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

Pushing forward: exploring the impact of the sitting position on muscle activation patterns and force generation during paralympic sit-cross-country skiing

Paralympic cross-country sit-skiing is a discipline of the Paralympic Winter Games where athletes use a specialized sledge. Athletes are classified into different groups according to their functional abilities. The double poling technique is used to push the sledge forward and generate speed. Different sitting positions in the sledge are used based on the individual impairment. To date there is no data available on the effects of these different positions on muscle activation patterns. The aim of this study was to analyze the muscle activation patterns of the trunk and upper body muscles in relation to the poling force. Nine Able-bodied athletes were tested on a treadmill at submaximal speed in three sitting positions for 4 min in a flat and uphill condition. Sitting positions included a "knee-high" position, a "knee-low" position, and a "neutral" position with the sitting platform parallel to the ground. Unilateral pole forces and surface EMG from three trunk muscles, two upper limb muscles, and one lower limb muscle were recorded simultaneously on the dominate side. Data were segmented into individual cycles and mean values and standard deviations calculated for each subject and condition. Statistical analyses, including a Friedman test and Bonferroni correction, were applied to examine significant differences across different sitting positions. Our findings demonstrate that while certain muscle groups such as the erector spinae and triceps show consistent patterns of activation across different sitting positions, there is considerable variability among individual athletes, suggesting individualized strategies for task execution. Overall, force application was most efficient in the "knee low" position with 691.33 ± 148.83 N and least efficient in the "knee high" position with 582.81 ± 115.11 N. Testing impaired athletes will be the next step in understanding the neurophysiological aspects of the poling movement. This experimental protocol provides a basis for understanding the movement of paralympic cross-country sit-skiing in greater depth.

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.

A Comparison of Double Poling Physiology and Kinematics Between Long-Distance and All-Round Cross-Country Skiers

Purpose

The objective of this study was to compare physiological and kinematic responses to double poling (DP) between long-distance (LDS) and all-round (ARS) cross-country skiers.

Methods

A number of five world-class LDS (28.8 ± 5.1 years, maximal oxygen uptake (VO_2max): 70.4 ± 2.9 ml·kg⁻¹·min⁻¹) and seven ARS (22.3 ± 2.8 years, VO_2max: 69.1 ± 4.2 ml·kg⁻¹·min⁻¹) athletes having similar training volumes and VO_2max performed three identical tests; (1) submaximal and incremental tests to exhaustion while treadmill DP to determine gross efficiency (GE), peak oxygen uptake (DP-VO_2peak), and peak speed; (2) submaximal and incremental running tests to exhaustion to determine GE, VO_2max (RUN-VO_2max), and peak speed; and (3) an upper-body pull-down exercise to determine one repetition maximum (1RM) and peak power. Physiological responses were determined during both DP and running, together with the assessments of kinematic responses and electromyography (EMG) of selected muscles during DP.

Results

Compared to ARS, LDS reached higher peak speed (22.1 ± 1.0 vs. 20.7 ± 0.9 km·h⁻¹, p = 0.030), DP-VO_2peak (68.3 ± 2.1 vs. 65.1 ± 2.7 ml·kg⁻¹·min⁻¹, p = 0.050), and DP-VO_2peak/RUN-VO_2max ratio (97 vs. 94%, p = 0.075) during incremental DP to exhaustion, as well as higher GE (17.2 vs. 15.9%, p = 0.029) during submaximal DP. There were no significant differences in cycle length or cycle rate between the groups during submaximal DP, although LDS displayed longer relative poling times (~2.4% points) at most speeds compared to ARS (p = 0.015). However, group × speed interaction effects (p < 0.05) were found for pole angle and vertical fluctuation of body center of mass, with LDS maintaining a more upright body position and more vertical pole angles at touchdown and lift-off at faster speeds. ARS displayed slightly higher normalized EMG amplitude than LDS in the muscles rectus abdominis (p = 0.074) and biceps femoris (p = 0.027). LDS performed slightly better on 1RM upper-body strength (122 vs. 114 kg, p = 0.198), with no group differences in power in the pull-down exercise.

Conclusions

The combination of better DP-specific aerobic energy delivery capacity, efficiency, and technical solutions seems to contribute to the superior DP performance found among specialized LDS in comparison with ARS.

