Balance Perturbations as a Measurement Tool for Trunk Impairment in Cross-Country Sit Skiing.

In cross-country sit-skiing, the trunk plays a crucial role in propulsion generation and balance maintenance. Trunk stability is evaluated by automatic responses to unpredictable perturbations; however, electromyography is challenging. The aim of this study was to identify a measure to group sit-skiers according to their ability to control the trunk. Seated in their competitive sit-ski, 10 male and 5 female Paralympic sit-skiers received 6 forward and 6 backward unpredictable perturbations in random order. k-means clustered trunk position at rest, delay to invert the trunk motion, and trunk range of motion significantly into 2 groups. In conclusion, unpredictable perturbations might quantify trunk impairment and may become an important tool in the development of an evidence-based classification system for cross-country sit-skiers.

Spinal posture and pelvic position during pregnancy: a prospective rasterstereographic pilot study.

PURPOSE: Despite the high prevalence of low back pain during pregnancy there is still a lack in the understanding of its aetiology. Changes of the spinal posture due to the anatomical changes of the pregnant body seem to be in part responsible for the back pain. In this pilot study we assessed the potential to accurately measure the spinal posture and pelvic position during pregnancy without any harmful radiation using a spine and surface topography system. METHODS: Thirteen pregnant women were examined during the second and third trimester of their pregnancy, and postpartum. Twenty female, non-pregnant volunteers comprised the control group. The spinal posture and pelvic position were measured with a radiation-free spine and surface topography system. RESULTS: We found a significant increase in thoracic kyphosis during the course of pregnancy, but no increased lumbar lordosis. The lateral deviation of the spine also decreased significantly. However, we did not measure significant changes of the pelvic position during or after pregnancy. CONCLUSIONS: The results of our study show that pregnancy has an effect on the spinal posture, and that spine and surface topography can be used to measure these changes three-dimensionally and without any harmful radiation. In future studies this technique could allow to further evaluate the relationship between posture and low back pain during pregnancy, helping to understand the aetiology of low back pain in pregnancy as well as to identify methods for its prevention and treatment.

Improvement of walking speed and gait symmetry in older patients after hip arthroplasty: a prospective cohort study.

BACKGROUND: Retraining walking in patients after hip or knee arthroplasty is an important component of rehabilitation especially in older persons whose social interactions are influenced by their level of mobility. The objective of this study was to test the effect of an intensive inpatient rehabilitation program on walking speed and gait symmetry in patients after hip arthroplasty (THA) using inertial sensor technology. METHODS: Twenty-nine patients undergoing a 4-week inpatient rehabilitation program following THA and 30 age-matched healthy subjects participated in this study. Walking speed and gait symmetry parameters were measured using inertial sensor device for standardized walking trials (2*20.3 m in a gym) at their self-selected normal and fast walking speeds on postoperative days 15, 21, and 27 in patients and in a single session in control subjects. Walking speed was measured using timing lights. Gait symmetry was determined using autocorrelation calculation of the cranio-caudal (CC) acceleration signals from an inertial sensor placed at the lower spine. RESULTS: Walking speed and gait symmetry improved from postoperative days 15-27 (speed, female: 3.2 and 4.5 m/s; male: 4.2 and 5.2 m/s; autocorrelation, female: 0.77 and 0.81; male: 0.70 and 0.79; P <0.001 for all). After the 4-week rehabilitation program, walking speed and gait symmetry were still lower than those in control subjects (speed, female 4.5 m/s vs. 5.7 m/s; male: 5.2 m/s vs. 5.3 m/s; autocorrelation, female: 0.81 vs. 0.88; male: 0.79 vs. 0.90; P <0.001 for all). CONCLUSIONS: While patients with THA improved their walking capacity during a 4-week inpatient rehabilitation program, subsequent intensive gait training is warranted for achieving normal gait symmetry. Inertial sensor technology may be a useful tool for evaluating the rehabilitation process during the post-inpatient period.

