing and dropped to 3.89 ± 0.52 till the end of the bypass. After seven days the red blood count was practically normalized with over 5,000,000 erythrocytes per mm3 at the end of the observation. Blood trauma evaluated in function of plasma haemoglobin and (thrombocyte) depletion showed the following results: prebypass: 2.3 ± 0.7 μmol/l plasma haemoglobin and (220 ± 24 thousand thrombocytes per mm3); after six hours perfusion: 26.2 ± 15.5 and (137 ± 12); after seven days: 9.3 ± 4.1 and (400 ± 125). Post mortem studies did not demonstrate any deleterious lesions.

Determination of significant differences in performance of the Bentley BOS-CM 40 hollow fibre membrane oxygenator and the Polystan VT5000 venotherm bubble oxygenator

Ten mongrel dogs were connected to cardiopulmonary bypass by cavoaortic cannulation, classic roller pump and either Bentley BOS-CM 40 hollow fibre membrane oxygenator or Polystan VT5000 Venotherm bubble oxygenator for eight hours, with mean flow rate of 100 ml/kg min. Platelet counts (all values corrected by prebypass haematocrit) were significantly lower in the bubble oxygenator group after two hours of cardiopulmonary bypass (p &lt; 0·01). Plasma haemoglobin production was significantly higher after two hours of cardiopulmonary bypass in the bubble oxygenator group (p &lt; 0·01). Venous oxygen saturation (SvO2) was above 65% during the eight hours perfusion in the membrane oxygenator group. In the bubble oxygenator group, however, SvO2 was below 60% after six hours of cardiopulmonary bypass. After eight hours perfusion the difference in SvO2 between the two groups was significant (p &lt; 0·05). Thus membrane oxygenators such as the Bentley BOS-CM 40 appear to be indicated in cardiopulmonary bypass of more than two hours duration.