How do elite cross-country skiers adapt to different double poling frequencies at low to high speeds?

Skiing economy and kinematic during a field double poling roller skiing among novice and experienced cross-country skiers

To assess the skiing economy (SE) and kinematics during double poling (DP) roller skiing between two groups of skiers in a field setting. Five experienced and five novice male skiers performed a SEDP test at 16 km∙h-1 on an outdoor athletics track. Gas exchange parameters were measured to determine SEDP. A two-dimensional video was filmed to measure the kinematics variables. Experienced skiers exhibited a 21% lower oxygen cost than novice skiers (p = 0.016) in DP, indicating a strong association between SEDP, cycle length and cycle rate (p < 0.001). Additionally, before the poling phase, experienced skiers manifested significantly greater maximum hip and knee extension angles than novice skiers (p < 0.001). During the poling phase, experienced skiers with a greater pole plant angle (p = 0.001), longer flexion time (p < 0.001) and higher flexion angular velocity in the elbow joint (p < 0.05) demonstrated better SEDP. There was an interaction effect of the one-repetition maximum bench press × group in SEDP (b = - 0.656, SE = 0.097, t = - 6.78, p = 0.001). Therefore, experienced skiers with better SEDP demonstrated more efficient cycles, potentially accomplished using dynamic full-body DP motion to ascertain effective propulsion. Combined upper body strength and ski-specific skill training may enhance SEDP in novice skiers.

Changes in roller skiing economy among Nordic combined athletes leading up to the competition season

The purpose of this study was to compare roller skiing economy during different training phases in Nordic combined (NC) athletes and determine the aerobic and anaerobic factors responsible for changes in skiing economy. Seven elite NC athletes underwent incremental load tests on a large buried treadmill in both spring and autumn using roller skis. Measurements included oxygen uptake, respiratory exchange ratio, and blood lactate concentration. Roller skiing economy was calculated from aerobic and anaerobic energy system contributions, and overall roller skiing economy was determined by combining the two. Comparisons were made between the skiing economies obtained in the two measurement sessions. Physical characteristics and incremental test performance remained consistent between the two measurement sessions. The overall skiing economy at each speed significantly improved toward the competition season (p < 0.05). Similarly, the contribution of anaerobic energy system at each speed showed significant improvement (p < 0.05). In contrast, the contribution of aerobic energy system did not change between the two measurement sessions. This study reveals that NC athletes enhance their skiing economy at the same speed during submaximal efforts in preparation for the competition season. This improvement is predominantly associated with an improvement in the contribution of anaerobic energy system.

Physiological responses and performance factors for double-poling and diagonal-stride treadmill roller-skiing time-trial exercise

PURPOSE

To compare physiological responses between a self-paced 4-min double-poling (DP) time-trial (TTDP) versus a 4-min diagonal-stride (DS) time-trial (TTDS). The relative importance of peak oxygen uptake ([Formula: see text]O2peak), anaerobic capacity, and gross efficiency (GE) for projection of 4-min TTDP and TTDS roller-skiing performances were also examined.

METHODS

Sixteen highly trained male cross-country skiers performed, in each sub-technique on separate occasions, an 8 × 4-min incremental submaximal protocol, to assess individual metabolic rate (MR) versus power output (PO) relationships, followed by a 10-min passive break and then the TTDP or TTDS, with a randomized order between sub-techniques.

RESULTS

In comparison to TTDS, the TTDP resulted in 10 ± 7% lower total MR, 5 ± 4% lower aerobic MR, 30 ± 37% lower anaerobic MR, and 4.7 ± 1.2 percentage points lower GE, which resulted in a 32 ± 4% lower PO (all P < 0.01). The [Formula: see text]O2peak and anaerobic capacity were 4 ± 4% and 30 ± 37% lower, respectively, in DP than DS (both P < 0.01). The PO for the two time-trial (TT) performances were not significantly correlated (R2 = 0.044). Similar parabolic pacing strategies were used during both TTs. Multivariate data analysis projected TT performance using [Formula: see text]O2peak, anaerobic capacity, and GE (TTDP, R2 = 0.974; TTDS, R2 = 0.848). The variable influence on projection values for [Formula: see text]O2peak, anaerobic capacity, and GE were for TTDP, 1.12 ± 0.60, 1.01 ± 0.72, and 0.83 ± 0.38, respectively, and TTDS, 1.22 ± 0.35, 0.93 ± 0.44, and 0.75 ± 0.19, respectively.

CONCLUSIONS

The results show that a cross-country skier's "metabolic profile" and performance capability are highly sub-technique specific and that 4-min TT performance is differentiated by physiological factors, such as [Formula: see text]O2peak, anaerobic capacity, and GE.

Kinematical effects of rifle carriage on roller skiing in well-trained female and male biathletes

PURPOSE

This study aimed to investigate how rifle carriage and skiing speed during biathlon roller skiing affect range of motion (ROM) in joint angles and equipment (skis and poles), the vertical distance between shoulders and treadmill (vert_dist ), as well as possible sex differences associated with rifle carriage.

METHODS

Fourteen biathletes (6 women, 8 men) roller-skied on a treadmill at submaximal and simulated race speeds, with (WR) and without (NR) a rifle, using gears 3 and 2. Kinematical data for the whole body, poles, roller-skis, rifle, and treadmill were monitored using a 3D motion capture system. Movements determined as flexion/extension (x), abduction/adduction (y), and/or internal/external rotation (z) were analyzed for the hip, shoulder, thorax, knee, ankle, elbow, poles, and roller skis. ROM (the difference between maximal and minimal angles) in joints and equipment, and vert_dist were analyzed over six skiing cycles during each condition (WR and NR) and speed.