Effects of athletic training on the spinal curvature in child athletes.

The purpose of this study was to examine the spinal posture in young athletes depending on training intensity. The spinal curvature of 245 children, age 8 to 12 years, was evaluated using rasterstereography. According to their weekly training time group 1 (mean age: 9.54 ± 1.18) did 2-6, group 2 (mean age: 9.49 ± 0.87) did 6-15 and group 3 (mean age: 9.68 ± 0.87) did over 15 hours of training. Group 1 had a significantly higher weight (p = 0.028) (33.86 ± 7. kg) than those of the more active groups (30.67 ± 6.49 kg and 29.46 ± 4.33 kg). The mean kyphotic angle decreased significantly (p < 0.001) with the amount of training per week from 46.86 ± 8.2° in group 1 to 40.08 ± 8° in group 3. We also found a significant decrease (p = 0.047) in lateral deviation with training from group 1 with 5.3 ± 3 mm to group 2 with 4.1 ± 1.6 mm. The results of our study suggest that higher training time can be associated with lower weight and decreases in thoracic kyphosis and lateral deviation of the spine.

Does age affect the response of pelvis and spine to simulated leg length discrepancies? A rasterstereographic pilot study.

PURPOSE: The purpose of this study was to investigate age differences in the response of the spine and pelvis to simulated leg length inequalities (LLIs). METHODS: A total of 107 subjects, separated into three age groups (group 1: 20-39 years, group 2: 40-59 years, group 3: >60 years), were used to evaluate for any age effects in the response to LLIs. LLIs of +10, +20, and +30 mm were simulated with a simulation platform on both sides, and the respective changes of pelvic position (pelvic obliquity, pelvic torsion) and spinal posture (lateral deviation, surface rotation, kyphotic, and lordotic angles) were measured with a rasterstereographic system. RESULTS: In all three age groups an increase in LLI led to significant changes in the pelvic position as measured by the parameters of pelvic obliquity and torsion. No significant differences in the response of the pelvis to the LLIs were found between the age groups. In all age groups an increase in surface rotation and lateral deviation of the spine with increasing LLIs was found. However, none of these parameters responded significantly different between the three age groups. CONCLUSIONS: Under static conditions, LLIs lead to significant changes of the pelvic position and spinal posture. Despite all known age-related changes, no significant differences of the measured pelvic and spinal parameters in elderly patients as a response to the simulated LLIs occurred.

Determination of the amount of leg length inequality that alters spinal posture in healthy subjects using rasterstereography.

PURPOSE: Leg length inequalities (LLIs) can result in an increased energy consumption, abnormal gait or osteoarthritis of the hip. In a previous study we simulated different LLIs of up to 15 mm and evaluated their effects on the pelvic position and spinal posture. We found a correlation between LLIs and resulting changes of the pelvic position. Despite suggestions in the literature we were not able to detect significant changes of the spinal posture. Therefore, the purpose of this study was to determine the amount of LLI that would in fact alter the spinal posture. METHODS: The subjects were placed on a simulation platform, whose height could be precisely controlled by the measuring device, to simulate different LLIs of up to 20 mm. For LLIs >20 mm, additional precision-cut wooden blocks were used under one foot. After an adaptation period the resulting changes of the pelvis and spine were measured with a rasterstereographic device. RESULTS: We found a significant correlation between platform height changes and changes of the pelvic position. The frontal spinal parameters surface rotation and lateral deviation changed significantly when simulating differences greater than 20 mm. No changes of the sagittal spinal curvature were measured, however, a trend to decreasing kyphotic angles was noted. CONCLUSIONS: Our study has shown for the first time that LLIs >20 mm will lead to significant changes in the spinal posture of healthy test subjects. However, these changes were only found in frontal (surface rotation and lateral flexion) spinal parameters, but not in sagittal parameters. Here for the kyphotic angle only a tendency to decreasing angles was noted. We have also found a significant correlation between different leg lengths and changes of the pelvic position. Further, females and males seem to react in the same way to LLIs.

