| 1. |
|
|
| 2. |
|
|
| 3. |
- Holmberg, Hans-Christer, 1958-, et al.
(författare)
-
Biomechanical analyses and predictors of diagonal stride performance in elite cross-country skiers
- 2008
-
Ingår i: Proceedings of the 13th Annual Congress of the European College of Sports Science. - Cologne : Sportools. - 9789727351565 ; , s. 568-
-
Konferensbidrag (refereegranskat)abstract
- Introduction: In cross-country (XC) skiing classical style was the only racing style until the mid 1980s and the main focus of early biomechanical studies was on the diagonal technique (DIAG). With the introduction of the new free style, research became more oriented toward this although both styles have gone through substantial development during the last decade (Smith, 2002). Recently, modern double poling technique has been thoroughly analyzed as regards its biomechanical characteristics and factors related to performance (Holmberg et al., 2005; 2006). However, there is still a lack of biomechanical data describing modern DIAG. Therefore, the aims of the present study were 1) to perform a basic biomechanical description of modern DIAG, and 2) to detect decisive factors related to DIAG performance. Methods: Twelve Swedish elite XC skiers (VO2max-DIAG: 72.3 ± 3.8 ml kg-1 min-1) performed DIAG roller skiing at a treadmill inclination of 9° at 11 km h-1 for biomechanical analyses. DIAG performance was defined by time to exhaustion (TTEDIAG) during a DIAG incremental pre-test (4°-11° [1°/min]; with a constant velocity of 11 km/h). Leg and arm joint angles (goniometers), pole forces (strain gauge transducers; 2000 Hz) and plantar forces (Pedar Mobile; 100 Hz) were recorded continuously. Correlations between DIAG performance (TTEDIAG) and biomechanical variables was examined using Pearson product-moment correlation coefficient tests (P<0.05). Results: Correlations were found for cycle time and cycle length (r=0.688; P<0.01), cycle rate (r=-0.731; P<0.01), relative foot ground contact time (r=-0.658; P<0.05), absolute and relative leg swing time (r=0.756, P<0.01; r=0.658; P<0.05), amplitude and angular velocity of hip angle during leg swing (r=0.634; r=0.652; P<0.05), hip angle at ski plant (r=-0.616; P<0.05), absolute and relative hip extension time (gliding phase) (r=0.689, P<0.01; r=0.592, P<0.05), absolute peak foot force (r=0.606, P<0.05), duration and amplitude of the knee angle extension from ski in, e.g. when the skis came in contact with the ground, to the knee angle maximum (r=0.743; r=0.710, P<0.01), rear foot force at minimal hip angle before push-off (r=-0.634; P<0.05), relative (%BW) peak pole force (r=-0.706; P<0.01), pole force at start of forward swing of the opposite leg (r=-0.681; P<0.01), amplitude of elbow extension during poling (r=0.741; P<0.01) and duration of elbow extension after pole out (r=-0.615; P<0.01). Discussion: It can be concluded that better DIAG skiers have 1) a longer and more distinct forward swing in their legs, 2) shorter ground contact, characterised by a lower body position when the skis come into contact with the ground, 3) a more distinct hip and knee angle extension (preparation) just before push-off, 4) a higher absolute production of leg force during push-off and 5) arm work characterised by lower and later peak pole forces (late accentuation).
|
|
| 4. |
- Holmberg, Hans-Christer, et al.
(författare)
-
Biomechanical analysis of double poling in elite cross-country skiers
- 2005
-
Ingår i: Medicine & Science in Sports & Exercise. - 0195-9131 .- 1530-0315. ; 37:5, s. 807-818
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
| 5. |
- Holmberg, Hans-Christer, et al.
(författare)
-
Contribution of the legs to double-poling performance in elite cross-country skiers.
- 2006
-
Ingår i: Medicine and science in sports and exercise. - : Ovid Technologies (Wolters Kluwer Health). - 0195-9131 .- 1530-0315. ; 38:10, s. 1853-60
-
Tidskriftsartikel (refereegranskat)abstract
- In the classical style of cross-country skiing, the double-poling (DP) technique, which is regarded as an upper-body exercise, is used on the flatter parts of a course. Limited biomechanical and physiological data are available about DP compared with other cross-country skiing techniques. The purpose of the present study was to evaluate the possible role of the lower body during DP.Eleven elite cross-country skiers performed two incremental tests using DP roller skiing at 1 degree inclination on a treadmill with or without locking the knee and ankle joints (DPLOCKED and DPFREE). Maximal and peak oxygen uptake (VO2max and VO2peak) during classic diagonal skiing and DP, respectively, were measured. In addition, heart rate, blood lactate concentration, and maximal DP velocity (Vmax) were determined. Pole-ground reaction forces and joint angles (elbow, hip, knee, and ankle) were analyzed.The skiers obtained 7.7% higher VO2peak, 9.4% higher Vmax, and 11.7% longer time to exhaustion during DPFREE compared with DPLOCKED (all P < 0.05). There was a higher heart rate and blood lactate concentration in DPLOCKED at submaximal stages (all P < 0.05), with no difference in oxygen consumption. At 85% Vmax, corresponding to approximately 81% VO2peak FREE, the differences in physiological variables were accompanied by a 13.6% higher poling frequency, a 4.9% shorter poling phase, 13.3% shorter recovery phase, and 10.9% lower relative pole force in DPLOCKED (all P < 0.05).Movements of the knee and ankle joints are an integrative part in the skillful use of the DP technique, and restriction of the motion in these joints markedly affects both biomechanical and physiological variables, impairing DP performance.
|
|
| 6. |
- Lindinger, Stefan, et al.