RESULTS

The maximal vert_dist was lower for WR compared with NR (gear 3: 1.53 ± 0.06 vs 1.54 ± 0.06 m; gear 2: 1.49 ± 0.06 vs 1.51 ± 0.06 m; both p < 0.001). ROM in the upper body was altered when roller skiing WR (movements decreased in thorax and shoulder (x) and increased in elbow (only gear 3) (x), thorax (only gear 2), and shoulder (y) and (z); all p < 0.05) and increased with speed, without differences between sexes (p > 0.05).

CONCLUSION

Since rifle carriage and speed appear to affect the kinematics of roller skiing, coaches, and biathletes are advised to perform skiing technique training under competition-like conditions (i.e., at race speeds while carrying the rifle).

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.

The Modern Double-Poling Technique Is Not More Energy Efficient Than the Old-Fashioned Double-Poling Technique at a Submaximal Work Intensity

The purpose of the study was to investigate whether there are energy-efficiency differences between the execution of the old-fashioned double-poling technique (DP_OLD) and the modern double-poling technique (DP_MOD) at a submaximal work intensity among elite male cross-country skiers. Fifteen elite male cross-country skiers completed two 4-min tests at a constant mechanical work rate (MWR) using the DP_MOD and DP_OLD. During the last minute of each test, the mean oxygen uptake (VO₂) and respiratory exchange ratio (RER) were analyzed, from which the metabolic rate (MR) and gross efficiency (GE) were calculated. In addition, the difference between pretest and posttest blood-lactate concentrations (BLa_diff) was determined. For each technique, skiers' joint angles (i.e., heel, ankle, knee, hip, shoulder, and elbow) were analyzed at the highest and lowest positions during the double-poling cycle. Paired-samples t-tests were used to investigate differences between DP_MOD and DP_OLD outcomes. There were no significant differences in either VO₂mean, MR, GE, or BLa_diff (all P > 0.05) between the DP_MOD and DP_OLD tests. DP_MOD execution was associated with a higher RER (P < 0.05). Significant technique-specific differences were found in either the highest and/or the lowest position for all six analyzed joint angles (all P < 0.001). Hence, despite decades of double-poling technique development, which is reflected in the significant biomechanical differences between DP_OLD and DP_MOD execution, at submaximal work intensity, the modern technique is not more energy efficient than the old-fashioned technique.

The influence of a rocking-motion device built into classic cross-country roller-ski bindings on biomechanical, physiological and performance outcomes

This study aimed to determine whether the recently developed Flow Motion Technology® roller-ski prototype could improve indicators of performance during sub-maximal and maximal cross-country roller skiing. Thirteen national and international cross-country skiers completed 2 experimental trials: 1 with Flow Motion Technology® activated, allowing a rocking motion between the foot and ski binding, and 1 with the foot fixed in a traditional manner. Each trial included 2 sub-maximal bouts using the diagonal-stride and double-poling sub-techniques, as well as a double-poling maximal velocity test and a diagonal-stride 6-min time trial. There were no differences in performance between Flow Motion Technology® and traditional roller skiing during the maximal velocity test or the time trial. However, reductions in mean plantar force during sub-maximal diagonal stride (p = 0.011) and ankle range of motion during sub-maximal (p = 0.010) and maximal (p = 0.041) diagonal stride were observed with Flow Motion Technology® versus traditional roller skiing. This, together with a reduced minimum horizontal distance of the hips in front of the ankles during sub-maximal double poling (p = 0.001), indicated impaired technique with Flow Motion Technology®, which may have contributed to the trend for reduced gross efficiency during double poling with Flow Motion Technology® (pη2 = 0.214). Significant physiological differences included a reduced sub-maximal double poling respiratory exchange ratio (p = 0.03) and a greater maximal heart rate during the time trial (p = 0.014) with Flow Motion Technology®. We conclude that the application of Flow Motion Technology® requires further examination before use in training and competition.

Mechanical energy and propulsion mechanics in roller-skiing double-poling at increasing speeds

Objectives

The aim of this study was to examine the effect of speed on mechanical energy fluctuations and propulsion mechanics in the double-poling (DP) technique of cross-country skiing.

Methods

Kinematics and dynamics were acquired while fourteen male skiers performed roller-skiing DP on a treadmill at increasing speeds (15, 21 and 27 km∙h^-1). Kinetic (E_kin), potential (E_pot), and total (E_body) body mechanical energy and pole power (P_pole) were calculated. Inverse dynamics was used to calculate arm power (P_arm). Trunk+leg power (P_T+L) was estimated, as was the power associated with body movements perpendicular to goal-direction (E.body⊥).

Results

E_kin and E_pot fluctuated out-of-phase throughout the cycle, at first sight indicating that pendulum-like behaviour occurs partly in DP. However, during the swing phase, the increase in E_pot (body heightening) was mainly driven by positive P_T+L, while the decrease in E_kin was lost to rolling friction, and during the poling phase, considerable positive P_arm generation occurs. Thus, possible exchange between E_kin and E_pot seem not to occur as directly and passively as in classic pendulum locomotion (walking). During the poling phase, E.body⊥fluctuated out-of-phase with P_pole, indicating a transfer of body energy to P_pole. In this way, power generated by trunk+leg mainly during the swing phase (body heightening) can be used in the poling phase as pole power. At all speeds, negative P_T+L occurred during the poling phase, suggesting energy absorption of body energy not transferred to pole power. Thus, DP seem to resemble bouncing ball-like behaviour more than pendulum at faster speeds. Over the cycle, P_arm contribution to P_pole (external power) was 63% at 15 km∙h^-1 and 66% at 21 and 27 km∙h^-1, with the remainder being P_T+L contribution.

