Poling forces during roller skiing: effects of grade

Comparative Analysis of the Diagonal Stride Technique during Roller Skiing and On-Snow Skiing in Youth Cross-Country Skiers

Roller skiing is one primary form of training method as it is an off-snow equivalent to cross-country (XC) skiing during the dry land preseason training, but the results could only be applied to on-snow skiing with appropriate caution. The aim of this present study was to investigate the similarities and differences in roller skiing and on-snow skiing with the diagonal stride (DS) technique. Six youth (age: 14.3 ± 2.9 years) skiers participated in this study. Two high-definition video camcorders and FastMove 3D Motion 2.23.3.3101 were used to obtain the three-dimensional kinematic data. The cycle characteristics and joint angle ROM of the DS technique while skiing on different surfaces were similar. Almost all joint angle-time curves that were obtained from roller skiing showed a moderate-to-high degree of similarity to the angle-time curves obtained from on-snow skiing, except the hip adduction-abduction angle. The differences between roller skiing and on-snow skiing were mainly found in the body and calf anteversion angles, and the joint angles at critical instants. DS roller skiing can simulate DS on-snow skiing to a large extent in youth athletes. The hip movement, knee flexion, and calf anteversion at ski/roller ski touchdown and take-off, pole inclination at pole touchdown, body anteversion angle, and trunk anteversion angle at pole touchdown were the points that required caution when transferring preseason practice roller skiing to on-snow skiing.

Contribution and effectiveness of ski and pole forces in selected roller skiing techniques on treadmill at moderate inclines

Background

Most of the studies about the effects of incline on cross-country skiing are related to the metabolic efficiency. The effective skiing biomechanics has also been indicated to be among the key factors that may promote good performance. The aims of this study were to provide biomechanical characteristics and investigate the relative contribution and effectiveness of ski and pole forces in overcoming the total external resistance with double poling (DP) and Gear 3 (G3) techniques at varying moderate uphill inclines.

Methods

10 male cross-country skiers participated in this study. Custom-made force measurement bindings, pole force sensors, and an 8-camera Vicon system were used to collect force data and ski and pole kinematics at 3°, 4° and 5° with 10 km/h skiing speed.

Results

The cycle length (CL) decreased by 10% and 7% with DP and G3 technique from 3° to 5° (p < 0.001, p < 0.001). The cycle rate (CR) increased by 13% and 9% from 3° to 5° with DP and G3 technique respectively. From 3° to 5°, the peak pole force increased by 25% (p < 0.001) and 32% (p < 0.001) with DP and G3 technique. With DP technique, the average cycle propulsive force (ACPF) increased by 46% (p < 0.001) from 3° to 5°and with G3 technique, the enhancement for ACPF was 50% (p < 0.001). In G3 technique, around 85% was contributed by poles in each incline.

Conclusion

The higher power output in overcoming the total resistance was required to ski at a greater incline. With DP technique, the upper body demands, and technical effectiveness were increasing with incline. With G3 technique, the role of external pole work for propulsion is crucial over different terrains while role of legs may stay more in supporting the body against gravity and repositioning body segments.

Kinematic differences between uphill roller skiing and on-snow skiing using the V2 skating technique

Purpose

Roller skiing is the primary sport-specific training and testing mode during pre-competition periods for cross-country skiers, biathletes, and Nordic combined athletes. The present study aimed to compare the kinematics between uphill roller skiing and on-snow skiing using the V2 sub-technique.

Methods

In a cross-over design, nine well-trained male skiers performed short trials (< 40 s) at constant inclination (8.0°), speed (3.0 m‧s⁻¹), and controlled rolling/gliding friction on asphalt (in the fall), on the treadmill (in the fall and winter), and during on-snow skiing (in the winter). Kinematic data were collected using a validated inertial measurement unit system.

Results

Repeated-measures ANOVAs revealed no differences between treadmill and asphalt roller skiing. Further, including on-snow skiing showed moderate to good reliability (ICC ≥ 0.63, p ≤ 0.001) for ground-contact temporal variables. However, on-snow skiing moderately increased hip range of motion around the longitudinal axis (22.2 ± 7.7° vs. 14.1 ± 4.7°), lateral hip displacement (44.1 ± 7.1 cm vs. 37.2 ± 6.6 cm) and pole push times (422 ± 41 ms vs. 386 ± 31 ms), and on-snow skiing was characterized by altered hip rotational patterns compared to roller skiing.

