Biomedical subjects

A Gollhofer

Publications and source records attributed to A Gollhofer.

At least 19 recordsLinked to original sources

PubMed2006

Development and evaluation of a new bicycle instrument for measurements of pedal forces and power output in cycling.

Determination of pedal forces is a prerequisite to analyse cycling performance capability from a biomechanical point of view. Comparing existing pedal force measurement systems, there are methodological or practical limitations regarding the requirements of scientific sports performance research and enhancement. Therefore, the aim of this study was to develop and to validate a new bicycle instrument that enables pedal forces as well as power output measurements with a free choice of pedal system. The instrument (Powertec-System) is based on force transducer devices, using the Hall-Effect and being mounted between the crank and the pedal. Validation of the method was evaluated by determining the accuracy, the cross talk effect, the influence of lateral forces, the reproducibility and, finally, a possible drift under static conditions. Dynamic tests were conducted to validate the power output measurement in reference to the SRM-System. The mean error of the present system was -0.87 +/- 4.09 % and -1.86 +/- 6.61 % for, respectively, the tangential and radial direction. Cross talk, lateral force influence, reproducibility and drift mean values were < +/- 7 %, < or = 2.4 %, < 0.8 % and 0.02 N x min (-1), respectively. In dynamic conditions, the power output measurement error could be kept below 2.35 %. In conclusion, this method offers the possibility for both valid pedal forces and power output measurements. Moreover, the instrument allows measurements with every pedal system. This method has an interesting potential for biomechanical analyses in cycling research and performance enhancement.

Bicycling↗

PubMed2006

Training induced adaptations in characteristics of postural reflexes in elderly men.

The aging neuromuscular system is affected by structural and functional changes which lead to a general slowing down of neuromuscular performance and an increased risk of falling. The impact of heavy resistance (HR) training in the elderly on maximum voluntary contraction (MVC) and rate of force development (RFD) has been investigated in the past. However, the influence of sensorimotor (SENSO) training and HR training on the ability to compensate for gait perturbations has not yet been investigated in the elderly. Therefore, the purpose of the study was to examine the impact of HR and SENSO training in elderly men on unexpected treadmill perturbations. Functional reflex activity was recorded by means of surface EMG in 40 male subjects (>60 years) before and after 13 weeks of HR and SENSO training and in another 20 male subjects (>60 years), which served as a CONTROL-group. SENSO training resulted in a decrease in onset latency, an enhanced reflex activity in the prime mover as well as a decrease in maximal angular velocity of the ankle joint complex during the perturbation impulses. No significant changes were observed in the HR- and in the CONTROL-group. The results clearly indicate that SENSO training has an impact on spinal motor control mechanisms in the elderly. Training induced improvements in perception and procession of afferent information could be a possible reason for the increase in reflex contraction. Due to these adaptive processes, SENSO training could be a well-suited method for fall preventive programs in elderly people.

Adaptation, Physiological↗

PubMed2006

Combinatory effects of high-intensity-strength training and sensorimotor training on muscle strength.

It has been shown in classical strength training studies using high loads that improvements in rate of force development are mainly due to adaptations in the intramuscular coordination. Adaptations following sensorimotor training were also characterized by improvements in the rate of force development during maximum voluntary isometric contraction. The purpose of the present study was to investigate neuromuscular adaptations of combined sensorimotor and classical strength training. Eighteen subjects were randomly assigned to two groups. Group 1 (SMT-HST) had to perform a period of sensorimotor training at first and a high-intensity strength training afterwards. Group 2 (HST-SMT) performed the high intensity strength training at first and the sensorimotor training after. Maximum voluntary isometric contraction and neuromuscular activation were measured at three occasions: Before training, after the first, and after the second period. The results after the first period confirmed the positive effects of both training regimen on rate of force development (13 % [SMT-HST] and 27 % [HST-SMT], p < 0.05) and on maximum strength (9 % [HST-SMT] and 12 % [SMT-HST], p < 0.05) during maximum voluntary contraction. Improvements caused by sensorimotor training could only be achieved, when it was performed at first. It is supposed that classical strength training with high loads basically improves the mechanical efficiency of the effectors, whereas sensorimotor training alters the afferent input on the central nervous system. In combination, the sensorimotor training can have preconditioning effects on the strength training. A combination of both training methods can thus be recommended, if the sensorimotor training is performed at first.