Conclusions

When speed increases in level DP, both power production and absorption by trunk+leg actions increase considerably. This enhanced involvement of the legs at faster speeds is likely a prerequisite for effective generation of pole power at high speeds with very short poling times. However, the relative trunk+leg power contribution did not increase at the speeds studied here.

Physiological Responses and Predictors of Performance in a Simulated Competitive Ski Mountaineering Race

Competitive ski mountaineering (SKIMO) has achieved great popularity within the past years. However, knowledge about the predictors of performance and physiological response to SKIMO racing is limited. Therefore, 21 male SKIMO athletes split into two performance groups (elite: VO_2max 71.2 ± 6.8 ml· min^-1· kg^-1 vs. sub-elite: 62.5 ± 4.7 ml· min^-1· kg^-1) were tested and analysed during a vertical SKIMO race simulation (523 m elevation gain) and in a laboratory SKIMO specific ramp test. In both cases, oxygen consumption (VO₂), heart rate (HR), blood lactate and cycle characteristics were measured. During the race simulation, the elite athletes were approximately 5 min faster compared with the sub-elite (27:15 ± 1:16 min; 32:31 ± 2:13 min; p < 0.001). VO₂ was higher for elite athletes during the race simulation (p = 0.046) and in the laboratory test at ventilatory threshold 2 (p = 0.005) and at maximum VO₂ (p = 0.003). Laboratory maximum power output is displayed as treadmill speed and was higher for elite than sub-elite athletes (7.4 ± 0.3 km h^-1; 6.6 ± 0.3 km h^-1; p < 0.001). Lactate values were higher in the laboratory maximum ramp test than in the race simulation (p < 0.001). Pearson's correlation coefficient between race time and performance parameters was highest for velocity and VO₂ related parameters during the laboratory test (r > 0.6). Elite athletes showed their superiority in the race simulation as well as during the maximum ramp test. While HR analysis revealed a similar strain to both cohorts in both tests, the superiority can be explainable by higher VO₂ and power output. To further push the performance of SKIMO athletes, the development of named factors like power output at maximum and ventilatory threshold 2 seems crucial.

Case Report: Adjusting Seat and Backrest Angle Improves Performance in an Elite Paralympic Rower

Paralympic rowers with functional impairments of the legs and trunk rely on appropriate seat configurations for performance. We compared performance, physiology, and biomechanics of an elite Paralympic rower competing in the PR1 class during ergometer rowing in a seat with three different seat and backrest inclination configurations. Unlike able-bodied rowers, PR1 rowers are required to use a seat with a backrest. For this study, we examined the following seat/backrest configurations: conA: 7.5°/25°, conB: 0°/25°, and conC: 0°/5° (usually used by the participant). All data was collected on a single day, i.e., in each configuration, one 4-min submaximal (100 W) and one maximal (all-out) stage was performed. The rowing ergometer provided the average power and (virtual) distance of each stage, while motion capture provided kinematic data, a load cell measured the force exerted on the ergometer chain, and an ergospirometer measured oxygen uptake (V˙O2). Where appropriate, a Friedman's test with post-hoc comparisons performed with Wilcoxon signed-ranked tests identified differences between the configurations. Despite similar distances covered during the submaximal intensity (conA: 793, conB: 793, conC: 787 m), the peak force was lower in conC (conA: 509, conB: 458, conC: 312 N) while the stroke rate (conA: 27 conB: 31, conC: 49 strokes·min⁻¹) and V˙O2 (conA: 34.4, conB: 35.4, conC: 39.6 mL·kg⁻¹·min⁻¹) were higher. During the maximal stage, the virtual distances were 7–9% longer in conA and conB, with higher peak forces (conA: 934 m, 408 N, conB: 918 m, 418 N, conC: 856 m, 331 N), and lower stroke rates (conA: 51, conB: 54, conC: 56 strokes·min⁻¹), though there was no difference in V˙O2peak (~47 ml⁻¹·kg⁻¹·min⁻¹). At both intensities, trunk range of motion was significantly larger in configurations conA and conB. Although fatigue may have accumulated during the test day, this study showed that a more inclined seat and backrest during ergometer rowing improved the performance of a successful Paralympic PR1 rower. The considerable increase in ergometer rowing performance in one of the top Paralympic rowers in the world is astonishing and highlights the importance of designing equipment that can be adjusted to match the individual needs of Paralympic athletes.

Biomechanical determinants of cross-country skiing performance: A systematic review

Cross-country skiing is a complex endurance sport requiring technical skills, in addition to considerable physiological and tactical abilities. This review aims to identify biomechanical factors that influence the performance of cross-country skiers. Four electronic databases were searched systematically for original articles in peer-reviewed journals addressing the relationship between biomechanical factors (including kinematics, kinetics, and muscle activation) and performance while skiing on snow or roller skiing. Of the 46 articles included, 22 focused exclusively on the classical technique, 18 on the skating technique, and six on both. The indicators of performance were: results from actual or simulated races (9 articles); speed on specific tracts (6 articles); maximal or peak speed (11 articles); skiing economy or efficiency (11 articles); and grouping on the basis of performance or level of skill (12 articles). The main findings were that i) cycle length, most often considered as a major determinant of skiing speed, is also related to skiing economy and level of performance; ii) higher cycle rate related with maximal speed capacity, while self-selected cycle rate improves skiing economy at sub-maximal speeds; iii) cross-country skiing performance appears to be improved by joint, whole-body, ski, and pole kinematics that promote forward propulsion while minimizing unnecessary movement.

Double-Poling Physiology and Kinematics of Elite Cross-Country Skiers: Specialized Long-Distance Versus All-Round Skiers

PURPOSE

Long-distance cross-country skiers specialize to compete in races >50 km predominantly using double poling (DP). This emphasizes the need for highly developed upper-body endurance capacities and an efficient DP technique. The aim of this study was to investigate potential effects of specialization by comparing physiological capacities and kinematics in DP between long-distance skiers and skiers competing using both techniques (skating/classic) in several competition formats ("all-round skiers").