Conclusion

V2 roller ski skating simulates on-snow ski skating to a large extent, but the mechanical properties of the skis and/or surface hardness systematically alter skiers’ hip movements and pole push times. This implies a potential for equipment optimization to increase training specificity during pre-competition periods and highlights a need for future studies to examine the kinematic effects of snow hardness on all sub-techniques.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00421-022-05007-0.

Embedded inertial measurement unit reveals pole lean angle for cross-country skiing

This study introduces an inertial measurement unit-based measurement system for resolving the dynamic lean angle of a ski pole during double poling while cross-country skiing. The measurement system estimates both the pole lean angle and pole–terrain contact events. Reported are results from 20 trials providing validated estimates of ski pole lean angle and the timing of pole plant and pole lift events. The pole lean angle is estimated from a complementary filter that fuses estimates of orientation from the embedded accelerometer and angular rate gyro. Validation follows from comparison with video capture measurements. Bland–Altman analysis showed agreement between the two measurement modalities with less than 5% bias in the mean differences (relative to the lean angle range of motion). Companion correlation analysis confirms strong correlation ($$r = 0.99$$ r = 0.99 ) between the inertial measurement unit and video-estimated lean angles and with mean root-mean-square errors below 4.5$$^{\circ }$$ ∘ .

Energy system contribution during competitive cross-country skiing

Energy system contribution during cross-country (XC) skiing races is dependent on several factors, including the race duration, track profile, and sub-techniques applied, and their subsequent effects on the use of the upper and lower body. This review provides a scientific synopsis of the interactions of energy system contributions from a physiological, technical, and tactical perspective. On average, the aerobic proportion of the total energy expended during XC skiing competitions is comparable to the values for other sports with similar racing times. However, during both sprint (≤ 1.8 km) and distance races (≥ 10 and 15 km, women and men, respectively) a high aerobic turnover interacts with subsequent periods of very high work rates at ~ 120 to 160% of VO_2peak during the uphill sections of the race. The repeated intensity fluctuations are possible due to the nature of skiing, which involves intermittent downhills where skiers can recover. Thus, the combination of high and sustained aerobic energy turnover and repeated work rates above VO_2peak, interspersed with short recovery periods, distinguishes XC skiing from most other endurance sports. The substantially increased average speed in races over recent decades, frequent competitions in mass starts and sprints, and the greater importance of short periods at high speeds in various sub-techniques, have demanded changes in the physiological, technical, and tactical abilities needed to achieve world-class level within the specific disciplines.

Pole lengths influence O2-cost during double poling in highly trained cross-country skiers

Purpose

In elite cross-country skiing, double poling is used in different terrain. This study compared O₂-cost and kinematics during double poling with four different pole lengths [self-selected (SS), SS − 5 cm, SS + 5 cm, SS + 10 cm] at Low versus Moderate incline.

Methods

Thirteen highly trained male cross-country skiers (mean ± SD 23 ± 3 years; 182 ± 4 cm; 77 ± 6 kg) completed eight submaximal trials with roller skis on a treadmill at two conditions: “Low incline” (1.7°; 4.5 m s⁻¹) and “Moderate incline” (4.5°; 2.5 m s⁻¹) with each of the four pole lengths. O₂-cost and 3D body kinematics were assessed in each trial.

Results

In Low incline, SS + 10 cm induced a lower O₂-cost than all the other pole lengths [P < 0.05; effect size (ES) 0.5–0.8], whereas no differences were found between the remaining pole lengths (P > 0.05; ES 0.2–0.4). In Moderate incline, significant differences between all pole lengths were found for O₂-cost, with SS − 5 cm > SS > SS + 5 cm > SS + 10 cm (P < 0.05; ES 0.6–1.8). The relative differences in O₂-cost between SS and the other pole lengths were greater in Moderate incline than Low incline (SS − 5 cm; 1.5%, ES 0.8, SS + 5 cm; 1.3%, ES 1.0, and SS + 10 cm; 1.9%, ES 1.0, all P < 0.05). No difference was found in cycle, poling or reposition times between pole lengths. However, at both conditions a smaller total vertical displacement of center of mass was observed with SS + 10 cm compared to the other pole lengths.

Conclusion

Increasing pole length from SS − 5 cm to SS + 10 cm during double poling induced lower O₂-cost and this advantage was greater in Moderate compared to Low incline.

Electronic supplementary material

The online version of this article (10.1007/s00421-017-3767-x) contains supplementary material, which is available to authorized users.

