IMPORTANCE OF PROPRIOCEPTIVE ACTIVATION ON FUNCTIONAL NEUROMUSCULAR PROPERTIES

Neuromuscular adaptation following strength training has been widely discussed in the literature. There is common consent that alterations in maximum voluntary contraction can be achieved either by muscular hypertrophic effects or by improvements in neuronal supply of the muscle. Both aspects address primarily the contribution of the efferent part of activation. For combination of muscular action, i.e. for the stretch-shortening cycle, the role of the afferent activation rocesses has been demonstrated. However, the question whether afferent contribution may also modulate the strength development in voluntary contractions has not been discussed in detail. Data are presented that emphasise the concept that, induced by proprioceptive training, the improvement in afferent sensitivity are in close relation to improvements in the capacity of the neuromuscular system for explosive power. Functional considerations are given with respect to rehabilitation and to adaptation in athletic strength training

ADAPTIVE RESPONSES OF NEUROMUSCULAR SYSTEM TO TRAINING

Contractile strength training has been investigated in a large variety of training designs. The purpose was to better understand the adaptive mechanisms of the human movement system to physical activity. In principle, for classical strength training two modalities of functional adaptations can be substantiated from those studies: Strength training can either lead to enhancements in the contractile muscular properties of the protein structures themselves or can lead to improvements in the neural supply of the contracting muscle or muscle group. Each type of adaptation can be addressed specifically by the design of the training programme, basically substantiated by the height of the training load, volume of training session and duration. Evidence has been produced, that training with relatively high number of repetitions within one set (Le. 6 -15 maximum repetition (RM) load), associated with an extensive exhaustion of the trained muscle group is preferentially followed by an enhancement in strength and power. Athletes working with this methods show adaptations in the muscular tissue, enhanced cross-sectional areas, altered pinnation angles and high endocrine involvement (Rutherford and Jones, 1992; Walker et al., 1998). However, many studies report also improvements in strength and in power capabilities after strength training without a substantial adaptation of the muscular profile. Thus, an alternative functional response modality must be considered. In recent publications evidence has been produced that spinal and supraspinal mechanisms can be drastically enhanced by a specific type of training. In contract to the muscular adaptations after training with high number of RMs, neuronal adaptation is associated with training using-low number of repetitions (1 -8 RM load), high loads, .intensive or explosive type of contraction and sufficient long periods between sets (Aagaard et aI., 2001). The present paper is focused on the neuromuscular adaptive mechanisms that may come along with intensive strength training and with sensorimotor training. The motoneuron in the spinal cord is in latest consequence directly linked to the muscle fibres. Due to the fact that the functional properties of the motor units (MU) are directly dependent on the discharge characteristics of the activating spinal motoneuron, lit appears logical to separate the various adaptive responses of the neu romuscular system to training in accordance to the different modalities of training

A NEW METHOD FOR ASSESSMENT OF FUNCTIONAL STABILITY AT THE KNEE JOINT

INTRODUCTION: Muscle forces are transmitted by the joints to the movement of the body. Sometimes high muscle forces are used, especially in sports practice. To stabilize the arthron, it is necessary to train the musculature in a functional way. Knowledge of the stability of the arthron during its function in athletic use is helpful to prevent the arthron from overuse or injury. The knee joint frequently becomes unstable due to disruption of the cruciate ligaments. Several methods and devices were developed to test the amount of the tibial translation. Among other things, tibial translation depends on the status of the cruciate ligaments. When the cruciate ligaments are examined, the patient usually sits down or lies on the back with the leg unloaded and the knee joint muscles relaxed (DANIEL et al. 1985, ANDERSON/LIBSCOMP 1989). The examination focuses on the passive stability of the knee joint. Measurement of the passive stability of the ankle joint cannot give an exact description of the active stability of the ankle joint during functional situations (GOLLHOFER et al. 1993, LOHRER et al. 1993, SCHEUFFELEN et al. 1993). Measurement of the functional stability of the knee joint gets more and more a subject of interest (LYSHOLM et al. 1994, PFEIFFER et al. 1996). At the same time the examination methods that are used remain the same as those used during examination of passive stability. We have developed a device to measure the tibial translation of the knee joint. The purpose of the study was to test our new device and the corresponding method in a simple functional situation like standing and to measure the functional stability of the knee joint. We measured the size of the tibial translation and the reflex activities of the knee joint muscles in dependence on aclstatus, load of the leg and size and dynamic of the applied mechanical stimulus

Force production capacity and functional reflex activity in young and elderly men

Background and aims: There is growing evidence that biological aging results in impaired force production of the lower extremities and deficits in reflex activity. This study therefore investigated maximal and explosive force production capacity, functional reflex activity (FRA) during gait perturbations, and the relationship between variables of force production capacity and FRA in young and elderly men. Methods: Twenty-eight young (age 27±3 yrs, n=14) and old (age 67±4 yrs, n=14) healthy active men were tested for decelerating impulses on a treadmill and for their maximal isometric leg extension force (MIF) and rate of force development (RFD) on a leg-press. Results: MIF and RFD were significantly lower in the elderly than in younger participants (MIF ≈45%, p<0.01; RFD ≈50%, p<0.01). Elderly subjects showed significant decreases in FRA in the prime mover which compensated for the decelerating impulse (FRA ≈29%, p<0.05). No significant correlations were found between FRA, MIF or RFD. Conclusions: Lower MIF, RFD and impaired FRA were found in old compared with young men. The absence of significant correlations between measures of strength performance and FRA may indicate that different mechanisms within the neuromuscular system are responsible for these capacities. This result may imply that force production and functional reflex activity are independent of each other and may have to be trained complementaril