Adaptation, Physiological↗

PubMed2006

Specific adaptations of neuromuscular control and knee joint stiffness following sensorimotor training.

The aim of this study was to examine how fixations of the ankle joint during sensorimotor training (SMT) influence adaptations in mechanical stiffness and neuromuscular control of the knee joint. Sixty-three healthy subjects were randomly assigned to three training groups that differed in their degree of ankle joint fixation, which was either barefooted, with an ankle brace or with a ski boot. Mechanical knee joint stiffness and reflex control of m. vastus medialis, m. vastus lateralis, m. biceps femoris, and m. semitendinosus were tested during force controlled anterior tibial displacements. This force was applied as both a fast and a slow stimulus. After the training period the group that trained barefooted showed an increase in mechanical stiffness of the knee joint from 79 +/- 21 (Mean +/- SD) N/mm to 110 +/- 38 N/mm (p < 0.05) in the fast stimulus. The training group that trained with ski boots was able to improve knee joint stiffness from 67 +/- 26 N/mm to 96 +/- 47 N/mm (p < 0.05) in the slow stimulus. These improvements correspond with an enhanced activity of the hamstring muscles (m. biceps femoris and m. semitendinosus). From a more functional point of view, specific adaptations due to the fixation of the ankle joint may be helpful in the prevention and rehabilitation of knee joint injuries.

Adaptation, Physiological↗

PubMed2004

The effects of a sensorimotor training and a strength training on postural stabilisation, maximum isometric contraction and jump performance.

Previous studies revealed that adaptations following sensorimotor training, performed to improve functional joint or postural stability, were characterized by improvements in the rate of force development during maximum voluntary isometric contraction. In classical strength training studies using intense loads it has been shown that improvements in rate of force development is mainly due to adaptations in the intramuscular coordination. The purpose of the present study was to compare possible neuromuscular adaptations in two training groups following either sensorimotor or classical strength training over a period of four weeks. Additionally a control group was investigated to contrast the adaptations seen after training. Postural stability, maximum voluntary isometric contraction and performance in squat-jump and in drop-jump were measured before and after training. The results confirmed the positive effects of both training regimen on rate of force development and on maximum strength during maximum voluntary contraction as well as on jump performance, while only the improvements after the strength training were significant. Strength training reduced iMEG, while it was enhanced after sensorimotor training in most testing situations. Strength training had positive effects also on concentric contractions like squat-jump. The sensorimotor training improved performance in reactive drop-jump by enhanced neuromuscular activity immediately after ground contact. It is concluded that classical strength training with high loads basically improves the mechanical efficiency of the efferent drive on the motoneurons, whereas sensorimotor training alters the afferent input on the central nervous system. Both adaptations yield to specific effects during force development.

Adult↗

PubMed2002

[Evaluation of mechanical and neurophysiological effects of wearing bandages for the knee joint in functional testing situations].

The purpose of the study was to estimate the stabilising effects of two functional bandages for the knee joint. Two mechanisms typically leading to knee injuries were simulated. Three-dimensional recordings of knee joint angles and recordings of the tibial displacement in anterior-posterior direction were used to determine the destabilisation of the knee joint as a result of the applied mechanical stimuli, as well as the stabilising support of wearing the bandages. Reflex activations of the knee joint muscles and their modulation by the bandages were measured by EMG. To estimate limitations of the sports performance by the bandages, the subjects performed an additional test for postural stability. The testing performance, the three-dimensional knee joint angles and muscle activities were measured. While the FUTURO(R)-knee joint bandage (BDF AG) caused both mechanical and neurophysiological effects, the action of the KASSELER bandage (Sporlastic(R) GmbH) relied solely on the enhancement of muscular activities. The applied methods proved to be a very useful tool for the evaluation of stabilising effects of bandages in functional situations.

Adult↗

PubMed1999

A multi-phase optimal control technique for the simulation of a human vertical jump.