(författare)
-
Control of speed during the double poling technique performed by elite cross-country skiers
- 2009
-
Ingår i: Medicine & Science in Sports & Exercise. - 0195-9131 .- 1530-0315. ; 41:1, s. 210-220
-
Tidskriftsartikel (refereegranskat)abstract
- PURPOSE: Double poling (DP) as a main technique in cross-country skiing has developed substantially over the last 15 yr. The purpose of the present study was to analyze the question, "How do modern elite skiers control DP speed?" METHODS: Twelve male elite cross-country skiers roller skied using DP at 9, 15, 21, and 27 km.h(-1) and maximum velocity (V(max)). Cycle characteristics, pole and plantar forces, and elbow, hip, and knee joint angles were analyzed. RESULT: Both poling frequency and cycle length increased up to 27 km.h (-1)(P < 0.05), with a further increase in poling frequency at V(max) (P < 0.05). Peak pole force, rate of force development, and rearfoot plantar force increased with submaximal velocities (V(sm)), whereas poling time and time-to-peak pole force gradually shortened (P < 0.05). Changes in elbow joint kinematics during the poling phase were characterized by a decreased angle minimum and an increased flexion and extension ranges of motion as well as angular velocities across V(sm) (P < 0.05), with no further changes at V(max). Hip and knee joint kinematics adapted across V(sm) by 1) decreasing angles at pole plant and angle minima during the poling phase, 2) increasing the ranges of motion and angular velocities during the flexion phases occurring around pole plant, and 3) increasing extension ranges of motion and angular velocities during the recovery phase (all P values <0.05), with no further changes at V(max). CONCLUSIONS: Elite skiers control DP speed by increasing both poling frequency and cycle length; the latter is achieved by increased pole force despite reduced poling time. Adaptation to higher speeds was assisted by an increased range of motion, smaller angle minima, and higher angular velocities in the elbow, the hip, and the knee joints.
|
|
| 7. |
|
|
| 8. |
|
|
| 9. |
- Stöggl, Thomas, et al.
(författare)
-
Sprint competitions and maximal speed in cross-country skiing - a physiobiomechanical update
- 2009
-
Ingår i: Proceedings of 14th Annual Congress of the European College of Sport Science. - 9788250204201
-
Konferensbidrag (refereegranskat)abstract
- Due to the recent introduction of sprint races and an increasing number of mass start competitions in the World Cup series, new aspects of training and testing are becoming fields of research. This could be attributed to the upcoming specialization of athletes in sprint racing, as well as to the technical modifications demonstrated for selected techniques, eg. double poling (Holmberg et al. 2005) and doublepush skating (Stöggl et al. 2008a). Both technical modifications were found to be superior to the conventional skiing style. In addition, the mean skiing velocity in WC sprint races has shown a steady increase in skiing speed (Stöggl et al. 2008b), reaching mean race speeds of up to 9.5m/s in classical style and up to 10m/s in skating. It should be noted that skiing speeds in the majority of scientific studies are quite apart to these values. It was demonstrated that there is a moderate to high correlation between sprint performance and performance in distance races (Stöggl et al. 2008b). It was recently shown that short duration maximal skiing speed and specific maximal and explosive strength are good predictors of cross-country skiing sprint performance (Stöggl et al. 2007a,b 2009). Interestingly it was found that skiers with higher maximal power output and maximal skiing speeds showed, in addition to their higher performance, less fatigue during all-out tests of the same duration as a sprint race. These results may be coupled to the prerequisites of modern sprint techniques, as characterized by high peak forces and high force impulses over a short time. The combination of high force output over a short time and thus a longer recovery time was found to be faster and more economical (Holmberg et al. 2005; Stöggl & Müller 2009). Furthermore, it was found that cycle length but not cycle rate was related to performance, especially at submaximal velocities. This was particularly true of the V2 technique and diagonal stride, whereas in double-poling there seems to be an optimum cycle length and cycle rate pattern (Stöggl & Müller 2009). Measures of aerobic capacity (VO2max) showed only low correlations to sprint performance. However, it should be noted that a high level of VO2max should be the basis but also that other factors that are mainly associated with neuromuscular factors and anaerobic capacity discriminate between weak and strong sprint skiers. These findings should lead to a reconsideration of concepts in the training and testing of cross-country skiers. In addition to common VO2max and incremental step tests, also strength and speed tests should be included. Maximal and explosive strength training sessions could also be useful additions to conventional aerobic and strength endurance training.
|
|
