Biomedical subjects

Beatrix Vereijken

Publications and source records attributed to Beatrix Vereijken.

4 recordsLinked to original sources

PubMed2007

The effect of rate of force development on maximal force production: acute and training-related aspects.

The force generated during a maximal voluntary contraction (MVC) is known to increase by resistance training. Although this increase cannot be solely attributed to changes in the muscle itself, many studies examining muscle activation at peak force failed to detect neural adaptations with resistance training. However, the activation prior to peak force can have an impact on maximal force generation. This study aims at investigating the role of rate of force development (RFD) on maximal force during resistance training. Fourteen subjects carried out 5 days of isometric resistance training with dorsiflexion of the ankle with the instruction to generate maximal force. In a second experiment, 18 subjects performed the same task with the verbal instruction to generate maximal force (instruction I) and to generate force as fast and forcefully as possible (instruction II). The main findings were that RFD increased twice as much as the 16% increase in maximal force with training, with a positive association between RFD and force within the last session of training and between training sessions. Instruction II generated a higher RFD than instruction I, with no difference in maximal force. These findings suggest that the positive association between RFD and maximal force is not causal, but is mediated by a third factor. In the discussion, we argue for the third factor to be physiological changes affecting both aspects of a MVC or different processes affecting RFD and maximal force separately, rather than a voluntary strategic change of both aspects of MVC.

Adult↗

PubMed2006

Effects of body position on slide boarding performance by cross-country skiers.

PURPOSE: In this study, we examined the effects of body position (from deep to high position) in slide boarding by well-trained cross-country skiers. The main hypothesis was that a deeper, more "crouched" position would lead to reduced air resistance and enhanced power production during explosive extension of the lower limbs, and thereby to an increased performance, even though the upper extremity may not be used for poling in this deep position. METHODS: Measurements (air resistance in a wind tunnel, power output, kinematics, gas exchange, and blood lactate levels) were performed during a 30-s maximal test and a 3-min maximal test performing (imitation) ski-skating movements on a sliding board at three different body positions (high, moderate, and deep). RESULTS: Our findings indicate that a deep position enhances power production by 24% and reduces air resistance by 30% for the 30-s maximal test. Power production did not increase in the 3-min test, but lactate levels after exercise were increased in the deep position. Calculated efficiency was not affected by body position. CONCLUSION: The current results indicate that for a short duration, the deeper sit provides sufficient advantages that it may prove useful to apply such a position in sprint ski-skating, even though the use of the upper extremities in poling will be strongly hampered.

Adult↗

PubMed2005

Changes in agonist EMG activation level during MVC cannot explain early strength improvement.

A substantial gain in strength is often observed in the early phase of resistance training. The aim of this study was to address whether improved strength in the early phase of resistance training, can be attributed to increased activation, or to intra-muscular changes of the agonist muscle during maximal isometric torque production. Fourteen male subjects trained maximal isometric dorsiflexion during 5 days. Each subject performed 9 sessions with 25 maximal voluntary contractions in a device that registered the dorsiflexion torque. Surface electromyography (SEMG) of the tibialis anterior (TA) was recorded with a 130-channel grid electrode. SEMG of the extensor digitorum longus, gastrocnemius and soleus muscles were recorded with bipolar electrodes. The main finding was that all subjects gained in strength while the SEMG activation level of the primer agonist, TA, decreased with no apparent intra-muscular spatial changes following 5 days of resistance training. The other muscles that influence dorsiflexion torque did not modify their activation level with training. These findings reject an increase in agonist activation level as the main source for early strength gain, and illustrate the need for further research to reveal the specific sites of neural adaptation and other physiological mechanisms that might contribute to increased strength during the early phase of resistance training.

Adaptation, Physiological↗

PubMedDate not supplied

What changes in infant walking and why.

This study compared the relative contributions of growing body dimensions, age, and walking experience in the development of walking skill in 9- to 17-month-old infants (N = 210), 5-6-year old kindergartners (N = 15), and college students (N = 13). Kinematic measures derived from participants' footprints showed characteristic improvements in walking skill. As children became bigger, older, and more experienced, their steps became longer, narrower, straighter, and more consistent. Improvements reflected a narrowing base of support and increasing control over the path of progression. Although both infants' age and the duration of their walking experience contributed to improvements in walking skill, experience was the stronger predictor. This finding suggests that practice is the more important developmental factor for helping infants to conquer their weak muscles and precarious balance.

Child↗