A multi-phase optimal control technique is presented that can be used to solve dynamic optimization problems involving musculoskeletal systems. The biomechanical model consists of a set of differential equations describing the dynamics of the multi-body system and the generation of the dynamic forces of the human muscles. Within the optimization technique, subintervals can be defined in which the differential equations are continuous. At the boundaries the dimension of the state- and control vector as well as the dimension of the right-hand side may change. The problem is solved by a multiple shooting approach which converts the problem into a non-linear program. The method is applied to simulate a human jump movement.

Computer Simulation↗

PubMed1999

Modelling, simulation and optimisation of a human vertical jump.

This paper describes an efficient biomechanical model of the human lower limb with the aim of simulating a real human jump movement consisting of an upword propulsion, a flying and a landing phase. A multiphase optimal control technique is used to solve the muscle force sharing problem. To understand how intermuscular control coordinates limb muscle excitations, the human body is reduced to a single lower limb consisting of three rigid bodies. The biomechanical system is activated by nine muscle-tendon actuators representing the basic properties of muscles during force generation. For the calculation of the minimal muscle excitations of the jump movement, the trajectory of the hip joint is given as a rheonomic constraint and the contact forces (ground reaction forces) are determined by force plates. Based on the designed musculoskeletal model and on the differential equations of the multibody system, muscle excitations and muscle forces necessary for a vertical jump movement are calculated. The validity of the system is assessed comparing the calculated muscle excitations with the registered surface electromyogramm (EMG) of the muscles. The achieved results indicate a close relationship between the predicted and the measured parameters.

Algorithms↗

PubMed1999

Functional properties of adhesive ankle taping: neuromuscular and mechanical effects before and after exercise.

The purpose of the study was to investigate effects of adhesive ankle taping. Using electromyographic, goniometric, and thermologic methods, different ankle tapes were tested before and after athletic exercise in simulated inversion trauma. Twelve subjects with stable ankle joints performed five trials: with two different materials, with two taping techniques, and one trial without tape as control. After the simulated inversion trauma, approximately 35% of the initial maximum inversion amplitude was decreased by ankle taping. Depending on the technique, there was a loss of tape stability < or =14% after 30 min of athletic exercise. Thermologic analysis revealed a postexercise 6 degrees C temperature increase in the foot, especially under the tape. Initially, interpreted as the primary effect, the improved joint stabilization is based on mechanical stiffness caused by the adhesive tape. Joint stability was influenced positively by neuromuscular proprioceptive and physiological processes, characterized by relatively increased electromyographic activation.

Adhesives↗

PubMed1998

Changes in reflex excitability following isometric contraction in humans.

Enhancement of muscle stretch following isometric contraction has been thought to occur as a result of inhibitory reflex mechanisms. Experiments with electrical stimulation (H-reflex) have demonstrated maximal H-reflex suppression during force relaxation followed by gradual recovery over the following 20 s. There has been considerable speculation as to whether electrical and mechanical stimulation elicit similar response behaviour. The present study examined postisometric reflex modulation following both stimulation modalities. In ten subjects dorsiflexion stimuli varying in speed and amplitude were applied after 30% and 60% maximal voluntary contraction (MVC). Modulation of the mechanically and electrically evoked responses following isometric plantarflexion was investigated. Reflex responses following both stimulation modalities were depressed during the course of force relaxation. A rather fast recovery was observed in mechanical stimulation. Postisometric response modulation was neither altered by the amount of isometric plantarflexion, nor by the amplitude of the applied stretch stimulus. With increasing velocity of the applied dorsiflexion, however, the shape of the reflex modulation persisted, but the magnitude of the responses was significantly enhanced. In electrical stimulation, however, recovery was delayed. It is suggested that postisometric reflex modulation is due to presynaptic inhibition. Moreover, possible peripheral mechanisms resulting from alpha-gamma-coactivation may also affect the stretch receptor itself because of inherent stiffness properties. The latter possibility particularly would explain the differences between mechanical and electrical stimulus modalities. With respect to practical implications, the very fast recovery (< 400 ms) of the stretch responses to control values strongly contradicts the interpretation that after isometric precontraction, suppression of reflex activity might be used for more efficient stretching of the tendomuscle system.

Adult↗

PubMed1993

Recovery of stretch reflex responses following mechanical stimulation.