The effect of simulating leg length inequality on spinal posture and pelvic position: a dynamic rasterstereographic analysis.

INTRODUCTION: Leg length inequalities (LLI) are a common finding. Rasterstereography offers a non-invasive, contact-free and reliable method to detect the effects of LLIs on spinal posture and pelvic position. MATERIALS AND METHODS: A total of 115 subjects were rasterstereographically examined during different artificially created leg length inequalities (5-15 mm) using a platform. The pelvic obliquity and torsion and the lateral and frontal deviation of the spine, as well as the surface rotation, were measured. RESULTS: Changes in platform height led to an increase of the pelvic tilt and torsion. Only minor changes in the spinal posture were found by different simulated leg length inequalities. CONCLUSIONS: Our study showed that there was a correlation between an artificial leg length inequality up to 15 mm and pelvic tilt or torsion, but only minor changes in the spinal posture were measured. Further studies should investigate the effects of greater leg length inequalities on spine and pelvis.

The rasterstereographic-dynamic analysis of posture in adolescents using a modified Matthiass test.

The Matthiass posture test is a clinical test to detect posture changes in children and adolescents. Aim of this study was to objectify this test using a dynamic rasterstereographic measuring device. We examined 31 healthy athletes during a modified Matthiass test with a dynamic rasterstereographic measuring system. Hereby the trunk inclination, kyphosis and lordosis angle were measured. The trunk inclination decreased by about 50% of the basic value just by raising the arms. Additional weight loads of only 5% body weight (bw) resulted in significant changes of the posture (lordosis and kyphosis angle) during this test. With this rasterstereographic measuring device it seems to be possible to determine spinal posture changes under dynamic conditions. The results suggest that additional weights of 5% bw during the Matthias-test are enough to create significant deviations in posture parameters, even in healthy subjects.

Effect of Sitting Posture on Sit-Skiing Economy in Non-disabled Athletes.

This study focused on resolving the differences in economy between two common sit-skiing postures used by disabled athletes, suspected to be the most and least effective. Ten experienced non-disabled male cross-country skiers went through an incremental testing protocol with an ergometer simulating double poling in two sitting postures "kneeing" and "knee-high." The protocol consisted of 3 × 4 min steady-state stages (13, 22, and 34% of maximal sprint power output). Subjects' respiratory gases and heart rate were measured and blood lactate concentrations were determined. In addition, pulling forces and motion capture recordings were collected. Oxygen consumption was 15.5% (p < 0.01) higher with "knee-high" compared to "kneeing" at stage three. At stage three cycle rate was 13.8% higher (p < 0.01) and impulse of force 13.0% (p < 0.05) and hip range of motion 46.6% lower (p < 0.01) with "knee-high" compared to "kneeing." "Kneeing" was found to be considerably more economical than "knee-high" especially at 34% of maximum sprint power output. This might have been due to higher cycle rate, lower impulse of force and smaller hip range of motion with "knee-high" compared to "kneeing." This indicates that sit-skiers should adopt, if possible, posture more resembling the "kneeing" than the "knee-high" posture. Combining such physiological and biomechanical measurements and to further develop them to integrated miniature wearable sensors could offer new possibilities for training and testing both in the laboratory and in the field conditions.

Changes in upper body muscle activity with increasing double poling velocities in elite cross-country skiing.

The purpose of this study was to investigate whether the stretch-shortening cycle (SSC) contraction is integrated in neuromuscular activation in upper body muscles during double poling in cross-country skiing. Thirteen elite skiers performed double poling roller-skiing at increasing treadmill velocities of 9, 15, 21, 27 km h(-1) and their individual maximal velocity. Elbow angle, axial pole force and surface EMG in the triceps brachii, pectoralis major, latissimus dorsi and teres major muscle were recorded. Increases in peak pole force, rate of force development and elbow flexion angular velocities were identified (P < 0.05). The mean MVC-normalized EMG amplitudes increased during the pre-activation phase before pole plant, elbow flexion and the reflex-mediated phase between 30 and 120 ms after pole plant due to velocity increases (P < 0.05). It is thus suggested that elite cross-country skiers use SSC during double poling, particularly in the triceps muscle in order to generate high forces.