Double-Poling Biomechanics of Elite Cross-country Skiers: Flat versus Uphill Terrain

INTRODUCTION

In light of the recent revolutionary change in the use of the double-poling (DP) technique in cross-country skiing, our purpose was to compare the associated kinetics and kinematics on flat (DPflat) and uphill terrain (DPup), as well as to identify factors that determine performance.

METHODS

Thirteen elite male cross-country skiers completed two incremental speed tests (Vpeak) involving roller skiing with the DP technique at moderate (13 and 24 km·h) and high speed (15 and 28.5 km·h) on a treadmill that was flat (1°) or tilted uphill (7°). Pole forces and three-dimensional whole-body kinematics were monitored simultaneously.

RESULTS

In comparison to DPflat, during DPup, swing times were much shorter (-48%) and peak pole forces greater (+13%) and generated later during the poling phase (+68%), with higher impulses for all force components (+87%-123%). Furthermore, pole forces were 18% more effectively oriented for propulsion. During DPup, the skiers demonstrated more flexed elbows, as well as shoulder angles that were less flexed in the forward direction and less abducted throughout the poling phase, together with more highly flexed knee and ankle joints, a more upright thorax, less flexed hips, and a shortened backward swing after pole off. With DPup, the skiers raised their center of mass 25% more, attaining maximal heel raise and maximal vertical position at a timepoint closer to pole plant compared with flat. On the uphill incline, the magnitude of Vpeak was positively related to body mass, relative pole length (% body height), and magnitude of heel raise.

CONCLUSIONS

The present findings provide novel insights into the coordination, kinetics and kinematics of elite skiers while DP on flat and uphill terrain.

Is There an Optimal Pole Length for Double Poling in Cross Country Skiing?

The aim of this study was to determine the effects of pole length on energy cost and kinematics in cross country double poling. Seven sub-elite male athletes were tested using pole sets of different lengths (ranging between 77% and 98% of participants' body height). Tests were conducted on a treadmill, set to a 2% incline and an approximate racing speed. Poling forces, contact times, and oxygen uptake were measured throughout the testing. Pole length was positively correlated with ground contact time (r = .57, p < .001) and negatively correlated with poling frequency (r = -.48, p = .003). Pole length was also positively correlated with pole recovery time and propulsive impulse produced per poling cycle (r = .36, p = .031; r = .35, p = .042, respectively). Oxygen uptake and pole length were negatively correlated (r = -.51, p = .004). This acute study shows that increasing pole length for double poling in sub-elite cross country skiers under the given conditions seems to change the poling mechanics in distinct ways, resulting in a more efficient poling action by decreasing an athlete's metabolic cost.

The Role of Power Fluctuations in the Preference of Diagonal vs. Double Poling Sub-Technique at Different Incline-Speed Combinations in Elite Cross-Country Skiers

In classical cross-country skiing, diagonal stride (DIA) is the major uphill sub-technique, while double poling (DP) is used on relatively flat terrain. Although, the dependence of incline and speed on the preference of either sub-technique seems clearly established, the mechanisms behind these preferences are not clear. Therefore, the purpose of this study was to compare kinetics and energy consumption in DP and DIA at the same submaximal workload in cross-country skiing under two different incline-speed combinations. We compared kinetics and physiological responses in DP and DIA at the same submaximal workload (≈200 W) under two different incline-speed conditions, (5%—12.5 km h⁻¹ vs. 12%—6.5 km h⁻¹) where DP and DIA were expected to be preferred, respectively. Fifteen elite male cross-country skiers performed four separate 6.5-min roller skiing sessions on a treadmill at these two conditions using DP and DIA during which physiological variables, rate of perceived exertion (RPE) and kinetics, including power fluctuations, were recorded. At 12% incline, DIA resulted in lower physiological response (e.g., heart rate) and RPE, and higher gross efficiency than DP, whereas at 5% incline these variables favored DP (P < 0.05). The skiers' preference for sub-technique (13 preferred DIA at 12% incline; all 15 preferred DP at 5% incline) was in accordance with these results. Fluctuation in instantaneous power was lowest in the preferred sub-technique at each condition (P < 0.05). Preference for DP at 5% incline (high speed) is most likely because the speed is too high for effective ski thrust in DIA, which is reflected in high power fluctuations. The mechanism for preference of DIA at 12% incline is not indicated directly by the current data set showing only small differences in power fluctuations between DIA and DP. Apart from the low speed allowing ski thrust, we suggest that restricted ability to utilize the body's mechanical energy as well as the use of arms in DP play an important role.