The recovery behaviour of mechanically evoked stretch responses was investigated. Stimuli which promoted identical dorsiflexing movements around the ankle joint were applied to ten subjects in two positions, seated and upright. The experimental sets comprised single as well as double dorsiflexing displacements. In the latter the stimuli were elicited for durations of either 100, 200 or 400 ms. Stretch responses following the first displacements were related to the stretch velocity but not to the amplitude. The responses of the plantar flexors following the second mechanical dorsiflexion were reduced with respect to the delay time between the first and second displacement. In addition, the magnitudes of these responses depended on the functional task: the stretch responses recovered much faster in the standing position when the triceps surae muscle was only slightly activated, whereas in the relaxed sitting position the reflexes remained suppressed. Both reciprocal inhibition, as well as the time course of the reformation of intrafusal cross-bridge links, may help to explain the depression of the monosynaptic stretch reflex.

Adult↗

PubMed1993

Orthotic devices in functional treatment of ankle sprain. Stabilizing effects during real movements.

Various orthotic devices generally employed for therapy of ankle sprain were tested under functional conditions. The experimental setup comprised inversion stimuli of 20 and 30 degrees (13 subjects) while standing on a tiltplatform as well as running movements of 8 and 12 km.h-1 on a treadmill (12 subjects). Ankle joint displacements were registered together with the surface EMGs from mm. peroneus long., tibialis ant., gastrocnemius med. and vastus med. In an additional study the relation between achilles tendon angle and talar tilt was determined under static conditions. Ten subjects with chronical instability were examined both in uni- and bipedal stance with the foot inverted to 20, 30 and 40 degrees. None of the tested devices could reduce achilles tendon angle movements completely neither during a sudden inversion nor during running. However, there were significant differences among the tested devices in the dorsal-plantar and in the eversion-inversion plane. In bipedal stance talar tilts were observed only when the foot was inverted more than 30 degrees. In unipedal stance these tilts were clearly reduced or disappeared totally. It is concluded that for functional rehabilitation, loading of the ankle joint is desirable in order to increase joint stability. The central importance of the treatment by orthotic devices may be regarded in an optimal passive joint stabilization combined with a correct fitting in order to preserve proprioceptive neuromuscular function for an active muscular stabilization.

Achilles Tendon↗

PubMed1993

[Novel functional studies of the stabilizing behavior of ankle joint ortheses].

For functional treatment of acute ankle sprain after surgical or nonsurgical management various special shoes and braces are in use. For a comparison under functional conditions we applied controlled inversion movements of 20 and 30 degrees to 13 subjects. The reduction of angular displacement was measured for the following orthosis: Aircast, Adimed Stabil 2, Adipromed Stabil Super, Mikros Ankle Brace, MHH-Splint Caligamed, Puschbrace and Tape. For evaluation of the neuromuscular activation surface EMGs of selected leg muscles were analyzed. A significant reduction of the induced inversion displacement was observed in all devices, although a complete inhibition of this movement was not possible. EMG activation was comparable to physiological conditions and is not correlated to the displacement characteristics. It is concluded that functional evaluation must take into consideration both the optimal reduction of the inversion and the high functional innervation.

Ankle Injuries↗

PubMed1993

[Biomechanical considerations of impact forces and foot stability in running].

The interaction between "man-shoe and surface" is presented as a model to discuss the complexity of human locomotion. Only if the physiological system "man" interacts positively with the physical requirements of shoe and surface quality running will become effective and economical. Especially during the early ground contact phase the hardness of the shoe construction determines the height of the vertical impact load. These adaptations have consequences in the emg amplitudes during the stretch activation phase of the contact. Comparing various jogging shoes with altered construction properties it can be shown that the "hardness" of the shoe material is well adapted by the variation in the emg amplitude. The influence of the amount of pronation on the impact forces has been confirmed in a separate study. Increased pronation resulted in an increased emg amplitude in the extensor muscles whereas activation in the flexor muscles was decreased. By means of different shoe and insole constructions it is possible to adjust the "man-shoe-surface" interaction to an optimum to carry loads by muscles, joints and ligaments and to avoid overuse and injuries.

Achilles Tendon↗

PubMed1992

Regulation of bipedal stance: dependency on "load" receptors.