Longitudinal sequencing in intramuscular coordination: A new hypothesis of dynamic functions in the human rectus femoris muscle.

The punctum fixum-punctum mobile model has been introduced in previous publications. It describes general principles of intersegmental neuromuscular succession patterns to most efficiently generate specific movement intentions. The general hypothesis of this study is that these principles-if they really do indicate a fundamental basis for efficient movement generation-should also be found in intramuscular coordination and should be indicated by "longitudinal sequencing" between fibers according to the principles of the punctum fixum-punctum mobile model. Based on this general hypothesis an operationalized model was developed for the rectus femoris muscle (RF), to exemplarily scrutinize this hypothesis for the RF. Electromyography was performed for 14 healthy male participants by using two intramuscular fine wire electrodes in the RF (placed proximal and distal), three surface electrodes over the RF (placed proximal, middle, and distal), and two surface electrodes over the antagonists (m. biceps femoris and m. semitendinosus). Three movement tasks were measured: kicking movements; deceleration after sprints; and passively induced backward accelerations of the leg. The results suggest that proximal fibers can be activated independently from distal fibers within the RF. Further, it was shown that the hypothesized function of "intramuscular longitudinal sequencing" does exist during dynamic movements. According to the punctum fixum-punctum mobile model, the activation succession between fibers changes direction (from proximal to distal or inversely) depending on the intentional context. Thus, the results seem to support the general hypothesis for the RF and could be principally in line with the operationalized "inter-fiber to tendon interaction model".

Muscle activity of leg muscles during unipedal stance on therapy devices with different stability properties.

OBJECTIVES: To test the hypotheses that less stable therapy devices require greater muscle activity and that lower leg muscles will have greater increases in muscle activity with less stable therapy devices than upper leg muscles. DESIGN: Cross-sectional laboratory study. SETTING: Laboratory setting. PARTICIPANTS: Twenty-five healthy subjects. MAIN OUTCOME MEASURES: Electromyographic activity of four lower (gastrocnemius medialis, soleus, tibialis anterior, peroneus longus) and four upper leg muscles (vastus medialis and lateralis, biceps femoris, semitendinosus) during unipedal quiet barefoot stance on the dominant leg on a flat rigid surface and on five therapy devices with varying stability properties. RESULTS: Muscle activity during unipedal stance differed significantly between therapy devices (P < 0.001). The order from lowest to highest relative muscle activity matched the order from most to least stable therapy device. There was no significant interaction between muscle location (lower versus upper leg) and therapy device (P = 0.985). Magnitudes of additional relative muscle activity for the respective therapy devices differed substantially among lower extremity muscles. CONCLUSIONS: The therapy devices offer a progressive increase in training intensity, and thus may be useful for incremental training programs in physiotherapeutic practice and sports training programs.

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.

Reduced lower leg muscle activity while balancing on cobblestone shaped surfaces.

The purpose of this study was to test the hypothesis that muscle intensity and ankle joint motion will be greater when balancing on a surface shaped like a cobblestone pathway than on a smooth surface. Nineteen healthy male and female subjects participated in this study. Electromyographic (EMG) activity of the soleus, gastrocnemii medialis and lateralis, peroneus longus and tibialis anterior and ankle dorsiflexion/plantarflexion and eversion/inversion were recorded for unilateral balancing tasks on a hard smooth (control), soft smooth and two cobblestone shaped balance surfaces. Mean ankle kinematics did not differ between conditions. EMG intensity of the lower leg muscles were significant lower for the cobblestone shaped surface than for the control surface (-40 to -80%; P<.01). EMG intensity of the lower leg muscles were significantly higher for the soft smooth surface than for the control surface (+12 to +30%; P<.01). Different balance strategies or tendon stretching may be responsible for these differences. Not only material properties but also surface shape of balance surfaces should be considered to optimize training output and tailored to the specific goal of a training regimen.