Hybrid high-intensity interval training using functional electrical stimulation leg cycling and arm ski ergometer for people with spinal cord injuries: a feasibility study

Aim

The aim was to assess safety and feasibility of Hybrid High-Intensity Interval Training (HIIT) using Functional Electrical Stimulation (FES) leg cycling and arm ski ergometer in people with Spinal Cord Injuries (SCI).

Method

Eight outpatients (mean age 42.8 years; 7 men) with stable SCI paraplegia (mean 14.5 years since injury) participated in hybrid HIIT (90% peak watts; 4 × 4–min intervals), three times a week (over 8 weeks). Primary outcomes were Adverse Events (AE), participant acceptability, shoulder pain, training intensity (% peak watts), and attendance.

Secondary outcomes were effect on peak oxygen uptake (VO₂peak) during FES hybrid poling, mean watts, self-reported leisure time physical activity, quality of life, and fatigue.

Results

No serious AE occurred; acceptability with the training modality was high, while shoulder pain increased by 9% (SD 95.2). During training, 50% of the participants reached > 90% peak watts during the intervals, three with the legs (FES cycle) and one with the arms (Ski-Erg). Overall, mean training intensity (% peak watts) was 92% (SD 18.9) for legs and 82% (SD 10.3) for arms. Proportion of fulfilled training minutes was 82% (range 36–100%); one participant dropped out after 6 weeks due to back pain. Mean VO₂peak increased by 17% (SD 17.5). Participants reported increased leisure time physical activity and health-related quality of life, besides reduced fatigue.

Conclusion

Hybrid HIIT was safe for people with SCI paraplegia. The majority of the criteria for feasibility were met with acceptable attendance rate, limited drop out, participants enjoyed training, and increased VO₂peak and mean watts. However, the intensity of 90% peak watts was reached by < 60% of the participants despite high RPE ratings during training. The method of measuring and calculating intensity needs to be studied further before a study using this HIIT protocol is undertaken.

Trial registration

Clinicaltrials.gov, NCT04211311, registered 12 December 2019 retrospectively registered

Supplementary Information

The online version contains supplementary material available at 10.1186/s40814-022-00997-2.

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.

Sustainable Sport: Cardio-Differentiated Planning of Fitness Programs for High School Boys Engaged in Speed Skiing

In speed skiing, an athlete’s functional readiness is tested by means of a bicycle ergometer (EGM). The purpose of this research is to make various mesocycle plans for high school boys, engaged in speed skiing, with due account for their cardio-functional indicators obtained by means of the EGM. The study was attended by the 16–17 years old, first-category and sub-master racing skiers, included in the junior regional teams of the Russian Federation (Republic of Tatarstan and Udmurtia). The total number of subjects included eight men. In training young racing skiers, a differentiated approach combined with leg muscle testing will allow an improvement in sports results more effectively at different stages, as well as monitoring the young athlete’s response to the cardiovascular load. Low cardiac capacity indices have a negative impact on the racing skier’s performance. EGM testing allows determining the maximum cardiac capacity by measuring the amount of oxygen delivered to the working muscles at the HR of 190 beats per minute. Therefore, case-specific aerobic load was planned for each mesocycle according to these data. Based on the cardiac capacity growth, such means of physical training as interval, high-speed, and tempo training were planned.

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.

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.

Developments in the Biomechanics and Equipment of Olympic Cross-Country Skiers

Here, our aim was to describe the major changes in cross-country (XC) skiing in recent decades, as well as potential future developments. XC skiing has been an Olympic event since the very first Winter Games in Chamonix, France, in 1924. Over the past decades, considerable developments in skiing techniques and improvements in equipment and track preparation have increased skiing speed. In contrast to the numerous investigations on the physiological determinants of successful performance, key biomechanical factors have been less explored. Today’s XC skier must master a wide range of speeds, terrains, and race distances and formats (e.g., distance races with individual start, mass-start or pursuit; knock-out and team-sprint; relays), continuously adapting by alternating between various sub-techniques. Moreover, several of the new events in which skiers compete head-to-head favor technical and tactical flexibility and encourage high-speed techniques (including more rapid development of propulsive force and higher peak forces), as well as appropriate training. Moreover, the trends toward more extensive use of double poling and skiing without grip wax in classical races have given rise to regulations in connection with Olympic distances that appear to have preserved utilization of the traditional classical sub-techniques. In conclusion, although both XC equipment and biomechanics have developed significantly in recent decades, there is clearly room for further improvement. In this context as well, for analyzing performance and optimizing training, sensor technology has a potentially important role to play.