According to recent observations, influence of body load has to be taken into account for the neuronal control of upright stance in addition to the systems known to be involved in this regulation (e.g. afferent input from vestibular canals, visual and muscle stretch receptors). The modulation of compensatory leg muscle electromyographic (EMG) responses observed during horizontal body posture indicates the existence of a receptor system which responds to loading of the body against the supporting platform. This receptor should be located within the extensor muscles because a compensatory EMG response and a loading effect on this response was only present following translational, but not rotational impulses. As the EMG responses were identical to those obtained during upright stance, it is argued that these load receptors activate postural reflexes. According to recent observations in the spinal cat, this afferent input probably arises from Golgi tendon organs and represents a newly discovered function of these receptors in the regulation of stance and gait.

Biomechanical Phenomena↗

PubMed1992

Behaviour of triceps surae muscle-tendon complex in different jump conditions.

The force-length relationship of the human muscle-tendon complex (MTC) of the triceps surae and the achilles tendon was investigated in various stretch load conditions. Six male subjects performed various vertical jumps with maximal effort: squat jumps (SJ), counter movement jumps (CMJ) and drop jumps (DJ) from a height of 24 cm, 40 cm and 56 cm. The force-length relationship was calculated from the signals of the components of the ground reaction forces and the kinematic data obtained from the high-speed film records. Surface electromyograms (EMG) of the soleus, gastrocnemius and tibialis anterior muscles were also recorded. The force-length diagrams showed individually high sensitivity to the imposed stretch load. In conditions with relatively low stretch load requirements there was a counter-clockwise direction observable, indicating that the energy absorbed during the eccentric, or lengthening phase was lower than the energy delivered during the concentric, or shortening phase. In high load conditions this relationship was reversed indicating a negative energy balance. The EMG-length diagrams of SJ and CMJ consisted of an initial isometric loading of the muscle, followed by a shortening phase with only slightly reduced EMG amplitudes. In DJ, however, the diagrams showed an initial lengthening of the MTC with fairly constant activation amplitudes. After 40 ms an isometric loading of the muscle, lasting for approximately 80 ms, was followed by a shortening phase. It was concluded that segmental stretch reflex activation represented the predominant activation process during the isometric loading phase, to meet the adequate stiffness properties of the MTC.

Achilles Tendon↗

PubMed1991

Neuromuscular control of the human leg extensor muscles in jump exercises under various stretch-load conditions.

Ten active males performed reactive drop jumps from a height of 40 cm in six experimental conditions: jumps with additional loads of 100 N (BW + 100 N) and 200 N (BW + 200 N), an ordinary jump with body weight (BW) and three jumps in which the body weight was artificially reduced (BW-172 N, BW-337 N and BW-495 N). The vertical ground reaction forces, the angular displacement in the knee and ankle joints as well as the surface electromyogram (EMGs) of the triceps surae muscles and tibialis ant. muscle were recorded. When compared to the control condition (BW) in the jumps with extra load and in the jumps with reduced body weight, both the take-off velocity as well as the mean vertical ground reaction force were decreased during the push-off phase. The integrated EMG before ground contact as well as the duration of the preactivation phase was significantly reduced as a function of the load condition. Upon the touchdown, the coactivation of the muscles acting around the ankle joint was greatest in the control jump. Through all experimental conditions, the mean activation amplitude remained rather constant both for the impact as well as for the push-off phase of the contact. It is concluded that the centrally programmed activity prior to the contact can be seen as the decisive mechanism in the regulation of the stiffness behavior of the tendomuscular system. The extent of the preprogrammed activity determines mainly the physical output of the entire jump exercise.

Adult↗

PubMed1991

[Specific methods of strength training also in rehabilitation].

Until now only minor attention was given to the importance of strength training methods as part of rehabilitation. Even though there are numerous methods in physical therapy which can, under certain limitations, be summed up as a type of strength training, a differentiated use of training methods which are recognized in sport has not been accepted. However, especially the search for a rapid rehabilitation of the body's performance capability brings up the question about effective training methods. In the following paper the physiological conditions are discussed first, on whose basis the motor requirement "strength" has been structured. This results in consequences for the practical training. For each strength component been introduced, practical suggestions for a strength training are given.

Humans↗