METHODS

Seven male long-distance (32 [6] y, 183 [6] cm, 76 [5] kg) and 6 all-round (25 [3] y, 181 [5] cm, 75 [6] kg) skiers at high international levels conducted submaximal workloads and an incremental test to exhaustion for determination of peak oxygen uptake (VO2peak) and time to exhaustion (TTE) in DP and running.

RESULTS

In DP and running maximal tests, TTE showed no difference between groups. However, long-distance skiers had 5-6% lower VO2peak in running (81 [5] vs 85 [3] mL·kg-1·min-1; P = .07) and DP (73 [3] vs 78 [3] mL·kg-1·min-1; P < .01) than all-round skiers. In DP, long-distance skiers displayed lower submaximal O2 cost than all-round skiers (3.8 ± 3.6%; P < .05) without any major differences in cycle times or cyclic patterns of joint angles and center of mass. Lactate concentration over a wide range of speeds (45-85% of VO2peak) did not differ between groups, even though each workload corresponded to a slightly higher percentage of VO2peak for long-distance skiers (effect size: 0.30-0.68).

CONCLUSIONS

The long-distance skiers displayed lower VO2peak but compensated with lower O2 cost to perform equally with the all-round skiers on a short TTE test in DP. Furthermore, similar submaximal lactate concentration and reduced O2 cost could be beneficial in sustaining high skiing speeds in long-duration competitions.

Mechanical energetics and dynamics of uphill double-poling on roller-skis at different incline-speed combinations

Objectives

The purpose of this study was to investigate the effect of different incline-speed combinations, at equal external power outputs, on the mechanics and energetics of the double-poling (DP) technique in cross-country skiing.

Methods

Fourteen elite male cross-country skiers performed treadmill DP on roller-skis at low, moderate, and high mean external power outputs (P_mean) up a shallow incline (5%, INC5), at which DP is preferred, and up a steep incline (12%, INC12), at which DP is not preferred. Speed was set to produce equal P_mean at both inclines. From recorded kinematics and dynamics, arm power (P_arm) and trunk+leg power (P_T+L) were derived, as were pole propulsion power (P_pole) and body mechanical energy perpendicular to the treadmill surface (E_body⊥).

Results

Over a locomotion cycle, the arms contributed 63% to P_mean at INC5 but surprisingly only 54% at INC12 (P<0.001), with no effect of P_mean (P = 0.312). Thus, the trunk and legs contributed substantially to P_mean both at INC5 (37%) and INC12 (46%). At both inclines, P_T+L generation during the swing phase increased approximately linearly with P_mean, which increased E_body⊥. Within the poling phase, ~30–35% of the body energy which was developed during the preceding swing phase was transferred into propulsive pole power on both inclines. At INC5, the amount of negative P_T+L during the poling phase was larger than at INC12, and this difference increased with P_mean.

Conclusions

The considerable larger amount of negative P_T+L during poling at INC5 than at INC12 indicate that the legs and trunk generate more power than ‘necessary’ during the swing phase and thus must absorb more energy during the poling phase. This larger surplus of P_T+L at INC5 seems necessary for positioning the body and poles so that high P_arm generation can occur in a short time. At INC12, less P_arm is generated, probably due to less advantageous working conditions for the arms, related to body and pole positioning. These incline differences seem linked to shorter swing and longer poling times during steep uphill DP, which are due to the increased influence of gravity and slower speed at steep inclines.

Biomechanical differences in double poling between sexes and level of performance during a classical cross-country skiing competition

Biomechanical differences in double poling (DP) between sex and performance level were investigated in female and male cross-country skiers during a classical race (10/15 km). Skiers were divided into faster and slower on basis of race performance: females faster (n=20), females slower (n=20), males faster (n=20), and males slower (n=20). Based on video analysis while DP in a flat section of the track, joint and pole angles at pole plant (PP) and pole-off, cycle characteristics and the use and coordination pattern of heel-raise (raise of heels from the ground to have a higher body position at PP) were analysed. Faster females and males had 4.3% and 7.8% higher DP velocity than their slower counterparts (both P<0.001). Faster males had 6.5% longer cycles than slower males (P<0.001). Faster skiers stopped heel-raise later than slower skiers (females: 2.0±3.4% vs. -1.0±3.5%, P<0.05; males: 3.9±2.4% vs. 0.8±3.2% of cycle time in relation to PP, P<0.001). At PP, faster skiers and male skiers had a smaller pole angle and greater ankle to hip and ankle to shoulder angle with respect to vertical, resulting in a more distinct forward body lean. However, the majority of the differences are likely due to higher DP velocity.

Following a Long-Distance Classical Race the Whole-Body Kinematics of Double Poling by Elite Cross-Country Skiers Are Altered

Introduction: Although short-term (approximately 10-min) fatiguing DP has been reported not to alter the joint kinematics or displacement of the centre of mass (COM) of high-level skiers, we hypothesize that prolonged DP does change these kinematics, since muscular strength is impaired following endurance events lasting longer than 2 h.

Methods: During the 58-km Marcialonga race in 2017, the fastest 15 male skiers were videofilmed (100 fps, FHD resolution in the sagittal plane) on two 20-m sections (inclines: 0.7 ± 0.1°) 48 km apart (i.e., 7 and 55 km from the start), approximating 50- km Olympic races. The cameras were positioned perpendicular to and about 40 m from the middle of each section and spatial dimensions adjusted for each individual track skied. Pole and joint kinematics, as well as displacement of the COM during two DP cycles were assessed.