Biomechanics of simulated versus natural cross-country sit skiing

The purpose of this study was to investigate the biomechanics of cross-country sit-skiing in simulated and natural skiing. Thirteen international level athletes participated in a ski ergometer test (simulated conditions) and a test on snow in a ski-tunnel (natural conditions) using their personal sit-ski. Tests in both conditions were performed at individual maximal speed. When comparing the two conditions the main results were: (1) maximal speed in simulated conditions was lower (p<0.05) but correlated well with the natural condition (r=0.79, p<0.001); (2) no differences in pole force variables were found; peak force (r=0.77, p<0.01) and average force (r=0.78, p<0.01) correlated well; (3) recovery time and time to peak did not differ and time to impact correlated with each other (r=0.88, p<0.01); (4) no differences were found in peak electromyography (EMG) and average EMG for Triceps, Pectoralis, and Erector Spinae; Rectus Abdominis did not differ in peak. EMG peak and average EMG of all muscles were correlated between the two conditions (r=0.65-0.94; p<0.05-0.01). Although some differences were observed, this study demonstrated that technical skill proficiency in natural and simulated cross-country skiing is comparable from a force production and muscle activation perspective.

Mechanical behaviour of cross-country ski racing poles during double poling

The purpose of this study was to evaluate the behaviour of cross-country ski poles during double poling on a treadmill using three-dimensional kinematics. The results were compared with standard laboratory tests of the pole manufacturers. A total of 18 skiers were analysed at two speeds (85% and 95% of the maximal speed) at grades of 1.5% and 7%. Variables describing cycle characteristics, bending stiffness, bending behaviour, and trajectories of the pole markers were analysed. Triangular-shaped poles demonstrated the greatest stiffness and lowest variability in maximal bending. Softer poles demonstrated greater variability in bending behaviour and lost ground contact at high skiing speeds, which for some skiers resulted in failure to complete high-speed tests. Considerable variations in pole behaviour for similar poles between skiers were observed, which might be attributed to differences in technique, indicating that mechanical properties of the poles did not exclusively determine pole behaviour in the dynamic situation. The greatest magnitude of pole bending was in the middle part of the pole, which differed from the standard static pole analysis of the manufacturer. Increases in grade demonstrated the greatest effect on pole bending. Distinct differences from the pole manufacturers' laboratory measures were apparent, suggesting that basic pole testing might be adapted.

A biomechanical approach to paralympic cross-country sit-ski racing

OBJECTIVE

To analyze the biomechanics of the double poling (DP) gesture in cross-country disabled sit-skiers in the field during competition.

DESIGN

Cross-sectional research.

SETTING

One-kilometer sprint race, Winter Paralympic Games, Vancouver 2010, Canada.

PARTICIPANTS

Paralympic athletes: 35 men and 15 women, classified in all the 5 classes of the sit-skier category.

INTERVENTION

Elite sit-skiers, with different disabilities, were recorded with a high-speed markerless stereophotogrammetric camera system. Reference points were semiautomatically tracked frame-by-frame on video images, according to a biomechanical model consisting of 7 anatomical and 4 technical points.

MAIN OUTCOME MEASURES

Coordinates of anatomical and technical points were evaluated for 2-dimensional kinematic analysis of the push gesture both with reference to a ground-fixed frame and with respect to the athletes' seat on the sledges.

RESULTS

Several graphical results represent the development of the DP gesture of each athlete with respect to both ground reference frame and sledge reference frame. The progression of the gesture is depicted by body and pole stick diagrams, trends of reference point positions and their gradients, and body joint trajectories in space. In addition, kinematic biomechanical parameters (eg, joints' range of motion) and technical parameters (eg, pole incline, sledge velocity) are reported.

CONCLUSIONS

This research demonstrates the feasibility of a markerless kinematic analysis of the poling gesture on a contest field. Results point out a wide variability of the gesture due to the residual functional capabilities and sitting postures of each athlete. However, the poling cycles of subjects classified into different classes present similar features. An original segmentation of the DP gesture in a sequence of 3 phases is proposed in the article.