The punctum fixum-punctum mobile model: a neuromuscular principle for efficient movement generation?

According to the "punctum fixum-punctum mobile model" that was introduced in prior studies, for generation of the most effective intentional acceleration of a body part the intersegmental neuromuscular onset succession has to spread successively from the rotation axis (punctum fixum) toward the body part that shall be accelerated (punctum mobile). The aim of the present study was to investigate whether this principle is, indeed, fundamental for any kind of efficient rotational accelerations in general, independent of the kind of movements, type of rotational axis, the current body position, or movement direction. Neuromuscular onset succession was captured by surface electromyography of relevant muscles of the anterior and posterior muscle chain in 16 high-level gymnasts during intentional accelerating movement phases while performing 18 different gymnastics elements (in various body positions to forward and backward, performed on high bar, parallel bars, rings and trampoline), as well as during non-sport specific pivot movements around the longitudinal axis. The succession patterns to generate the acceleration phases during these movements were described and statistically evaluated based on the onset time difference between the muscles of the corresponding muscle chain. In all the analyzed movement phases, the results clearly support the hypothesized succession pattern from punctum fixum to punctum mobile. This principle was further underlined by the finding that the succession patterns do change their direction running through the body when the rotational axis (punctum fixum) has been changed (e.g., high bar or rings [hands] vs. floor or trampoline [feet]). The findings improve our understanding of intersegmental neuromuscular coordination patterns to generate intentional movements most efficiently. This could help to develop more specific methods to facilitate such patterns in particular contexts, thus allowing for shorter motor learning procedures of context-specific key movement sequences in different disciplines of sports, as well as during non-sport specific movements.

Patterns of anterior and posterior muscle chain interactions during high performance long-hang elements in gymnastics.

In a prior study with high level gymnasts we could demonstrate that the neuromuscular activation pattern during the "whip-like" leg acceleration phases (LAP) in accelerating movement sequences on high bar, primarily runs in a consecutive succession from the bar (punctum fixum) to the legs (punctum mobile). The current study presents how the neuromuscular activation is represented during movement sequences that immediately follow the LAP by the antagonist muscle chain to generate an effective transfer of momentum for performing specific elements, based on the energy generated by the preceding LAP. Thirteen high level gymnasts were assessed by surface electromyography during high performance elements on high bar and parallel bars. The results show that the neuromuscular succession runs primarily from punctum mobile towards punctum fixum for generating the transfer of momentum. Additionally, further principles of neuromuscular interactions between the anterior and posterior muscle chain during such movement sequences are presented. The findings complement the understanding of neuromuscular activation patterns during rotational movements around fixed axes and will help to form the basis of more direct and better teaching methods regarding earlier optimization and facilitation of the motor learning process concerning fundamental movement requirements.

Neuromuscular onset succession of high level gymnasts during dynamic leg acceleration phases on high bar.

In several athletic disciplines there is evidence that for generating the most effective acceleration of a specific body part the transfer of momentum should run in a "whip-like" consecutive succession of body parts towards the segment which shall be accelerated most effectively (e.g. the arm in throwing disciplines). This study investigated the question how this relates to the succession of neuromuscular activation to induce such "whip like" leg acceleration in sports like gymnastics with changed conditions concerning the body position and momentary rotational axis of movements (e.g. performing giant swings on high bar). The study demonstrates that during different long hang elements, performed by 12 high level gymnasts, the succession of the neuromuscular activation runs primarily from the bar (punctum fixum) towards the legs (punctum mobile). This demonstrates that the frequently used teaching instruction, first to accelerate the legs for a successful realization of such movements, according to a high level kinematic output, is contradictory to the neuromuscular input patterns, being used in high level athletes, realizing these skills with high efficiency. Based on these findings new approaches could be developed for more direct and more adequate teaching methods regarding to an earlier optimization and facilitation of fundamental movement requirements.