Results: The 10 skiers who fulfilled our inclusion criteria finished the race in 2 h 09 min 19 s ± 28 s. Displacements of the joints and COM were comparable to previous observations on skiers roller skiing on a flat treadmill at similar speeds in the laboratory. 55 km after the start, cycle velocity and length were lower (P < 0.001 and P = 0.002, respectively) and the angular range of elbow joint flexion during the initial part of the poling phase reduced, while shoulder angle was greater during the first 35% of the DP cycle (all P < 0.05). Moreover, the ankle angle was increased and forward displacement of the COM reduced during the first 80% of the cycle.

Conclusion: Prolonged DP reduced the forward displacement of the COM and altered arm kinematics during the early poling phase. The inefficient utilization of COM observed after 2 h of competition together with potential impairment of the stretch-shortening of arm extensor muscles probably attenuated generation of poling force. To minimize these effects of fatigue, elite skiers should focus on maintaining optimal elbow and ankle kinematics and an effective forward lean during the propulsive phase of DP.

Changing relative crank angle increases the metabolic cost of leg cycling

PURPOSE

Historically, the efficiency of leg cycling has been difficult to change. However, arm cycling research indicates that relative crank angle changes can improve efficiency. Therefore, we investigated if leg cycling with different relative crank angles affects efficiency.

METHODS

Ten healthy, male, recreational bicycle riders (27.8 ± 8.2 years, mean ± SD, mass 69.8 ± 3.2 kg) pedaled a pan-loaded cycle ergometer at a fixed power output of 150 watts at a cadence of 90 RPM. Each subject completed six, 5-min trials in random order at relative crank angles of 180°, 135°, 90°, 45°, 0°, and 180°. We averaged rates of oxygen uptake ([Formula: see text]) and carbon dioxide production ([Formula: see text]), and respiratory exchange ratio (RER) for the last 2 min of each trial.

RESULTS

Crank angles other than 180° required a greater metabolic cost. As relative crank angle decreased from 180°, metabolic power monotonically increased by 1.6% at 135° to 8.2% greater when the relative crank angle was 0° (p < 0.001).

CONCLUSIONS

We find that, unlike arm cycling, radically changing the relative crank angle on a bicycle from an out-of-phase (180°) to in-phase (0°) position decreases leg cycling efficiency by ~8%. We attribute the increase to changes in cost of breathing, muscle co-activation, trunk stabilization, power fluctuations, and possibly lifting the legs during the upstroke. Our findings may have relevance in the rehabilitation of patients recovering from stroke or spinal cord injury.

Full course macro-kinematic analysis of a 10 km classical cross-country skiing competition

In this study micro-sensors were employed to analyse macro-kinematic parameters during a classical cross-country skiing competition (10 km, 2-lap). Data were collected from eight male participants during the Australian championship competition wearing a single micro-sensor unit (MinimaxX™, S4) positioned on their upper back. Algorithms and visual classification were used to identify skiing sub-techniques and calculate velocities, cycle lengths (CL) and cycle rates (CR) over the entire course. Double poling (DP) was the predominant cyclical sub-technique utilised (43 ± 5% of total distance), followed by diagonal stride (DS, 16 ± 4%) and kick double poling (KDP, 5 ± 4%), with the non-propulsive Tuck technique accounting for 24 ± 4% of the course. Large within-athlete variances in CL and CR occurred, particularly for DS (CV% = 25 ± 2% and CV% = 15 ± 2%, respectively). For all sub-techniques the mean CR on both laps and for the slower and faster skiers were similar, while there was a trend for the mean velocities in all sub-techniques by the faster athletes to be higher. Overall velocity and mean DP-CL were significantly higher on Lap 1, with no significant change in KDP-CL or DS-CL between laps. Distinct individual velocity thresholds for transitions between sub-techniques were observed. Clearly, valuable insights into cross-country skiing performance can be gained through continuous macro-kinematic monitoring during competition.

Effect of prolonged racing on muscle activity and spatiotemporal variables: double-poling technique

[Purpose] The purpose of this study was to examine the effect of a 40-minute race on muscle activity and spatiotemporal cycle variables at four-time points during a 12-km roller skiing test using the double-poling technique. [Subjects and Methods] Five elite cross-country (XC) skiers on the Korean National reserve team participated in the study. Part of a biathlon course that consisted of both flat land and slopes was selected, and three measurements were recorded after every 4-km lap. Spatiotemporal variables, mean frequency and mean amplitude of 6 muscles were the chosen computational parameters. [Results] Significant differences were observed in cycle time and rate. The mean frequency of the upper-body muscles exhibited declining trends, with statistically significant differences for the triceps brachii. In addition, there were significant differences in the mean amplitude of the tibialis anterior and gastrocnemius. The activity of the triceps brachii, tibialis anterior, and gastrocnemius showed some degree of dependence on the technique. [Conclusion] Training and race strategies that improve the function of elbow extensors and ankle dorsiflexors are important in XC skiing; the application of roller-ski training research to actual XC skiing competitions is needed.

The effects of strength training versus ski-ergometer training on double-poling capacity of elite junior cross-country skiers

PURPOSE

To compare the effects of strength training versus ski-ergometer training on double-poling gross efficiency (GE), maximal speed (V _max), peak oxygen uptake ([Formula: see text]) for elite male and female junior cross-country skiers.

METHODS

Thirty-three elite junior cross-country skiers completed a 6-week training-intervention period with two additional 40-min training sessions per week. The participants were matched in pairs and within each pair randomly assigned to either a strength-training group (STR) or a ski-ergometer-training group (ERG). Before and after the intervention, the participants completed three treadmill roller-skiing tests to determine GE, V _max, and [Formula: see text]. Mixed between-within subjects analysis of variance (ANOVA) was conducted to evaluate differences between and within groups. Paired samples t tests were used as post hoc tests to investigate within-group differences.