Analysis of a sprint ski race and associated laboratory determinants of world-class performance

This investigation was designed to analyze the time-trial (STT) in an international cross-country skiing sprint skating competition for (1) overall STT performance and relative contributions of time spent in different sections of terrain, (2) work rate and kinematics on uphill terrain, and (3) relationships to physiological and kinematic parameters while treadmill roller ski skating. Total time and times in nine different sections of terrain by 12 world-class male sprint skiers were determined, along with work rate and kinematics for one specific uphill section. In addition, peak oxygen uptake (VO_2peak), gross efficiency (GE), peak speed (V_peak), and kinematics in skating were measured. Times on the last two uphill and two final flat sections were correlated to overall STT performance (r = ~−0.80, P < 0.001). For the selected uphill section, speed was correlated to cycle length (r = −0.75, P < 0.01) and the estimated work rate was approximately 160% of peak aerobic power. VO_2peak, GE, V_peak, and peak cycle length were all correlated to STT performance (r = ~−0.85, P < 0.001). More specifically, VO_2peak and GE were correlated to the last two uphill and two final flat section times, whereas V_peak and peak cycle length were correlated to times in all uphill, flat, and curved sections except for the initial section (r = ~−0.80, P < 0.01). Performances on uphill and flat terrain in the latter part were the most significant determinants of overall STT performance. Peak oxygen uptake, efficiency, peak speed, and peak cycle length were strongly correlated to overall STT performance, as well as to performance in different sections of the race.

Double-push skating versus V2 and V1 skating on uphill terrain in cross-country skiing

PURPOSE

The aims of the study were a) to compare the double-push skating technique with the V2 and the V1 skating techniques on an uphill terrain by a kinematic and kinetic analysis, b) to provide kinetic and kinematic data of the V1 technique at maximal skiing speeds, and c) to test the hypotheses that the double-push skating technique is faster compared with the V2 and the V1 skating techniques.

METHODS

Six elite skiers performed maximum speed sprints over a 60-m uphill section (7 degrees -10 degrees) using the double-push, the V2, and the V1 techniques. Pole and plantar forces and cycle characteristics were analyzed.

RESULTS

The double-push skating technique was approximately 4.3% faster (P < 0.05) compared with the V2 skating technique and equally fast compared with the V1 skating technique. The double-push and the V2 techniques demonstrated longer cycle lengths, lower cycle rates (both P < 0.05), and equal poling frequencies and pole forces compared with the V1 technique. Cycle length, peak foot force, and knee extension ranges of motion and velocities were higher in the double-push technique compared with the V2 technique (all P values <0.05). Center of pressure was located more laterally in the double-push technique compared with the other two techniques (P < 0.05). All measured skiing speeds were drastically higher compared with former studies.

CONCLUSION

The higher skiing speeds of the V1 and the double-push techniques compared with the V2 technique stress the mechanical advantage of those techniques on uphill terrain. Because of larger cycle lengths, lower cycle rate, longer recovery times, and equal poling frequency, the double-push technique might be seen as more economic on steep uphills compared with the V1 technique. From a tactical point of view compared with the V1 technique, the double-push technique needs less space due to less lateral displacement, and no technique transitions are necessary when entering and leaving an uphill section.

Grade influences blood lactate kinetics during cross-country skiing

The purpose of this study was to examine the effects of level vs. graded skate skiing on capillary blood lactate (B(La)), heart rate (HR), oxygen consumption (V(O2)), and training intensity prescriptions. Eleven Nordic skiers completed 2 submaximal skate roller skiing treadmill protocols during which intensity was increased either by grade (G(inc)) or by speed (S(inc)). The protocols were compared for prethreshold BLa, HR, and V(O2) at lactate threshold (LT) and the HR/V(O2) relationship. Additionally, double-pole (primarily upper body) and skating (arms and legs combined) protocols were used to measure peak V(O2) and peak HR. Heart rate and V(O2) at LT were lower during G(inc) compared with S(inc) (154.9 +/- 6.8 b.min(-1) vs. 162.0 +/- 9.1 b.min(-1) and 46.3 +/- 2.8 ml.kg(-1).min(-1) vs. 49.1 +/- 1.6 ml.kg(-1).min(-1), respectively, both p < 0.01). Pre-threshold B(La) and the HR/V(O2) relationship were not different between the submaximal protocols. V(O2) and HRpeak were higher in skating compared with double poling (64.6 +/- 1.8 ml.kg(-1).min(-1) vs. 60.3 +/- 2.8 ml.kg(-1).min(-1), 192.6 +/- 5.8 b.min(-1) vs. 187.8 +/- 6.7 b.min(-1), respectively, both p < 0.01). Greater reliance on upper-body musculature during graded skiing and its associated lower aerobic capacity increases B(La) when compared with level skiing. The leftward shift in the B(La) vs. intensity curve during uphill skiing should be recognized to properly prescribe training intensity as well as interpret laboratory results.

