Biomedical subjects

Gertjan Ettema

Publications and source records attributed to Gertjan Ettema.

7 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↗

PubMed2006

A comparison between novices and experts of the velocity-accuracy trade-off in overarm throwing.

Expert team-handball players do not show the typical trade-off between speed and accuracy in overarm throwing. Van den Tillaar and Ettema (2003a) attributed this result to the uniqueness of the training experience of this group. The purpose of this study was to test their hypothesis by comparing experts with novices on overarm throwing by manipulating the goal of the task using different instructions. No trade-off between speed and accuracy was found for novices (n = 13; M age = 22.7 yr., SD = 2.2) or experts (n = 9; Mage = 24 yr., SD = 2.2): accuracy did not change by instruction. Furthermore, the linear velocities of the ball and endpoints of body segments and their timing were affected by instruction in a similar fashion in both groups. This finding indicates that training experience is not related to speed-accuracy tradeoff in overarm throwing.

Acceleration↗

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↗

PubMed2003

Effect of body size and gender in overarm throwing performance.

The purpose of this study was to examine the relationship between maximum isometric strength, anthropometry and maximum velocity in overarm throwing for male and female experienced handball players. Twenty male and 20 female handball players were tested. The mean ball velocity was 23.2 m s(-1) and 19.1 m s(-1) for male and female handball players, respectively. For males and females, similar correlations were found between maximal isometric strength and throwing velocity (men, r=0.43, P=0.056; women, r=0.49, P=0.027). Univariate analysis of variance between isometric strength and throwing velocity for men and women showed no significant effect of gender (F(2,36)=0.116, P=0.89). Body size had a strong positive effect on the throwing performance and isometric strength. Throwing velocity appeared to be affected by gender when size was expressed by mass or height (P<0.001). However, this dependence was completely explained by size differences when expressed as fat-free body mass (FFM). For strength, no gender effect was found at all, i.e. all gender differences were explained by size differences, irrespective on how this was expressed. The finding that strength and velocity show a gender independent relationship strengthens the notion that gender difference is based on difference in muscle bulk. We conclude that FFM, as an approximation for skeletal muscle mass, is the best measure to express body size when related to physical performance.

Adult↗

PubMed2003

Influence of instruction on velocity and accuracy of overarm throwing.

This study investigated the influence of instruction on the ball velocity and accuracy of a goal-directed overarm throw. 9 experienced Norwegian male team handball players executed a throwing task randomly seven times under 5 different instructions varying from emphasizing speed to accuracy. When instructions increasingly emphasized accuracy, velocity decreased. However, accuracy did not improve when subjects were instructed to focus on it. A possible explanation for this finding could lie in the specific subject group. The subjects were highly experienced team handball players with an average of 12 years in the sport. Thus, the accuracy they demonstrated at high velocity might actually be already extremely high and difficult to improve upon when reducing throwing velocity. Further, the velocity of throwing when instruction emphasized accuracy was approximately 85% of the maximal velocity, indicating that experienced team handball players are trained to throw accurately at relatively high velocity.

Adult↗

PubMed2003

Instructions emphasizing velocity, accuracy, or both in performance and kinematics of overarm throwing by experienced team handball players.

On motor tasks like the overarm throw, velocity and accuracy are two important parameters of performance that may be incompatible and require different strategies in the execution of the motor task. The purpose was to investigate the effects of instruction (emphasizing velocity, accuracy, or both) on performance and kinematics of overarm throwing. Results for 9 experienced male team handball players (M age = 24 +/- 2.2 yr.) showed type of instruction affected the maximal ball velocity. The difference in ball velocity reflected the significant difference in maximal linear velocity of the wrist, elbow, and hip segments together with their absolute timing before ball release. The subjects did not seem to change their throwing technique, i.e., the relative timing of movement initiation of the different body segments.

Adult↗