COORDINATIVE ASPECTS OF ARCHERY - AN APPROACH USING SURFACE-ELECTROMYOGRAPHY

The process of a shot in archery can be described as follows: The archer draws the bow, pulls the arrow to the clicker1, fixes in this position and aims. Before he releases the arrow, the archer pulls the arrow through the clicker so that a click can be heard. Shortly after this sound, the archer releases. Immediately before the shot there are changes in the muscle activity of shoulder and back. From a biomechanical point of view, the archer must cope with the release of the balance of force between the external tension and the muscular forces (see Fig. 1) immediately after the shot by means of his neuromuscular system. The quality of the anticipation of the balance's release strongly influences the result: After the release of the hand from the string, which also means the release of the static force balance, the arrow still sticks to the string (Leroyer et al. 1993). Thus each motion of the bow is transferred to the arrow. The goal of the archer is to keep the bow steady during and after the release of the balance up to the moment when the arrow leaves the string

IS TRUNK NEUROMUSCULAR CONTROL DIFFERENT BETWEEN MALES AND FEMALES DURING A CHANGE OF MOVEMENT DIRECTION?

The purpose of this study was to evaluate the influence of gender and the cutting angle on trunk control and knee joint moments during cutting maneuvers. Male and female athletes performed unanticipated cuttings to 30° and 60°. Gender had no influence on trunk kinematics, muscles activation or knee joint moments. A sharper cutting angle increased trunk flexion (p = 0.02) and decreased trunk rotation away from the new movement direction (p \u3c 0.001). Moreover, knee joint abduction moment was significantly increased (p \u3c 0.001), together with altered trunk muscles co-contractions. In the early phase of the movement, the antagonist external oblique muscle appeared to work eccentrically. This might be useful to maintain the trunk lateral flexion at a certain level prior to initiate the trunk rotation towards the new movement direction

The effects of a single bout of exercise on motor memory interference in the trained and untrained hemisphere

Increasing evidence suggests that cardiovascular exercise has positive effects on motor memory consolidation. In this study, we investigated whether a single session of high-intensity interval training (HIIT) mitigates the effects of practicing an interfering motor task. Furthermore, learning and interference effects were assessed in the actively trained and untrained limb as it is known that unilateral motor learning can cause bilateral adaptations.Subjects performed a ballistic training and then the HIIT either before (HIIT_before) or after (HIIT_after) practicing an interfering accuracy task (AT). The control group (No_HIIT) did not participate in the HIIT but rested instead. Performance in the ballistic task (BT) was tested before and after the ballistic training, after the exercise and practice of the AT and 24 h later. After ballistic training, all groups showed comparable increases in performance in the trained and untrained limb. Despite the practice of the AT, HIIT_before maintained their BT performance after the high-intensity interval training whereas HIIT_after (trend) & No_HIIT showed prominent interference effects. After 24 h, HIIT_before still did not show any interference effects but further improved ballistic motor performance. HIIT_after counteracted the interference resulting in a comparable BT performance after 24 h than directly after the ballistic training while No_HIIT had a significantly lower BT performance in the retention test. The results were similar in the trained and untrained limb. The current results imply that a single session of cardiovascular exercise can prevent motor interference in the trained and untrained hemisphere. Overall learning was best, and interference least, when HIIT was performed before the interfering motor task

ANKLE JOINT INSTABILITY IN BASKETBALL: A COMPLEX BIOMECHANICAL CLINICAL AND RADIOLOGICAL INVESTIGATION

INTRODUCTION: In this study biomechanical, clinical and radiological parameters of the lower extremity were investigated with regard to their importance as risk factors for ankle sprains in basketball. The relation of all these results should allow a special individual forecast of a higher risk of ankle injury. Those players who belong to a high injury-risk group should be advised to wear an external support such as an orthosis or obtain special training for a sufficient ankle sprain prophylaxis. METHODS: For this study 36 German second division basketball players were examined with at least one recent ankle sprain in their histories. A complex clinical investigation of the lower extremity including several torsional parameters like femoral anteversion, tibial torsion and the malleolar detorsion measured by the Lerat method was followed by the measurement of a modified Naviculareindex by Debrunner. On a visual analogical scale the players indicated their subjective feeling of ankle instability for both joints. A stress radiography followed a clinical investigation of talar tilt and anterior drawer sign. The EMG activity of the m. peroneus was measured during a sudden combined inversion-plantarflexion movement on a specially constructed tilt platform with and without an orthosis. RESULTS: The player’s subjective feeling of functional ankle instability did not correlate with clinical or radiological instability parameters. The torsional parameters, especially a high malleolar detorsion angle, seem to influence a player’s higher risk of suffering an ankle sprain. The modified Naviculareindex has no significant correlation to a high injury risk group. The integrated EMG during the tilt movement was reduced significantly by an average of 20% by wearing an orthosis. The amplitude and velocity of the inversion movement was decreased by an average of 30% compared to the baseline value without orthosis. DISCUSSION: Most of the parameters measured in this investigation were insufficient to explain a player’s subjective feeling of functional instability, and further research is needed, especially in psychological and physiological aspects. Most of the clinical, radiological and biomechanical parameters did not correlate with higher injury risk. Only torsional parameters seem to affect a player’s risk. These results should be regarded in further studies to detect risk factors for ankle injuries