Evaluation of a novel spine and surface topography system for dynamic spinal curvature analysis during gait.

INTRODUCTION: The assessment of spinal deformities with rasterstereography can enhance the understanding, as well as can reduce the number of x-rays needed. However, to date this technique only allows measurements under static conditions. Since it would be of great value to be able to also analyze the spine in dynamic conditions, the present study evaluated a novel rasterstereographic system. MATERIALS AND METHODS: A new rasterstereographic device was evaluated in a comparison with the gold standard in motion analysis, the VICON system. After initial testing using 12 flat infrared markers adhered to a solid plate, the two systems were evaluated with the markers adhered onto the backs of 8 test subjects. Four triangles were defined using the markers, and the sides of each triangle were measured under static and dynamic conditions. RESULTS: On the solid plate, the sides of the 4 triangles were measured with a measuring tape and then by the two optical systems. Rasterstereography showed a high accuracy in marker detection on the solid plate. Under dynamic conditions, with the subjects walking on a treadmill, the rasterstereographically-measured side lengths were compared with the lengths measured by the VICON system as an assessment of marker detection. No significant differences (p>0.05) were found between the systems, differing only 0.07-1.1% for all sides of the four triangles with both systems. DISCUSSION: A novel rasterstereographic measurement device that allows surface and spine topography under dynamic conditions was assessed. The accuracy of this system was with one millimeter on a solid plate and during dynamic measurements, to the gold standard for motion detection. The advantage of rasterstereography is that it can be used to determine a three-dimensional surface map and also allows the analysis of the underlying spine.

Spinal posture and pelvic position in three hundred forty-five elementary school children: a rasterstereographic pilot study.

Children's posture has been of growing concern due to observations that it seems to be impaired compared to previous generations. So far there is no reference data for spinal posture and pelvic position in healthy children available. Purpose of this pilot study was to determine rasterstereographic posture values in children during their second growth phase. Three hundred and forty-five pupils were measured with a rasterstereographic device in a neutral standing position with hanging arms. To further analyse for changes in spinal posture during growth, the children were divided into 12-month age clusters. A mean kyphotic angle of 47.1°±7.5 and a mean lordotic angle of 42.1°±9.9 were measured. Trunk imbalance in girls (5.85 mm±0.74) and boys (7.48 mm± 0.83) varied only little between the age groups, with boys showing slightly higher values than girls. The trunk inclination did not show any significant differences between the age groups in boys or girls. Girls' inclination was 2.53°±1.96 with a tendency to decreasing angles by age, therefore slightly smaller compared to boys (2.98°±2.18). Lateral deviation (4.8 mm) and pelvic position (tilt: 2.75 mm; torsion: 1.53°; inclination: 19.8°±19.8) were comparable for all age groups and genders. This study provides the first systematic rasterstereographic analysis of spinal posture in children between 6 and 11 years. With the method of rasterstereography a reliable three-dimensional analysis of spinal posture and pelvic position is possible. Spinal posture and pelvic position does not change significantly with increasing age in this collective of children during the second growth phase.

Reliability and validity of 4D rasterstereography under dynamic conditions.

Purpose of this study was to evaluate the reliability and validity of 4D rasterstereography under dynamic conditions. Therefore simulated anatomical fixed points on a wooden plate were measured during different movements. Seven different motion patterns in all three angles of space were evaluated. The simulated parameter trunk length was measured with an accuracy of 3.58 mm (SD±3.29 mm) and the dimple distance was detected with an accuracy of 0.88 mm (SD±1.04 mm). With this rasterstereographic prototype it is possible to examine dynamically the spinal posture with adequate accuracy.