Paced Breathing in Roller-Ski Skating: Effects on Metabolic Rate and Poling Forces

Purpose:

This study aimed (1) to determine whether paced breathing (synchronization of the expiration phase with poling time) would reduce the metabolic rate and dictate a lower rate of perceived exertion (RPE) than does spontaneous breathing and (2) to analyze the effects of paced breathing on poling forces and stride-mechanics organization during roller-ski skating exercises.

Methods:

Thirteen well-trained cross-country skiers performed 8 submaximal roller-skiing exercises on a motorized driven treadmill with 4 modes of skiing (2 skating techniques, V2 and V2A, at 2 exercise intensities) by using 2 patterns of breathing (unconscious vs conscious). Poling forces and stride-mechanics organization were measured with a transducer mounted in ski poles. Oxygen uptake (VO2) was continuously collected. After each bout of exercise RPE was assessed by the subject.

Results:

No difference was observed for VO2 between spontaneous and paced breathing conditions, although RPE was lower with paced breathing (P < .05). Upper-limb cycle time and recovery time were significantly (P < .05) increased by paced breathing during V2A regardless of the exercise intensity, but no changes for poling time were observed. A slight trend of increased peak force with paced breathing was observed (P = .055).

Conclusion:

The lack of a marked effect of paced breathing on VO2 and some biomechanical variables could be explained by the extensive experience of our subjects in cross-country skiing.

Biomechanical validation of a specific upper body training and testing drill in cross‐country skiing

The aim of this study was to perform a biomechanical validation of a double poling imitation drill on a rollerboard. Six elite cross-country skiers performed three imitation drill trials at maximal speed at 13 degrees inclination and in double poling on roller skis on a paved road of 3 degrees. Pole and strap forces, elbow and hip angles and EMG activity of eight upper body muscles were measured. Force curves showed similar characteristics, except for impact force occurring only at pole plant in double poling on roller skis. Double poling on a rollerboard includes an eccentric roll-down phase not appearing in double polling on roller skis. Forces on the rollerboard were similar to those on roller skis. Courses of the elbow angles indicated similar shapes, except for the angle at the start of the propulsion phase and, consequently, during flexion (p < 0.01). Propulsion time and cycle duration were longer and frequency lower on the rollerboard (all p < 0.001). Muscle activities were not significantly different, except for stronger biceps brachii (p < 0.01) and weaker erector spinae activation (p < 0.05) on the rollerboard. Muscle coordination patterns showed similar onset and offset points of each muscle and comparable activations in both activities, except for biceps brachii. Two movement strategies on the rollerboard were found, which led to small differences in measured variables. The biomechanical validity of double poling on a rollerboard can be judged as moderately high, being aware of the differences in some variables that might be considered in training sessions on the rollerboard, particularly when using intervals with high number of repetitions.

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.

Poling forces during roller skiing: effects of technique and speed

PURPOSE

Although it has been reported that the majority of propulsive forces are generated through the poles with ski skating, no study has systematically examined poling forces among different skating techniques. The objective of the present study was to examine poling forces and timing during roller skiing on a 2.1% uphill.

METHODS

Nine highly skilled cross-country skiers roller skied at three paced speeds and maximal speed using the V1 skate (V1), V2-alternate (V2A), V2 skate (V2), and double pole (DP) techniques while poling forces and timing were measured with piezoelectric transducers.

RESULTS

Peak force (PF) values with the skating techniques were significantly lower than with DP and ranged from 18.9 +/- 3.1% of body weight (BW) to 31.5 +/- 5.6% BW across the speeds of the study. Average force over the entire cycle (ACF) increased with speed with DP, V2A and V1 (P < 0.01) but not with V2. PF and ACF were higher (P < 0.01) with V2 than V1 and V2A. Poling time was longer (P < 0.01) with V2A compared with V1 and V2.

CONCLUSIONS

The results of this study suggest that 1) the use of the upper body is greater with V2 than with other skating techniques while there is a relatively greater reliance on the lower body for generation of the additional propulsive forces required to increase velocity, and (2) poling forces do not appear to be as effectively applied with V2 as with V2A.