RESULTS

Both groups improved their V _max and [Formula: see text] expressed absolutely (all P < 0.01). For the gender-specific sub-groups, it was found that the female skiers in both groups improved both V _max and [Formula: see text] expressed absolutely (all P < 0.05), whereas the only within-group differences found for the men were improvements of V _max in the STR group. No between-group differences were found for any of the investigated variables.

CONCLUSIONS

Physiological and performance-related variables of importance for skiers were improved for both training regimes. The results demonstrate that the female skiers' physiological adaptations to training, in general, were greater than those of the men. The magnitude of the physiological adaptations was similar for both training regimes.

Changes in upper and lower body muscle involvement at increasing double poling velocities: an ecological study

This study evaluated muscle activity changes in different body compartments during on-snow double poling at increasing velocities. 21 well-trained, male cross-country skiers performed five 3-min double poling trials on a snowy track at 15, 16.5, 18, 19.5, and 21 km/h (set by an audio-pace system). A sixth trial was performed by maintaining a constant maximal speed. Actual skiing velocities were verified using a photocell system. Only 11 subjects met the pre-defined inclusion criteria during the trials and were included in the data analysis. Electromyographical signals from seven muscles, wrist acceleration and heart rate during the last minute of each trial were recorded. Cycle and poling times were measured from acceleration signals; mean muscular activation over a cycle was calculated for each muscle. With increasing double poling velocities from aerobic to maximal intensity (from 65% to 100% of maximal heart rate), upper limb muscles activation was maintained constant (P > 0.05), while trunk and lower limb involvement increased significantly (P < 0.01) with a linear trend. Rectus abdominis and rectus femoris muscles showed the higher rate of change. Trunk and lower limbs provide a progressively greater contribution to the propulsion when increasing double poling velocities are performed, to support the limited capacity of exercise response of upper body muscles. The remarkable rate of involvement of the muscles near the core region of the body becomes strategic to cope with the increased demands of propulsive power.

The effect of swinging the arms on muscle activation and production of leg force during ski skating at different skiing speeds

The study investigated the effects of arm swing during leg push-off in V2-alternate/G4 skating on neuromuscular activation and force production by the leg muscles. Nine skilled cross-country skiers performed V2-alternate skating without poles at moderate, high, and maximal speeds, both with free (SWING) and restricted arm swing (NOSWING). Maximal speed was 5% greater in SWING (P<0.01), while neuromuscular activation and produced forces did not differ between techniques. At both moderate and high speed the maximal (2% and 5%, respectively) and average (both 5%) vertical force and associated impulse (10% and 14%) were greater with SWING (all P<0.05). At high speed range of motion and angular velocity of knee flexion were 24% greater with SWING (both P<0.05), while average EMG of m. biceps femoris was 31% lower (all P<0.05) in SWING. In a similar manner, the average EMG of m. vastus medialis and m. biceps femoris were lower (17% and 32%, P<0.05) during the following knee extension. Thus, swinging the arms while performing V2-alternate can enhance both maximal speed and skiing economy at moderate and, in particularly, high speeds.

Effects of short-term fatigue on biomechanical and physiological aspects of double poling in high-level cross-country skiers

The study aim was to evaluate biomechanical and physiological alterations in double poling technique (DP) after a short-term fatiguing exercise. Eight high-level skiers performed a sub-maximal DP trial (20kmh(-1), 1°) before (PRE) and after (POST) a DP test to exhaustion while roller skiing on a treadmill. An integrated analysis of DP technique during PRE and POST included measurement of pole, joint, and centre of mass (COM) kinematics, poling forces, cycle timing, and metabolic parameters. Muscle fatigue in three upper-body muscles was assessed by calculating the Dimitrov' fatigue index (FInms5) of specific electromyographic segments. FInms5 tended to increase in the latissimus dorsi and teres major muscles (P=0.023 and P=0.030, respectively) across consecutive DP cycles, as did blood lactate concentration (P=0.001) and rating of perceived exertion (P=0.005). The changes indicated a state of fatigue during POST and coincided with the reduction in poling force exertion capacity (P=0.020). Pole, joint and COM kinematics did not differ between PRE and POST (P>0.050), whereas recovery phase and cycle times were shorter at POST (P<0.001 and P=0.001, respectively). Short-term fatigue led to a reduction in poling force exertion capacity and cycle time in high-level skiers, without altering body and pole kinematics.

Using micro-sensor data to quantify macro kinematics of classical cross-country skiing during on-snow training

Micro-sensors were used to quantify macro kinematics of classical cross-country skiing techniques and measure cycle rates and cycle lengths during on-snow training. Data were collected from seven national level participants skiing at two submaximal intensities while wearing a micro-sensor unit (MinimaxX™). Algorithms were developed identifying double poling (DP), diagonal striding (DS), kick-double poling (KDP), tucking (Tuck), and turning (Turn). Technique duration (T-time), cycle rates, and cycle counts were compared to video-derived data to assess system accuracy. There was good reliability between micro-sensor and video calculated cycle rates for DP, DS, and KDP, with small mean differences (Mdiff% = -0.2 ± 3.2, -1.5 ± 2.2 and -1.4 ± 6.2) and trivial to small effect sizes (ES = 0.20, 0.30 and 0.13). Very strong correlations were observed for DP, DS, and KDP for T-time (r = 0.87-0.99) and cycle count (r = 0.87-0.99), while mean values were under-reported by the micro-sensor. Incorrect Turn detection was a major factor in technique cycle misclassification. Data presented highlight the potential of automated ski technique classification in cross-country skiing research. With further refinement, this approach will allow many applied questions associated with pacing, fatigue, technique selection and power output during training and competition to be answered.

Are gender differences in upper-body power generated by elite cross-country skiers augmented by increasing the intensity of exercise?

In the current study, we evaluated the impact of exercise intensity on gender differences in upper-body poling among cross-country skiers, as well as the associated differences in aerobic capacity, maximal strength, body composition, technique and extent of training. Eight male and eight female elite skiers, gender-matched for level of performance by FIS points, carried out a 4-min submaximal, and a 3-min and 30-sec maximal all-out test of isolated upper-body double poling on a Concept2 ski ergometer. Maximal upper-body power and strength (1RM) were determined with a pull-down exercise. In addition, body composition was assessed with a DXA scan and training during the previous six months quantified from diaries. Relative to the corresponding female values (defined as 100%), the power output produced by the men was 88%, 95% and 108% higher during the submaximal, 3-min and 30-sec tests, respectively, and peak power in the pull-down strength exercise was 118% higher (all P<0.001). During the ergometer tests the work performed per cycle by the men was 97%, 102% and 91% greater, respectively, and the men elevated their cycle rate to a greater extent at higher intensities (both P<0.01). Furthermore, men had a 61% higher VO2peak, 58% higher 1RM, relatively larger upper-body mass (61% vs 56%) and reported considerably more upper-body strength and endurance training (all P<0.05). In conclusion, gender differences in upper-body power among cross-country skiers augmented as the intensity of exercise increased. The gender differences observed here are greater than those reported previously for both lower- and whole-body sports and coincided with greater peak aerobic capacity and maximal upper-body strength, relatively more muscle mass in the upper-body, and more extensive training of upper-body strength and endurance among the male skiers.

The effects of prior high intensity double poling on subsequent diagonal stride skiing characteristics

PURPOSE

To investigate the influence of prior high intensity double poling (DP) on physiological and biomechanical responses during subsequent diagonal stride (DIA).

METHODS

Eight well-trained male cross-country skiers (age 22 ± 3 yr; VO2max 69 ± 3 ml · kg(-1) · min(-1)) roller-skied on a treadmill sequentially for 3 min at 90% DIA VO2max (DIA1), 3 min at 90% DP VO2peak and 3 min at 90% DIA VO2max (DIA2). Cardio-respiratory responses were monitored continuously and gases and metabolites in blood from the a. femoralis, v. femoralis and v. subclavia determined. Pole and plantar forces and EMG from 6 lower- and upper-body muscles were measured.

RESULTS

VO2 decreased from DIA1 to DP and increased again to DIA2 (both P < 0.05), with no difference between the DIA sessions. Blood lactate rose from DIA1 to DP to DIA2. O2 extraction was attenuated during DP (P < 0.05), but was the same during DIA1 and DIA2. EMGRMS for arm muscles during poling phase, as well as peak pole force and cycle rate were higher, while leg muscle activity was lower during DP than both sessions of DIA (all P < 0.05). The ratio of upper-/whole-body EMGRMS correlated negatively with O2 extraction in the arms during both sessions of DIA (P < 0.05).

CONCLUSIONS

In well-trained skiers skiing at high-intensity DP prior to DIA did not influence VO2, muscle activation or forces in the latter. At race intensity DP does not influence the distribution of work between upper- and lower-body during a subsequent bout of DIA. O2 extraction is coupled to technical skills during skiing.

Energetics and biomechanics of double poling in regional and high-level cross-country skiers

PURPOSE

The aim of this study was to evaluate the energetics and the biomechanics of double poling technique (DP) in two groups of cross-country skiers.

METHODS

Eight high-level (HLG) and eight regional-level (RLG) skiers performed a 5-min sub-maximal DP trial, roller skiing on a treadmill at 14 km h(-1) and 2°. Energetic cost (ECDP), center of mass (COM) vertical displacement range, body inclination (θ, i.e., the angle between the vertical line and the line passing through COM and a fixed pivot point identified at feet level) and mechanical work associated to COM motion were analyzed. Pole and joint kinematics, poling forces and cycle timing were also considered.

RESULTS

HLG showed lower ECDP than RLG, smaller COM vertical displacement range and mechanical work, whereas higher θ during the early part of the poling phase (P < 0.05). In HLG, pole inclination was higher, poling forces greater and cycle duration longer (P < 0.05). Considering all skiers, a forward multiple regression revealed that the maximum value of θ (θ max) and the minimum value of COM vertical displacement resulted the COM-related parameters that better predict ECDP (AdjR (2) = 0.734; P < 0.001). Moreover, θ max positively related to poling force integrals and cycle duration (P < 0.05).

CONCLUSIONS

A pronounced body inclination during the early poling phase and a reduced COM vertical displacement range concur in explaining the differences in ECDP found between the groups and among the skiers. A mechanically advantageous motion of COM during DP improves poling effectiveness, reduces cycle frequency and the mechanical work sustained.

Exercise economy in skiing and running

Substantial inter-individual variations in exercise economy exist even in highly trained endurance athletes. The variation is believed to be determined partly by intrinsic factors. Therefore, in the present study, we compared exercise economy in V2-skating, double poling, and uphill running. Ten highly trained male cross-country skiers (23 ± 3 years, 180 ± 6 cm, 75 ± 8 kg, VO2peak running: 76.3 ± 5.6 mL·kg(-1)·min(-1)) participated in the study. Exercise economy and VO2peak during treadmill running, ski skating (V2 technique) and double poling were compared based on correlation analysis. There was a very large correlation in exercise economy between V2-skating and double poling (r = 0.81) and large correlations between V2-skating and running (r = 0.53) and double poling and running (r = 0.58). There were trivial to moderate correlations between exercise economy and the intrinsic factors VO2peak (r = 0.00-0.23), cycle rate (r = 0.03-0.46), body mass (r = -0.09-0.46) and body height (r = 0.11-0.36). In conclusion, the inter-individual variation in exercise economy could be explained only moderately by differences in VO2peak, body mass and body height. Apparently other intrinsic factors contribute to the variation in exercise economy between highly trained subjects.

Biomechanical characteristics and speed adaptation during kick double poling on roller skis in elite cross-country skiers

Recent developments in cross-country ski racing should promote the use of kick double poling. This technique, however, has not been the focus in athletes' training and has barely been investigated. The aims of the present study were to develop a function-based phase definition and to analyse speed adaptation mechanisms for kick double poling in elite cross-country skiers. Joint kinematics and pole/plantar forces were recorded in 10 athletes while performing kick double poling at three submaximal roller skiing speeds. A speed increase was associated with increases in cycle length and rate, while absolute poling and leg push-off durations shortened. Despite maintained impulses of force, the peak and average pole/leg forces increased. During double poling and leg push-off, ranges of motion of elbow flexion and extension increased (p < 0.05) and were maintained for hip/knee flexion and extension. Cycle length increase was correlated to increases in average poling force (r = 0.71) and arm swing time (r = 0.88; both p < 0.05). The main speed adaptation was achieved by changes in double poling technique; however, leg push-off showed high variability among elite skiers, thus illustrating important aspects for technique training.

Multi-dimensional coordination in cross-country skiing analyzed using self-organizing maps

This study sought to ascertain how multi-dimensional coordination patterns changed with five poling speeds for 12 National Standard cross-country skiers during roller skiing on a treadmill. Self-organizing maps (SOMs), a type of artificial neural network, were used to map the multi-dimensional time series data on to a two-dimensional output grid. The trajectories of the best-matching nodes of the output were then used as a collective variable to train a second SOM to produce attractor diagrams and attractor surfaces to study coordination stability. Although four skiers had uni-modal basins of attraction that evolved gradually with changing speed, the other eight had two or three basins of attraction as poling speed changed. Two skiers showed bi-modal basins of attraction at some speeds, an example of degeneracy. What was most clearly evident was that different skiers showed different coordination dynamics for this skill as poling speed changed: inter-skier variability was the rule rather than an exception. The SOM analysis showed that coordination was much more variable in response to changing speeds compared to outcome variables such as poling frequency and cycle length.

Kinematic, kinetic and electromyographic adaptation to speed and resistance in double poling cross country skiing

This study incorporated variations in speed and the horizontal resistance acting upon elite female skiers during double poling (DP) on a treadmill and specifically analyzed biomechanical adaptations to these variations. Whole body kinematics and pole force data were recorded and used to calculate the moment of force acting on the shoulder and elbow joints. Data were obtained with a 3D optoelectronic system using reflective markers at given anatomical landmarks. Forces along the long axis of the right pole were measured with a piezoelectric force transducer. Surface electrodes were used to record EMG activity in the rectus femoris, rectus abdominis, latissimus dorsi and triceps brachii muscles. In a first set of recordings, the participants double poled with zero elevation at five different speeds from 8 to 17 km h(-1). In a second set of recordings, horizontal resistance was added by weights (0.4-1.9 kg) attached to a pulley system pulling the skier posteriorly during DP at 14 km h(-1). Results showed increasing relative duration of the thrust phase with increasing resistance, but not with speed. Significant kinematic differences occurred with increase in both speed and resistance. The mean (±SD) horizontal force components ranged between 1.7 (±1.3) and 2.8 (±1.1) percent (%) bodyweight (BW) in the speed adaptation and 3.1 (±0.6) and 4.0 (±1.3) % BW in the adaptation to horizontal resistance. Peak muscle activity showed a central to peripheral (proximo-distal) activation sequence. The temporal cycle phase pattern in the adaptation to speed and horizontal resistance differed.

Identification of cross-country skiing movement patterns using micro-sensors

This study investigated the potential of micro-sensors for use in the identification of the main movement patterns used in cross-country skiing. Data were collected from four elite international and four Australian athletes in Europe and in Australia using a MinimaxX™ unit containing accelerometer, gyroscope and GPS sensors. Athletes performed four skating techniques and three classical techniques on snow at moderate velocity. Data from a single micro-sensor unit positioned in the centre of the upper back was sufficient to visually identify cyclical movement patterns for each technique. The general patterns for each technique were identified clearly across all athletes while at the same time distinctive characteristics for individual athletes were observed. Differences in speed, snow condition and gradient of terrain were not controlled in this study and these factors could have an effect on the data patterns. Development of algorithms to process the micro-sensor data into kinematic measurements would provide coaches and scientists with a valuable performance analysis tool. Further research is needed to develop such algorithms and to determine whether the patterns are consistent across a range of different speeds, snow conditions and terrain, and for skiers of differing ability.

Skiing efficiency versus performance in double-poling ergometry

This study is on how leg utilisation may affect skiing efficiency and performance in double-poling ergometry. Three experiments were conducted, each with a different style of the double-poling technique: traditional with small knee range-of-motion and fixed heels (TRAD); modern with large knee range-of-motion and fixed heels (MOD1) and modern with large knee range-of-motion and free heels (MOD2). For each style, motion data were extracted with automatic marker recognition of reflective markers and applied to a 3D full-body musculoskeletal simulation model. Skiing efficiency (skiing work divided by metabolic muscle work) and performance (forward impulse) were computed from the simulation output. Skiing efficiency was 4.5%, 4.1% and 4.1% for TRAD, MOD1 and MOD2, respectively. Performance was 111, 143 and 149 Ns for TRAD, MOD1 and MOD2, respectively. Thus, higher lower body utilisation increased the performance but decreased the skiing efficiency. These results demonstrate the potential of musculoskeletal simulations for skiing efficiency estimations.